Countersink Hole Inspection - Old School Technique.

M

MysterHK

#1
From time to time, I ask my father, who is a retired aerospace machinist, some advice.

Today, I explained to him that I was checking a 120 degree countersink hole but did not have the correct countersink gage available to check the tolerance.

He told me of an "old school" method where some special type of wax would be directly poured into the countersink hole to create a mold of the hole and then the mold would be checked.

Is anyone familiar with this technique?
 
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Kingsld1

Involved In Discussions
#2
There's a product called Repo Rubber that works well for those type of applications. I believe Flexbar distributes it. Basically, you mix two compounds together and put it in the hole. After 10-15 minutes cure time you can pop it out and do an optical inspection of the feature. I think they claim a 1 -2 % accuracy.
 

Jim Wynne

Staff member
Admin
#3
From time to time, I ask my father, who is a retired aerospace machinist, some advice.

Today, I explained to him that I was checking a 120 degree countersink hole but did not have the correct countersink gage available to check the tolerance.

He told me of an "old school" method where some special type of wax would be directly poured into the countersink hole to create a mold of the hole and then the mold would be checked.

Is anyone familiar with this technique?
There is such a thing, and I've used it, but I'll be d*mned if I can remember what it's called. The stuff I've seen comes in powder form (like plaster of paris) and is mixed with water, then poured into the cavity, where it sets up in a matter of minutes. Maybe someone else will have a brand name for you or know of a similar product. Unless it's particularly critical, you can always use a fastener with a 120° (or whatever) head, or check the tool used to cut the c'sink if it's an internal operation. A 120° tool isn't too likely to cut an 82° c'sink.
 
M

MysterHK

#5
Unless it's particularly critical, you can always use a fastener with a 120° (or whatever) head, or check the tool used to cut the c'sink if it's an internal operation. A 120° tool isn't too likely to cut an 82° c'sink.
Jim,

My Dad, concurs. I was thinking of possibly making a new type of standards board as a back-up using metrology casts. Sometimes, due to circumstances beyond my control, no one is available in the stockroom to get me the correct fastener.

Thanks again! :tg:
 

Jim Wynne

Staff member
Admin
#6
Jim,

My Dad, concurs. I was thinking of possibly making a new type of standards board as a back-up using metrology casts. Sometimes, due to circumstances beyond my control, no one is available in the stockroom to get me the correct fastener.

Thanks again! :tg:
You're welcome. Whatever works for you. :agree1: When I used to deal with sheet metal with countersunk holes, my biggest pain was engineers who would specify a hole diameter and c'sink diameter without regard for material thickness. The result was a c'sink that opened up the hole considerably past the tolerance. The additional pain was that it really didn't matter much in most instances; the holes were usually just for clearance and certainly didn't need the standard ± .005 tolerance. :mad:
 
#7
In the dim and distant past, I used 'Acrylite' what was (back then) a fast acting acrylic plastic (I think) that you could mix up and (quickly, before it set up) use to take molds of technical features like threads, countersinks (in this case).

It was pretty hard, got into all the nooks and crannies and had no shrinkage etc. Then we put the shape up on the shadograph to see what we'd got.

And that was back in 1970 something............
 

Caster

An Early Cover
Trusted Information Resource
#8
There's a product called Repo Rubber that works well for those type of applications. I believe Flexbar distributes it. Basically, you mix two compounds together and put it in the hole. After 10-15 minutes cure time you can pop it out and do an optical inspection of the feature. I think they claim a 1 -2 % accuracy.
Check here for Repro Rubber, we have used it for a feature that is hard to get a gage on.

http://www.flexbar.com/reprorubber.htm
 
5

56flh

#9
There's a product called Repo Rubber that works well for those type of applications. I believe Flexbar distributes it. Basically, you mix two compounds together and put it in the hole. After 10-15 minutes cure time you can pop it out and do an optical inspection of the feature. I think they claim a 1 -2 % accuracy.

Another product from Flexbar that works well is Facsimile.
 
T

True Position

#10
Another product from Flexbar that works well is Facsimile.
I find Facsimile to be a much bigger mess to deal with then Reprorubber. Reprorubber remains soft, you can kneed it in your hand, no need for a release agent, cures faster, no chemical odor, etc. Facsimile is better if you need a hard casting, like you're trying to check an internal thread on an optical comparator, but for something simple like that chamfer check if you can use Reprorubber it seems much less of a hassle.

A great product all around.
 
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