Sigh...another question from StudentLand, that strange area where,
after reading the textbook, being shown what to do by the teacher, the
results are STILL all over the place......

Was shown how to use a boring head at school - (always wondered what
they were for) nice big Bridgeport mill, good quality tooling, so
cannot blame anything in that department.

Trying to bore a hole to press fit a 15mm OD bearing for an optical
chopper project I am working on. Learnt how to use the thing on bits
of scrap of the same material as the project - aluminium, cut from the
same bar as the rest. By trial and error, managed to set up the boring
head to get a good result in a piece of the scrap - it is , for me
anyway, virtually impossible to actually measure the diameter of the
hole via the telescopic bore gauge/micrometer method, so crept up on
it till it was a nice fit with the arbor press - ie , went in easily
but strongly retained, not so tight as to wreck the bearings getting
them in or too sloppy so they fell out. (And yes, was taught how to
use the "limits of fit" tables to get a theoretical value, but as I
said it was impossible to get two consecutive measurements of the same
hole the same..AND yes, I did check the zeroing of the micrometer)

OK. Having got it right, did two more practice holes in the scrap, all
went well. Been fooled before by blind luck, so wanted to check it was
consistent - it had taken EONS to size and square the two end bearing
retainer blocks, so didnt want to stuff them up.

(BTW - NEVER buy powder coated aluminium from the scrapyard, the only
way to get it off is to face mill it, and then your left with marks
from the cutter, so HOURS of hand sanding with decreasing grades of
wet and dry paper to get a nice finish - it will be buried in a radio
project, no one will ever see it, but I will know it looks crap)

Put the job pieces in the mill vice, locked the tables, drilled a
14.5mm hole and then, without changing anything in the X-Y dimensions,
used the boring head, Result - holes were undersize...stuffed 2 more
bearings.....(thats ok, had heaps of them from discarded VCR's)

So, whats going on - same methodology used both on the practice pieces
and the job pieces - the only physical difference was the job pieces
were wider than the practice scrap pieces - the vise distorted it
somehow? - it is 15mm thick aluminium plate ...any clues....?

Basically, it took 12 hours to drill two holes. Not good. Unlikely to
get a job as a machinist. Finished my 8 hour day class, the teacher
kindly let me stay on for the 4 hour night class as the setup was a
real pig. (and it was getting a bit tense, as well...) The only good
thing was not having to drive home in 5pm peak traffic....

The regular day shift storeman had cracked it over something (who
knows what) so denied having an adjustable reamer to do it the easy
way. (the so called "correct " reamer was oversize...) The storeman on
night duty said "no worries" and got one out of the store for me,
showed me how to set it up, so I reamed them to the right size at
last.....

And, another query - somewhere, somehow, in internet land, I saw a
home made device to hold a piece of emery cloth with a "flapper" fold
in it for precisely this sort of final "****it this will get it to
size" application. Anyone can point me to the right place, stuffed if
I can find it again...

Grrrr - still finding machining absolutely fascinating, but, bloody
hell, sometimes the learning curve is just about vertical...

Regards,

Andrew VK3BFA.

Andrew,
you didn't actually say, but I suspect you changed out the boring head
for other
tooling then put it back in for finishing the other pieces, etc.
That's where the error lies. Don't expect R8 tooling in a worn mill
spindle to
repeat position precisely. Won't happen. The boring head has to be
redialed in
each time it's replaced.
RichD KT4IZ

On Feb 28, 5:44 pm, RichD wrote:
Andrew,
you didn't actually say, but I suspect you changed out the boring head
for other
tooling then put it back in for finishing the other pieces, etc.
That's where the error lies. Don't expect R8 tooling in a worn mill
spindle to
repeat position precisely. Won't happen. The boring head has to be
redialed in
each time it's replaced.
RichD KT4IZ

Rich, that sounds quite plausible....it is an old machine, its got
"Adcock and Shipley" cast in the side rather than being plastered with
American flags like the 2 new ones they have. And while its got an X-Y
digital readout, theres no Z axis readout like the new ones ( which
dont need to be periodically whacked to stop the display
flickering...) And it is R8 - I think (and correct me if I am wrong)
that the new ones use MT3 - it took the storeman a while to find a R8
to MT2 adapter for the 14.5mm drill. There was only one in the store,
and is apparently only used on this particular machine. Drill fell out
of the adapter the first time I used it - was told, "yes, its worn -
wack it in with the copper headed hammer.." The boring head was also
marked "Bridgeport" so it would have been the same vintage as the
machine....

I had marked out the hole locations in the two end blocks using a
vernier height gauge and the marking out table and an angle plate and
layout blue to ensure correct alignment of the shaft - even so, they
were out of alignment. I had put it down to doing something stupid on
my part. (yes, I had centre drilled, then pilot drilled, then final
size to 14.5 - it was a bloody tedious process I can assure you, lots
of tool swapping...)

I did do 2 practice bores, and got good results each time - maybe I
fluked the correct positioning....???

I am a relative novice at his, have a mini-mill at home, and its no
comparison as far as rigidity and precision (or sheer grunt) compared
to the mill I was using at school. Would gladly swap if given the
chance...

I was swapping tooling between the drill and the boring head - by the
end of the day, my arm was sore from raising/lowering the table, and
the bloody boring head had got me fingers a few times when it released
- I could spin it in/out from the bottom rather than struggle with the
stiff drawbar at the head end. The newer machines have some sort of
guide pin so you cannot do that - (Yes, I did pack it out with rags
underneath so as not to damage the cutter) That, and the speed changes
each time from drilling to milling - the high/low range thing where it
also changes direction of rotation is a pain, especially as it didnt
want to lock in all the time - only crunched it once, then realised
that in high range you could rotate the boring head by hand till it
engaged properly....

