Press fit tolerances

flatgrinder

flatgrinder

Joined
Dec 20, 2005
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Anyone know what size drill bit I would need in order to make a hole (into which a 0.124" hardened steel dowel pin can be press fitted) in a piece of steel?

Also, does the hole need to be reamed or can it just be drilled?

Thanks! :thumbup:
 
A .1240" hardened dowel pin would be a very unusual animal. Most standard 1/8" dowel pins are more like .1252". If you're measuring standard dowel pin with calipers and finding it undersized, I'd see that as evidence that your calipers are out of calibration. It is not unusual for a dint or flaw on the tip of the jaws, or dirt to prevent them from closing all the way and be zeroed improperly. It is also not uncommon for play in the moving jaw to allow it to wiggle, giving inaccurate measurements. There are two small screws on the back that can be used to adjust that play out.

Short answer: what Richard said...
 
OOpps.... Did that backwards. The ream should be .001 smaller as they pointed out.

Still, like Nathan pointed out, I would bet a .125 reamed hole will press fit his stock.
 
Yup, .125 dowels are .12525. I ream out to .1245. That will be a press fit. If you have more than one mate up hole you are making, be sure you drill the parts to be joined together.
 
It'll be pressed into a 5/32" thick piece of ATS-34.

I'll double check the measurements. Thank you for all the replies and the advice. :thumbup:
 
Standard practice for most precision assemblies with steel components is dowel pin holes that are .0005" undersize - with a tolerance +/- .0002".
 
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