Hi folks,

Can anyone tell me what the typical accuracy of a decent pair of vernier
calipers is (when used carefully and correctly)? I just bought a dial
bore gauge and am wondering if I can reasonably set the zero point with
vernier calipers instead of having to buy a 3" to 4" micrometer. The
calipers are Etalon brand, heavy and made in Switzerland. The bore gauge
dial is graduated down to 0.0005". I'm not reboring an engine, I just
want an idea of the wear, so I don't need the highest accuracy. From
using these calipers, my own guess is that they're probably good to
0.002", but some of that might be my errors in reading them. I'd be
interested to hear what other people think.

Best wishes,

Chris

"Christopher Tidy" wrote in message
...
Hi folks,

Can anyone tell me what the typical accuracy of a decent pair of vernier
calipers is (when used carefully and correctly)? I just bought a dial bore
gauge and am wondering if I can reasonably set the zero point with vernier
calipers instead of having to buy a 3" to 4" micrometer. The calipers are
Etalon brand, heavy and made in Switzerland. The bore gauge dial is
graduated down to 0.0005". I'm not reboring an engine, I just want an idea
of the wear, so I don't need the highest accuracy. From using these
calipers, my own guess is that they're probably good to 0.002", but some
of that might be my errors in reading them. I'd be interested to hear what
other people think.

Best wishes,

Chris

Keep them within a few degrees of some standard (68 deg. F being the most
common one); keep your hands off of them and wear gloves; develop a good
feel, and you should be able to measure to +/- 0.001" with them. Your Etalon
probably is like my TESA Swiss vernier caliper, which is my best one.

You can easily check it with a few gage blocks. If you're going to do
precision work, you need at least a few of them. A set is great but for
checking mikes, calipers, height gages and so on, you only need a few in
different sizes. Then you won't be chasing your tail. You'll know with good
assurance how accurate your gages are. And they'll help you develop a feel
for how much force to use when you're measuring. A couple of gage pins, like
1/4" and 5/8", or something like that, are also useful for that purpose. I
have some precision toolmaker's buttons that serve that purpose.

--
Ed Huntress

Christopher Tidy writes:

I don't have any gauge blocks. Do you think they'd be a better
investment than a 3" to 4" micrometer?

The import 1-2-3 blocks are $10 at Enco. Then you have standards for whole
inches 1 through 6 to better than 0.001". Add a granite slab and you have
the beginnings of some serious metrology for all of $35. Just buy $15 more
worth of anything and they'll ship it free, including the 61 lb stone!

http://www.use-enco.com/CGI/INSRIT?PMAKA=630-4010
http://www.use-enco.com/CGI/INSRIT?PMAKA=640-0120

This spacer set is only $30 and does 0.050" to 4 or 5 inches in most
0.001" increments:

http://www.use-enco.com/CGI/INSRIT?PMAKA=630-4050

Richard J Kinch wrote:
Christopher Tidy writes:

I don't have any gauge blocks. Do you think they'd be a better
investment than a 3" to 4" micrometer?

The import 1-2-3 blocks are $10 at Enco. Then you have standards for
whole inches 1 through 6 to better than 0.001".

And you just answered the question I was about to ask . Thanks !
--
Snag
Still learnin'
after all
these years .

On Feb 19, 10:27*pm, Christopher Tidy
wrote:

Can anyone tell me what the typical accuracy of a decent pair of vernier
calipers is (when used carefully and correctly)? I just bought a dial
bore gauge and am wondering if I can reasonably set the zero point with
vernier calipers instead of having to buy a 3" to 4" micrometer. ...
Chris

I have good 0.0001" micrometers with a 1" setting standard for 0-1 and
1-2", cheaper second-hand ones for the larger ranges.

At home I almost never need to measure larger sizes with absolute
accuracy. I have both the inside and outside pieces and only need to
cut them to fit together. I use an unzeroed bore gauge to check for
taper while I'm boring the cylinder, and compare that to the bore
gauge's reading of the micrometer set to the piston's OD.

I've had Starrett and Phase 2 dial calipers checked for accuracy. The
Starrett was considerably better than 0.001" over its range, nearly as
good as I could read by interpolation. The Phase 2 barely held 0.001".
When I checked the cal standards myself I noticed that the Phase 2
reading was sensitive to how I held it.

So I bought an incomplete set of gage blocks cheap at an auction and
practiced on them. After a while I could get the 0.0001" mikes to read
to one division but don't believe my dial and vernier calipers to
better than 0.001", if that.

This Enco 1-2-3 block here shows 2.0002" at both ends, at 14C (my
normal room temperature). That's good enough to set a 2-3" micrometer
that reads to 0.001".

jsw

"Christopher Tidy" wrote in message
...
Hi folks,

Can anyone tell me what the typical accuracy of a decent pair of vernier
calipers is (when used carefully and correctly)? I just bought a dial bore
gauge and am wondering if I can reasonably set the zero point with vernier
calipers instead of having to buy a 3" to 4" micrometer. The calipers are
Etalon brand, heavy and made in Switzerland. The bore gauge dial is
graduated down to 0.0005". I'm not reboring an engine, I just want an idea
of the wear, so I don't need the highest accuracy. From using these
calipers, my own guess is that they're probably good to 0.002", but some
of that might be my errors in reading them. I'd be interested to hear what
other people think.

Best wishes,

Chris



I would suggest that you calibrate it against a new bearing bore. The
accuracy that those are ground to is amazing.

Richard J Kinch wrote:

Christopher Tidy writes:

I don't have any gauge blocks. Do you think they'd be a better
investment than a 3" to 4" micrometer?

The import 1-2-3 blocks are $10 at Enco. Then you have standards for whole
inches 1 through 6 to better than 0.001". Add a granite slab and you have
the beginnings of some serious metrology for all of $35. Just buy $15 more
worth of anything and they'll ship it free, including the 61 lb stone!

http://www.use-enco.com/CGI/INSRIT?PMAKA=630-4010
http://www.use-enco.com/CGI/INSRIT?PMAKA=640-0120

This spacer set is only $30 and does 0.050" to 4 or 5 inches in most
0.001" increments:

http://www.use-enco.com/CGI/INSRIT?PMAKA=630-4050

I belive Christopher is a bit far away for free shipping.

Wes

Grumpy wrote:
"Christopher wrote in message
...
Hi folks,

Can anyone tell me what the typical accuracy of a decent pair of vernier
calipers is (when used carefully and correctly)? I just bought a dial bore
gauge and am wondering if I can reasonably set the zero point with vernier
calipers instead of having to buy a 3" to 4" micrometer. The calipers are
Etalon brand, heavy and made in Switzerland. The bore gauge dial is
graduated down to 0.0005". I'm not reboring an engine, I just want an idea
of the wear, so I don't need the highest accuracy. From using these
calipers, my own guess is that they're probably good to 0.002", but some
of that might be my errors in reading them. I'd be interested to hear what
other people think.

Best wishes,

Chris



I would suggest that you calibrate it against a new bearing bore. The
accuracy that those are ground to is amazing.




Yup, I use bearings as standards after checking them, usually for
setting dial snap gauges and bore gauges. An ABEC 1 bearing can be
smaller than the nominal size but if you can check it against known
standards they are an inexpensive was to have a working standard for
checking and setting measuring instruments.

John

On 2010-02-20, Christopher Tidy wrote:
Hi folks,

Can anyone tell me what the typical accuracy of a decent pair of vernier
calipers is (when used carefully and correctly)?

