Precision hole making methods for small holes

[Mikelangelo]

I'm designing a fixture for quality control and need a few precision holes. Their diameters range from 1/8" to 5/16" and need to be ±0.0002" with a depth of 1/2". I've been looking into EDM hole making and honing, but neither seem to be great for that range of diameters. Anyone know of any other processes that would work or if EDM hole making or honing would work for a hole that size. Its very important for the process to accurately duplicate the hole. There will be two of these fixtures built and the holes need to yield the same result. The hole is used during the QC test and the results are dependent on it.

 

[Nidum]

Are the holes right through or blind ended ??

 

[Mikelangelo]

Are the holes right through or blind ended ??

Currently they're designed as through but I could do them blind. I just assume blind would be easier to manufacture

 

[Nidum]

Through holes are usually much easier to manufacture in smaller sizes .

For your application some simple engineering will work . Using modern quality tooling those holes could just be drilled and reamed by a controlled process and still end up well within tolerance .

The hole sizes and tolerances you quote are common ones for things like dowel pins and these are certainly just drilled and reamed .

This work can be done perfectly well on a standard milling machine or jig borer but best way nowadays would be to get the whole of your component CNC machined and have the holes done at same time . That way you can get precision location of holes as well as precision fit .

 

[Mikelangelo]

Through holes are usually much easier to manufacture in smaller sizes .

For your application some simple engineering will work . Using modern quality tooling those holes could just be drilled and reamed by a controlled process and still end up well within tolerance .

The hole sizes and tolerances you quote are common ones for things like dowel pins and these are certainly just drilled and reamed .

This work can be done perfectly well on a standard milling machine or jig borer but best way nowadays would be to get the whole of your component CNC machined and have the holes done at same time . That way you can get precision location of holes as well as precision fit .

I'm now realizing I forgot to mention that its very important for the process to accurately duplicate the hole. There will be two of these fixtures built and the holes need to yield the same result. The hole is used during the QC test and the results are dependent on it.

 

[MRFMengineer]

I Nidum is right, reaming should be able to do it. Wire EDM as well (not sinker).

Do they really need to be 1/2" deep? That is pretty deep for a precision 1/8" hole.

Does it have to be one plate? Can you somehow use ring gages in tooling?

 

[Baluncore]

The most accurate holes are through holes. 0.0002” on diameter is a close tolerance to meet. It will be necessary to have a temperature controlled environment for the machine operation and possibly when using the fixture.

One way to make calibrated holes is as follows. Drill a pilot hole, then take the hole out close to size with an undersize reamer. Next, hone the hole to dull the finish and remove any reamer marks. Finally, press a lubricated steel bearing ball all the way through the hole. That will deform the honed surface to the final diameter. Keep the reamer and the one ball together as the master for generating those fixtures.

 

[Baluncore]

This might be useful info on ball sizing of holes. https://www.precisionballs.com/Ball_Sizing.php