[hall6ppc]

My question ,

Is about the quality of threads produced by the Tormach lathe . I am looking at purchasing one to do custom barrel work for custom rifle builds and high quality thread finish is a must . My concern is how good are the threads with re guard to finish when cutting steel or stainless steel ( when using good carbide tooling inserts) . My concern is the stepper motor will it give a good finish like a servo ?

Thanks

[LeeWay]

I haven't gotten far enough along to answer the question yet. I haven't done much on it yet, but I can say that the motion is very smooth. That will not be the limiting factor. I see several videos of threading with these lathes and one thing I see most often is that the threading is done usually with a little boring bar style tool. I think you might see better results from the turret or the QCTP tools. They are probably a factor or two more rigid and can hold larger threading tools and inserts. Properly setup, I think it would make some very nice threads. Give me a few weeks and I might be that far along.

[300sniper]

I have my doubts about it being able to peel off that last half thou to get that perfect thread fit, but I've never used one. I see no reason the thread finish wouldn't be good enough with proper tooling though.

[hall6ppc]

I have my doubts about it being able to peel off that last half thou to get that perfect thread fit, but I've never used one. I see no reason the thread finish wouldn't be good enough with proper tooling though.

Yea that's kinda my thoughts too . My main concern is getting a "faceted" finish due to the micro steeping of the stepper motor . Maybe some of the other owners can chime in with some experiences.

[saabaero]

Yea that's kinda my thoughts too . My main concern is getting a "faceted" finish due to the micro steeping of the stepper motor . Maybe some of the other owners can chime in with some experiences.

I have just ordered a Slant Pro lathe that I intend on using for precision threading but have not used (or seen) one yet. I based my purchase on my experience with a Series II PCNC1100 I have had for several years. When I purchased the mill it had the regular series II motors & drives (I think they were poly-phase) motors but upgraded to the series III (3 phase) motors & drives. The series III motors and drives are silky smooth as compared to the series II but even when I did thread milling with the series II motors the threads were absolutely smooth. From what I have seen in the schematics of the lathe it is my belief that it also uses the series III (3 phase) motors & drives.

Thread milling on the PCNC 1100 relies on circular interpolation (i.e. coordinated motion of the x, y axes combined with motion of the z axis whereas threading on the lathe would use a continuous linear move along the z axis combined with the continuous rotation of the spindle (no different than with a manual lathe). So even though there would be more chance for faceting on the mill I never saw any. Based on that I'm not at all worried about the quality of the threads on the lathe. There are plenty of steps per .0001" with a continuous move with steppers that you won't see any facets from the individual steps. The only time I have ever seen any faceting on the mill was due to a curve being broken down into small straight line segments that weren't short enough.

I am confident enough that the Slant pro mill will be as good as or better than my manual lathe that I wasn't hesitant to plunk down $20,000.00 (w/accessories & tooling) ! And...my manual lathe has a 3 axis DRO that has a .00005" resolution (.0001" on the diameter) and I can typically cut to tenths with it.

[hall6ppc]

I have just ordered a Slant Pro lathe that I intend on using for precision threading but have not used (or seen) one yet. I based my purchase on my experience with a Series II PCNC1100 I have had for several years. When I purchased the mill it had the regular series II motors & drives (I think they were poly-phase) motors but upgraded to the series III (3 phase) motors & drives. The series III motors and drives are silky smooth as compared to the series II but even when I did thread milling with the series II motors the threads were absolutely smooth. From what I have seen in the schematics of the lathe it is my belief that it also uses the series III (3 phase) motors & drives.

Thread milling on the PCNC 1100 relies on circular interpolation (i.e. coordinated motion of the x, y axes combined with motion of the z axis whereas threading on the lathe would use a continuous linear move along the z axis combined with the continuous rotation of the spindle (no different than with a manual lathe). So even though there would be more chance for faceting on the mill I never saw any. Based on that I'm not at all worried about the quality of the threads on the lathe. There are plenty of steps per .0001" with a continuous move with steppers that you won't see any facets from the individual steps. The only time I have ever seen any faceting on the mill was due to a curve being broken down into small straight line segments that weren't short enough.

I am confident enough that the Slant pro mill will be as good as or better than my manual lathe that I wasn't hesitant to plunk down $20,000.00 (w/accessories & tooling) ! And...my manual lathe has a 3 axis DRO that has a .00005" resolution (.0001" on the diameter) and I can typically cut to tenths with it.

Please share your findings when you get your machine up and running .

Thanks

[saabaero]

Please share your findings when you get your machine up and running .

Thanks

I promised to post a reply as to my findings regarding the quality of the thread (and machined surface) finish from my lathe when I finally got it running and figured out how to use it, so here it is:

I machined a 13/16 - 16 thread yesterday into a remnant of a stainless steel rifle barrel. I stepped the barrel blank down from 1.250 inches to .975" and then cut the thread feature for an AR15 barrel extension.

The surface finish was superb and the barrel extension threaded smoothly onto the barrel remnant without any play at all. I was able to fine tune the thread depth to the .0001" on the diameter for a near perfect fit. I examined the thread with a magnifying loupe and there was no sign of faceting. There were the normal tool marks from the carbide thread mill but nothing else.

I have to say that so far I have been extremely pleased and impressed with the lathe and that it continues to exceeded my expectations.

Attachment 289438

[tmarks11]

Since the SPL lathe will be able to cut threads at a high rpm, you don't need to worry about a "faceted" thread. That is more a function of when you cut threads well below optimum cutting ipr & rpm in a manual lathe, which is forced on you because many people don't have a quick enough reactions to thread at speeds in excess of 900 rpm (HSS) or 2700 rpm (carbide) (YMMV: example is based on steel of 0.5" diameter).