How new are the calipers? I would expect 0.001" accuracy, if
zeroed properly, if the gibs are set right so the head does not rotate,
and if you have sufficient light and magnification to read the vernier
properly.

I'm assuming that you are not calling dial calipers "vernier".
Just to be sure, I'll cover them too.

Digital calipers typically have a resolution of 0.0005", but
check the actual accuracy against gauge blocks -- in particular at the
size you want to set.

Dial calipers can have cyclic errors a function of the gear
pinion which engages the rack.

I just bought a dial
bore gauge and am wondering if I can reasonably set the zero point with
vernier calipers instead of having to buy a 3" to 4" micrometer. The
calipers are Etalon brand, heavy and made in Switzerland. The bore gauge
dial is graduated down to 0.0005".

Ideally, it should be set to a ring gauge, not a micrometer.
These will typically be accurate to 0.000050". You really want the
standard to be more accurate than what is being set.

If you use a 4-5" micrometer, you will need a 4" standard to
zero it before you use it. (And I'm assuming that the micrometer has a
tenths vernier around the barrel so you can set it to 0.0001".

Also -- you really don't want to hold the micrometer's C-frame,
as it can expand with heat from the hand. Put it in a micrometer bench
clamp so you can set it and not worry about it drifting as it cools off.

I'm not reboring an engine, I just
want an idea of the wear, so I don't need the highest accuracy. From
using these calipers, my own guess is that they're probably good to
0.002", but some of that might be my errors in reading them. I'd be
interested to hear what other people think.

A lot of the variation in calipers comes from a loose fit of the
head to the bar, allowing it to tilt when pressure is put on the jaw
tips. If you have it pretty snug, you can keep this from being a
problem. And the closer to the bar you do the measurement, the less the
problem from a tilting head and jaws.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

Wes writes:

I belive Christopher is a bit far away for free shipping.

Oh, right.

Don Foreman wrote:

Hi Don,

Sorry to everyone for the slight delay in replying.

No. Calipers are not as accurate as micrometers because they spring
more and provide less "feel". Their value is wide range and quick
operation for ballpark measurements to within a coupla thou. That's
often quite sufficient, certainly in roughing or intermediate
operations.

That was about the accuracy I was guessing. As calipers go, these are
about as stiff as you can get. Probably weigh between 1 and 2 lbs. But
obviously there's no mechanism to ensure a constant closing force, like
a micrometer thimble.

I figure that as I'm not reboring an engine (I just want to know how
severe the wear on each part is, so I can decide what to replace), a
measurement to a couple of thousandths is good enough for me. After all,
the smallest oversize piston I've seen is +0.010". But if anyone thinks
this is a bad plan, do let me know.

I've found the Asian import micrometers to be very good value, and
some come with a reference with which to check them. Don't know about
sources in the UK but an Asian 3-4" mike can be bought here for about
$35. I have some good mikes (Etalon, Starrett, Fowler) and some Asian
imports. They agree to well under .001", usually to better than half
a thou. The better mikes do have better ratchets or friction
thimbles. I prefer a friction thimble, not found on cheap mikes.

I've never seen a micrometer without a thimble. My 0.0001" Tesa
micrometer (Swiss I think) has a friction thimble and my cheap Draper
metric micrometer still has a ratchet thimble.

What do people think of micrometers with interchangeable anvils, to give
several measurement ranges? So for example you have four anvils which
fit a 4" micrometer frame to give measuring ranges of 0" to 1", 1" to
2", 2" to 3" and 3" to 4"? My gut reaction is that they won't be as
consistent as a single range micrometer, but for brand new ones,
Mitutoyo's website claims this isn't the case.

If calipers are good to a couple of thousandths, my inclination is to
use them for the moment.

Best wishes,

Chris

Ed Huntress wrote:

Hi Ed,

The reason is thermal expansion of the caliper. If you're pushing for the
best accuracy, and particularly if the room is cold, holding it in your hand
for a few minutes can make a difference. If you warm a three-inch-long piece
of steel by 30 deg. F, from your 40 deg. shop to 70 deg., it will expand by
almost 0.001". If the piece you're measuring is the same temperature as the
caliper, and if they're both steel, the actual temperature matters little,
but a difference in their temperatures, if it's more than a few degrees, can
result in inaccurate measurement.

Right. I rarely wear gloves except for particularly dirty jobs. I prefer
barrier cream.

But it's time to back up. I suppose you realize that a slide caliper is not
a high-accuracy gage. It's usually used for moderate-accuracy work. You were
asking what accuracy you can achieve with it, and the answer is, using a
good caliper, cotton gloves, and calibration with gage blocks, you probably
can achieve +/- 0.001". But not everyone does. Some people have the touch
and some don't.

Thanks. That's the figure I wanted. These are good calipers and I think
my touch is fair, but I'm not being careful about temperature and the
scale on the calipers cannot be moved to calibrate them. Sounds like my
guess of +/- 0.002" is probably fair.

But it depends on whether you're measuring *relative* dimensions or
*absolute* dimensions. If it's the former, you don't need a well-calibrated
gage. If it's the latter, you'll never know for sure how accurately your
gages measure unless you check them from time to time against a gage block
(or a stack) that's somewhere in the middle of the gage's range, and another
one near its largest opening. For a 3" - 4" mike, I'd want at least a 3"
block (or a stack to make that dimension) and a 4" block or stack. I'd like
to have a 1/2" block, too, to wring with the 3" block to test the midrange.

What's a stack?

If any of this is unclear, ask, and I or someone else will explain. FWIW,
most home-shop work doesn't require accurate measurement of absolute
dimensions. Usually we're trying to make two things fit together, and what
you need to know for that is their *relative* dimensions. If that's the
case, forget the gage blocks for now.

In this case, I think it's the absolute dimensions. The engine's piston
wobbles noticeably in the bore. It's an aluminium piston in a cast iron
bore, so I suspect there could be much more wear on the piston than the
bore (the bore looks good, without a ridge at the top). So I want to
know how well a brand new piston will fit in the existing bore, before I
buy one.

Best wishes,

Chris

"Christopher Tidy" wrote in message
...
Don Foreman wrote:

Hi Don,

Sorry to everyone for the slight delay in replying.

No. Calipers are not as accurate as micrometers because they spring
more and provide less "feel". Their value is wide range and quick
operation for ballpark measurements to within a coupla thou. That's
often quite sufficient, certainly in roughing or intermediate
operations.

That was about the accuracy I was guessing. As calipers go, these are
about as stiff as you can get. Probably weigh between 1 and 2 lbs. But
obviously there's no mechanism to ensure a constant closing force, like a
micrometer thimble.

I figure that as I'm not reboring an engine (I just want to know how
severe the wear on each part is, so I can decide what to replace), a
measurement to a couple of thousandths is good enough for me. After all,
the smallest oversize piston I've seen is +0.010". But if anyone thinks
this is a bad plan, do let me know.

I've found the Asian import micrometers to be very good value, and
some come with a reference with which to check them. Don't know about
sources in the UK but an Asian 3-4" mike can be bought here for about
$35. I have some good mikes (Etalon, Starrett, Fowler) and some Asian
imports. They agree to well under .001", usually to better than half
a thou. The better mikes do have better ratchets or friction
thimbles. I prefer a friction thimble, not found on cheap mikes.

I've never seen a micrometer without a thimble. My 0.0001" Tesa micrometer
(Swiss I think) has a friction thimble and my cheap Draper metric
micrometer still has a ratchet thimble.

