Making and measuring small holes (<8mm)

For small holes, I use my pin gages. If you have a oversize and undersize set, you can come in to within about a half a thou. e.g, your shaft size is between ,2350" and .2354" by your measure and the standard over and under sizes would be .2348" , .2352", and .2358".

Barring that, prior to making the hole, I would turn a set of custom pins, one the exact size required and one or two smaller pins, perhaps a thou undersized for one and a half thou under for another.

I have made custom boring bars out of old drills or taps for holes as small as three mm.
 
An end mill can be pressed into service as a boring bar. If you want to bore a hole at 6mm, drill about 0.02” undersize. Then grip an end mill in your tool post (drill chuck, collet chuck, small vee block - do what ever you need to). Position the end mill (say 3/16” dia)) so only one cutting edge is over at the 9:00 position - just like a small boring bar. Then bore away like normal. Even better if you use a carbide EM (carbide is stiffer).

You didn’t state how deep the hole was, if shallow, you could even use a 1/8” EM. Of course you still need to be able to measure the hole (see comments by others above).
 
Chipper5783 said:
An end mill can be pressed into service as a boring bar. If you want to bore a hole at 6mm, drill about 0.02” undersize. Then grip an end mill in your tool post (drill chuck, collet chuck, small vee block - do what ever you need to). Position the end mill (say 3/16” dia)) so only one cutting edge is over at the 9:00 position - just like a small boring bar. Then bore away like normal. Even better if you use a carbide EM (carbide is stiffer).

You didn’t state how deep the hole was, if shallow, you could even use a 1/8” EM. Of course you still need to be able to measure the hole (see comments by others above).
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I have done this for very small holes , works very well and was more rigid than a cutter I could grind, you can also grind off flutes if you need to go into a small starter hole.

Stu
 
dbb-the-bruce said:
I have both the small hole gauges and a gauge pin set that tops out and .25" along with the fractional inch pin set to .5"
I use the gauge pins more than the small hole gauges but both work pretty well. The small hole gauges don't work well or at all in holes with a bottom less than 1/2 diameter deep.

You could also grind a D-bit and make test holes with it to sneak up on the fit that you want.
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If you buy the small hole gages with the flattened ends, they can be used in quite shallow holes, I refer to Starrett #830 and #831 small hole gages.
 
Small hole gauges look like the missing piece of measuring that I need. I'll definitely be picking up some of them.

I redid my shaft coupler to pulley part. I used a number "1" drill to get into the 5.8mm range. I then carefully lubricated the "A" drill and ran it thru.....shutting the lathe off before backing it out. It did the trick and made something in the 5.97 range. Which is what I needed. In my first try, I think I ran the "A" drill in more than once (bad idea).

The use of a mill cutter for a boring bit seems like a great idea. I have some grossly undersized 6mm carbide mills (about 5.85mm) and some 1/8" mills that I could see working for light cuts. Of course the lathe doesn't turn quite as fast as my PrintNC router mill, but I suspect I can get them to work....once I build an appropriate holder. They are already single flute mills, so they should work w/o any grinding.

Thanks for all the advice! Very helpful.
 
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MrWhoopee said:
As the name implies, Small Hole Gages are the tool for measuring small holes.
View attachment 471573
(Holy crap, those things have gotten expensive!)

Did you simply drill with the A drill? If I was trying to hold close to size, I would drill about .010 -.015 undersize, then "ream" with the A drill. This prevents the grind of the drill point from affecting size.
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I have a set of those. Never used them. I don't know why.
I'll have to give them a try.
I use pin gauges for smallish holes.
 
Janderso said:
That is an amazing price.
$4.59 for 4-6-8-10 mm reamers (4) pack. Plus shipping. OOPS = Free Shipping
Any good??
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It will be a crap shoot, as things can be. But overall, I've had decent experiences for AliExpress stuff. Bought a whole stack of diamond grit wheels for a few bucks a disk, way cheaper than any domestic source could touch. Bought some specialized (weird size) reamers a while back and they were on size and inexpensive as well. Give it a try. I might buy some too, since I have practically no metric reamers.
 
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