Has anyone done or heard of someone doing a measurment on a small dia
bore with the low temp melting point alloy that Brownells sells for
taking gun chamber measurements?

The reason I ask is that I recently had to try and press a part with a
..254 boss into a hole that I tried to measure with a small bore gauge.
I tried taking repeat measurements of the hole to make sure that my
part would press in with a light press fit. What I call a light press
fit in this case is about .0003.

The problem was I could get a good mesaurement on the boss but my
technique was really tested by taking the id measurement. Eventually I
gave up and tried to do the press fit anyway. As usual getting
frustrated and rushing caused me to make a press fit that was too
difficult and the part did not get fully seated.

After the fact I thought about using the alloy that Brownells sells. I
figure that it alot easier to make an accurate measurement on the od of
a part so it would be helpful to make a casting of the id and then
meausure the resulting casting. I am assuming that the casting would be
within a few tenths of the bore size.

I would try wax first. Making sure the hole surface is lubricated enough to
pull the wax plug after setting. Get hold of machining wax or investment
casting wax.

wrote in message
oups.com...
Has anyone done or heard of someone doing a measurment on a small dia
bore with the low temp melting point alloy that Brownells sells for
taking gun chamber measurements?

The reason I ask is that I recently had to try and press a part with a
.254 boss into a hole that I tried to measure with a small bore gauge.
I tried taking repeat measurements of the hole to make sure that my
part would press in with a light press fit. What I call a light press
fit in this case is about .0003.

The problem was I could get a good mesaurement on the boss but my
technique was really tested by taking the id measurement. Eventually I
gave up and tried to do the press fit anyway. As usual getting
frustrated and rushing caused me to make a press fit that was too
difficult and the part did not get fully seated.

After the fact I thought about using the alloy that Brownells sells. I
figure that it alot easier to make an accurate measurement on the od of
a part so it would be helpful to make a casting of the id and then
meausure the resulting casting. I am assuming that the casting would be
within a few tenths of the bore size.

On 22 Dec 2005 09:21:30 -0800, "
wrote:
Has anyone done or heard of someone doing a measurment on a small dia
bore with the low temp melting point alloy that Brownells sells for
taking gun chamber measurements?
The reason I ask is that I recently had to try and press a part with a
.254 boss into a hole that I tried to measure with a small bore gauge.
I tried taking repeat measurements of the hole to make sure that my
part would press in with a light press fit. What I call a light press
fit in this case is about .0003.
The problem was I could get a good mesaurement on the boss but my
technique was really tested by taking the id measurement. Eventually I
gave up and tried to do the press fit anyway. As usual getting
frustrated and rushing caused me to make a press fit that was too
difficult and the part did not get fully seated.
After the fact I thought about using the alloy that Brownells sells. I
figure that it alot easier to make an accurate measurement on the od of
a part so it would be helpful to make a casting of the id and then
meausure the resulting casting. I am assuming that the casting would be
within a few tenths of the bore size.
=======================
This is the type of situation that lead to the wide use of GDT
[geometric dimensioning and tolerancing] in production
environments. The diameter of part and hole are "point"
measurements and indeed are critical, however other factors such
as the straightness and concentricity of both the pin and the
hole are involved. It is entirely possible to have a pin that
measures 0.250 and hole that measures 0.255 on the diameters and
still be unable to assemble one in the other.

FWIW -- unless you have a special need for a press fit, use of
newer techniques such as loctite can be a real time saver.
Another technique is to chill the pin and heat the hole
[material] for a shrink fit.

In [too] many cases we get hung up on technique and overlook the
desired result/end use.

Uncle George

I think you'd be frustrated. That low-temperature alloy shrinks
initially, then expands. Gunsmiths know this and make allowances, but
after awhile, the casting ends up larger than the initial cavity. If
you didn't have an absolutely smooth and polished cavity, the stuff
would lock itself in, don't ask how I know. In any case, measuring to
tenths probably wouldn't happen. Your material is probably going to
expand that much just from the hot metal being poured in. Cerro-Safe
is handy to have around for a lot of other uses, though. I've used my
little bars a lot.

My usual method is to finish the hole, use pin gauges to find out what
size I've ended up with, then fit the part to the hole. Much easier
measuring the outside of a part than the inside of a hole. Tenths
tolerance on that small a hole would be tough without some special
equipment for measuring or making up special plug gauges for Go/NoGo.
At the tenths level, you've got to watch your temperatures, too.

Stan

I'm not a machinist, but if I were, I think I would turn a test piece for a
snug fit, mike it, and then add a smidge for the real one.

wrote in message
oups.com...
snip----

.. Tenths
tolerance on that small a hole would be tough without some special
equipment for measuring or making up special plug gauges for Go/NoGo.
At the tenths level, you've got to watch your temperatures, too.

Stan


What is lacking is experience. Those of us that have worked in the trade
accomplish such things on a regular basis. Measuring holes with small
hole gauges can yield consistent results within a tenth, but it takes
practice.

