Facets in my 16 TPI Threads - Need some help!

[rock_breaker]

It looks like you have filed the top of the threads and wire brushing won't change the cause but it may help the finish.

 

[macardoso]

In my journey to solve the exact same problem as OP, I purchased a bar of bearing bronze and turned a thrust bearing 0.045" thick, 15mm ID and stock OD. This took up all the slack in the screw with about 1-2 thou left over. I still need to cut some threads to test, but everything feels so much better. The thread lever engages tightly and I don't need to guess if it actually seated correctly in the threads!

 

[TX COWDOC]

UPDATE:
I'd like to begin with expressing my gratitude to the posters on this thread. A few members contacted my privately with ideas and suggestions based upon their experiences.
I also wanted to thank Z2V and Bamban for local support with materials and tools. Granted this is a global forum, these 2 in particular are 'local' since they are less than 2 hours away.
Also thanks to Darkzero for his My PM1236 thread and MKSJ for his contributions to other similar threads.
Lastly, thanks to Matt and Mike from Precision Matthews for the calls and offer of support.

Here's all the things I did since last posting.....
I took the motor off and remounted with rubber washers, swapped out the belts to linked belts as suggested by Mark (MKSJ), replaced the compound bolts per Will's PM1236 thread. Go to use my PM833T for this part.; I also torqued the spindle bearings a tiny bit to address some play I was seeing in my TIR measurements at the chuck.

There is a substantial improvement in the vibration and noise. Note the difference in the vibration in the glass of water.

For the work piece (aluminum): I repeated the 16 TPI using the same set up and then again using HSS. The HSS is best and validates the concerns by many (including Matt) but the Carbide was much improved with the vibration resolved.

I will chuck up some steel barrel drops courtesy of Bamban and post those.

 

[kb58]

While I'm glad it's fixed, the frustration for anyone using this as a reference will be left to wonder which of the half dozen factors was the actual problem, unless (worst case) it was a little of everything...

 

[Z2V]

Glad to hear that your moving in a positive direction.

 

[jonesn7]

Most every comment in this thread was informative. Giving an outcome is a part misding from so many threads, and is much appreciated here. I get so little time to tune my little 7x10 (primarily used to knock out motorcycle spacers or polish MC parts), but I've found some very helpful things throughout the thread.

 

[Illinoyance]

The speed for manual threading is way below the optimal speed for carbide. I suggest you try a sharp HSS tool. Grinding the tool is no big deal. Use the fish gauge as a template. Hone to a fine edge after grinding. Use a stone to create the flat at the tip of the tool.

 

[Shootymacshootface]

These are all good things to check and could be contributing factors. Put a dial indicator from the cross slide top surface to the top of the threading tool, and observe the readings while cutting threads. That will give you some indication of the rigidity of your setup.
Based on your water-glass videos, it does not appear to me to be single-phase motor induced harmonics. When those issues have come up, the videos make it crystal clear that the motor harmonics are at issue, and I do not see that in your videos. What I do see is probably belt thrashing or out-of-balance pulleys on the motor or on the headstock end where the belt attaches. Have you observed the belt-thrashing behavior while threading? I replaced both pulleys with balanced high-quality version, and the OEM belt with a notched Gates Tri-Power belt on my 1340 and was rewarded with better surface finishes.

View attachment 349886

But the kind of surfaces you are getting while threading suggest more severe fluctuations at the cutter-to-part interface. This could be rigidity issues stemming from the relatively weak mounting T-nuts for the compound on this lathe, or it could be some other loose gib in the compound or cross slide, or a loose tool post. An indicator from the cross slide to the top of the tool doing the cutting will tell a story.

I am glad that I finally got around to reading this thread. My lathe sat idle for 15 or 20 years before I acquired it. There has always been a rumble and a vibration coming from the Reeves Drive, from a set in the belts I'm sure. I will definitely stop thinking about replacing them, and make it a priority.
This thread contains a lot of great information!
Good job everyone!

 

[TX COWDOC]

I am glad that I finally got around to reading this thread. My lathe sat idle for 15 or 20 years before I acquired it. There has always been a rumble and a vibration coming from the Reeves Drive, from a set in the belts I'm sure. I will definitely stop thinking about replacing them, and make it a priority.
This thread contains a lot of great information!
Good job everyone!

I did not get time to turn / thread any stainless today. The link belts seem to make a nice improvement. The machine overall is much quieter with the vibration addressed. As DavidPBest suggested, the glass of water is a quick and dirty way to rule out vibration / harmonics. In this case, I think it was vibration. It's been a good learning experience sans the time I've lost troubleshooting the issue.

 

[Shootymacshootface]

I did not get time to turn / thread any stainless today. The link belts seem to make a nice improvement. The machine overall is much quieter with the vibration addressed. As DavidPBest suggested, the glass of water is a quick and dirty way to rule out vibration / harmonics. In this case, I think it was vibration. It's been a good learning experience sans the time I've lost troubleshooting the issue.

My lathe has definitely been vibrating since day one for me, no need to test. Does anybody know if link belts would work with a Reeves Drive? My guess would be no.