Anthony wrote:

"Harold and Susan Vordos" wrote in news:NF5aj.41023
:



Interesting!

Large parts?


3" to 8" diameter parts, 2.5" to about 12" in length. Both aluminum and
steel.



Much easier accomplished in the miniature.



Nothing is easy when you are trying to hold that tight of a tolerance,
especially when you are making that many. *Everything* about the operation
matters. The list of variables that have an effect on the finished quality
magnifies expotentially.


Sounds like hydraulics spool valves or such.

Cheers
Trevor Jones

On 2007-12-19, Nick Mueller wrote:
Harold and Susan Vordos wrote:

which is, a long travel
indicator is able to measure. * *A DTI is distinctly different from a long
travel indicator in that it is specifically made for comparison readings,
due in part to the adjustable tip, which includes parallax error, a
function of the angle of the tip.

Math often helps: :-)
Length of feeler: 19mm
Travel: 0.2mm
Resolution: 0.002mm

Swing in degrees: 0.6°
cos(0.6°) = 0.999945
The error is in the 5th place, two magnitudes less than the resolution

An other one:
Length: 19mm
travel: 1mm
resol.: 0,01mm

- swing 3° - error 0.9986, almost two magnitudes less than the resolution

Note that this is assuming that the feeler is set at the proper
angle to the workpiece surface. Since it is adjustable, it is easy to
set at the wrong angle. Some of these are designed to give the correct
readings with the feeler at a 30 degree angle to the surface, others with
the feeler tangent to the surface.

And add to that the fact that many of these indicators have
interchangeable tips -- of differing lengths. It is accurate (as much
as possible with a swinging tip) only with a single length. Put another
on and you either multiply or divide the readings by some figure.

None of that is an issue with a long
travel indicator, assuming it is set up in the proper attitude in
relationship to the work in question.

Certainly, for long travels you are absolutely right. But that's the reason
why the other type has only such short travels.

So -- how do you make sure that the right tip is used on the
short travel ones -- and at the proper angle to the surface of the
workpiece?

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 ---

"Nick Mueller" wrote in message
...
Ed Huntress wrote:

I see he's getting so many different instructions that we probably have
him thoroughly confused by now. I'll have to leave it to him to sort them
out. d8-)

So maybe he needs the book "Machine Tool Reconditioning".
A friend lent it to me two days ago. I just wanted to have a look at it.
Now I need to buy it. But I knew that before. :-))

Ah, a unique book. You'll probably never see another like it, so you'll want
one to hang on to.

--
Ed Huntress

DoN. Nichols wrote:

Note that this is assuming that the feeler is set at the proper
angle to the workpiece surface.

The same is true for a long travel indicator (LTI). Admittedly, it's easier
to align the LTI properly.

Some of these are designed to give the correct
readings with the feeler at a 30 degree angle to the surface, others with
the feeler tangent to the surface.

And mine even has a table of correction factors depending on the angle. 0.96
for 15°

And add to that the fact that many of these indicators have
interchangeable tips -- of differing lengths.

That's why the manual clearly states: "Length of stylus: The use of stylii
of inappropriate lengths leads to measuring errors!"
RTFM. :-)

So -- how do you make sure that the right tip is used on the
short travel ones

Easy. I never change it. I don't even see a reason to to so. And *IF*, I'll
only buy genuine parts from Mahr.

-- and at the proper angle to the surface of the
workpiece?

By looking at it?

No really, a LTI has his own problems as the DTI has. In both cases, you
have to know how to use them. But I'm not telling you news.
Especially a LTI is a bitch if you want to meassure to a round bar with a
small diameter (OK, "use the flat tip, idiot!"). That's where the DTI
shines.


Nick
--
The lowcost-DRO:
http://www.yadro.de

Trevor Jones wrote in
news:Mx8aj.27659$UZ4.78@edtnps89:



Sounds like hydraulics spool valves or such.


Not really. These are internal engine components.



--
Anthony

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

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Ed Huntress wrote:
"Nick Mueller" wrote in message
...

