Facets in my 16 TPI Threads - Need some help!

[TX COWDOC]

Happy New Year -
I've spent the last 2 days troubleshooting an irregular finish to my 16 TPI threading with my PM1236 (Single Phase Baldor). I received the lathe in July and it has taken me several months to finally get to a point where I was able to practice threading. I thought I was going to build a 6.5 PRC this week but obviously not until I get this resolved. I'm using ISCAR SER 0625 H16 RH threading tool in an Aloris BXA holder. Bits are ISCAR 16ER AG 60 IC908. Lathe settings are appropriate for the 16 TPI. Feed rates on the compound are per the ISCAR 16TPI charts. I've tried 2 different chucks (6 jaw and 3 jaw), 2 different materials (round stock from McMaster in Aluminum and Steel). I've tried different tool heights.

I'm hoping there is an answer to what is causing this issue. I will be emailing Precision Matthews for technical support as well. Thank you in advance for your help.

 

[Aukai]

Single phase 60 cycle impressions?

 

[Lo-Fi]

The ISCAR charts may well be for a much more rigid CNC setup. They look like classic chatter marks to me. Try a less aggressive feed and different speeds.

Are you infeeding with the compound set slightly less than half the included angle, or straight in?

 

[Batmanacw]

Are you above center? Or right on?

 

[TX COWDOC]

The ISCAR charts may well be for a much more rigid CNC setup. They look like classic chatter marks to me. Try a less aggressive feed and different speeds.

Are you infeeding with the compound set slightly less than half the included angle, or straight in?

65 RPM (which is the slowest setting on the PM1236). Compound only.

 

[TX COWDOC]

Are you above center? Or right on?

As close to perfect as I can make it. Also repeated it with a slightly lower than center setting.

 

[TX COWDOC]

I have the impression that the chatter is visible in the turned and faced surfaces in my pictures as well. ?

 

[Batmanacw]

When you feed in at 29.5° you should only be cutting on the left side of the insert so the other side of the thread shouldn't have chatter. There should be a difference.

 

[danallen]

I agree that it looks like chatter. Are you feeding the tool straight in or at 29.5 degrees with the compound? I also agree the insert may not be ideal for the lathe. Do you have a HSS blank you could grind into a threading tool? I would try that and feed at 29.5 degrees in small increments and take a .001 finish cut straight in and then repeat the cut without advancing the tool.

 

[TX COWDOC]

I'm feeding on the compound at 29.5 degrees. Not sure how well I will do grinding a 60 deg threading tool.