What do people think of micrometers with interchangeable anvils, to give
several measurement ranges? So for example you have four anvils which fit
a 4" micrometer frame to give measuring ranges of 0" to 1", 1" to 2", 2"
to 3" and 3" to 4"? My gut reaction is that they won't be as consistent as
a single range micrometer, but for brand new ones, Mitutoyo's website
claims this isn't the case.

Interchangeable anvils are fine if you keep them very clean, and if you
check them against gage blocks.


If calipers are good to a couple of thousandths, my inclination is to use
them for the moment.

Best wishes,

Chris

Ed Huntress wrote:

Interchangeable anvils are fine if you keep them very clean, and if you
check them against gage blocks.

Sounds like I should avoid them unless I buy the gauge blocks then.

Chris

"Christopher Tidy" wrote in message
...
Ed Huntress wrote:

Hi Ed,

The reason is thermal expansion of the caliper. If you're pushing for the
best accuracy, and particularly if the room is cold, holding it in your
hand for a few minutes can make a difference. If you warm a
three-inch-long piece of steel by 30 deg. F, from your 40 deg. shop to 70
deg., it will expand by almost 0.001". If the piece you're measuring is
the same temperature as the caliper, and if they're both steel, the
actual temperature matters little, but a difference in their
temperatures, if it's more than a few degrees, can result in inaccurate
measurement.

Right. I rarely wear gloves except for particularly dirty jobs. I prefer
barrier cream.

But it's time to back up. I suppose you realize that a slide caliper is
not a high-accuracy gage. It's usually used for moderate-accuracy work.
You were asking what accuracy you can achieve with it, and the answer is,
using a good caliper, cotton gloves, and calibration with gage blocks,
you probably can achieve +/- 0.001". But not everyone does. Some people
have the touch and some don't.

Thanks. That's the figure I wanted. These are good calipers and I think my
touch is fair, but I'm not being careful about temperature and the scale
on the calipers cannot be moved to calibrate them. Sounds like my guess of
+/- 0.002" is probably fair.

But it depends on whether you're measuring *relative* dimensions or
*absolute* dimensions. If it's the former, you don't need a
well-calibrated gage. If it's the latter, you'll never know for sure how
accurately your gages measure unless you check them from time to time
against a gage block (or a stack) that's somewhere in the middle of the
gage's range, and another one near its largest opening. For a 3" - 4"
mike, I'd want at least a 3" block (or a stack to make that dimension)
and a 4" block or stack. I'd like to have a 1/2" block, too, to wring
with the 3" block to test the midrange.

What's a stack?

Multiple gage blocks "wrung" together, which add up to their combined
dimension. If you wring three 1" gage blocks together, they'll equal a
single, 3" block. The wringing technique excludes air between them, and adds
less than 2 millionths of an inch to the stack height.

This only works with good-quality gage blocks. Some of the other setting
tools that have been recommended in this thread can't be stacked up with
that kind of accuracy.

The ideal accuracy of dimensional standards, such as gage blocks, is ten
times or more the accuracy of what you're trying to measure. In other words,
if you're trying to determine the accuracy of your micrometer to +/- 0.0001
in., you ideally should have gage blocks that are accurate to +/- 0.000,01
in. That's a workshop-quality gage block, grade A or a good quality grade B,
which today is called a "grade 3" (or AS-1) in new blocks.

If you're going metric, the picture is a little different.

Having said all that, a cheap workshop-grade gage block will be more
accurate than you need for most shop work. But the troubles with cheap sets
are twofold: they have parallelism problems, as well as looseness in
absolute dimensions; and they often won't wring.

Back to Earth: For what you want, almost anything will do. g Any decent
gage standard is a whole lot better than nothing. But you have at least one
mike, and you might want to use it for more demanding work at some time. For
that, get a few gage blocks.


If any of this is unclear, ask, and I or someone else will explain. FWIW,
most home-shop work doesn't require accurate measurement of absolute
dimensions. Usually we're trying to make two things fit together, and
what you need to know for that is their *relative* dimensions. If that's
the case, forget the gage blocks for now.

In this case, I think it's the absolute dimensions. The engine's piston
wobbles noticeably in the bore. It's an aluminium piston in a cast iron
bore, so I suspect there could be much more wear on the piston than the
bore (the bore looks good, without a ridge at the top). So I want to know
how well a brand new piston will fit in the existing bore, before I buy
one.

Best wishes,

Chris

It would really help to have a good engine man chime in here. There are
several around; try a new thread with a title like "Measuring engine bores"
or something like that. You may drag one up.

Many of us can help you with handling gages but engine cylinders have other
issues, like taper and ovality, etc. If it's an old engine, the pistons may
be cylindrical. If it's a newer one, they're probably elliptical ("oval").
And they're tapered along their lengths, too.

In engine work, you have to know not only how to measure, but what it is
you're really measuring. It's not difficult but you do have to know what
you're doing. You want to ask someone who really knows his stuff.

Good luck!

--
Ed Huntress

"Christopher Tidy" wrote in message
...
Ed Huntress wrote:

Interchangeable anvils are fine if you keep them very clean, and if you
check them against gage blocks.

Sounds like I should avoid them unless I buy the gauge blocks then.

Chris

I'd avoid them unless you really need them. Full disclosure -- Mitutoyo was
my client for many years, and I wrote all of their articles during those
years and some of their instructional materials. They're quite honest about
what they claim. Just be aware that things like interchangeable-anvil
micrometers sacrifice some assurance for the sake of convenience. They can
be as accurate as any mike; you just have to be a bit more careful.

--
Ed Huntress

"Pete Snell" wrote in message
...
One thing to be very careful of with all calipers, is the comparative
accuracy of the inner and outer jaws. On one set cheapie Chinese digital
calipers I have, the difference between an inside and outside measurement
(of identical dimension) was about 0.003"

Pete

Save that one for woodwork. g

--
Ed Huntress

On Mon, 22 Feb 2010 03:58:39 +0000, the infamous Christopher Tidy
scrawled the following:

Ed Huntress wrote:

Hi Ed,

The reason is thermal expansion of the caliper. If you're pushing for the
best accuracy, and particularly if the room is cold, holding it in your hand
for a few minutes can make a difference. If you warm a three-inch-long piece
of steel by 30 deg. F, from your 40 deg. shop to 70 deg., it will expand by
almost 0.001". If the piece you're measuring is the same temperature as the
caliper, and if they're both steel, the actual temperature matters little,
but a difference in their temperatures, if it's more than a few degrees, can
result in inaccurate measurement.

Right. I rarely wear gloves except for particularly dirty jobs. I prefer
barrier cream.

Now that I'm no longer doing greasy mechanical work, I tend to wear
gloves more often, to keep my finnernails clean. Barrier cream is
great, except for that.


But it's time to back up. I suppose you realize that a slide caliper is not
a high-accuracy gage. It's usually used for moderate-accuracy work. You were
asking what accuracy you can achieve with it, and the answer is, using a
good caliper, cotton gloves, and calibration with gage blocks, you probably
can achieve +/- 0.001". But not everyone does. Some people have the touch
and some don't.

Thanks. That's the figure I wanted. These are good calipers and I think
my touch is fair, but I'm not being careful about temperature and the
scale on the calipers cannot be moved to calibrate them. Sounds like my
guess of +/- 0.002" is probably fair.

Fair to high. 2 thou to start, 1 thou after you get used to it, 5
tenths once you're good and comfortable with your dial calipers. But
for critical measurements, micrometers are the way to go.