Ed Huntress wrote:


I see he's getting so many different instructions that we probably have
him thoroughly confused by now. I'll have to leave it to him to sort them
out. d8-)

So maybe he needs the book "Machine Tool Reconditioning".
A friend lent it to me two days ago. I just wanted to have a look at it.
Now I need to buy it. But I knew that before. :-))


Ah, a unique book. You'll probably never see another like it, so you'll want
one to hang on to.

--
Ed Huntress


Borrow it from a public library before you dump a pile of money down!

It IS a good book, but it is strong on the "why" and "where", and not
much on the "how" for a guy that does not have a strong background in
scraping or machine tool accuracy checking.

I borrowed it, and determined that if I ever need the info within, I
can borrow it from the library again, rather than spend the money. I
don't mind spending money on books, and this one was a poor candidate.

As good to have as a test bar! :-)

(running and ducking!)

Cheers
Trevor Jones

"Trevor Jones" wrote in message
news:Vkhaj.8838$wy2.1943@edtnps90...
Ed Huntress wrote:
"Nick Mueller" wrote in message
...

Ed Huntress wrote:


I see he's getting so many different instructions that we probably have
him thoroughly confused by now. I'll have to leave it to him to sort
them
out. d8-)

So maybe he needs the book "Machine Tool Reconditioning".
A friend lent it to me two days ago. I just wanted to have a look at it.
Now I need to buy it. But I knew that before. :-))


Ah, a unique book. You'll probably never see another like it, so you'll
want one to hang on to.

--
Ed Huntress
Borrow it from a public library before you dump a pile of money down!

It IS a good book, but it is strong on the "why" and "where", and not
much on the "how" for a guy that does not have a strong background in
scraping or machine tool accuracy checking.

I borrowed it, and determined that if I ever need the info within, I can
borrow it from the library again, rather than spend the money. I don't
mind spending money on books, and this one was a poor candidate.

The thing about it is that you won't find a lot of that information in any
other place, should you need it. The details about machine tool rebuilding
were mostly confined to oral instructions and proprietary notes until that
came along.

At McGraw-Hill I once had access to what was without a doubt the best
machine tool library in North America. It went back to 1877, with _American
Machinist_ and all of the books M-H published, plus many others. I probably
spent several hundred hours in that library and I never saw so much
information about the subject as in _Machine Tool Reconditioning_.

It won't make you a scraper or much of anything else, but the information
about procedures is there if you should need it. You can learn to scrape
from other sources. In that regard _Machine Tool reconditioning_ shares a
place with Wayne Moore's _Foundations of Mechanical Accuracy_. There's
nothing like either of them.

--
Ed Huntress

"Anthony" wrote in message
...
"Harold and Susan Vordos" wrote in news:NF5aj.41023
:


Interesting!

Large parts?

3" to 8" diameter parts, 2.5" to about 12" in length. Both aluminum and
steel.


Much easier accomplished in the miniature.


Nothing is easy when you are trying to hold that tight of a tolerance,
especially when you are making that many. *Everything* about the operation
matters. The list of variables that have an effect on the finished quality
magnifies expotentially.

--
Anthony

That's true when working under a half thou, but even more so with the work
you're doing. Very impressive, Anthony. I always enjoyed the tight
tolerance work---but only rarely had to be concerned about less than .0002".
It's a whole different world,

Harold

"Harold and Susan Vordos" wrote in
. net:

That's true when working under a half thou, but even more so with the
work you're doing. Very impressive, Anthony. I always enjoyed the
tight tolerance work---but only rarely had to be concerned about less
than .0002". It's a whole different world,


Unfortunately, that's not the tightest tolerance on the part. Have to
hold a bore to +/- 2 microns, and it has to be round within 2.5 microns,
tighter on some parts.
It is a whole different world, from the actual machining to the gauging.
Gauging is more important than the machining, really, because if you
don't have accurate, repeatable measurement results, you will _never_ get
the machining correct.
It's also an entirely different world when you are doing one or two
parts, vs. doing very high volume production (millions/yr).

