Use a DRAP bit??

[Alan B]

I have an ABS plastic part that I drill and then tap 1/4-NPT. I do a bunch of these from time to time. Question is, should I consider a drill and tap combination bit?

I do this on the mini-mill and have to mount up the parts for each operation, so it would save me one put and take.

Any thoughts?

Thanks,

 

[precisionworks]

They work well if the material thickness is no more than 2X the diameter of the tap. Stopping the tap at the correct depth is going to be the trick.

 

[Alan B]

Thanks for the reply.

There are only about three threads at 18 tpi so that meets those requirements. I believe the tap is NPTF but that is apparently okay. The fit is a brass male part into the female ABS part.

For stopping the tap I mark it and then use the mill stop and watch when the mill contacts the stop. Perhaps later I'll put a DRO on the mill.

One problem with this bit is clearance below the part. I'll need a lot more than with the separate tools.