Harold

Harold and Susan Vordos wrote:
wrote in message
oups.com...
snip----

. Tenths

tolerance on that small a hole would be tough without some special
equipment for measuring or making up special plug gauges for Go/NoGo.
At the tenths level, you've got to watch your temperatures, too.

Stan



What is lacking is experience. Those of us that have worked in the trade
accomplish such things on a regular basis. Measuring holes with small
hole gauges can yield consistent results within a tenth, but it takes
practice.

Harold


What type of small hole gauges have you used that consistently yield
results within a tenth?

"tomcas" wrote in message
...
Harold and Susan Vordos wrote:
wrote in message
oups.com...
snip----

. Tenths

tolerance on that small a hole would be tough without some special
equipment for measuring or making up special plug gauges for Go/NoGo.
At the tenths level, you've got to watch your temperatures, too.

Stan



What is lacking is experience. Those of us that have worked in the
trade
accomplish such things on a regular basis. Measuring holes with small
hole gauges can yield consistent results within a tenth, but it takes
practice.

Harold


What type of small hole gauges have you used that consistently yield
results within a tenth?

My choice is Starrett, but it's not so much the make as the experience.
They're no better than the hands that use them. It helps to have something
like Deltronic pins to verify that you are reading them correctly. The
hardest part of using them is in achieving a similar feel with a micrometer.
Finish differences between the mic and the hole make that challenging.
One's background tends to make a difference. If you've always done fine
work, your approach to such things is far different from that of someone
that rarely does so.

Harold

Hey Tex,

Me??? I'd taper a piece of 5/16" soft aluminum with a pull stud end
to a VERY slow taper and drive/tap it into the hole to extrude it,
then stud pull it absolutely straight out, and measure it. Go from
there.

I think I can measure that close with my small bore gages, but I have
a TERRIBLE time now holding things steady to do it. "HOLD" age I
think?? VBG

Take care.

Brian Lawson,
Bothwell, Ontario.
XXXXXXXXXXXXXXXXXXXXXXXXX

On 22 Dec 2005 09:21:30 -0800, "
wrote:

Has anyone done or heard of someone doing a measurment on a small dia
bore with the low temp melting point alloy that Brownells sells for
taking gun chamber measurements?

The reason I ask is that I recently had to try and press a part with a
.254 boss into a hole that I tried to measure with a small bore gauge.
I tried taking repeat measurements of the hole to make sure that my
part would press in with a light press fit. What I call a light press
fit in this case is about .0003.

The problem was I could get a good mesaurement on the boss but my
technique was really tested by taking the id measurement. Eventually I
gave up and tried to do the press fit anyway. As usual getting
frustrated and rushing caused me to make a press fit that was too
difficult and the part did not get fully seated.

After the fact I thought about using the alloy that Brownells sells. I
figure that it alot easier to make an accurate measurement on the od of
a part so it would be helpful to make a casting of the id and then
meausure the resulting casting. I am assuming that the casting would be
within a few tenths of the bore size.

On Thu, 22 Dec 2005 09:21:30 -0800, wrote:

Has anyone done or heard of someone doing a measurment on a small dia
bore with the low temp melting point alloy that Brownells sells for
taking gun chamber measurements?

The reason I ask is that I recently had to try and press a part with a
.254 boss into a hole that I tried to measure with a small bore gauge.
I tried taking repeat measurements of the hole to make sure that my
part would press in with a light press fit. What I call a light press
fit in this case is about .0003.

The problem was I could get a good mesaurement on the boss but my
technique was really tested by taking the id measurement. Eventually I
gave up and tried to do the press fit anyway. As usual getting
frustrated and rushing caused me to make a press fit that was too
difficult and the part did not get fully seated.

After the fact I thought about using the alloy that Brownells sells. I
figure that it alot easier to make an accurate measurement on the od of
a part so it would be helpful to make a casting of the id and then
meausure the resulting casting. I am assuming that the casting would be
within a few tenths of the bore size.

Ask the guy who made the hole? ;-)

Seriously, though, I've used go-no gages, but only to within .001".

Good Luck!
Rich

In article .com,
says...

After the fact I thought about using the alloy that Brownells sells. I
figure that it alot easier to make an accurate measurement on the od of
a part so it would be helpful to make a casting of the id and then
meausure the resulting casting. I am assuming that the casting would be
within a few tenths of the bore size.

That guess is incorrect, as you've probably figured out by now.

There are many ways to measure small bores to high precision, but
rarely is a casting used to do so.

Any of the above could be used: small hole gages (of the kind that
harold is talking about), air gages, gage pins, and so on. All of
those will be better than a casting technique, in terms of accuracy.

If you are only trying to achieve a nice press-fit, I suggest you make
the pin slightly over-long, and turn the extra bit down until it just
slips in. Then turn the rest a thou, or a half thou, over that.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================