I kind of chuckle at some of the posts I read about people saying they
are holding +/-0.0005 when they are measuring with a two-point contact
0.0001 dial bore indicator....sorry guys & gals...but you may as well be
measuring with a set of vernier calipers.

--
Anthony

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

Remove sp to reply via email

On 2007-12-19, Nick Mueller wrote:
DoN. Nichols wrote:

Note that this is assuming that the feeler is set at the proper
angle to the workpiece surface.

The same is true for a long travel indicator (LTI). Admittedly, it's easier
to align the LTI properly.

Yes -- it simply needs to be put at 90 degrees to the surface
being measured. And the increased diameter sleeve around the plunger is
an excellent surface for that setting -- or the flat part of the back of
the case.

And if you mount it above a surface plate or baseplate so that
it reads zero (almost full extension) when contacting the plate, you can
then measure by simply lifting the tip and putting the object to be
measured under the tip.

Some of these are designed to give the correct
readings with the feeler at a 30 degree angle to the surface, others with
the feeler tangent to the surface.

And mine even has a table of correction factors depending on the angle. 0.96
for 15°

So you actually have a manual for yours. All of mine are from
swap meets, eBay auctions, or the like, and came without manuals, so I
have to experiment with gauge blocks or at least feeler gauges to
determine what is the proper angle for mine.

And add to that the fact that many of these indicators have
interchangeable tips -- of differing lengths.

That's why the manual clearly states: "Length of stylus: The use of stylii
of inappropriate lengths leads to measuring errors!"
RTFM. :-)

If I *had* the manual, I would. But then why do they supply
multiple interchangeable styli with them? This even goes back to the
level where the Starrett "Last Word" DTIs have spare styli in different
lengths.

So -- how do you make sure that the right tip is used on the
short travel ones

Easy. I never change it. I don't even see a reason to to so. And *IF*, I'll
only buy genuine parts from Mahr.

O.K. Those would not work on most of my DTIs, because they are
of different brands -- and often different stylus mounting systems.

-- and at the proper angle to the surface of the
workpiece?

By looking at it?

:-)

No really, a LTI has his own problems as the DTI has. In both cases, you
have to know how to use them. But I'm not telling you news.
Especially a LTI is a bitch if you want to meassure to a round bar with a
small diameter (OK, "use the flat tip, idiot!"). That's where the DTI
shines.

For measuring the diameter of a small round bar, I would use a
micrometer, not an indicator if I really cared about the results.

To my mind, the DTI has as its primary function determining
centering of a workpiece in a 4-jaw chuck, or in a 3-jaw or collet chuck
with a Set-Tru backplate. The ones which have resolution down to a
"tenth" (0.0001"), or to 0.001mm, simply make it take longer to achieve
the best you can measure. :-)

The long travel ones are mostly used for measuring carriage or
cross-slide travel on a lathe or milling machine (or a jig borer), often
with the aid of a stack of cylindrical standards in a V-groove between
the indicator's tip and the moving part of the machine.

Only secondarily are they to be used for quick-and-dirty
dimension measurements -- usually with a stand whose base acts as a
surface plate.

Oh yes -- I have also seen them mounted in snap gauges, where
you can be sure that the stem is parallel to the dimension being
measured.

And on a surface plate, with a height gauge, you can use a DTI
(mounted to the arm of the height gauge) to compare a workpiece to a
stack of wrung gauge blocks with the assumption that the two are very
close in height, so you are measuring only the difference -- with a
minimum of cosine error -- perhaps verified by using a feeler gauge on
the lower of the two.

