reaming a smaller hole

if you ream a hole and for some reason want it to be smaller than usual, put ethanol on the reamer. this little tip just saved my day. (e.g., holes in thin material tend to come out too large.)

oh, i forgot to mention, this is in steel. in aluminum its actually the other way round, using alcohol will make the hole larger and usind oil will make it smalle.

Brake cleaner makes reamers (and drills) cut to size on most plastics - especially PTFE etc - if not they'll be undersize.

i have noticed a difference in reamed hole size using coolant and a thicker tapping fluid.
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i always thought if what ever is used is not concentrated enough you get a rougher and bigger hole size. i cannot say i have ever seen a hole smaller than the reamer except for plastic which stretches when reamer is in hole and when reamer removed hole relaxes a bit smaller especially noticeable if reamer is dull
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i will have to try alcohol, break cleaner, etc and see if there is a difference on different metals and plastics

Is this due to the fact that alcohol, brake cleaner etc all have a cooling effect and putting it on a reamer would reduce the size very slightly?

CountryBoy19 said:

Is this due to the fact that alcohol, brake cleaner etc all have a cooling effect and putting it on a reamer would reduce the size very slightly?

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Yeah.. not too sure about these anectodes. I wouldn't have imagined it making a difference other than thermal expansion issues as you have raised between having a fluid used or not. Technically if runout and tool diameter are similar, and its doing a cut, it should make that cut. Not sure how a fluid plays to over or under cutting, other than the thermal expansion issue.

On that note, when roughing, normally a lot of heat is generated, especially when you are doing dry minimal lubrication machining. I normally let the part cool down before doing a finishing pass. It actually makes a big difference to surface finish also, apart from just the part tolerance issue.

cncdumm said:

On that note, when roughing, normally a lot of heat is generated, especially when you are doing dry minimal lubrication machining. I normally let the part cool down before doing a finishing pass. It actually makes a big difference to surface finish also, apart from just the part tolerance issue.

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Same here. If I'm finishing hot I'll intentionally shoot a few thou over desired to account for thermal shrink when the part cools. Hasn't come back to bite me yet.

i dont think you get much heat when reaming. with alcohol, you get a smallel hole in steel and a larger hole in aluminum. try it. it took me from a medium interferrence fit to a light press fit with a h7 reamer and a m6 6mm pin in steel.

dian said:

i dont think you get much heat when reaming. with alcohol, you get a smallel hole in steel and a larger hole in aluminum. try it. it took me from a medium interferrence fit to a light press fit with a h7 reamer and a m6 6mm pin in steel.

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Yeah, we were just trying to figure out the logic or science behind it. Could be one makes a better lubricant to do cuts, while the other rubs and leaves a smaller hole. Not sure the logic behind the observation.