So, I will have another go next week on one of the new machines - (get
in early, be first in line at the tool store for the milling kit for
one of the new ones.) See if that makes a difference.

The problem for me, as I said, is my sheer inability to measure the
tiny tolerances involved in boring the holes - the only way to check
was to remove the job and then take it over to the arbor press and see
if it worked - but this meant that you lost tool registration so
couldn't put it back in the machine to try again - maybe there is some
"easy" way of doing this - any old hands got any helpful hints here?

BTW - noticed your callsign - the project is for going to be the
rotary optical chopper for the "PICASTAR" DDS DSP transceiver. The
bearing housing machining is the tightest tolerance thing I have
attempted to date...the actual PICASTAR is in the same category of
complexity as far as HB radio goes....

Regards,

Andrew VK3BFA.

wrote in news:e69e0683-12c0-4d97-bdbb-0e47cffe4f71
@u72g2000hsf.googlegroups.com:

The most logical problem to your measuring issue is you do not have the
telescoping gauge square to the hole each time. As a simple thing, square
up two edges of two blocks the same or slightly thinner than the handle
stem on your telescoping gauge. Drill a couple of holes in the blocks. Then
use some wire ties to strap the Telescoping gauge stem to the blocks, with
the blocks being about 90 degrees to each other. This should square up the
gauge in the hole for more repeatable measurement.



--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

On Feb 28, 10:20 pm, Anthony wrote:
wrote in news:e69e0683-12c0-4d97-bdbb-0e47cffe4f71
@u72g2000hsf.googlegroups.com:

The most logical problem to your measuring issue is you do not have the
telescoping gauge square to the hole each time. As a simple thing, square
up two edges of two blocks the same or slightly thinner than the handle
stem on your telescoping gauge. Drill a couple of holes in the blocks. Then
use some wire ties to strap the Telescoping gauge stem to the blocks, with
the blocks being about 90 degrees to each other. This should square up the
gauge in the hole for more repeatable measurement.

--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

Quite true - I do know how to do it - your method is a bit more
elaborate than what I knew, so thank you.

But it wouldn't work - the table doesn't go down far enough to clear
the gauge handle to get it vertical.(Have tried....) And if I remove
the job, or the tooling, to do so, then that introduces more
complications....

Andrew VK3BFA.

wrote in message
...
Put the job pieces in the mill vice, locked
the tables, drilled a
14.5mm hole and then, without changing
anything in the X-Y dimensions,
used the boring head, Result - holes were
undersize...stuffed 2 more
bearings.....(thats ok, had heaps of them from
discarded VCR's)

Look at the bright side----the holes were
undersize. Beats the crap out of the
other alternative, oversize holes. Been
there/done that. Sucks. Bore it
bigger/machine and press in a sleeve/recut the
bore.

Bill

How smooth is the bottom of the clamping slot in the telescoping
gauge? A poorly machined one can shift as it's tightened.

If the quill is worn, the boring head may deflect and cut smaller as
it extends down. I have to clamp the quill tightly and raise the table
to get a parallel bore.

Jim Wilkins

FWIW, when I do something like this I:

Clamp directly to the table. Use parallels or 123 blocks to keep it
slightly raised. Limit the downstroke with the stop and put some
scrap
underneath just in case.

Cut out as much material as possible before I get to the boring head
part. Then start the few thou at a time boring part. :-)

Use a telescoping gage to check progress.

Try never to change the setup until it's done.

Also, when I start to get stressed things start to go WRONG. So I try
to back off,
do something else, ...



It sounds to me like your main problem is that you are not comfortable
with
telescoping gages. They are a little fiddley so I would suggest that
you play
around with them a bit until you get the hang.

Not using a vise will make the setup more reliable and give you more
clearance to measure.

DOC

On Feb 28, 9:59*am, wrote:


It sounds to me like your main problem is that you are not comfortable
with
telescoping gages. They are a little fiddley so I would suggest that
you play
around with them a bit until you get the hang.

True. You have to learn that you do not set the gauge to the bore,
but use the bore to set the gauge. You don't try to square it up in
the bore and then lock it. That will give you a false reading, as you
may or may not be square in the bore, and you may or may not be at the
largest diameter. Instead, you lightly lock it at an oversize and
gently wiggle it through the bore, allowing the bore to compress it to
the true size. Lock that size and then continue to wiggle it - there
is a lot of feel involved.

John Martin

Andrew,

I'm going to try and answer some points that may not have been
covered, and offer alternative answers.

I agree with the previous answers, all good.

If you don't have a telescope gage, then there is an alternative.
Make a plug gage on the lathe. A rod with 3mm long sections at 14.95,
then 14.96, 14.97, 14.98, 14.99, 15.00, 15.01 will possibly do the
trick for you. Then it is used as a go-no-go gage. You don't need to
remove the part.
Some folks prefer to make a gradually tapered gage and use bluing, or
use commercial taper pins. When using a tapered pin, you measure at
the exact point of contact.

As to your inquiry about the flapper. I would use a piece of scrap
about 10mm diameter, and saw it on the bandsaw along the central axis
for about 5mm (A round tuning fork), Insert a 4mm wide strip of emory
and wrap it around, grit out. When you get to about 14mm diameter,
that's enough. Use in a drill chuck.

This is a good time to insert a safety note: (since the thought may
have crossed your mind): ABSOLUTELY NEVER stick your finger into a
rotating part with sandpaper.

Morse taper mill quills are typically very old, Bridgeport invented
the R8 and is considered better by most. Shorter fatter tapers are
more ridgid and found on heavier machines.


Dave

On Thu, 28 Feb 2008 07:21:19 -0800 (PST), John Martin
wrote:

On Feb 28, 9:59=A0am, wrote:


It sounds to me like your main problem is that you are not comfortable
with
telescoping gages. They are a little fiddley so I would suggest that
you play
around with them a bit until you get the hang.

