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Author Topic: lathe threading pitch error  (Read 10907 times)

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Offline mc

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Re: lathe threading pitch error
« Reply #10 on: January 20, 2013, 09:34:36 AM »
If you're confident the Z-axis is accurate, the only thing that can be of is the spindle speed.

How confident are you that the spindle speed is correct?
Re: lathe threading pitch error
« Reply #11 on: January 20, 2013, 10:39:26 AM »
where is the spindle sensor

Offline fast89

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Re: lathe threading pitch error
« Reply #12 on: January 20, 2013, 11:49:07 AM »
Slotted disc is on the back of the headstock on the spindle shaft with an optical sensor thru the c3 board then to the breakout board. I'm going to borrow an optical tach later today and double check it. I just did some more testing and for a 20tpi it was off by .0008" per tooth. I changed the pitch on the g76 line and it came out good. But i can't do this for every thread. I tried a 13tpi to see if it had the same inaccuracy and it did not, it was out further, maybe .001-.0013 per tooth.

Offline Hood

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Re: lathe threading pitch error
« Reply #13 on: January 20, 2013, 12:26:54 PM »
Can you load a mill screenset and tell me what time in int and frequency say on diagnostics page. You will then have to go back to the lathe screenset.
Hood

Offline fast89

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Re: lathe threading pitch error
« Reply #14 on: January 20, 2013, 01:24:48 PM »
Hood,
I use a modified mill screenset. I never liked the lathe multiple screen setup. Time in is unstable , bounces around 4.0-4.3 with intermittent blips to 8.1. pulse frequency is at 72665. I have this lathe running on a new very fast 3.2ghz pc with a solid state hard drive. I have Mach set to 75khz.

Offline Hood

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Re: lathe threading pitch error
« Reply #15 on: January 20, 2013, 01:33:58 PM »
Agreed on the screenset, never used the standard one myself.
I had seen in your xml your kernel was 75KHz and that was why I was wondering. Time in Int is fine so no probs there.
Now regarding the under size you mentioned, did you mean  0.008" under size instead of 0.0008"?
If it is I am just wondering if that could be the cause, not sure how the driver locks in nowadays, think Rich will know more as he did some testing with Art. I havent use the parallel port for a long time now.
Ok my thinking
Pitch called for divided by pitch cut = 0.05/0.048 = 1.04
Frequency called divided by frequency actual = 1.03
Fairly close.

Hood

« Last Edit: January 20, 2013, 01:36:18 PM by Hood »

Offline Hood

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Re: lathe threading pitch error
« Reply #16 on: January 20, 2013, 01:37:47 PM »
Or lets do it another way.
72665/75000 X 0.05 = 0.04844

Hood

Offline fast89

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Re: lathe threading pitch error
« Reply #17 on: January 20, 2013, 01:40:30 PM »
No i meant .0008" off.  Called for .050" thread pitch and if i made it .0508" it would cut a good thread.

Offline Hood

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Re: lathe threading pitch error
« Reply #18 on: January 20, 2013, 01:46:05 PM »
just realised I can divide and multiply but cant subtract ;D

Next thought, think you said you had electronic gearing in the drive. Can you set it 1:1 and adjust your steps per unit accordingly. You will also have to drop the Vel to suit.
Run and see if its the same or not.
Hood

Offline Hood

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Re: lathe threading pitch error
« Reply #19 on: January 20, 2013, 01:50:15 PM »
Also, have you turned off the Turn Diagnostics plugin, rebooted and tried again?
Hood