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Re: Problems threading on the lathe
« Reply #40 on: February 26, 2009, 02:04:44 PM »
I forgot to mention that I did try the experiment with the 80 some very shallow cuts on a inked shaft with perfect results all three times that I tried it.  Thanks.

Also my apologies for taking over this thread with my questions, though I think that my problem is pretty much the same as the original one that started this thread.

Thanks
« Last Edit: February 26, 2009, 02:07:04 PM by TrevorH »

Offline Rieks

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Re: Problems threading on the lathe
« Reply #41 on: February 26, 2009, 02:36:32 PM »
Hello TrevorH,

I have no problem that You are jumping in ;).
At first my unwanted X movemend was also in the inside (minus) direction,
later trials wend the other way.
My PC broke down today, so I can not try out new suggestions for a wile.

Rieks

Offline Rieks

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Re: Problems threading on the lathe
« Reply #42 on: February 26, 2009, 02:48:11 PM »
Hello Rich,

If a cut is missed, caused by the walking out of the X-Axis, it dus not cut.
In the next cut, when it is good, it tries to cut twice the cut depth, which causes
a overload of the Spindle with a lot of sadness as the consequence.
Re: Problems threading on the lathe
« Reply #43 on: February 26, 2009, 03:26:32 PM »
I have done some more experimenting.I now think the critical issue
is a stable spindle.After installing the s/s and mucking with encoder pulse
I thought that I was ok.However this was with sharp tool,soft mat'l.
With tool dulling in some 4140 studs the erattic x feed came back.
I then worked on the drive ,MORE POWER.I'm now threading at 800
rpm and all is well.I tried to slow the spindle with a 2X4 jammed against it
and the treading is fine.

Offline RICH

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Re: Problems threading on the lathe
« Reply #44 on: February 26, 2009, 06:11:18 PM »
Rieks,
My question is this.......how are you missing a cut? Are you really missing a pass?
 
Backlash in the system and the resulting pass cuts can take on a strange appearence / illusion.
It is very difficult to definitively say / see  what happened. Even with a measuring microscope attached to
the lathe carriage. And you need to be very disciplined in the observence.  

Are you taking out the X & Z backlash on setup?
This will help.....to some degree....i won't debate the point as logic says one thing but in my experience it just dosen't cut it over numerous pressured passes. It just takes one or two thou and then a move in the other direction and now your cutting what seems like almost a double depth of cut. I can mimic that somewhat  just with or without cutting fluid.

Try this, put ten 0.0001" spring cuts in. Try it in the begining, mid-way, and at the end of the threading.
What happened during the spring cutting?  
  
I would like you to do something. Do two threading operatons. One using G32 and one using G76.
Both of them should be done with "exactly" the same paramters, metal etc. ie; spindle speed, depth of cut, etc.
In fact use a threading operation that caused fault.
One is a canned cycle and the other numerous X/Z moves.
What are your results?

Try the same using G32 with and with out backlash compensation.
What are your results?

Try another run, the only variable change is exact stop and constant velocity.
What are your results?

Try another run, the only variable change is not to provide cutting fluid on some cuts.
What are your results?

Please take the above in this light. Only trying to help not judge. I quess i believe there is nothing wrong
wth the threading cycle, that the built in compensations work to within some resonable degree, and that if things get
out of whack too much the thread is history. Every part of the system has an effect on the outcome.

RICH

Offline Rieks

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Re: Problems threading on the lathe
« Reply #45 on: February 26, 2009, 06:51:20 PM »
hello Ritch,

Yes, I miss cut's, while the X-Axis walks out of the material during the Z move, as if a taper is requested.
Not only physical, bud also the X-DRO, as TrevorH wrote.
During this pass there is no cutting material.
Obviously the program keeps count of the passes and the infeed's
The next one, when it is not walking away, takes the new value, and makes the next cut, witch will be the double infeed.
If only the axis would move by it self, and not the DRO then I would think about noise pulses.
As a retired Electronic engineer, I can think about noise, while I don't use screened cables.
Close to the X Steppermotor are two cables from a measuring device.
For me as a Hobby metalworker the problem is not very serious, so, don't stay awake about it, but it would be nice if
everything  would work in the end.

Rieks
 

Offline Hood

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Re: Problems threading on the lathe
« Reply #46 on: February 26, 2009, 06:56:19 PM »
Rieks
looked over your xml and so far dont see anything wrong.
I am trying to think of a way I could simulate your problem but as I have no way of slowing the spindle down on my lathe manually I dont know how I can,  even a 10mm DOC wouldnt slow it down.
Hood

Offline Rieks

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Re: Problems threading on the lathe
« Reply #47 on: February 26, 2009, 07:12:22 PM »
Hello Hood,

I really don't think that the problem is in the software.
"Keithmech" thinks that he has solved the problem, and I tend to think that he is right.
The only thing I can't explane is why the X-DRO is moving as well.
I am making my Hobby-Lathe CNC Controlled, so it is not very serious in my case.
There are more people with the same problem, so I'm curious about the solution of this problem.

Rieks
Re: Problems threading on the lathe
« Reply #48 on: February 26, 2009, 07:32:38 PM »
I just finished running 100 pieces.5/16 nf in 4140.
Not one missed thread.six passes per.at about 1000 rpm.
Threading takes more power than we think.I struggled with the same
issue and tried several work arounds but Hood, who has more horse power
than Zeus, has never seen our issue.Try a bigger motor.
Re: Problems threading on the lathe
« Reply #49 on: February 26, 2009, 07:40:05 PM »
Here's a thought for Hood.Try cutting a 4 tpi acme in some 4340.
set your gear change to the top speed and adjust the vfd down
so it is at about 15%.Motor should lug under these conditions.
I know it is alot of work or you could wedge a large timber up against the chuck
to simulate a spindle variation.I use a 2x4 but my Hardinge is just up from puny.