But it depends on whether you're measuring *relative* dimensions or
*absolute* dimensions. If it's the former, you don't need a well-calibrated
gage. If it's the latter, you'll never know for sure how accurately your
gages measure unless you check them from time to time against a gage block
(or a stack) that's somewhere in the middle of the gage's range, and another
one near its largest opening. For a 3" - 4" mike, I'd want at least a 3"
block (or a stack to make that dimension) and a 4" block or stack. I'd like
to have a 1/2" block, too, to wring with the 3" block to test the midrange.

What's a stack?

When a gage block isn't thick enough, you stack another on top of it.


If any of this is unclear, ask, and I or someone else will explain. FWIW,
most home-shop work doesn't require accurate measurement of absolute
dimensions. Usually we're trying to make two things fit together, and what
you need to know for that is their *relative* dimensions. If that's the
case, forget the gage blocks for now.

In this case, I think it's the absolute dimensions. The engine's piston
wobbles noticeably in the bore. It's an aluminium piston in a cast iron
bore, so I suspect there could be much more wear on the piston than the
bore (the bore looks good, without a ridge at the top). So I want to
know how well a brand new piston will fit in the existing bore, before I
buy one.

Remember that the COE is different for steel and aluminum, with steel
expanding less by half. Aluminum pistons are wobblier by nature.

Don't go by the piston, go by the bore. It sounds like your engine is
in fairly good shape, but check for elongation perpendicular to the
crankshaft. Bores become oval from wear, where the connecting rod
pushes 'em up and drags 'em down the opposite sides. If you bore it
out, you'll need all new pistons by default.

--
"Just think of the tragedy of teaching children not to doubt."
-- Clarence Darrow

On Mon, 22 Feb 2010 04:09:32 +0000, the infamous Christopher Tidy
scrawled the following:

DoN. Nichols wrote:

Hi Don,

How new are the calipers? I would expect 0.001" accuracy, if
zeroed properly, if the gibs are set right so the head does not rotate,
and if you have sufficient light and magnification to read the vernier
properly.

Probably 30+ years old, but in very good condition. A few scratches here
and there, but no noticeable wear to the jaws and no sign of having been
dropped.

I'm assuming that you are not calling dial calipers "vernier".
Just to be sure, I'll cover them too.

They're genuine verniers.

Then your 2 thou is likely more hopeful. Get a pair of dials, boy!
They're less easy to misread. I forgot you were talking about
verniers. Got a good magnifying glass?

--
"Just think of the tragedy of teaching children not to doubt."
-- Clarence Darrow

On Sun, 21 Feb 2010 08:31:27 +1100, "Grumpy"
wrote:




I would suggest that you calibrate it against a new bearing bore. The
accuracy that those are ground to is amazing.


It is pretty amazing what you get for your money when purchasing
bearings. But even though the vast majority of bearings will likely be
better, the bore of a bearing in this size range could be close to
..001 low and another .001 out of round. As you might expect, thin
section bearings have a wider roundness tolerance than the standard
62xx and 63xx series. So, trust, but verify. g

--
Ned Simmons

On 2010-02-22, Christopher Tidy wrote:
Don Foreman wrote:

Hi Don,

Sorry to everyone for the slight delay in replying.

No. Calipers are not as accurate as micrometers because they spring
more and provide less "feel". Their value is wide range and quick
operation for ballpark measurements to within a coupla thou. That's
often quite sufficient, certainly in roughing or intermediate
operations.

That was about the accuracy I was guessing. As calipers go, these are
about as stiff as you can get. Probably weigh between 1 and 2 lbs. But
obviously there's no mechanism to ensure a constant closing force, like
a micrometer thimble.

Indeed -- you need to develop a feel for the sliding force on
the caliper jaws once closed. (And, of course, the jaws are not carbide
faced, so they will wear more rapidly than most micrometer jaws.)

I figure that as I'm not reboring an engine (I just want to know how
severe the wear on each part is, so I can decide what to replace), a
measurement to a couple of thousandths is good enough for me. After all,
the smallest oversize piston I've seen is +0.010". But if anyone thinks
this is a bad plan, do let me know.

Probably adequate -- especially as you are closing the calipers
to a given setting (using the adjustment screw with the extra traveling
head clamped down) and then using it as a reference for the dial gauge.
If you had a set of gauge blocks, you could close it to a light sliding
fit on those (to free yourself from the possible errors in the vernier
and in reading it) and hold it in a vise to eliminate the problems from
hand heat causing expansion of the beam.

I've found the Asian import micrometers to be very good value, and
some come with a reference with which to check them. Don't know about
sources in the UK but an Asian 3-4" mike can be bought here for about
$35. I have some good mikes (Etalon, Starrett, Fowler) and some Asian
imports. They agree to well under .001", usually to better than half
a thou. The better mikes do have better ratchets or friction
thimbles. I prefer a friction thimble, not found on cheap mikes.

I've never seen a micrometer without a thimble. My 0.0001" Tesa
micrometer (Swiss I think) has a friction thimble and my cheap Draper
metric micrometer still has a ratchet thimble.

My first one from about 1960 (long gone, and I don't remember
the brand) had only a small diameter spinner, not a ratchet or friction
thimble, and I developed a feel for letting my fingers slip on the
knurled portion of the man thimble.

I've got others with various designs, including a 0-6" Brown &
Sharpe set which still have no torque limiting features, along with
others with very good friction thimbles.

What do people think of micrometers with interchangeable anvils, to give
several measurement ranges? So for example you have four anvils which
fit a 4" micrometer frame to give measuring ranges of 0" to 1", 1" to
2", 2" to 3" and 3" to 4"? My gut reaction is that they won't be as
consistent as a single range micrometer, but for brand new ones,
Mitutoyo's website claims this isn't the case.

Remember that you have to zero them against a standard each time
you change the anvils -- or for that matter if you pick it up a week
later and want to measure -- the room temperature might have changed
between the zeroing and the time of the intended measurement.

My main consideration of the problems with the multi-range
micrometers is that you have the large C frame so there is more metal to
expand as your hand warms it, thus more error from the thermal
expansion.

If you can prevent this (including hand warming of the standards
you use when you zero the micrometers) you should be OK. Often a bench
clamp stand for the micrometer is indicated.

If calipers are good to a couple of thousandths, my inclination is to
use them for the moment.

And potentially good for better than that as you will be using
them in zeroing the bore gauge. If you use gauge blocks to set the
calipers, you will be better than the caliper.

But then, if you have a stack of gauge blocks, and two longer
blocks at the ends, and you have a setting reference which won't need
the calipers at all. There are devices designed for just this purpose
-- a rectangular tube to hold the blocks, a pair of long blocks for the
ends, and provisions for clamping it down firmly.

Good Luck,
DoN.

--
Email: | Voice (all times): (703) 938-4564
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--- Black Holes are where God is dividing by zero ---

On 2010-02-22, Christopher Tidy wrote:
Ed Huntress wrote:

Interchangeable anvils are fine if you keep them very clean, and if you
check them against gage blocks.

Sounds like I should avoid them unless I buy the gauge blocks then.

They *should* come with standards for zeroing the micrometer
after changing the anvils -- as many standards as you have anvils.
These should be enough to assure accuracy at the zero point at least,
and you can use gauge blocks to check for errors in mid spindle travel,
but this should not be a problem with new micrometers anyway -- only
after a lifetime of use by you, or someone else.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On 2010-02-22, Christopher Tidy wrote:
Ed Huntress wrote:

Hi Ed,

The reason is thermal expansion of the caliper. If you're pushing for the
best accuracy, and particularly if the room is cold, holding it in your hand
for a few minutes can make a difference. If you warm a three-inch-long piece
of steel by 30 deg. F, from your 40 deg. shop to 70 deg., it will expand by
almost 0.001". If the piece you're measuring is the same temperature as the
caliper, and if they're both steel, the actual temperature matters little,
but a difference in their temperatures, if it's more than a few degrees, can
result in inaccurate measurement.