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 ---

"Anthony" wrote in message
...
"Harold and Susan Vordos" wrote in
. net:

That's true when working under a half thou, but even more so with the
work you're doing. Very impressive, Anthony. I always enjoyed the
tight tolerance work---but only rarely had to be concerned about less
than .0002". It's a whole different world,


Unfortunately, that's not the tightest tolerance on the part. Have to
hold a bore to +/- 2 microns, and it has to be round within 2.5 microns,
tighter on some parts.
It is a whole different world, from the actual machining to the gauging.
Gauging is more important than the machining, really, because if you
don't have accurate, repeatable measurement results, you will _never_ get
the machining correct.

Agreed.

Only once have I been called upon to do any seriously close tolerance work.
I had to size a set of go/no go ring gauges, many years ago. Had .000020"
tolerance. Got them very close, but small, then they were submitted to
the certified secondary standards lab, where they were seasoned for 24
hours, then measured. They were then returned to the shop with the size
known, for final sizing. It's clear that measuring is typically beyond the
ability of the shop when it gets down to such tight tolerances. There are
far too many variables over which the operator has no control. Mind you,
I'm speaking from the position of the modern shop 30 years ago----I have no
clue what is happening today, obvious by the things you've been stating.

It's also an entirely different world when you are doing one or two
parts, vs. doing very high volume production (millions/yr).

I'd agree, although likely far more reasonable in today's world--with modern
technology.


I kind of chuckle at some of the posts I read about people saying they
are holding +/-0.0005 when they are measuring with a two-point contact
0.0001 dial bore indicator...

Fact is, in the world from which I came, it's not uncommon at all to work
to .0002" by such a method and to be able to measure reliably. You learned
to work accordingly, or you failed. I turned out .0002" tolerance work
routinely, measuring bores with nothing more than a telescoping gauge.
It's all in the training, and certainly not for the feint of heart. The
nature of my work was primarily aero-space and defense, so it was subject to
good and proper inspection. As I've stated on many occasions, this is what
sorts those that can from those that think they can.

While it may be a bit of a stretch for you to come to terms with what I'm
about to say, when I was grinding I could measure with a tenths mic and hit
the size, *reliably*, within .000050". We had a Sheffield shadowgraph at
our disposal, which verified our readings. Probably not very impressive
in today's world, but a Sheffield was cutting edge when I was in the shop.

sorry guys & gals...but you may as well be
measuring with a set of vernier calipers.

I wouldn't go quite that far, but I agree in principle. Anyone that uses a
caliper, be it digital, vernier, or dial, for measurements with a tolerance
of less than .005" is kidding themselves, especially if the measurement must
then be duplicated for a mating part. The transition from inside to
outside, even with very good or new calipers, tends to be less than
acceptable, and introduces more error than the typical tolerance for tight
work. It amazes me that folks don't "get it". I've had serious
ongoing discussions about this very subject. Strangely, the guy that
argues the loudest is often the same guy that has trouble establishing a
desired fit, be it a proper press, or an acceptable snug slip, but fails to
make the connection with his measuring instrument. Might just as well be a
scale. As you suggested, if you can't measure properly, you have almost
no chance of establishing desired dimensions. If you happen to enjoy
success, it's more the luck of the draw.

Harold

"Harold and Susan Vordos" wrote in
. net:

While it may be a bit of a stretch for you to come to terms with what
I'm about to say, when I was grinding I could measure with a tenths
mic and hit the size, *reliably*, within .000050". We had a
Sheffield shadowgraph at our disposal, which verified our readings.
Probably not very impressive in today's world, but a Sheffield was
cutting edge when I was in the shop.

While it _can_ be done, I fail to agree that it can be done reliably over
the long haul. You may be able to do it repeatably, but the day you are
out on vacation, Bob your coworker most likely won't be able to repeat
your success.

By today's quality standards, a gauge must have a resolution a minimum of
10x finer than the tolerance you are measuring. It _must_ long-form R & R
(Range & Repeatability) at less than 20% of your tolerance for general
work, and most all precision component customers require R & R of 10% or
less.
All of our work falls into the latter 10% category.

A long form R & R requires the range and repeatability of the gauge to be
measured, including the human factor, cumulatively all the way back to
the NIST standard.

