Another threading help question...

[mcostello]

If You ever suspect a tool is rubbing and cannot see it, just coat the tool with a permanent marker or layout dye. Makes something seen that is hard to see.

 

[markba633csi]

Yes put some Dykem on and see where it rubs

 

[westsailpat]

It might be possible to adjust the tool off center in this case down , to get clearance or grind the bar .

 

[Silverbullet]

Do you do a spring cut when close to size. It does sound like clearance issues. Do you have problems when cutting external threads. If not that helps rule out some of the rigidity problems , with internal threads rigidity is a cause , the bar flexes and skips the cut. Chatter...

 

[Bob Korves]

Negative rake for the tool mounting will help the clearance and the chatter. Aluminum cuts very easily, and the pics show little stickout of the bar from the tool holder. I suspect that rubbing is the issue, sometimes rubbing sounds like chatter, deal with that before changing anything else. TiN Coated inserts are not usually recommended for aluminum because of metal sticking. Unless you are threading at high speed, you should not have welding issues with that setup. Personally, I would use a boring bar with a HSS tool for that job, sharp and with plenty of rake, clearance, and relief.

 

[cdhknives]

External threads are good...not great...with my ground HSS bits. There are occasional tear outs but nothing like the regular wave pattern I see on these internal cuts. I put that down to the aluminum sticking issue. I have not run the external threading bar that came with this set yet. I do run multiple spring passes, and by the second or third (outside threads) I get foil thin strips coming off...literally feathery cuts. I take that to mean my tools are adequately sharp. 17-4PH outside threads are perfect.

 

[cdhknives]

Hopefully tomorrow I'll get more machine time...tending the pit doesn't leave much time to make chips.

 

[derf]

You need to learn how to cheat. Fine threads like that in aluminum are easy to do without the aggravation you are facing. Instead of using a single point threading tool, use a tap, in this case a 1/2-28. Set the tap up in the tool holder just like the boring bar, making sure it is true with the spindle, and the cutting edge is on center. You should be able to chase that size in 2-3 passes.
Mark the tap with a sharpie where it has went full depth. Once you hit that mark, crank the cross feed in and disengage the half nut.

 

[Guyton]

One thing often overlooked it the tool length. I always keep the tool 'short' don't matter what operation I'm doing and diameter the boring bar, internal threading tool is. Also, relieving the insert helps, just as grinding/forming HS blank. Good Luck.