Saabaero: the surface finish on the part you showed looks outstanding. Is that the as-cut piece, or did you use emery cloth to polish it?

[saabaero]

Saabaero: the surface finish on the part you showed looks outstanding. Is that the as-cut piece, or did you use emery cloth to polish it?

Believe it or not it is as cut!

[tmarks11]

Believe it or not it is as cut!

Awesome. Belt drive probably helps quite a bit.

[300sniper]

I was able to fine tune the thread depth to the .0001" on the diameter for a near perfect fit.

You may be able to program it to the tenth on a diameter but I will guarantee that the machine isn't responding to a controlled .00005" movement.

[saabaero]

How do you know that for sure?

I am questioning your statement because this is something I have been wondering about myself.

I do know that the rapid speeds are slower for the lathe than the mill so there is the possibility that there are more steps per inch. The rapid speeds are slower by a factor of 2 so it is possible that the resolution can be twice as great. The DRO does read to the tenth on the diameter (which is .00005" on the radius). In addition, I can hear the stepper motor advance with each increment of the jog dial when set to .0001" increments.

Another thing I noticed was that when I got to the point that the barrel extension just started to screw on and got a little snug after a couple turns I did an additional spring pass which did not change the fit the slightest. However, when I changed the diameter by .0001" and made another pass over the thread the fit was perfect.

[300sniper]

How do you know that for sure?

I am questioning your statement because this is something I have been wondering about myself.

I do know that the rapid speeds are slower for the lathe than the mill so there is the possibility that there are more steps per inch. The rapid speeds are slower by a factor of 2 so it is possible that the resolution can be twice as great. The DRO does read to the tenth on the diameter (which is .00005" on the radius). In addition, I can hear the stepper motor advance with each increment of the jog dial when set to .0001" increments.

Another thing I noticed was that when I got to the point that the barrel extension just started to screw on and got a little snug after a couple turns I did an additional spring pass which did not change the fit the slightest. However, when I changed the diameter by .0001" and made another pass over the thread the fit was perfect.

I bet if you did another spring pass or two at your original diameter, you probably would have gotten the same results and I am betting those results were not .0001". If you are really threading to .0001" of pitch diameter clearance, you are going to lock up a thread sooner than later.

[saabaero]

My impression at the time was that additional spring passes would not have made a difference as I had been working up to the minor diameter in small increments toward the end. That combined with the fact that the spring pass showed no perceptible difference in the fit at all and essentially appeared to be cutting air. That is why I didn't bother with additional spring passes.

In addition, I have done a lot of precision threads on my manual lathe in the past which has a DRO with a resolution of .0001" on the diameter so I have a fair amount of experience on how a tenth or two affects the thread fit. In the case of the manual lathe since the tool is connected directly to the DRO scale I'm pretty confident the tool is moving the amount I am seeing on the readout.

With all that being said I do understand where you are coming from and that the distance commanded by the controller may not be what is exactly translated to the cutting tool in the case of the CNC. There is a lot going on in between. But hey, If everything is tight enough there should be the potential of moving the tool .00005" if the control is able to resolve to that small an increment. Right or wrong, based on my experience with using my manual lathe to cut threads my perception was that the Tormach lathe was able to do just that, and that achieving the "perfect fit" was much easier.

So my question goes back to - Does the Tormach lathe have the control and drive resolution to be able to position to tenths on the diameter discounting mechanical limitations!? I guess the starting point would be to check the drive settings.

...But if the DRO can increment by.0001 on the diameter I would have to guess that it does.

P.S. The lack of a compound rest reduces spring considerably.

[300sniper]

Be real easy to see with a DTI. Every two taps on the X jog set to .0001 should read .0001 and jogging back two increments should put you back to zero. I'd love to see a video of a stepper driven machine do this.

[saabaero]

Your right about the DTI but since the DRO increments are in .0001" for the diameter the indicator should read .00005" movement for each jog increment. (or at least that increment times the number of jog steps)

To move back exactly .00005" if the jog direction is reversed would introduce the backlash and the effect of stiction which I'm also certain wouldn't bring the indicator back to the start point.

But you do make a good point about checking the movement with a DTI (at least in one direction). I will try it tonight!

[daniellyall]

have a look at nyccnc on youtube he has video`s of threading

[saabaero]

His videos were what peaked my interest in purchasing the SPL! He did in minutes what took me hours on my manual lathe.

[saabaero]

But you do make a good point about checking the movement with a DTI (at least in one direction). I will try it tonight!

I put a tenth indicator on the SPL last night and found that the control does respond to .00005" increments on the radius. If I advance the jog shuttle wheel or arrow key on the keyboard ten times I move a half thousandth. 20 times equals a full thousandth. The distance of the .00005" movement isn't however precise, I guess it depends how the microstep falls with the actual rotor step angle. Most times I will see a .00005" movement but every now and then I don't see a movement or sometimes I see a full .0001" movement for the increment. Despite that 10 clicks still equals .0005" repeatably.

If I reverse direction it takes roughly 7 clicks (.00035") to see movement of the dial indicator in the opposite direction.

All in all, I still believe that is as good as or better than what I can do on my manual lathe with a .0001" (on the diameter) DRO. Since this is a mechanical cutting process and not a grinding process I think that resolution is pretty darn good.

[daniellyall]

it`s not NASA but its close, would servo`s be better ??????