From Newsgroup: rec.crafts.metalworking

I have a small pin gage set that has been useful a couple times. .061
to .25 if I recall. I also have a larger pin gage set that has also
only been useful a couple times. I don't recall the range.

Some time back I picked up a set of fractional drill blanks to use as
quick and dirty gages to quickly indentify holes. In atleast one group I
was soundly mocked for it. I don't recall which group. I don't think
it was this one. They are ground pretty accurately their size even if
they have a large gap from one size to the next. I miced them all after
using a Starrett standard to check the mic. They were all 0.0002 to
0.0001 under size. If I am checking a variety of bolt and pin holes on
an assembly its more than good enough most of the time. I've actually
used it more often than both on my precision pin gage sets combined.
Probably a couple times over. I do also have a set of two point inside micrometers, a bore gage, a couple sets telescoping gages, and a set of radiused edge parallel gages. I can measure a round hole "good enough"
for most of my needs.

Today I was doing some planning on reverse engineering a plastic part.
It was broken into three major pieces and there is some distortion. As
near as I can tell it was probably injection molded acetal. Somebody
tried to use CA glue on it, and that was a waste of time. Nothing
chemically glues acetal that I am aware of, and you can only
mechanically glue with epoxies if you prepare the surface for a good mechanical hold. I won't say absolutely can't, but for practical
purposes you can't glue acetal. You screw or pin parts together, you injection mold it in a single piece, or you can melt it together with a
hot knife or a soldering iron, or if you are ballsy a flame. I trimmed
away a lot of distorted bits behind the surface break lines with a
knife, and then stuck it together with a soldering iron.

I need (well want - I'm not getting paid for it) to produce a working facsimile of the part. At first I thought I would 3D scan it, brute
force 4 axis machine it in mild steel, and then dip it in zinc, but
there are two holes whose relative position I think are pretty important
for the function of the mechanism. I do have a probe, but standard hole probing operations are just a straight cross. If you want to be as
accurate as possible you probe the hole, zero the machine, rotate the
probe 180 degrees, probe it again, and divide the result by 2. For
probing multiple holes this way it helps to probe each one using a
different machine offset. This way you can change the current offset,
and move to zero and you are above that hole. You can use one as your
overall reference point or use some other reference entirely, and then
just switch back and forth between the work offset your reference is in
and the current zero position in the work offset for the hole (or other feature) you are zeroed on. You can take this information back to CAD
for finishing the hole layout on your part. It sounds a lot more
complicated than it is. I've probe control panels for reproduction this
way.

In this case I just have two holes so I could probe them both and just
use one as my reference point. Except one of them is bisected on both
sides of the part by one of the break lines and as hard as I tried I was
not able to get a complete undistorted hole. The plastic warped and
stretched a little during failure.

Now this is the clever bit. As near as I can tell one hole is the exact
size of an R drill (0.339) and the other is the exact size of an F drill (0.257). I could press drill blanks into the holes and outside both
holes relative to each other using the pins. Unfortunately I don't have
a set of letter drill blanks. I just have a set of fractions drill
blanks. LOL.

Now here is the stupid part. Or rather the part that shows how stupid I
am. One hole is undamaged totally intact. The other has about 60%-75%
of the hole that looks intact (depends on which side of the part). It
may be distorted a little, but I can locate both holes with an test
indicator on an Indicol (Indicol clone). If I can get zero deflection sweeping the complete hole I have its location relative to whatever my reference is. Then if I can sweep more than half of the broken hole and
get zero or near zero deflection I have its location as good as I am
going to get it. I can do it in the big manual mill with its DRO. And
yes I know how to use an indicator and indicol for edge finding as well.
I think it will be easier to measure on the manual mill than to probe
on one of the CNC mills.

As I sit here thinking about it I keep coming up with ideas for easier
and easier ways to use a test indicator to probe and measure this part.
I may not even need to sweep the holes, but I will anyway to check my
results. Since the holes are small I don't really even need the
indicol. I can just put it on a stem in the spindle.

To be fair having the right size drill blanks would still help.

Never mind all that. Go back to your regularly scheduled program.
--
Bob La Londe
CNC Molds N Stuff

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From Newsgroup: rec.crafts.metalworking

On 4/20/2026 7:14 PM, Bob La Londe wrote:

I have a small pin gage set that has been useful a couple times.-a .061
to .25 if I recall.-a I also have a larger pin gage set that has also
only been useful a couple times.-a I don't recall the range.

Some time back I picked up a set of fractional drill blanks to use as
quick and dirty gages to quickly indentify holes. In atleast one group I
was soundly mocked for it.-a I don't recall which group.-a I don't think
it was this one.-a They are ground pretty accurately their size even if
they have a large gap from one size to the next.-a I miced them all after using a Starrett standard to check the mic.-a They were all 0.0002 to
0.0001 under size.-a If I am checking a variety of bolt and pin holes on
an assembly its more than good enough most of the time.-a I've actually
used it more often than both on my precision pin gage sets combined. Probably a couple times over.-a I do also have a set of two point inside micrometers, a bore gage, a couple sets telescoping gages, and a set of radiused edge parallel gages.-a-a I can measure a round hole "good enough" for most of my needs.