Right. I rarely wear gloves except for particularly dirty jobs. I prefer
barrier cream.

Gloves are a *very* bad idea when operating machine tools, but
when measuring with micrometers or calipers are a good way to reduce
thermal transfer resulting in errors. (Of course -- the thermal errors
can be in the workpiece as well -- if you have just turned a steel
workpiece in the lathe, it will measure significantly larger than after
it has cooled for a couple of hours -- which can lead to fit problems
when fitting a backplate to a lathe chuck for example. Finish the rough
turning, go eat dinner and read a book or watch a TV show, and come back
later to measure it and take the final passes to get the desired size.

[ ... ]

But it depends on whether you're measuring *relative* dimensions or
*absolute* dimensions. If it's the former, you don't need a well-calibrated
gage. If it's the latter, you'll never know for sure how accurately your
gages measure unless you check them from time to time against a gage block
(or a stack) that's somewhere in the middle of the gage's range, and another
one near its largest opening. For a 3" - 4" mike, I'd want at least a 3"
block (or a stack to make that dimension) and a 4" block or stack. I'd like
to have a 1/2" block, too, to wring with the 3" block to test the midrange.

What's a stack?

Multiple gauge blocks wrung together to make up a precise size.

A good set of blocks will have something like:

1.000"
2.000"
3.000"
4.000"

0.100"
0.200"
0.300"
0.400"
0.500"
0.600"
0.700"
0.800"
0.900"

0.110"
0.120"
0.130"
0.140"
0.150"
0.160"
0.170"
0.180"
0.190"

0.101"
0.102"
0.103"
0.104"
0.105"
0.106"
0.107"
0.108"
0.109"

0.1001"
0.1002"
0.1003"
0.1004"
0.1005"
0.1006"
0.1007"
0.1008"
0.1009"

And -- in a separate box, I also have:

0.10000"
0.10001"
0.10002"
0.10003"
0.10004"
0.10005"
0.10006"
0.10007"
0.10008"
0.10009"

"Wringing" two blocks together involves cleaning the surfaces
about to mate, crossing them at right angles, and rotating them until
the two blocks are parallel. A good block will cling to its neighbor,
and you can progress to a fairly long stack of blocks which can be
lifted by the top-most block and they will all stay together. (The
cheap Chinese sets, supposedly accurate to 0.000050", tend to not have a
good enough finish to bond together properly -- at least my set does
not. But I have a good B&S/"Jo"hansen block set which does this well,
and which comes with a certificate of calibration listing the actual
size of each block.

The combination of multiple blocks will allow you to build up
almost any dimension as long as it is shorter than the multiplicity of
ones which are just above '0.10000"' (they don't often make thinner ones
because they can warp more easily). As a result, some sine plates have
an extra section ground 0.20000" or 0.30000" below the main surface, so
you can build a stack of blocks which will achieve the small angle you
want to make.

If any of this is unclear, ask, and I or someone else will explain. FWIW,
most home-shop work doesn't require accurate measurement of absolute
dimensions. Usually we're trying to make two things fit together, and what
you need to know for that is their *relative* dimensions. If that's the
case, forget the gage blocks for now.

In this case, I think it's the absolute dimensions. The engine's piston
wobbles noticeably in the bore. It's an aluminium piston in a cast iron
bore, so I suspect there could be much more wear on the piston than the
bore (the bore looks good, without a ridge at the top).

Then again, softer materials tend to embed abrasive particles so
they wear away the harder material against which they are run. This is
the principle of a "lap".

At a guess, I would expect the measurement down into the bore at
right angles to the crankshaft axis to measure larger than the dimension
at that height parallel to the axis. (The forces from the crankshaft
and connecting rod would tend to apply more force along that cross axis.)

So I want to
know how well a brand new piston will fit in the existing bore, before I
buy one.

Understood -- and also to discover whether you need to bore
0.100" oversized to fit the next size piston up.

Note that the skirts of some pistons are designed to move with
temperature to fit well at operating temperature. The solid part near
the top remains more constant in dimensions than the bottom of the
skirts.

Good Luck,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

Ed Huntress wrote:

It would really help to have a good engine man chime in here. There are
several around; try a new thread with a title like "Measuring engine bores"

Might do that, but I'm going to try taking the measurements first. I
have the urge to get into the workshop :-).

Many of us can help you with handling gages but engine cylinders have other
issues, like taper and ovality, etc. If it's an old engine, the pistons may
be cylindrical. If it's a newer one, they're probably elliptical ("oval").
And they're tapered along their lengths, too.

Interesting. Why are pistons intentionally made elliptical? I've heard
of pistons where the top land is of a smaller diameter (apparently it
reduces wear because the lubrication is poorer at the top), but I've not
heard of an elliptical piston. I'm surprised it doesn't increase the
wear on the sides due to the reduced surface area, and I'd have thought
it could allow the piston to vibrate in an angular sense about the
gudgeon pin. Any more information, Ed?

Best wishes,

Chris

Ed Huntress wrote:

I'd avoid them unless you really need them. Full disclosure -- Mitutoyo was
my client for many years, and I wrote all of their articles during those
years and some of their instructional materials. They're quite honest about
what they claim. Just be aware that things like interchangeable-anvil
micrometers sacrifice some assurance for the sake of convenience. They can
be as accurate as any mike; you just have to be a bit more careful.

Thanks. I'll remember you're the guy to ask about Mitutoyo gear! The
interchangeable anvil micrometer I saw advertised doesn't include all
the calibration standards Don mentioned, so I'll avoid it.

Best wishes,

Chris

Larry Jaques wrote:

Don't go by the piston, go by the bore. It sounds like your engine is
in fairly good shape, but check for elongation perpendicular to the
crankshaft. Bores become oval from wear, where the connecting rod
pushes 'em up and drags 'em down the opposite sides. If you bore it
out, you'll need all new pistons by default.

The piston is wobblier perpendicular to the crankshaft that it is in the
parallel direction, which suggests to me that there's some significant
wear. Also, the compression isn't great. But the bore itself looks fine,
hence the bore gauge purchase.

Chris

DoN. Nichols wrote:

"Wringing" two blocks together involves cleaning the surfaces
about to mate, crossing them at right angles, and rotating them until
the two blocks are parallel. A good block will cling to its neighbor,
and you can progress to a fairly long stack of blocks which can be
lifted by the top-most block and they will all stay together. (The
cheap Chinese sets, supposedly accurate to 0.000050", tend to not have a
good enough finish to bond together properly -- at least my set does
not. But I have a good B&S/"Jo"hansen block set which does this well,
and which comes with a certificate of calibration listing the actual
size of each block.

Thanks for the explanation. Won't a stack be somewhat less accurate than
a single block manufactured to the right size? Or is the tolerance on
gauge blocks so small that it doesn't matter?

The combination of multiple blocks will allow you to build up
almost any dimension as long as it is shorter than the multiplicity of
ones which are just above '0.10000"' (they don't often make thinner ones
because they can warp more easily). As a result, some sine plates have
an extra section ground 0.20000" or 0.30000" below the main surface, so
you can build a stack of blocks which will achieve the small angle you
want to make.

