cutting issues

[bolton78]

(sorry admin,didnt know where to put this post)

Hi all,

Just a quick question,has anybody machined black acetal before? I got a few issues

1) drilling with 3.3mm drill,12mm deep,16 holes,but no matter wot we do we cant get the drill to ‘chip’ the material it just keeping getting trapped around the drill and marking the face of the job
2) same problem with my M4 tap

any ideas would be gratefull

[CNCRim]

Drill a hole seem so simple but not easy huh?
Try hyperbolic HSS with alot of cooling when cut, oil work better if the vendor OK with it, but still, chip can build up.

[guru]

I would use low RPM, higher feedrate and short and quick pecking and high blast of coolant

[Geof]

It is called Delrin over here and I machine tons of it; okay maybe not tons probably hundreds of pounds a year.

You are not going to get it to chip with a drill nor with a tap. Yes it does wrap around the drill and if you are not using any coolant it melts against the face of the work and makes marks. Also it wraps around the tap and if you do not clean it off between holes it gums up in the next hole and wrecks the thread.

If you can use coolant do so, plenty of it. Drill at moderate speeds, maybe a bit slower than you would for brass, but double the feed.

If coolant is not permitted rig up a very strong air blast to blow the swarf away and provide some cooling for the drill and swarf so it doesn't melt against the part.


It just happens that I am tooling up for a Delrin job with 10-24 tapped holes 3/4" deep. To avoid the problem with swarf wrapping around the tap I am building an extending airblast nozzle which will come down between holes to within 1/4" of the tap to blow the swarf away and then retract again. I am also using coolant.