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Author Topic: lathe threading pitch error  (Read 11268 times)

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Offline fast89

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lathe threading pitch error
« on: January 19, 2013, 08:03:18 PM »
Jut got my clausing 12x36 up and running. Using machmotion breakout board and teco ac servo drives and a homemade tool turret. Machmotion does not support threading with their apollo I breakout board. I figured it was just a timing issue. I can cut a thread and it looks beautiful and the tool starts exactly the same on every pass. i mean the thread looks great. the problem is that the pitch is off. If i program a 20tpi, if i hold a tap up to it, the pitch is off considerably. My rpm is stable at 310 and drops to 308 for the first two or three passes then it is stable at 310 again. If i cut male and female threads , they fit good, so it is not a consistency issue. I messed with the debounce with no luck. i don't think it is the problem. I  have spindle speed  averaging checked. i also double checked the steps per for z axis. Anyone else have a similar problem? I'm running out of ideas.

Offline Hood

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Re: lathe threading pitch error
« Reply #1 on: January 19, 2013, 08:29:43 PM »
Is the Apollo not just a breakout board? ie you use the computers parallel port.
If so then it will do threading as Mach controls it.
Are your axis moves correct, in other words if you command a move does it move that amount exactly?
Do you have a licence for Mach as threading doesnt work in demo mode.
Hood

Offline fast89

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Re: lathe threading pitch error
« Reply #2 on: January 19, 2013, 08:55:57 PM »
Hood,
Thanks for the quick reply.I do have a license.  The Apollo I has two parallel port inputs. The axis have been accurate, I've run a few jobs on it. It threads great, but the pitch is off.

Offline Hood

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Re: lathe threading pitch error
« Reply #3 on: January 19, 2013, 09:01:10 PM »
Does the Apollow use a plugin? If not then it would seem it is just a breakout board and thus threading should not be a problem.
If you attach your xml I will have a look.
Hood

Offline RICH

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Re: lathe threading pitch error
« Reply #4 on: January 20, 2013, 07:41:53 AM »
What version of Mach are you using?
Are you using a VFD?
What are you using to generate the threading code? ie; threading wizard, G76,?

Suggest you do a scribe test. Is the pitch correct for the scribe test?
RICH
« Last Edit: January 20, 2013, 07:51:16 AM by RICH »

Offline fast89

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Re: lathe threading pitch error
« Reply #5 on: January 20, 2013, 08:49:47 AM »
I'm using version R3.043.022. Using a Vfd with a 5hp 1750 motor driven driving spindle 1-1. I am using the wizard and it is outputting g76. I did try it with g32 also and same difference. It is working great, just doesn't have the .050 pitch i specified. Looking under magnification, the pitch is smaller than .050" My rpm drops from 310 to 309 fir the first few cuts then it stays at 310 fro the remainder of the cuts.

Offline fast89

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Re: lathe threading pitch error
« Reply #6 on: January 20, 2013, 08:51:29 AM »
Here is a thread i cut this morning. The tips of the threads are the original stock. You can see it picked up the thread on every pass. Just not making the right pitch.

Offline Hood

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Re: lathe threading pitch error
« Reply #7 on: January 20, 2013, 09:05:25 AM »
Not seeing anything wrong in the xml regards threading, you seem to have that all set correctly.
Can you confirm your steps per unit for Z are correct, ie encoder count, pitch of screw (is it a ballscrew?) and gearing between motor and screw? Does your servo drive have any electronic gearing set?
Do you have a hand held tach you could use to compare spindle RPM to displayed RPM?
Hood

Offline fast89

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Re: lathe threading pitch error
« Reply #8 on: January 20, 2013, 09:11:31 AM »
The servo is directly coupled to the ballscrew with a zero backlash coupling. The drive does have gearing and encoder gearing. Mach is set for 5000 steps per inch with the right gearing in the drive. I can jog it .01" and get exactly that on an indicator. I checked that last night before the wine started flowing. . I opened the turn diagnostics wizard and watched that while it was threading. The rpm was within 1rpm of programmed speed and actual speed displayed and it never showed a missed timing signal.???????

Offline Hood

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Re: lathe threading pitch error
« Reply #9 on: January 20, 2013, 09:15:14 AM »
Disable turn diagnostics wizard, it is of no use except for the versions it was being used in to find problems, yours is not one and really it should be removed as it may cause issues.
Not sure if you had it enabled in previous tests or not?

Cant think what to suggest if the rpm is indeed being reported properly, the Z motion is accurate then all should be fine.
Hood