Just briefly, what's a sine plate used for?

Understood -- and also to discover whether you need to bore
0.100" oversized to fit the next size piston up.

I've not seen +0.100" oversize pistons. For this engine the options are
+0.020" or +0.040".

Note that the skirts of some pistons are designed to move with
temperature to fit well at operating temperature. The solid part near
the top remains more constant in dimensions than the bottom of the
skirts.

I haven't removed the piston yet. The wobble I can see is adjacent to
the solid part, at the top.

Best wishes,

Chris

Ned Simmons wrote:

The Starrett 123 series calipers have adjustable scales and are as
good as verniers get. The 50 division scales with the vernier and main
scale in the same plane make them very easy to read. I can read them
without glasses in a pinch, though I don't recommend it.

http://www.starrett.com/download/62_123_caliper.pdf

Thanks. I'll bear them in mind if I ever need another set.

Chris

DoN. Nichols wrote:

Well ... the ones which I have are quite old. These days, most
people buy either dial or digital calipers. Dial is nice if you can
keep chips out of the rack, but Digital (if good) is far more
convenient, including the ability to zero at any point (such as on what
you are fitting to) and then measure how much more needs to be removed
to reach the proper dimensions. Also, measuring the distance between
the centers of two holes of identical size by zeroing it while measuring
the ID of one hole, then shift to measuring the distance between two
opposite sides of the two holes in question. This subtracts the
diameter of one hole from the final measurement which is the sum of the
center distance and half of each hole's diameter, giving the actual
center-to-center distance.

I chose the vernier calipers because I wanted both imperial and metric
on the same tool, and I wanted them to last. I hate replacing tools.

O.K. But it misses three-lobed bores, which can be in a shape
which actually measures the same between any two opposite points, but
still is potentially seriously out of round. (This is more likely to be
formed by certain machining operations -- including centerless grinding
for OD shapes, and in a used automobile engine, the ovality is more
likely, and for that your bore gauge is probably quite adequate.

I've not seen a three-point bore gauge intended for measuring engine
cylinders. All the gauges I found on the market were two-point with a
centring device. I picked the one I mentioned because it's complete with
all the anvils, locking nuts and the spanner, and is in good condition.
There were more accurate gauges available (measured down to 0.0001"
instead of 0.0005"), but they were much more worn and had missing parts.
Also, I figured that for investigating wear as opposed to reboring,
having a 40 thousandths range on the dial might be more useful than a 10
thousandths range. If people are interested, I can take a picture of the
bore gauge and calipers.

Best wishes,

Chris

DoN. Nichols wrote:

Well ... this one is for setting an air gauge, so it has to be
pretty close to the diameter of the probe. An air gauge is hollow with
both ends sealed, and air feed in through one end, with a hole of a
specific size (or maybe more holes? -- I haven't actually seen one --
just read about them in books). The air goes out the hole, and flows
out between the probe walls and the ID of the bore being checked, and
the pressure built up in the interior of the gauge is measured and is a
very good indication of the difference between the OD of the gauge and
the ID of the bore -- over a fairly narrow range. So -- this ring was
for setting something quite close to 16.8349 mm --- maybe 16.8350 mm is
the actual target size. Anyway -- the rings are made too small,
hardened, and then ground to a diameter near what is needed, and then
marked as measured. They may be lapped as a final finishing pass.

Thanks. That's interesting. I wasn't sure what an air gauge was.

A lot of the variation in calipers comes from a loose fit of the
head to the bar, allowing it to tilt when pressure is put on the jaw
tips. If you have it pretty snug, you can keep this from being a
problem. And the closer to the bar you do the measurement, the less the
problem from a tilting head and jaws.

Good tip. But fortunately the jaws on my calipers are snug.


If the image which I saw was yours, the traveling body is long
enough to minimize the jaw tilt which I was worrying about. I've seen
others which were much shorter (including the digitals which I have)
which make the gib setting more critical.

That picture isn't actually my set of calipers, but is a very similar
set. Same brand, but shorter and perhaps made a little earlier.

Chris

Larry Jaques wrote:

Then your 2 thou is likely more hopeful. Get a pair of dials, boy!
They're less easy to misread. I forgot you were talking about
verniers. Got a good magnifying glass?

Looks like I might regret buying verniers as I get older :-).

Chris

"Christopher Tidy" wrote in message
...
Ed Huntress wrote:

It would really help to have a good engine man chime in here. There are
several around; try a new thread with a title like "Measuring engine
bores"

Might do that, but I'm going to try taking the measurements first. I have
the urge to get into the workshop :-).

Many of us can help you with handling gages but engine cylinders have
other issues, like taper and ovality, etc. If it's an old engine, the
pistons may be cylindrical. If it's a newer one, they're probably
elliptical ("oval"). And they're tapered along their lengths, too.

Interesting. Why are pistons intentionally made elliptical?

Because the thicker sections, which are the boss areas for the wrist pins
(piston pins) expand with much more force than the thin sections. So the
pistons have a smaller diameter across the boss area.

I've heard of pistons where the top land is of a smaller diameter
(apparently it reduces wear because the lubrication is poorer at the top),
but I've not heard of an elliptical piston.

Almost all production automobile pistons made today are elliptical. In fact,
they're often elliptical with the major axis in one direction at the top of
the piston, and in the other direction at the bottom. The bottom ellipse is
for better sealing, to meet emission requirements. It has to do with
differential friction and heating between the neutral axis, which is
parallel to the crankshaft, versus the other axis.

When I was at Wasino we had some drawings from Ford that actually had three
different ellipses along their length, from top to bottom, and they had to
blend into each other.

I'm surprised it doesn't increase the wear on the sides due to the reduced
surface area, and I'd have thought it could allow the piston to vibrate in
an angular sense about the gudgeon pin. Any more information, Ed?

If you don't get an expert to chime in here, I'll see what I can dig up for
you. There is one guy who stops in here from time to time who is an engineer
for one of the world's top piston manufacturers; you won't get any better
info than that from him.

If you're eager to search on it yourself, try both "elliptical piston" and
"oval piston." They're often, incorrectly, called "oval pistons" in the
trade.

--
Ed Huntress

"Christopher Tidy" wrote in message
...
Larry Jaques wrote:

Then your 2 thou is likely more hopeful. Get a pair of dials, boy!
They're less easy to misread. I forgot you were talking about
verniers. Got a good magnifying glass?

Looks like I might regret buying verniers as I get older :-).

Chris

You'll get in the habit of wearing a swing-away loupe on your glasses when
you're reading gages, after you pass a certain age. g

You original reasons for buying a vernier caliper were good ones. Dial
calipers are no more accurate; they're just easier to read. The same is true
for the digitals.

I use my TESA vernier caliper when I'm not in a hurry and I want to keep up
the skill of reading them. But if I'm doing a lot of measuring, I'll pull
out one of my digitals. I've never owned a dial caliper.

--
Ed Huntress

On Tue, 23 Feb 2010 05:04:18 +0000, the infamous Christopher Tidy
scrawled the following:

Larry Jaques wrote:

Then your 2 thou is likely more hopeful. Get a pair of dials, boy!
They're less easy to misread. I forgot you were talking about
verniers. Got a good magnifying glass?

Looks like I might regret buying verniers as I get older :-).

We all do.