True. You have to learn that you do not set the gauge to the bore,
but use the bore to set the gauge. You don't try to square it up in
the bore and then lock it. That will give you a false reading, as you
may or may not be square in the bore, and you may or may not be at the
largest diameter. Instead, you lightly lock it at an oversize and
gently wiggle it through the bore, allowing the bore to compress it to
the true size. Lock that size and then continue to wiggle it - there
is a lot of feel involved.

John Martin

Your absolutely correct John. I see a lot of people that don't measure
using telescoping gauges correctly. And they call them snap gauges. I
hate that!
What works for me is this, I place the T-gauge in the bore with the
large diameter pin pointed towards me and I have the gauge tilted away
from me a little. I snug up the gauge and keeping the larger pin
stationary, roll the gauge towards myself so the small pin finds the
center of the bore and the gauge collapses slightly. I tighten the
gauge a little as it rolls out of the bore towards me. I measure and
measure until I have at least 3 readings that coincide with each
other. I get very consistent readings doing it this way.
This is what works for me.

- it is , for me
anyway, virtually impossible to actually measure the diameter of the
hole via the telescopic bore gauge/micrometer method,

I understand convictions like that. I was certain for 40 years that I
could never hit the other side of a room with an M1911. I now have 2
of 'em and I can hit the other side of a room with both. G

Telescoping gages are fiddley, but they are somewhere between useful
and indispensable in a task like yours. A machinist must be able to
measure accurately. Get someone who is capable with them to coach
you a bit. Plan on spending a patient hour or whatever it takes to
become functional and comfortable with these tools. It'll be a
good investment of your time to gain a skill you need and will use.

Boring heads don't always or often get things "tits" on the first
pass. Make subsequent passes until the tool is no longer cutting.
Things flex and wiggle under load, the only question is how much. This
is particularly true in home shops and in schools with old machines
that have seen a lot of use.

It is possible to do the task you describe with a boring head on a
mill, but for accurate work I would choose a lathe whenever possible
because it is possible to get a more rigid setup and it's easier to
sneak up on a precise dimension -- once you can measure your work.
Grab your work on a faceplate or in a 4J, center it (more fiddly
work), then start boring. Again, as you get close (within a thou or
three), make more than one pass without changing anything on the
machine. This doesn't always work well with stainless but that's
another matter -- it works fine with mild steel, ally or brass and a
sharp, well-ground HSS cutter. Use carbide tooling on cast iron.

Flap paper is not a good approach because it can give you an hourglass
or barrel-shaped hole. If you want a precise cylindrical hole you
must generate it with rigid tooling. Fine finishing can be done with
a lap or rigid hone, but that isn't necessary for a bearing housing
and particularly not for one made of ally.

wrote:

Was shown how to use a boring head at school - (always wondered what
they were for) nice big Bridgeport mill, good quality tooling, so
cannot blame anything in that department.


OK. Having got it right, did two more practice holes in the scrap, all
went well. Been fooled before by blind luck, so wanted to check it was
consistent - it had taken EONS to size and square the two end bearing
retainer blocks, so didnt want to stuff them up.

Put the job pieces in the mill vice, locked the tables, drilled a
14.5mm hole and then, without changing anything in the X-Y dimensions,
used the boring head, Result - holes were undersize...stuffed 2 more
bearings.....(thats ok, had heaps of them from discarded VCR's)
So, you crept up on the diameter with many fine passes of the
boring head, then tried to bore the real part in one pass,
without changing the setting on the boring head?

Well, you have just met Mr. tool deflection! The boring bar
(and maybe the head, too) has bent away from the workpiece due
to the thicker cut, and you didn't cut as much as you expected.
No surprise. Possibly the alloy was different, too.

I also use those awful telescoping bore gages, and they give
erratic readings, but I know why. By feel, I can tell when I am
getting an accurate reading. The trick is to tighten the
locking knob while the measuring points are at an angle in the
bore, then straighten them out so the bore pushes them inward.
When you have them straight across the bore, wiggle the handle
to see if the points are truly on the diameter or have gotten
stuck across a chord. If not on the diameter, you can make the
points move at right angles to the diameter they are supposed to
be reading. I've always wondered if a Starret set of gauges
would work better than these Chinese klunkers.

Jon

"Jon Elson" wrote in message
...
wrote:

Was shown how to use a boring head at school - (always wondered what
they were for) nice big Bridgeport mill, good quality tooling, so
cannot blame anything in that department.


OK. Having got it right, did two more practice holes in the scrap, all
went well. Been fooled before by blind luck, so wanted to check it was
consistent - it had taken EONS to size and square the two end bearing
retainer blocks, so didnt want to stuff them up.

Put the job pieces in the mill vice, locked the tables, drilled a
14.5mm hole and then, without changing anything in the X-Y dimensions,
used the boring head, Result - holes were undersize...stuffed 2 more
bearings.....(thats ok, had heaps of them from discarded VCR's)
So, you crept up on the diameter with many fine passes of the boring head,
then tried to bore the real part in one pass, without changing the setting
on the boring head?

Well, you have just met Mr. tool deflection! The boring bar (and maybe
the head, too) has bent away from the workpiece due to the thicker cut,
and you didn't cut as much as you expected.
No surprise. Possibly the alloy was different, too.

I also use those awful telescoping bore gages, and they give erratic
readings, but I know why. By feel, I can tell when I am getting an
accurate reading. The trick is to tighten the locking knob while the
measuring points are at an angle in the bore, then straighten them out so
the bore pushes them inward.
When you have them straight across the bore, wiggle the handle
to see if the points are truly on the diameter or have gotten stuck across
a chord. If not on the diameter, you can make the
points move at right angles to the diameter they are supposed to be
reading. I've always wondered if a Starret set of gauges would work
better than these Chinese klunkers.

