Thoughts on my threading...

[Dave in WI]

Anybody have a magic answer on what I may be doing wrong on threading? Not a total newbie, but don't consider myself a "machinist". I think I am turning out good threads as far as fit and function are concerned. But, I always seem to get a "wave" pattern on the side of the thread. I've tried HSS vs Carbide cutters. Straight plunge vs 29° and a combination of both. I've tried cutting at 70rpm and 115rpm. Is it painfully obvious looking at the pictures of something I might be doing wrong? TIA

 

[Dusty Stevens]

By the second pic it appears your compound is not set at the correct angle and youre advancing the cross slide after each pass. By the first pic it appears you are either using a single plase motor or your machine is not rigid.

 

[paperpuncher]

Chatter. Look closely at your set up. You are loosing rigidity somewhere. Is the cutter hanging way out of the holder? Is the tennon sticking way out of the chuck? How are you holding the barrel?
You could have a vibration issue with the lathe. I had this when I used the spider chuck I built the bolts were small and really didnt hold the barrel firmly enough. I switched to bigger bolts with a ball bearing and a pad to give better holding power and still allow the barrel to gimble. Chatter gone.

 

[Dusty Stevens]

Looks like the threads are leaning toward the chamber end

 

[Dave in WI]

By the second pic it appears your compound is not set at the correct angle and youre advancing the cross slide after each pass. By the first pic it appears you are either using a single plase motor or your machine is not rigid.

Good catch, Dusty. This is just a chunk of barrel that I set to thread to get pictures. In hind sight, the compound was set at 45 degrees, I had forgotten to change to 29.5 (rookie mistake).
It was fed in by the compound.
Lathe is Grizzly G0776 and running on single phase.
I try to keep tool as close to holder as possible and try to thread as close to chuck as possible.
I have noticed vibration in the lathe when running above 1000ish rpm, though.

 

[Danny1788]

Set your compound to 60 or 59.5

 

[Walt Krafft]

Address all the above issues and then go faster. If you are able to safely do it, 300 rpm would be where I would start.

 

[Dusty Stevens]

I spotted the single phase right off the bat. What kind of feet is your machine sitting on?

 

[Someoldguy]

Lap it in with some compound and no one but you will know.

 

[carlsbad]

Lots of random advice here. If I were the OP I would have no idea what to do. I'm reluctant to add my advice, especially since it contradicts some of the advice above.

Bottom line it, learning to machine on the internet isn't optimal.

Jerry

 

[Someoldguy]

Lots of random advice here. If I were the OP I would have no idea what to do. I'm reluctant to add my advice, especially since it contradicts some of the advice above.

Bottom line it, learning to machine on the internet isn't optimal.

Jerry

That's a copout. State your opinion. Give us something to mull about.

 

[carlsbad]

Chatter is caused by lack of rigidity.

Chatter generally gets better if you go slower

If you aren't sure about your compound angle, feed in with your cross slide.

 

[Someoldguy]

Chatter is caused by lack of rigidity.

Chatter generally gets better if you go slower

If you aren't sure about your compound angle, feed in with your cross slide.

Solid advice here.

 

[Danny1788]

I spotted the single phase right off the bat. What kind of feet is your machine sitting on?

I agree I have changed my feet three times now to get better surface finish. Hard rubber feet gave my machine a very strange vibration feeling. I switched to solid steel adjustable feet.

 

[Rustytigwire]

My recent purchase of Sxxxxx 6mm has those chatter marks but like yours clean and no "tearing" of the surface.
Im going to run em as is.
Edit.
My response did not answer your post. No offense intended.
I do want to compliment your attention to detail and the wisdom of the other responses. Perfection will come but good enough for now is how we get to perfection.
Next to yours my threads look pretty crappy!

 

[GenePoole]

I'm with Dusty on this. The pictures aren't great, but I've seen finish like this before with single-phase machines. It might be something else, since the machines I've seen this on were also basically the same Asian design as the Grizzlies.

 

[B Nettesheim]

Try using your tailstock to hold that between centers
Double check your center height of your tool

 

[msalm]

Some things I remember being mentioned in the past would be vibration/rigidity. Some said switching your belt to the twist lock style helped, adjustment of tension of that belt, adjust gibs on compound and cross slide, along with verifying and adjusting your lathes spindle bearings.

If all those are adjusted properly, then look at amount of barrel extending past the chuck if through the headstock. Just a few thoughts.

 

[boltfluter]

I would also experiment with different depths of cut. Sometimes more or less load on the tool will cancel out the vibration. My rule of thumb with vibration is slow down the rpm or increase feed rate/depth of cut. Just a passing thought. Good luck.

Paul

 

[Stan Taylor]

By the second pic it appears your compound is not set at the correct angle and youre advancing the cross slide after each pass. By the first pic it appears you are either using a single plase motor or your machine is not rigid.

Very perceptive there Dusty on my single phase machine at home I am able to eliminate that wavyness in a couple ways I thread between centers for one and I grind my own threading tools.