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Author Topic: Problems threading on the lathe  (Read 336616 times)

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Problems threading on the lathe
« on: September 11, 2008, 10:41:28 PM »
I hooked up the encoder on my big lathe to the breakout board today and am having some problems .  The encoder is a tamagawa qaud with index pulse , I have the index hooked to pin 12 input on my breakout board and I am getting a very accurate RPM reading on screen. The lathe is new with ball screws and no measurable backlash .  Threading tool is Carmex IP carbide threading tool , held very rigidly in VDI 30 tool holder.

I am using threading files that run perfectly on my other two lathes , both with ball screws and mach .  Everything seems to be working as it should but 4 out of 5 parts I thread at come out looking like I have rammed the tool holder into them . Everything will be running well and on the 5 -6 pass it I will get a shhh sound from the tool and the threads are pretty much wiped out . I have cut some where around 70 sets of thread today and might have 5 that are acceptable. I have cut thousands of threads on my other two lathes and just unsure whats going wrong here . 

I have tried adjusting the j value from .001 to .010 , changed the number of spring passes, tried two diff types of coolant , synthetic and oil based , trans fluid , trichlor , and gtx cutting fluid , still no luck , on at least two of  6-12 passes when cutting .05 pitch (20 tpi) threads the tool will just kind of wipe all the threads out .
Are there some params I need to look at or adjust  in the software that relate to the index pulse?

I think I have checked all the mechanical and wiring issues and have tried to eliminate the cutting tools, cutting fluids , feeds and speeds as possible problems .
Any help or thoughts greatly appreciated RT
Re: Problems threading on the lathe
« Reply #1 on: September 11, 2008, 11:51:11 PM »
I was told early on that the index pulse from an encoder was most likely WAY to short of a duration to work reliably with Mach.
200 microsecond minimum pulse needed.
Might reduce spindle speed by half to verify.
Didn't see any mention of a SS in your post.
RC

Well......you did say "Any help OR thoughts...."
These are "Thoughts"........not necessarily any HELP.  :)
RC
« Last Edit: September 12, 2008, 12:03:20 AM by Overloaded »

Offline Hood

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Re: Problems threading on the lathe
« Reply #2 on: September 12, 2008, 02:43:20 AM »
Do you have your SS on this machine? If not then the Index is most likely the problem as RC said.
Hood
Re: Problems threading on the lathe
« Reply #3 on: September 12, 2008, 10:38:57 AM »
no SS on this machine until the encoder can be attached .  The readout in mach is showing what appear to be accurate RPM readings across the entire range . I will make a slotted disk and attach the encoder I got from cnc4pc today and see if the threading is better

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Re: Problems threading on the lathe
« Reply #4 on: September 12, 2008, 10:48:07 AM »
What version of Mach are you using?
There have been problems with some lathes and threading. I have never had a problem but some people have and still do, the latest version of Mach has cleared up these problems for most but some still have issues. When threading the spindle speed DRO is locked so it looks like the speed is constant even though it might not be, the latest version however should work best but as its still in development and there have been a lot of changes you should use with caution.
Hood
Re: Problems threading on the lathe
« Reply #5 on: September 12, 2008, 06:50:08 PM »
I am running the latest lock down version , 2.64 I think, the other two lathes are running 2.57 .

I upgraded to the latest developmental version and the problem still exist . I am getting nice accurate readings on the tach on screen , never waivers more than 1or 2 rpm .  Problem still exist , it doesnt look like its getting out of time , appears to be starting and ending at the correct time , just looks like the threads are torn some what , kind of like a dull tool that is dragging instead of cutting .  I am using a commercial boring bar type internal threading tool and carmex inserts , same tool I have used on the other machines to cut thousands of threads.


I am going to try a different threading tool in the morning , although I dont think its the problem , and if that doesnt make a diff I will make a disk and try the CNC4pc pulse generator

Offline Hood

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Re: Problems threading on the lathe
« Reply #6 on: September 12, 2008, 06:58:04 PM »
Do you have a SmoothStepper ready for that Lathe?
Hood

Offline RICH

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Re: Problems threading on the lathe
« Reply #7 on: September 12, 2008, 07:06:03 PM »
Hood,
Will the SS do threading with R3.042.008 and an index pulse for testing purposes?
RICH
Re: Problems threading on the lathe
« Reply #8 on: September 12, 2008, 07:06:04 PM »
I can probably talk shepard out of his SS in the morning , The one I ordered has found a home in my mill.

Offline Hood

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Re: Problems threading on the lathe
« Reply #9 on: September 12, 2008, 07:13:16 PM »
 I have just been using the slotted disc and opto  so far for threading on the lathe as I have also been jumping back and forth between SS and PP doing testing so have not fitted the encoder yet. I think however a few of the testers have encoders on their lathes and seem to be fine but as I said no experience of it myself.
 You need a plugin that only the beta testers have at the moment for threading with the SS but I think Tuesday there is supposed to be a new plugin which will contain the threading as well as SoftLimits, thats if there are no final problems with it.
 Hood