I have a couple of sets of Starrett telescoping bore gages, and they work
pretty well. I've compared their readings with those from a Mitutoyo
three-fingered bore gage, testing them inside of ring gages, and I could get
final readings to agree plus or minus 0.0005" or so. (Getting to test things
like that was one of the perks of having had Mitutoyo for an advertising
client.)

But that was with "perfect" bores in top-quality ring gages. (I think they
were Mitutoyo, too, but I don't remember.) I wouldn't expect great accuracy
from telescoping gages unless the surface and the cylindricity are perfect.

--
Ed Huntress

I had to exercise a set of Chinese telescoping gauges for a few minutes
each to get rid of a lot of the rough travel (but not all!). Wonder how
PEC telescoping gauges are finished?

Jon Elson wrote:
reading. I've always wondered if a Starret set of gauges would work
better than these Chinese klunkers.

Jon

On Thu, 28 Feb 2008 12:07:26 -0600, Jon Elson
wrote:

wrote:

Was shown how to use a boring head at school - (always wondered what
they were for) nice big Bridgeport mill, good quality tooling, so
cannot blame anything in that department.


OK. Having got it right, did two more practice holes in the scrap, all
went well. Been fooled before by blind luck, so wanted to check it was
consistent - it had taken EONS to size and square the two end bearing
retainer blocks, so didnt want to stuff them up.

Put the job pieces in the mill vice, locked the tables, drilled a
14.5mm hole and then, without changing anything in the X-Y dimensions,
used the boring head, Result - holes were undersize...stuffed 2 more
bearings.....(thats ok, had heaps of them from discarded VCR's)
So, you crept up on the diameter with many fine passes of the
boring head, then tried to bore the real part in one pass,
without changing the setting on the boring head?

Well, you have just met Mr. tool deflection! The boring bar
(and maybe the head, too) has bent away from the workpiece due
to the thicker cut, and you didn't cut as much as you expected.
No surprise. Possibly the alloy was different, too.

I also use those awful telescoping bore gages, and they give
erratic readings, but I know why. By feel, I can tell when I am
getting an accurate reading. The trick is to tighten the
locking knob while the measuring points are at an angle in the
bore, then straighten them out so the bore pushes them inward.
When you have them straight across the bore, wiggle the handle
to see if the points are truly on the diameter or have gotten
stuck across a chord. If not on the diameter, you can make the
points move at right angles to the diameter they are supposed to
be reading. I've always wondered if a Starret set of gauges
would work better than these Chinese klunkers.

Not really. Ive got Starrets, and its much the same. If you really
really work at it..and take multiple readings, you might get within
..001 of actual hole size..on average.

I think of them as Telescoping Aproximaters.

Shrug
Gunner


Jon

There is another method for precision measuring of holes. Inside
micrometers.

http://www.shars.com/product_categor...de_Micrometers

I have been using them for years, and wouldn't be without them,
although I only have up to two inch.
Since the barrel travel is not intuitive (to me), I always check the
reading with a caliper to verify, or a calibrated outside micrometer
for precise measurements. The 2" does have some spring, and a good
feel is required to get better than .0005".

Usual disclaimers about Shars, and Chinese tools.
Dave

wrote:

Sigh...another question from StudentLand, that strange area where,
after reading the textbook, being shown what to do by the teacher, the
results are STILL all over the place......

I always insert the telescoping gage with the points as close to center line
but the handle tilted off bore axis and 'wipe' the bore with the screw
locked. The only way the gage can come out is by the bore forcing the gage
to a more closed position.

A developed sense of feel is essential along with duplicate measuring to
deal with errors in technique. I use some ancient Starrets where only one
side telescopes. Haven't let me down yet.

I assume you have access to a lathe and sand paper. You could make your own
dedicated plug gages to check the fit of the hole. Turn it close, sand to
final diameter.

Wes

Nobody's yet mentioned that there are 2 types of these telescoping bore
gauges. One has a fixed anvil, the other both anvils move. I find the
fixed anvil type better to use. They can be easily adjusted by tapping
the handle on a suitable object, say a toolpost, so that the movable
anvil either gives a smaller reading. Or, by turning it over, the
movable anvil gives a bigger reading. I don't think I'd trust any
measurement taken by locking the gauge while it's in the bore.
A nice old-fashioned spring caliper could be used too.
Jordan

On 2008-02-28, wrote:
On Feb 28, 5:44 pm, RichD wrote:
Andrew,
you didn't actually say, but I suspect you changed out the boring head
for other
tooling then put it back in for finishing the other pieces, etc.
That's where the error lies. Don't expect R8 tooling in a worn mill
spindle to
repeat position precisely. Won't happen. The boring head has to be
redialed in
each time it's replaced.
RichD KT4IZ

[ ... ]

The problem for me, as I said, is my sheer inability to measure the
tiny tolerances involved in boring the holes - the only way to check
was to remove the job and then take it over to the arbor press and see
if it worked - but this meant that you lost tool registration so
couldn't put it back in the machine to try again - maybe there is some
"easy" way of doing this - any old hands got any helpful hints here?

It depends on what is in the shop's toolroom. If you can get a
tri-mike in the appropriate size range, you can get much better readings
-- to 0.0002" IIRC. Tri-mike is the Brown & Sharpe/Tesa brand's name.
Mitutoyo makes another model and Etalon yet another. These have three
arms which project at 120 degree intervals, so the tool is
self-centering. But they are quite expensive new, so a school shop may
not have them.

But -- another consideration is thermal expansion. You drilled
with a large bit through a thicker workpiece than the original one (thus
generating more heat) -- or perhaps just wider and thus more distant
from the jaws (so it cools more slowly). This means that the heat of
the drilling will expand the workpiece and the hole will be bored to
size *before* the workpiece cools off and shrinks. Once it shrinks, the
hole will get smaller along with the workpiece. (This in addition to
the uncertainty of the cutting radius of the boring head being exactly
the same with each reinstallation which has already been brought up.)