It's a fairly easy task for a +/-0.001" tolerance, it's an entirely
different story for +/-0.00005" tolerance.

--
Anthony

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

Remove sp to reply via email

On Thu, 20 Dec 2007 08:52:20 GMT, "Harold and Susan Vordos"
wrote:

Anyone that uses a
caliper, be it digital, vernier, or dial, for measurements with a tolerance
of less than .005" is kidding themselves, especially if the measurement must
then be duplicated for a mating part. The transition from inside to
outside, even with very good or new calipers, tends to be less than
acceptable, and introduces more error than the typical tolerance for tight
work. It amazes me that folks don't "get it". I've had serious
ongoing discussions about this very subject. Strangely, the guy that
argues the loudest is often the same guy that has trouble establishing a
desired fit, be it a proper press, or an acceptable snug slip, but fails to
make the connection with his measuring instrument. Might just as well be a
scale. As you suggested, if you can't measure properly, you have almost
no chance of establishing desired dimensions. If you happen to enjoy
success, it's more the luck of the draw.

Hence why they are often called 'very near calipers'

The only reason I've been using a digital caliper recently is my
eyesight is now hopeless when trying to read a conventional micrometer
- I've finally bit the bullet and bought a digital micrometer. It's
just somewhere in the Christmas post and has been for the last week or
so.



--

"Anthony" wrote in message
...
"Harold and Susan Vordos" wrote in
. net:

While it may be a bit of a stretch for you to come to terms with what
I'm about to say, when I was grinding I could measure with a tenths
mic and hit the size, *reliably*, within .000050". We had a
Sheffield shadowgraph at our disposal, which verified our readings.
Probably not very impressive in today's world, but a Sheffield was
cutting edge when I was in the shop.

While it _can_ be done, I fail to agree that it can be done reliably over
the long haul. You may be able to do it repeatably, but the day you are
out on vacation, Bob your coworker most likely won't be able to repeat
your success.

As I've already stated, that's what separates those that can from those that
think they can. Those of us that were successful kept our jobs. Not all
did.


By today's quality standards, a gauge must have a resolution a minimum of
10x finer than the tolerance you are measuring. It _must_ long-form R & R
(Range & Repeatability) at less than 20% of your tolerance for general
work, and most all precision component customers require R & R of 10% or
less.
All of our work falls into the latter 10% category.

I'm not convinced anything has changed where any of that is concerned. It
was common knowledge that tools had to be built with 1/10 tolerance as
compared to the parts for which they were created.


A long form R & R requires the range and repeatability of the gauge to be
measured, including the human factor, cumulatively all the way back to
the NIST standard.

Univac was certified accordingly. While it was not my area of expertise, I
rubbed shoulders with them on a regular basis. It was required that all
measuring instruments in the plant (including personal tools) be certified
monthly. They banded each tool with a given color, designating the last
certification.


It's a fairly easy task for a +/-0.001" tolerance, it's an entirely
different story for +/-0.00005" tolerance.

I thought I said that! :-)

As an operator of grinding equipment, all it took to get on my bad side was
to walk up to the machine and lean on it. That was strictly forbidden, but
few understood the ramifications. I'm sure you must enforce similar, if
not identical, restrictions.

Harold

"Harold and Susan Vordos" wrote in
. net:

As an operator of grinding equipment, all it took to get on my bad
side was to walk up to the machine and lean on it. That was strictly
forbidden, but few understood the ramifications. I'm sure you must
enforce similar, if not identical, restrictions.


We aren't grinding, we are turning. But yes, environmental conditions are
very important, as well as vibration dampening, etc. Even adding coolant to
the machine can only be done in small increments, as a 5 gallon dump of 5
degree different temperature coolant into an 80 gallon tank will change the
diameters the machine cutting.
We also use adaptive control, where you measure the actual
growth/shrinkage of critical parts of the machine due to temperature
changes and compensate for that automatically, as well as automated
feedback compensation from inline measuring equipment, based on statistical
control.

--
Anthony

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

Remove sp to reply via email