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12mm h7 hole tolerance

skennan

Plastic
Joined
Dec 1, 2015
Hi guys

I have a job that requires 29 12mm holes marked with a tolerance of h7 +0 -0.018.
I have had a practice and tried piloting and reaming the holes using a 12mm reamer, but they are coming out oversized.

I was wondering what the best way to machine these holes was?

The material is 25mm thick mild steel and I am operating a Wadkin CNC bed mill with Fanuc controls if its important.

Thanks in advance! :)
 
First of all ,do you have an H7 reamer and what does it measure ,I find that they are usually ground to top tolerance when new ,which means they tend to cut big.

I would drill around 11.7mm and if position is important I would bore as the reamer will follow the drilled hole if it is out ,boring also helps with all the other problems but obviously adds another opp.

Assuming you have the right reamer, you want to be running a slow spindle speed and fast feed rate ,in and out with spindle rotating .

Ideally you want to be using a floating holder but if everything is true you might get away without ,lastly plenty of coolant.

You may be getting a slow response here as you have posted in the wrong forum ,better in the CNC forum or general.
 








 
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