Thermal expansion is a killer when you are aiming for precision.
If you have flood coolant, you will have less problem with this.
Otherwise, the only choice is letting it cool for a *long* time between
rough cut and finish cut.

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 2008-02-28, Wes wrote:
wrote:

Sigh...another question from StudentLand, that strange area where,
after reading the textbook, being shown what to do by the teacher, the
results are STILL all over the place......

I always insert the telescoping gage with the points as close to center line
but the handle tilted off bore axis and 'wipe' the bore with the screw
locked. The only way the gage can come out is by the bore forcing the gage
to a more closed position.

Hmm ... with aluminum, at least, you want the gauge only
semi-locked. The aluminum is probably soft enough to deform instead of
forcing the gauge to proper dimensions with it seriously locked. Once
you have the feel right, then try fully locking the gauge and make sure
that it still wipes through with the same drag as before. If it
produces more drag, the gauge has shifted when you fully locked it, and
it is time to try again.

A developed sense of feel is essential along with duplicate measuring to
deal with errors in technique. I use some ancient Starrets where only one
side telescopes. Haven't let me down yet.

They are good ones. Some which I have had from GSA were really
rough. Interestingly enough, a Craftsman set from the early 1970s was
as good as the Starrett. But they shift makers from time to time. At
that time, they were using Scherr Tumico as the maker of their
micrometers.

I assume you have access to a lathe and sand paper. You could make your own
dedicated plug gages to check the fit of the hole. Turn it close, sand to
final diameter.

Indeed.

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 ---

"John Martin" wrote in message
...
On Feb 28, 9:59 am, wrote:


It sounds to me like your main problem is that you are not comfortable
with
telescoping gages. They are a little fiddley so I would suggest that
you play
around with them a bit until you get the hang.

True. You have to learn that you do not set the gauge to the bore,
but use the bore to set the gauge. You don't try to square it up in
the bore and then lock it. That will give you a false reading, as you
may or may not be square in the bore, and you may or may not be at the
largest diameter. Instead, you lightly lock it at an oversize and
gently wiggle it through the bore, allowing the bore to compress it to
the true size. Lock that size and then continue to wiggle it - there
is a lot of feel involved.

John Martin

Not a lot-----it's everything. If the method you described is not used, they
won't provide a reading worth having.

I've done .0002" tolerance work with telescoping gauges all my active years.
If you acquire the feel, they're very accurate, assuming you understand that
you must duplicate the feel of the bore with your mic when you check the
reading. It's all about experience, which comes from doing it again and
again and again-------you get the idea.

Harold

"Mechanical Magic" wrote in message
...
There is another method for precision measuring of holes. Inside
micrometers.

http://www.shars.com/product_categor...de_Micrometers

I have been using them for years, and wouldn't be without them,
although I only have up to two inch.
Since the barrel travel is not intuitive (to me), I always check the
reading with a caliper to verify, or a calibrated outside micrometer
for precise measurements. The 2" does have some spring, and a good
feel is required to get better than .0005".

Chuckle!

You're joking about using calipers to verify your readings, aren't you?

I don't give a damn about the type of caliper, or how many places it will
display a reading, they can NOT be relied upon for measurements closer than
+/- .003", particularly if you're attempting a press fit with a pin, using
both inside and outside jaws. They're simply not made that precisely, nor
do they retain their original precision after being used for a period of
time.

Where I was trained, QC could not accept or reject any dimension closer than
+/- ,005" with calipers. They were caught way too many times missing the
boat by a thou or two.

Aside from dial bore gauges, or inside mics, there's nothing quite as good
as telescoping gauges in the hands of someone that knows how to use them.

Harold

"Jordan" wrote in message
u...
Nobody's yet mentioned that there are 2 types of these telescoping bore
gauges. One has a fixed anvil, the other both anvils move. I find the
fixed anvil type better to use. They can be easily adjusted by tapping the
handle on a suitable object, say a toolpost, so that the movable anvil
either gives a smaller reading. Or, by turning it over, the movable anvil
gives a bigger reading. I don't think I'd trust any measurement taken by
locking the gauge while it's in the bore.
A nice old-fashioned spring caliper could be used too.
Jordan

Worst possible way you can use them if you expect a proper reading. Learn to
use them as they should be used. The exact way you suggest doesn't work is
proper. Those made by Starrett, the ones the double telescope are far
better, keeping the forces centered. I wouldn't trust one that telescopes
only on one side.

Harold

Harold and Susan Vordos wrote:
"Jordan" wrote in message
u...
Nobody's yet mentioned that there are 2 types of these telescoping bore
gauges. One has a fixed anvil, the other both anvils move. I find the
fixed anvil type better to use. They can be easily adjusted by tapping the
handle on a suitable object, say a toolpost, so that the movable anvil
either gives a smaller reading. Or, by turning it over, the movable anvil
gives a bigger reading. I don't think I'd trust any measurement taken by
locking the gauge while it's in the bore.
A nice old-fashioned spring caliper could be used too.
Jordan

Worst possible way you can use them if you expect a proper reading. Learn to
use them as they should be used. The exact way you suggest doesn't work is
proper. Those made by Starrett, the ones the double telescope are far
better, keeping the forces centered. I wouldn't trust one that telescopes
only on one side.

Harold


I didn't invent it, but state as I was taught by a metalworking teacher.
You're pretty dismissive, but don't say what the grumble is.
Rather than say yours is the only way, I say there could be more than
one way to skin a cat.