--
"Politics is the art of looking for trouble, finding it whether it
exists or not, diagnosing it incorrectly, and applying the wrong
remedy." -- Ernest Benn

On 2010-02-23, Christopher Tidy wrote:
DoN. Nichols wrote:

Well ... the ones which I have are quite old. These days, most
people buy either dial or digital calipers. Dial is nice if you can
keep chips out of the rack, but Digital (if good) is far more
convenient, including the ability to zero at any point (such as on what
you are fitting to) and then measure how much more needs to be removed
to reach the proper dimensions. Also, measuring the distance between
the centers of two holes of identical size by zeroing it while measuring
the ID of one hole, then shift to measuring the distance between two
opposite sides of the two holes in question. This subtracts the
diameter of one hole from the final measurement which is the sum of the
center distance and half of each hole's diameter, giving the actual
center-to-center distance.

I chose the vernier calipers because I wanted both imperial and metric
on the same tool, and I wanted them to last. I hate replacing tools.

O.K. There *are* dial calipers with dual scales, and two
separately geared pointers -- but you still have the problem of the
pinion skipping a tooth shifting the zero point either from a shock or
from chips getting into the rack gear in the bar.

Digital are nice for switching between metric and imperial, but
have the problem of keeping fresh cells around to power them, as some
will kill their cells in six months, and I think a year and a half is
pretty long for one to last.

And -- they are more easily damaged -- things like the liquid
crystal display are rather fragile -- behind the clear plastic window.

O.K. But it misses three-lobed bores, which can be in a shape
which actually measures the same between any two opposite points, but
still is potentially seriously out of round. (This is more likely to be
formed by certain machining operations -- including centerless grinding
for OD shapes, and in a used automobile engine, the ovality is more
likely, and for that your bore gauge is probably quite adequate.

I've not seen a three-point bore gauge intended for measuring engine
cylinders.

For checking *wear* in the cylinders (as you want) what you got
is better -- quicker to use and all. And it lets you measure parallel
to and at right angles to the crankshaft to check for oval wear.

For checking a reboring job, I would prefer the three-point,
since the boring had *better* be cylindrical. :-) But since this is
going to be in an automobile, and you have dissimilar metals between the
cylinder and the piston, you have differing thermal coeifficents of
expansion, and the temperature range between sitting outside on a really
cold day (maybe -40 in some areas, where special lubricants and coolants
are also needed, and a bit over 212 F (100 C) would really require a
good starting clearance, or it will seize at one extreme or the other.

All the gauges I found on the market were two-point with a
centring device. I picked the one I mentioned because it's complete with
all the anvils, locking nuts and the spanner, and is in good condition.
There were more accurate gauges available (measured down to 0.0001"
instead of 0.0005"), but they were much more worn and had missing parts.

Any idea what the required starting clearance is between the
pistons and the bores? *That* would settle how accurate you need the
measurement to be for checking a rebore.

Also, I figured that for investigating wear as opposed to reboring,
having a 40 thousandths range on the dial might be more useful than a 10
thousandths range. If people are interested, I can take a picture of the
bore gauge and calipers.

If so -- post it to the dropbox, or on a private web site and
post the URL to find it.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On 2010-02-23, Christopher Tidy wrote:
DoN. Nichols wrote:

"Wringing" two blocks together involves cleaning the surfaces
about to mate, crossing them at right angles, and rotating them until
the two blocks are parallel. A good block will cling to its neighbor,
and you can progress to a fairly long stack of blocks which can be
lifted by the top-most block and they will all stay together. (The
cheap Chinese sets, supposedly accurate to 0.000050", tend to not have a
good enough finish to bond together properly -- at least my set does
not. But I have a good B&S/"Jo"hansen block set which does this well,
and which comes with a certificate of calibration listing the actual
size of each block.

Thanks for the explanation. Won't a stack be somewhat less accurate than
a single block manufactured to the right size? Or is the tolerance on
gauge blocks so small that it doesn't matter?

As someone else mentioned, the joint between a properly wrung
pair of blocks is on the order of two microinches (0.000002"), so only
with the highest grade blocks do you need to take account of the
interface thickness.

The combination of multiple blocks will allow you to build up
almost any dimension as long as it is shorter than the multiplicity of
ones which are just above '0.10000"' (they don't often make thinner ones
because they can warp more easily). As a result, some sine plates have
an extra section ground 0.20000" or 0.30000" below the main surface, so
you can build a stack of blocks which will achieve the small angle you
want to make.

Just briefly, what's a sine plate used for?

It is a plate (or a bar -- the more common ones are sine bars)
which has a pair of cylindrical surfaces at each end, separated by a
precise center distance. The most common is 5.000", though I have one
at 2.500", and have seen some offered at 10.000").

For a sine bar, there is no captive base plate, so you set it on
a surface plate, and with both cylinders in contact, its top is parallel
to the surface plate.

Now -- let's say you want a precise fifteen degrees. O.K. Look
up the sine of 15 degrees (0.258819045) and multiply by the length of
the bar (5.000"), so you get 1.294095226". Wring a stack of gauge
blocks to get 1.2941" and you will get very close to 15 degrees.
Calculating back from that, I get 15.000056 degrees +/- a bit given
the accuracy of the gauge block set. I stopped the blocks at 1.2941"
assuming a cheap Chinese set with +/- 0.000050 accuracy. You can get
greater precision with the more expensive and accurate sets.

But -- to get that 1.2941" -- we need to build a stack. Let's
see -- start with a 0.1001" block, add a 0.1040" block, then a 0.1900"
block, so we are up to 0.3941" and need only 0.9000" to make up our
total size. When calculating/building a stack, always start with the
last decimal place and work backwards. Here, for example, if you had
started at the big end, you would have picked up a 1.0000" block, and
when you got the lesser digits you would have discovered that the total
was too long.

Now -- a sine plate is like a sine bar, except that it is wider
(the sine bar may be 1" wide) and is captive to a base, so you can build
the angle and lock it in and then carry it to the magnetic chuck of a
surface grinder to grind the desired angle on something mounted to the
top (angled) plate.

To see a sine bar -- here is one on MSC's site:

http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=17520867&PMT4NO=80436460

Or MSC part number 85005502 in case the url above turns out to
be a temporary one built by my search.

The toe on one end is to keep the workpiece from sliding off the
end while measuring.

An example sine plate (much larger and *much* more expensive
than the one which I have) is MSC item 08020216

http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=1778994&PMT4NO=80436812

You can see the near roll under the top plate in the image, and a raised
block for the zero point, which is a precise height above the base
plate. So you can either build blocks above the raised block, or above
the base plate - whichever lets you reach your desired height more
easily.

Note that there are double sine plates -- a second one hinged at
right angles to the first to allow compound angles.

I've used mine to make Acme threading tools to fit a boring bar.
I first used the smallest sine bar that I have (2.5" long between
centers) to machine a 14 degree angle plate (half of an Acme) guide to
hold a HSS tool bit at that angle in a small vise, then mounted the vise
on the sine plate, and set the gauge blocks under it for the desired
side relief on one side of the bit. This went onto the surface grinder,
and was used to make the desired angle on that side. Then I reversed
the bit and angle plate, and built a different stack of gauge blocks to
provide the different relief angle on the other side of the bit. (This
was calculated based on the helix angle of the thread. After this was
complete, I put the bit upright in the vise and set a nose relief angle
to grind while I ground the nose back for the proper nose width for that
particular Acme thread pitch.

Understood -- and also to discover whether you need to bore
0.100" oversized to fit the next size piston up.

I've not seen +0.100" oversize pistons. For this engine the options are
+0.020" or +0.040".