Today I was doing some planning on reverse engineering a plastic part.
It was broken into three major pieces and there is some distortion.-a As near as I can tell it was probably injection molded acetal.-a Somebody
tried to use CA glue on it, and that was a waste of time.-a Nothing chemically glues acetal that I am aware of, and you can only
mechanically glue with epoxies if you prepare the surface for a good mechanical hold.-a I won't say absolutely can't, but for practical
purposes you can't glue acetal.-a You screw or pin parts together, you injection mold it in a single piece, or you can melt it together with a
hot knife or a soldering iron, or if you are ballsy a flame.-a I trimmed away a lot of distorted bits behind the surface break lines with a
knife, and then stuck it together with a soldering iron.

I need (well want - I'm not getting paid for it) to produce a working facsimile of the part.-a At first I thought I would 3D scan it, brute
force 4 axis machine it in mild steel, and then dip it in zinc, but
there are two holes whose relative position I think are pretty important
for the function of the mechanism.-a I do have a probe, but standard hole probing operations are just a straight cross.-a If you want to be as accurate as possible you probe the hole, zero the machine, rotate the
probe 180 degrees, probe it again, and divide the result by 2.-a For
probing multiple holes this way it helps to probe each one using a
different machine offset.-a This way you can change the current offset,
and move to zero and you are above that hole.-a You can use one as your overall reference point or use some other reference entirely, and then
just switch back and forth between the work offset your reference is in
and the current zero position in the work offset for the hole (or other feature) you are zeroed on.-a You can take this information back to CAD
for finishing the hole layout on your part.-a-a It sounds a lot more complicated than it is.-a I've probe control panels for reproduction this way.

In this case I just have two holes so I could probe them both and just
use one as my reference point.-a Except one of them is bisected on both sides of the part by one of the break lines and as hard as I tried I was
not able to get a complete undistorted hole.-a The plastic warped and stretched a little during failure.

Now this is the clever bit.-a As near as I can tell one hole is the exact size of an R drill (0.339) and the other is the exact size of an F drill (0.257).-a I could press drill blanks into the holes and outside both
holes relative to each other using the pins.-a Unfortunately I don't have
a set of letter drill blanks.-a I just have a set of fractions drill blanks.-a LOL.

Now here is the stupid part.-a Or rather the part that shows how stupid I am.-a One hole is undamaged totally intact.-a The other has about 60%-75%
of the hole that looks intact (depends on which side of the part).-a It
may be distorted a little, but I can locate-a both holes with an test indicator on an Indicol (Indicol clone).-a If I can get zero deflection sweeping the complete hole I have its location relative to whatever my reference is.-a Then if I can sweep more than half of the broken hole and get zero or near zero deflection I have its location as good as I am
going to get it.-a I can do it in the big manual mill with its DRO.-a And yes I know how to use an indicator and indicol for edge finding as well.
-aI think it will be easier to measure on the manual mill than to probe
on one of the CNC mills.

As I sit here thinking about it I keep coming up with ideas for easier
and easier ways to use a test indicator to probe and measure this part.
I may not even need to sweep the holes, but I will anyway to check my results.-a Since the holes are small I don't really even need the
indicol.-a I can just put it on a stem in the spindle.

To be fair having the right size drill blanks would still help.

Never mind all that.-a Go back to your regularly scheduled program.

If nothing else I provided Jim atleast a score of jumping off points to
take off on a tangent.
--
Bob La Londe
CNC Molds N Stuff
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From Newsgroup: rec.crafts.metalworking

"Bob La Londe" wrote in message news:10s6n7e$1qa8s$1@dont-email.me...

On 4/20/2026 7:14 PM, Bob La Londe wrote:

If nothing else I provided Jim atleast a score of jumping off points to
take off on a tangent.
------------------------

You actually invited me?? This is just practice, I failed Technical Writing twice in college because I think in multiple dimensions and struggled to
pick a single path to write. The 3D Graphics night school course was easy
for me while the others dropped out and he gave me solo advanced lessons.

I bought an old Microcentric 5C mount chuck that takes customizable pie jaws and practiced an old watchmaking technique to lay out and drill the mounting holes for new jaws.

https://www.gutenberg.org/files/69061/69061-h/69061-h.htm
See figure 8.

The chuck has two protruding 1/8" dowel locating pins to which I fitted two disks that lightly contact. After drilling and reaming one pie jaw hole I inserted a dowel pin and put one disk on it and the other on a dowel pin in the mill collet, and adjusted them to barely let one turn the other. My new jaws all fit snugly.

For one job it was a lot of effort, I now know I can do it and in this case
I might use the disks to make more pie jaws. I located the center of a less critical bearing hole that was heavily worn on the loaded side with the
shank of an inverted (end mill/drill?) in the chuck, then bored larger until it would retain a bronze bushing.

These old methods were useful when I had to locate mounting holes for a
module with a cast plastic case or irregular base that wasn't a good zero reference. Fine old measuring tools without digital readouts sold very
cheaply at auctions.

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