Jordan

On Feb 29, 4:28*am, "Harold and Susan Vordos" wrote:
...You're joking about using calipers to verify your readings, aren't you?....
Harold

I do too, just in case I misread a line on the mic barrel or made a
mental error adding the thimble reading to .075.

Jim Wilkins

Chuckle!

You're joking about using calipers to verify your readings, aren't you?

I don't give a damn about the type of caliper, or how many places it will
display a reading, they can NOT be relied upon for measurements closer than
+/- .003", particularly if you're attempting a press fit with a pin, using
both inside and outside jaws. They're simply not made that precisely, nor
do they retain their original precision after being used for a period of
time.

Where I was trained, QC could not accept or reject any dimension closer than
+/- ,005" with calipers. They were caught way too many times missing the
boat by a thou or two.

Aside from dial bore gauges, or inside mics, there's nothing quite as good
as telescoping gauges in the hands of someone that knows how to use them.

Harold

Harold,
No, I was very serious.

But, to clarify, the error I tend to make with that thimble is being
off by .025" or .050" because I misinterpret the direction. So, I'm
using the caliper to that accuracy.

I don't know why I have such a problem with those inside mics, never
have a problem with depth mics or normal mics.
Maybe it's a dsylxic tool?

I could not agree with you more, about the accuracy of calipers (on an
outside measurement), and the need for developing a "feel" when using
measuring tools. I learned the art of telescope gage use 40 years ago
while boring motorcycle cylinders. That said, I am more comfortable
using an inside mike and a direct measurement, which still requires
the same level of "feel", practice, and calibration of the measuring
tool.

Where I disagree: measuring a smallish hole with calipers. To suggest
that +-.005" is to be expected, is leading the inexperienced down the
wrong path. I have tried all my calipers with a .2000" ring, and they
ALL read a smaller diameter, by different amounts. I don't believe a
hole measurement to within .010"

Dave

"Mechanical Magic" wrote in message
...


Chuckle!

You're joking about using calipers to verify your readings, aren't you?

I don't give a damn about the type of caliper, or how many places it will
display a reading, they can NOT be relied upon for measurements closer
than
+/- .003", particularly if you're attempting a press fit with a pin,
using
both inside and outside jaws. They're simply not made that precisely,
nor
do they retain their original precision after being used for a period of
time.

Where I was trained, QC could not accept or reject any dimension closer
than
+/- ,005" with calipers. They were caught way too many times missing the
boat by a thou or two.

Aside from dial bore gauges, or inside mics, there's nothing quite as
good
as telescoping gauges in the hands of someone that knows how to use them.

Harold

Harold,
No, I was very serious.

But, to clarify, the error I tend to make with that thimble is being
off by .025" or .050" because I misinterpret the direction. So, I'm
using the caliper to that accuracy.

I don't know why I have such a problem with those inside mics, never
have a problem with depth mics or normal mics.
Maybe it's a dsylxic tool?

I could not agree with you more, about the accuracy of calipers (on an
outside measurement), and the need for developing a "feel" when using
measuring tools. I learned the art of telescope gage use 40 years ago
while boring motorcycle cylinders. That said, I am more comfortable
using an inside mike and a direct measurement, which still requires
the same level of "feel", practice, and calibration of the measuring
tool.

Where I disagree: measuring a smallish hole with calipers. To suggest
that +-.005" is to be expected, is leading the inexperienced down the
wrong path. I have tried all my calipers with a .2000" ring, and they
ALL read a smaller diameter, by different amounts. I don't believe a
hole measurement to within .010"

Dave

Are you talking about spring calipers or sliding calipers, Dave? If we were
to sit down and try it together I could demonstrate repeatable accuracy in a
2" ring of +/- 0.002" with spring calipers; probably half that with good
instruments. An expert can do even better. But if you're talking about
sliding-scale calipers, they're next to useless for measuring the inside of
a ring.

--
Ed Huntress

On Fri, 29 Feb 2008 08:29:21 -0800 (PST), Mechanical Magic
wrote:

Where I disagree: measuring a smallish hole with calipers. To suggest
that +-.005" is to be expected, is leading the inexperienced down the
wrong path. I have tried all my calipers with a .2000" ring, and they
ALL read a smaller diameter, by different amounts. I don't believe a
hole measurement to within .010"

Dave

Mygod, a metalworking post on RCM!

Look carefully at your calipers. On most of them the inside jaws have
a slight flat rather than a knife edge. So, when using them to
measure a hole, you're actually measuring the distance between the two
very tiny chords formed by these flats - a distance that will always
be less than the true diameter of the hole

Are you talking about spring calipers or sliding calipers, Dave? If we were
to sit down and try it together I could demonstrate repeatable accuracy in a
2" ring of +/- 0.002" with spring calipers; probably half that with good
instruments. An expert can do even better. But if you're talking about
sliding-scale calipers, they're next to useless for measuring the inside of
a ring.

--
Ed Huntress

Ed,
I'm speaking of direct measuring sliding calipers, I have vernier,
dial and electronic.

I think they are greatly over-rated.
Dave

On Fri, 29 Feb 2008 09:31:25 GMT, "Harold and Susan Vordos"
wrote:


"Jordan" wrote in message
. au...
Nobody's yet mentioned that there are 2 types of these telescoping bore
gauges. One has a fixed anvil, the other both anvils move. I find the
fixed anvil type better to use. They can be easily adjusted by tapping the
handle on a suitable object, say a toolpost, so that the movable anvil
either gives a smaller reading. Or, by turning it over, the movable anvil
gives a bigger reading. I don't think I'd trust any measurement taken by
locking the gauge while it's in the bore.
A nice old-fashioned spring caliper could be used too.
Jordan

Worst possible way you can use them if you expect a proper reading. Learn to
use them as they should be used. The exact way you suggest doesn't work is
proper. Those made by Starrett, the ones the double telescope are far
better, keeping the forces centered. I wouldn't trust one that telescopes
only on one side.