Sorry -- yes, 0.100" is a bit large for automotive pistons at
least. :-)

Note that the skirts of some pistons are designed to move with
temperature to fit well at operating temperature. The solid part near
the top remains more constant in dimensions than the bottom of the
skirts.

I haven't removed the piston yet. The wobble I can see is adjacent to
the solid part, at the top.

O.K.

Good Luck,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On Feb 23, 5:26*pm, "DoN. Nichols" wrote:
On 2010-02-23, Christopher Tidy wrote:
DoN. Nichols wrote:
...

Just briefly, what's a sine plate used for?
...
* * * * Now -- let's say you want a precise fifteen degrees. *O..K. *Look
up the sine of 15 degrees (0.258819045) and multiply by the length of
the bar (5.000"), so you get 1.294095226". *....

* * * * * * * * DoN.

Nice description.

A sine bar can also be used to measure an unknown angle, such as the
taper on a shaft. Lay the taper on a flat surface and clamp the sine
bar on top of it, rolls up. A ground toolmakers vise works well for
this. Measure the difference in the heights of the rolls.

If you have only a short-range 0.0001" test indicator and can't
measure that much distance, tweak an adjustable parallel to make up
the height difference, so the indicator reads the same on both, then
measure the parallel with a micrometer.

jsw

On 2010-02-23, Jim Wilkins wrote:
On Feb 23, 5:26*pm, "DoN. Nichols" wrote:
On 2010-02-23, Christopher Tidy wrote:
DoN. Nichols wrote:
...

Just briefly, what's a sine plate used for?
...
* * * * Now -- let's say you want a precise fifteen degrees. *O.K. *Look
up the sine of 15 degrees (0.258819045) and multiply by the length of
the bar (5.000"), so you get 1.294095226". *....

Nice description.

Thanks!

A sine bar can also be used to measure an unknown angle, such as the
taper on a shaft. Lay the taper on a flat surface and clamp the sine
bar on top of it, rolls up. A ground toolmakers vise works well for
this. Measure the difference in the heights of the rolls.

If you have only a short-range 0.0001" test indicator and can't
measure that much distance, tweak an adjustable parallel to make up
the height difference, so the indicator reads the same on both, then
measure the parallel with a micrometer.

Aha! A nice trick which I had not thought of.

I've got one much smaller sine bar -- 1.000" between rolls --
which is mounted on a micrometer, with a bar of the same length as the
anvil, so it can be used to measure the sine of existing angles within a
limited range of diameters.

Of course -- you lose the multiplier effect of a 5" or 10" sine
bar, so you don't get the accuracy that you can with one of those, but
it is still quite good and a lot more convenient for quick readings.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

DoN. Nichols wrote:

Hi Don,

Thanks for the description of the sine plate. Sorry I've taken a few
days to reply. Bad week!

Just briefly, what's a sine plate used for?


It is a plate (or a bar -- the more common ones are sine bars)
which has a pair of cylindrical surfaces at each end, separated by a
precise center distance. The most common is 5.000", though I have one
at 2.500", and have seen some offered at 10.000").

For a sine bar, there is no captive base plate, so you set it on
a surface plate, and with both cylinders in contact, its top is parallel
to the surface plate.

Now -- let's say you want a precise fifteen degrees. O.K. Look
up the sine of 15 degrees (0.258819045) and multiply by the length of
the bar (5.000"), so you get 1.294095226". Wring a stack of gauge
blocks to get 1.2941" and you will get very close to 15 degrees.
Calculating back from that, I get 15.000056 degrees +/- a bit given
the accuracy of the gauge block set. I stopped the blocks at 1.2941"
assuming a cheap Chinese set with +/- 0.000050 accuracy. You can get
greater precision with the more expensive and accurate sets.

But -- to get that 1.2941" -- we need to build a stack. Let's
see -- start with a 0.1001" block, add a 0.1040" block, then a 0.1900"
block, so we are up to 0.3941" and need only 0.9000" to make up our
total size. When calculating/building a stack, always start with the
last decimal place and work backwards. Here, for example, if you had
started at the big end, you would have picked up a 1.0000" block, and
when you got the lesser digits you would have discovered that the total
was too long.

Now -- a sine plate is like a sine bar, except that it is wider
(the sine bar may be 1" wide) and is captive to a base, so you can build
the angle and lock it in and then carry it to the magnetic chuck of a
surface grinder to grind the desired angle on something mounted to the
top (angled) plate.

To see a sine bar -- here is one on MSC's site:

http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=17520867&PMT4NO=80436460

Or MSC part number 85005502 in case the url above turns out to
be a temporary one built by my search.

The toe on one end is to keep the workpiece from sliding off the
end while measuring.

An example sine plate (much larger and *much* more expensive
than the one which I have) is MSC item 08020216

http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=1778994&PMT4NO=80436812

You can see the near roll under the top plate in the image, and a raised
block for the zero point, which is a precise height above the base
plate. So you can either build blocks above the raised block, or above
the base plate - whichever lets you reach your desired height more
easily.

Note that there are double sine plates -- a second one hinged at
right angles to the first to allow compound angles.

I've used mine to make Acme threading tools to fit a boring bar.
I first used the smallest sine bar that I have (2.5" long between
centers) to machine a 14 degree angle plate (half of an Acme) guide to
hold a HSS tool bit at that angle in a small vise, then mounted the vise
on the sine plate, and set the gauge blocks under it for the desired
side relief on one side of the bit. This went onto the surface grinder,
and was used to make the desired angle on that side. Then I reversed
the bit and angle plate, and built a different stack of gauge blocks to
provide the different relief angle on the other side of the bit. (This
was calculated based on the helix angle of the thread. After this was
complete, I put the bit upright in the vise and set a nose relief angle
to grind while I ground the nose back for the proper nose width for that
particular Acme thread pitch.

Not what I was expecting! I had imagined a steel plate with a surface
shaped like a sine wave, sitting on a table (though what you'd use that
for, I don't know). Thanks for the explanation. Some day I'll probably
need one!

Best wishes,

Chris

DoN. Nichols wrote:

For checking *wear* in the cylinders (as you want) what you got
is better -- quicker to use and all. And it lets you measure parallel
to and at right angles to the crankshaft to check for oval wear.

For checking a reboring job, I would prefer the three-point,
since the boring had *better* be cylindrical. :-) But since this is
going to be in an automobile, and you have dissimilar metals between the
cylinder and the piston, you have differing thermal coeifficents of
expansion, and the temperature range between sitting outside on a really
cold day (maybe -40 in some areas, where special lubricants and coolants
are also needed, and a bit over 212 F (100 C) would really require a
good starting clearance, or it will seize at one extreme or the other.

Actually, it's a big motor lawnmower (80 mm bore).

All the gauges I found on the market were two-point with a
centring device. I picked the one I mentioned because it's complete with
all the anvils, locking nuts and the spanner, and is in good condition.
There were more accurate gauges available (measured down to 0.0001"
instead of 0.0005"), but they were much more worn and had missing parts.


Any idea what the required starting clearance is between the
pistons and the bores? *That* would settle how accurate you need the
measurement to be for checking a rebore.

I've found that figure in the manual. I'll post it along with my
measurements in a new thread shortly.

Also, I figured that for investigating wear as opposed to reboring,
having a 40 thousandths range on the dial might be more useful than a 10
thousandths range. If people are interested, I can take a picture of the
bore gauge and calipers.


If so -- post it to the dropbox, or on a private web site and
post the URL to find it.

Here's a picture of my actual calipers:
http://www.mythic-beasts.com/~cdt22/...r_calipers.jpg

Best wishes,

Chris