PDA

View Full Version : Internal Thread Q



pntrbl
05-27-2007, 11:11 AM
The last and only time I did an internal thread the threads started right at the face of the part. One of the problems I was having is I didn't grind enough clearance on the leading edge of the bit. Got the "buck and rub" right from the git go.

This time the threads start a half inch in and we're talking 8 tpi vs 20. I'm thinking it might be wise to do my boring on the half inch section with a 60 on the bit. That way I'll have a slope for the threading bit to start on instead of a 90.

Good idea? Bad? Or am I thinking too much? LOL!

SP

japcas
05-27-2007, 11:55 AM
Bore it with a normal boring bar. Then before you start threading use the threading tool to cut a chamfer on the face of the thread.

wierdscience
05-27-2007, 06:43 PM
I usually start out with a 60* chamfer,if you used a 90* shoulder the part would thread okay,but it would also end up with a wire edged thread at the start which is perfect for galling.

laddy
05-27-2007, 07:44 PM
Repeated running through steel with alot of lubricant finally freed the aluminum from the endmill. Many thanks to all for the help. Fred

pntrbl
05-28-2007, 10:04 AM
Thanx for nursing me along on this guys. I've got the 60* chamfer cut so I'm anticipating a good entry, but now I'm planning the other end! :)

I'm holding my threading bit in a 1" boring bar at the 90* end. If I attempt to run the threads all the way thru tho the boring bar is gonna run into a set of rotating chuck jaws. :eek: Don't wanna go there.

I used the same boring bar to do the ID but with the bit at the 45* end so it wasn't an issue then. Grinding a 60* threading bit for the 45* end seems like a difficult thing to get right. To many angles. But what do I know?

There is an extra 1/2" of meat on the other side so I could maybe get a clearance groove in there for the bit to run off into.

Or just pick a spot and attempt to pull out at the same place.

I dunno. Any suggestions? I sure as h*ll don't wanna wreck it now.....

SP

JCHannum
05-28-2007, 11:12 AM
You can cut a runout groove at the end, or simply let the part make a few revolutions before pulling the threading tool out of the cut. This will make it's own runout groove.

Remember that the toolholder will advance over the course of the thread, and leave room for it.

wierdscience
05-28-2007, 11:19 AM
Ahh relief cuts,I am a believer in reliefs,why punish oneself if you don't have to.

pntrbl
05-28-2007, 11:29 AM
Thanx guys. I should of thought of the bit making it's own relief groove. It was accidental .... but I've done that a couple of times already!

SP