Harold

My Starrets only telescope on one side.....

Gunner

"Mechanical Magic" wrote in message
...

Are you talking about spring calipers or sliding calipers, Dave? If we
were
to sit down and try it together I could demonstrate repeatable accuracy
in a
2" ring of +/- 0.002" with spring calipers; probably half that with good
instruments. An expert can do even better. But if you're talking about
sliding-scale calipers, they're next to useless for measuring the inside
of
a ring.

--
Ed Huntress

Ed,
I'm speaking of direct measuring sliding calipers, I have vernier,
dial and electronic.

I think they are greatly over-rated.
Dave

Yes, I agree. I have some good ones myself, including Swiss vernier types,
digital Mitutoyos, and dial Starretts. I only use them for approximate
measurements.

Spring calipers, though, are a topic unto themselves. I use them mostly for
comparative measurements but you can get surprisingly accurate absolute
measurements from them, checking them with a micrometer. They're a great
boon to the hobby machinist who learns how to use them well.

--
Ed Huntress

Here is a way to get a feel for telescoping gauges. I checked two
tenth-reading mikes with a 1" standard, then left one at 1.0000, set a
telescoping gauge in it, and measured the gauge with the other, a high
quality Federal indicating mike. The first try was 0.004" off but
after several attempts I can hit within 0.0001". This may not work
nearly as well on a bored surface as a polished mike anvil, though.

Jim Wilkins.

Disclaimer: I'm not a machinist, but I am a metalworker/blacksmith.

I've read this entire fascinating thread and my question is:
"Who manufactures precision measuring tools, and what are *their*
methods and techniques; Etc.?"

I ask this partly because I have experience successfully smelting iron
from ore in a bloomery I made, on a regular demo basis and my spiel
includes describing how "tools make tools that make better tools".

The manufacturing of precision measuring tools (or concepts involved)
is an art that appeals to me. It is the result of natural resources,
time, and a homonid brain.
It's chaos and order, analog and digital. A man's "random" fingers,
hands and eyes create an orderly tool using a tool...

I'm young, still learning, and sure others have written on just this
subject.

Any comments or links I might enjoy?

Thanks ~Dave

Gunner wrote:

My Starrets only telescope on one side.....

So do mine. I'm going to have to try measuring some ring gages in the qa
lab this week to test my hand.

Wes

"Dave" wrote in message
...

Disclaimer: I'm not a machinist, but I am a metalworker/blacksmith.

I've read this entire fascinating thread and my question is:
"Who manufactures precision measuring tools, and what are *their*
methods and techniques; Etc.?"

I ask this partly because I have experience successfully smelting iron
from ore in a bloomery I made, on a regular demo basis and my spiel
includes describing how "tools make tools that make better tools".

The manufacturing of precision measuring tools (or concepts involved)
is an art that appeals to me. It is the result of natural resources,
time, and a homonid brain.
It's chaos and order, analog and digital. A man's "random" fingers,
hands and eyes create an orderly tool using a tool...

I'm young, still learning, and sure others have written on just this
subject.

Any comments or links I might enjoy?

Thanks ~Dave

It sounds like you'd enjoy a book titled _The Foundations of Mechanical
Accuracy_, by Wayne Moore. You can find it in some big libraries. Your
research librarian probably can order it on an inter-library loan. Also look
for any of the earlier books on accuracy and machine tools by his father,
Richard Moore.

--
Ed Huntress

On 2008-02-29, Harold and Susan Vordos wrote:

"Mechanical Magic" wrote in message
...
There is another method for precision measuring of holes. Inside
micrometers.

http://www.shars.com/product_categor...de_Micrometers

I have been using them for years, and wouldn't be without them,
although I only have up to two inch.
Since the barrel travel is not intuitive (to me), I always check the
reading with a caliper to verify, or a calibrated outside micrometer
for precise measurements. The 2" does have some spring, and a good
feel is required to get better than .0005".

Chuckle!

You're joking about using calipers to verify your readings, aren't you?

I don't know for sure, but I think that it may be a case of
using calipers to be sure about the more significant digits. The ones
which I saw at the web site were not what I was thinking of, which was
the short 0.500" range micrometer thimble with screw-on tubular
extensions to allow it to measure the inside of a bore. Since there is
the basic length of the micrometer itself, plus the possible added
length of tubular spacers on either side, it is easy to lose track of
what the zero length should be, so it is easy to be off by 0.500" if you
add the parts incorrectly. Using the calipers to get the approximate
length will help you to be sure that your readings are in the right
ballpark, and is something that I would do to be sure if I did not use
the tubular inside mics often enough to trust how they read. IIRC, the
set which I used at work had a non-intuitive 1.250" length for fully
closed with just the basic end caps and no extensions.

I certainly don't think that he meant that he was using the
calipers to get the final digits right, just the coarser measurements.

I don't give a damn about the type of caliper, or how many places it will
display a reading, they can NOT be relied upon for measurements closer than
+/- .003", particularly if you're attempting a press fit with a pin, using
both inside and outside jaws. They're simply not made that precisely, nor
do they retain their original precision after being used for a period of
time.

Of course.
Where I was trained, QC could not accept or reject any dimension closer than
+/- ,005" with calipers. They were caught way too many times missing the
boat by a thou or two.

Aside from dial bore gauges, or inside mics, there's nothing quite as good
as telescoping gauges in the hands of someone that knows how to use them.

My own favorite is the tri-mics which will be self-centering and
pretty much self squaring as well. I've got a few sets (picked up in
eBay sales) covering from something lke 1/2" up to about 2", plus one or
two much larger ones. They are what I use when I really want to be
sure, and I check them against the ring standards which come with the
sets before use.

