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Author Topic: Problems threading on the lathe  (Read 330055 times)

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Offline RICH

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Re: Problems threading on the lathe
« Reply #540 on: October 14, 2009, 09:48:06 PM »
ART,
I'll try it it tomorrow. My luck, the rat will stay in it's hole and not come out!
RICH

Offline ART

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Re: Problems threading on the lathe
« Reply #541 on: October 14, 2009, 09:49:12 PM »
Rich:

 Yup, I always find that when the trap is set..the buggers stay away. LOL

Art

Offline RICH

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Re: Problems threading on the lathe
« Reply #542 on: October 15, 2009, 05:47:18 PM »
Hood,
Got the SS installed today and decided to run a few threading tests out of curiousity.

These were done using  MACH Ver.027 with the SS and also shown below are prior test using using the PP with ver .027.

.1P / 40 PASSES / .0001" PER PASS

PORT    RPM       DECREASE / INCH
-------    ---------   --------------------------
PP         115         .008"
SS         115         .006"   COMMENT#1
PP         402         .0035"
SS         402         .0032"

COMMENT #1 - There were multiple cuts due to varing lead ( almost as if you were doing an alternate flank cut thread ) but enventualy going back to the center of the scribe. They occured at pass 16, 22, 30, 37, 38.
The SS @ 402 rpm test had similar effect.

Frankly, just based on what has been done recently, i would say the PP  threading has improved over the SS based on scribing tests. I would have to explore it some more though.  :o

ART,
I did about 20 dry runs and the rat never took the baite, so nothing to say about error reporting. I did everything i could image to screw up the timing, nothing!. The error report did pick up that i disconnected the pulse plug though and resumed the threading.  ;D
RICH

Offline ART

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Re: Problems threading on the lathe
« Reply #543 on: October 15, 2009, 06:01:43 PM »
Rich:

  Was there listed in the lasterrors.txt file a bunch of feedrates?

 Lines such as "Threading run: Velocity: xx.*********" should have been in the file. Can you let me know how variable they were? Or were they all the same..

Thanks
Art

Offline Hood

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Re: Problems threading on the lathe
« Reply #544 on: October 15, 2009, 06:03:57 PM »
Very interesting Rich, from that it would seem that you have some issue with either the computer or index pulse or something that I don't have. Granted I never did all the passes you are doing,  if you post the code you are using I can give it a shot tomorrow and see what my results are using the exact same method.
 I dont have the means of optical measuring that you have but if each pitch is off by the amount you are saying it will add up to a lot over the 200mm I will do so I can easily detect.
 With my last test to confirm I measured with digi cals, mic and also zeroed the Z axis in the root of the first thread and moved it by MDI to Z -190mm and then wound in the X and again it was exactly in the root so I have to conclude it was spot on.

Hood

Offline RICH

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Re: Problems threading on the lathe
« Reply #545 on: October 15, 2009, 06:43:35 PM »
Art,
They feedrates were were all the same for every pass associated with a thread run. 40 passes with a listing of 4
or five per pass all the same.
RICH

Offline RICH

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Re: Problems threading on the lathe
« Reply #546 on: October 15, 2009, 08:22:03 PM »
Hood,
It is interesting, and you need to remember that this is three computers, before with the Dell and the Sherline i never got good threading past say 1" with the SS, then you have a borrowed computer and my new one. Now i just got a replacement opto so i can do index and timing now if i want. But the tests we just did with a friends equipment kind of rules the pulse out. His instrument can actualy pick up the difference in a timing belt timing riding up in the timing pulleys or not seating properly, but, that is "very small" contributor  to rpm or feedrate varience  to the "lathe system". He can also identify the effect it has on an encoder. You can actualy measure the effect of say not using an idler on the belt. We didn't do all that but he knows his "stuiff" and has folled with his owne setup.
There are four of us here that all see the same effect of the threading, granted, i'm somewhat different in the sense that i am trying to put data against it.

You would certainly see and can measure the effect on a long thread of 200mm / 4" . If  a single point tool is used
the pitch diameter would decrease, the nut would become loose, and you would see the difference in outside diameter also / tapering in.

If you use a tool / chaser insert the lead will be more constant per grouping of threads, but, the lead would also decrease overall. Likewise on the outside diamter, if your using one of those inserts which shaves the thread OD as it cuts the v , you would not visualy see it as compared to a single pointed tool.

There is a big difference as i think you are using servos and encoders with your lathe. I am not putting my pulse into the SS board, but rather into the PP. Not sure what you have there in terms of a PLC and what it's doing.
So the "lathe systems" are quite different.

The code is generated by the threading wizard.
I like to have the M1076 .MIS generate the code as G32 since i can relate to a pass number what i see visualy as threading progresses. Very small passes .0001" cuts and a lot of them ( 40  ) as i figure if something is going to get screwy over time it will happen over that manny passes and most folks won't do that manny in practice. The depth then is limited to .004" which saves time. The angle is set to 30 degrees so it radial cutting / no z offsets occuring. That reduces the trigger/acceleration/feedrate to the equivilant of a commanded  move to point as you did.
G01  Z-1.0 F1.0  equivilant to G32 Z-1.0 F1.0 ( it just adds the triggering ) but in terms of distance actauly moved there should be none fom a common start point. It's also a good comparitive test to do if your going to try picking up a thread.The rpm used is always the same  ( ie; DRO says 402 i use 402, if you use something higher like 404, if that was a high seen in the diagnostics, i still use the DRO as didn't see any change in the resulting scribe lines. That's the logic i have used.

RICH

Offline RICH

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Re: Problems threading on the lathe
« Reply #547 on: October 15, 2009, 08:42:40 PM »
 Here is a typical code and the inputs to wizard. The only change would be rpm if lower or higher.
RICH

Offline Hood

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Re: Problems threading on the lathe
« Reply #548 on: October 15, 2009, 08:47:30 PM »
Rich, its certainly a strange one.
I use a carbide insert cutter but it is just a single point.
Index is now from the encoder and through the SS differential input on port 3 with a servo motor on the spindle.
Previously on the PP I used an opto and slotted disc and motor was induction via gearbox.As can be seen here http://www.machsupport.com/forum/index.php/topic,8040.msg52277.html#msg52277 in these  pics I posted a long while back the threads were perfect, two were  done with SS and 2 with PP.
So I can safely say I have never had the pitch error with either PP or SS and that is what is puzzling me.

Spindle sensor seems to be out of the equation, firstly by your friends measurements but more importantly is your errorfile results show Mach is seeing it correctly.
I have always had servos on the axis so possibly there could be some issue with steppers but what?
I thread in metric, could that have anything to do with it I wonder.


Hood

Offline ART

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Re: Problems threading on the lathe
« Reply #549 on: October 15, 2009, 08:55:24 PM »
Hood:

  Good question.. I wonder if metric has anythign to do with it. Ill search the code to see if Im clipping to 4 decimals or something, that may explain a mm difference.. ( I dont think thats th ecase though).

Art