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Author Topic: Threading Deviation  (Read 11135 times)

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Offline Ben

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Re: Threading Deviation
« Reply #10 on: March 19, 2012, 12:05:52 PM »
What a wonderful Monday morning. You were right, it was the version. It now runs smooth as a babies bottom.
Thanks you guys, good job as always, Ben

Offline RICH

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Re: Threading Deviation
« Reply #11 on: March 19, 2012, 04:52:33 PM »
Just to clarify, Ver 3.042.038 was a bummer on threading for you?
Did you try or know of any any other version's that didn't work properly after .038?
RICH

Offline Ben

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Re: Threading Deviation
« Reply #12 on: March 19, 2012, 08:14:49 PM »
Welllll I left for awhile and when I returned it did it again. I checked my wiring and made sure my rpm signal wire was shielded to ground and well away from
any other wiring. This is with V 3.043.022. I haven't tried any versions between this one and 38. I knew I was getting excited too soon. Maybe
it was because I spelled babies wrong and then didn't use  "baby's".

Offline RICH

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Re: Threading Deviation
« Reply #13 on: March 19, 2012, 10:03:11 PM »
Are you generating the threading code from a wizard?
If not, try the threading wizard, and make sure when your done with the inputs  that the calc check dosen't warn you that your exceeding your feedrate. I only say this since looking at the pic it starts off well but the threading path shows  like the motor  has skipped. It should be a straight line. Use a slower motor rpm and see if it still does it.

There could be problems with your index. The threading won't begin until it sees an index and the index sampling is based on debounce settings. I never tried to see what would happen if the index was lost during the actual threading / after the threading
starts. Mach is monitoring the rpm during the threading and will  adjust feedrate based on the rpm, if the averaging goes to some low value in that cycle can't be repaired but the threading will continue as the next cycle is modified.

RICH






Offline Ben

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Re: Threading Deviation
« Reply #14 on: March 20, 2012, 10:45:10 AM »
I'm using "Simple Threading (Lathe) Rev1.17" wizard. My spindle RPM is 113 as measured by
Calibrate Spindle ( I don't have spindle feedback control) and varies within 1 rpm.  I've had skipped
steps before in other projects but this isn't skipping initially, it's changing direction which causes skips.
Usually at the start of the cut but then sometimes minor bumps occur mid cut the tool moves out then back in.
These bumps are so fast that it misses steps so when it goes back on track the tool is not where Mach
thinks it is.
I also feel that its related to index so I bypassed the BOB and moved the index signal wire away from other wiring.
I don't have a scope so I rely on Calibrate Spindle pop-up. My next step is to try a different computer.
 
Ben

Offline Hood

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Re: Threading Deviation
« Reply #15 on: March 21, 2012, 05:58:24 PM »
Does your VFD have compensation for speed? I am not sure how the parallel port driver handles it now but I do know that if a spindle speeded up before it could go wonky. If the VFD senses the spindle slowing and it has speed compensation then it will try and increase the speed, in the mean time Mach has seen the spindle slow so adjusts the axis and thus the two are fighting each other. I am sure Rich will know if that still holds true or not as I think he still uses the parallel port.
 If that is an option in your VFD try turning it off in the parameters.
Hood

Offline Ben

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Re: Threading Deviation
« Reply #16 on: March 21, 2012, 06:24:34 PM »
I don't have VFD. I need to change belts.  Right now I'm changing computers to eliminate one variable.
Ben

Offline Hood

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Re: Threading Deviation
« Reply #17 on: March 21, 2012, 08:00:09 PM »
Ok so what are you on about when you are saying calibrate spindle was used?
What are you using it for?
Hood

Offline Ben

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Re: Threading Deviation
« Reply #18 on: March 21, 2012, 09:12:35 PM »
When I was trying a optical device to measure rpm that saw reflective tape on a pulley I was getting  rpm spikes
on the normal spindle rpm dro. The graph on "calibrate spindle" also showed spikes. As I messed with it
I noticed that the graph would show any signal instability. The device was seeing all kinds of reflections even though the pulley was painted flat black.
That's when I changed to a slotted disk. Now the signal is stable but I'm still getting the quick deviations from the programed path.
Ben

Offline RICH

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Re: Threading Deviation
« Reply #19 on: March 21, 2012, 10:22:34 PM »
Hood, your correct on what you posted in reply #5 and still holds true as far I kow.

Ben,
Nothing wrong with checking the rpm but if your rpm is stable like you said +- 1 rpm  then threading should be no problem.
Mach will try to ajust for a spindle slow down but will not do anything for an increase. The real time rpm read by Mach is out to 3 or 4
digits ie; 100.1234. Read the info on you tach / optical device as it may be +- 1 to 5% of reading which is a greater range than the DRO is displaying.

Lower the spindle speed in the the threading wizard and try air cutting. Make sure you allow 3 to 5 x pitch so you steppers can accelerate to required feedrate. You could be skipping during the move from standstill ( index seen ) to required threading feedrate.
I can't duplicate your problem here.  It's one thing to have an index not working, another if the stepper can't accelerate properly,
 and yet another if the stepper dosn't have the torque to do the threading.
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To simulate the threading you will need to have the spindle turning so an index is seen,but, if you disengage  the x & z drive
and try threading you elininate axis possiblity. The graphics display should be correct if not then you have something going on with
the index......that includes the sensor, any electronics, the PP, etc.

So simulate threading  to see what shows in the graphics window.

RICH