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 Thu, 28 Feb 2008 13:24:32 -0500, "Ed Huntress"
wrote:


"Jon Elson" wrote in message
m...
wrote:

Was shown how to use a boring head at school - (always wondered what
they were for) nice big Bridgeport mill, good quality tooling, so
cannot blame anything in that department.


OK. Having got it right, did two more practice holes in the scrap, all
went well. Been fooled before by blind luck, so wanted to check it was
consistent - it had taken EONS to size and square the two end bearing
retainer blocks, so didnt want to stuff them up.

Put the job pieces in the mill vice, locked the tables, drilled a
14.5mm hole and then, without changing anything in the X-Y dimensions,
used the boring head, Result - holes were undersize...stuffed 2 more
bearings.....(thats ok, had heaps of them from discarded VCR's)
So, you crept up on the diameter with many fine passes of the boring head,
then tried to bore the real part in one pass, without changing the setting
on the boring head?

Well, you have just met Mr. tool deflection! The boring bar (and maybe
the head, too) has bent away from the workpiece due to the thicker cut,
and you didn't cut as much as you expected.
No surprise. Possibly the alloy was different, too.

I also use those awful telescoping bore gages, and they give erratic
readings, but I know why. By feel, I can tell when I am getting an
accurate reading. The trick is to tighten the locking knob while the
measuring points are at an angle in the bore, then straighten them out so
the bore pushes them inward.
When you have them straight across the bore, wiggle the handle
to see if the points are truly on the diameter or have gotten stuck across
a chord. If not on the diameter, you can make the
points move at right angles to the diameter they are supposed to be
reading. I've always wondered if a Starret set of gauges would work
better than these Chinese klunkers.

I have a couple of sets of Starrett telescoping bore gages, and they work
pretty well. I've compared their readings with those from a Mitutoyo
three-fingered bore gage, testing them inside of ring gages, and I could get
final readings to agree plus or minus 0.0005" or so. (Getting to test things
like that was one of the perks of having had Mitutoyo for an advertising
client.)

But that was with "perfect" bores in top-quality ring gages. (I think they
were Mitutoyo, too, but I don't remember.) I wouldn't expect great accuracy
from telescoping gages unless the surface and the cylindricity are perfect.

This is why I recommended some coaching from someone skilled in the
use of telescoping gages. They are machinist's tools, simple but
quite capable of accuracy to a tenth or two if used properly. They
definitely can and will indicate matters of surface, departure from
cylindricty, taper and other distortions. It's up to the user to use
them both skillfully and intelligently. It ain't that hard to do.

Measuring a bore with a telescoping gage and a mike is not a 15-second
operation. It should be no more than a 30-second operation if the
job is to make a bore in ally to fit a bearing.

I once knew an old machinist that could use ordinary inside transfer
calipers and a mike to measure bores to well under half a thou. It's
all in the feel, drag in the hole and then drag on the mike. Decent
telescoping gages are easy peasy once learned. My Starretts are
slightly better than my Chinese imports, but not a lot better.

"Don Foreman" wrote in message
...
On Thu, 28 Feb 2008 13:24:32 -0500, "Ed Huntress"
snip-------

This is why I recommended some coaching from someone skilled in the
use of telescoping gages. They are machinist's tools, simple but
quite capable of accuracy to a tenth or two if used properly. They
definitely can and will indicate matters of surface, departure from
cylindricty, taper and other distortions. It's up to the user to use
them both skillfully and intelligently. It ain't that hard to do.

Absolutely true-----and proven in practice by my years in the shop.

Don't blame the tool if you can't make it work----they've always worked for
my peers and me. We trusted them to get us through rigid inspection
processes by well qualified and well tooled inspectors in the defense
industry.

Using telescoping gauges successfully, just like running a mill or lathe, or
any other machine tool, requires some skill and experience. I would be
more than insulted for anyone to assume they could step up to these
instruments or tools and expect to enjoy the same degree of success that
those of us that have worked in the trade for years, and paid serious dues
in the process (no, I do not mean union dues), to be able to perform at the
same level. Best thing you can do is get started using them. You can't
gain experience from a book.

Harold

"Mechanical Magic" wrote in message
...
snip----

Where I disagree: measuring a smallish hole with calipers. To suggest
that +-.005" is to be expected, is leading the inexperienced down the
wrong path. I have tried all my calipers with a .2000" ring, and they
ALL read a smaller diameter, by different amounts. I don't believe a
hole measurement to within .010"

Dave

Grin!

I was trying to avoid an ugly confrontation with those the seem to think
that a caliper, particularly a digital, is the ultimate in precision. I've
had conversations with such individuals, and they rarely will be denied
their opinion. What fools they are. I have used a decent scale
(Starrett C305R) with as much precision as I've achieved with calipers.
I use them only when it clearly does not matter. They're great for checking
the size of raw stock.

I got baptism by fire, violating my own rules of not trusting a caliper.
Some time ago, I purchased a Wilson Rockwell hardness tester off ebay. Got
it right, but it had no weights, and had to make new lenses for the
indicator and its cover because they had been warped. Looks like the
instrument had been stored in a hot location, or it had been in the
proximity of a fire, although with no fire or water damage.

I have a fair amount of 4" diameter 304 stainless, a material that I do not
enjoy machining. I knew I'd likely never choose it for a project, so using
some of it for making the weights was a great idea. The design is one of
my own creation, although similar to that of the original maker. I
wanted a counterbore to fit a shouldered turn, so when the weights were
stacked in use, they'd be fairly concentric, and remain on center as they
should. I used an old Helios caliper I've owned since late '57. I know
damned well they aren't perfect, but figured I could use a little Kentucky
windage and achieve a loose slip fit. That's what I got-----but too
loose. I would have been pleased with two or three thou----but had to live
with ten.

Will I ever learn? :-(

Harold