Machsupport Forum
Third party software and hardware support forums. => LazyTurn => Topic started by: Ben on March 16, 2012, 04:10:44 PM
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I tried to post this with attachments (picture & XML) but couldn't. I posted on the Machsupport page as "Post Problem" (this can be erased or moved) so now I'm in two places.
While threading the carriage makes an unauthorized triangular jog at the start of the thread.
The pass it happens on is never consistent but it always happens no matter which threading wizard I use.
I have tried other gcode shapes and they run OK. I use a slotted optical spindle speed sensor bypassing
the BOB and have tried denounce from 0 to 10. I'm stuck but I have faith in you guys. Thanks, Ben
It seems like when you have one problem everything else becomes a problem while trying to solve the first. Murphy ?
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What version of Mach are you using?
Post the gcode file.
Post your xml file that you are using.
RICH
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To attach something, after you click the preview button, click the Additional Options, then Browse button which will provide for selecting the file you want to upload.
RICH
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I'm using 3.042.038
When I attach something I get this--Sorry! There is already an attachment with the same filename as the one you tried to upload. Please rename the file and try again.
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I'm using 3.042.038
When I attach something I get this--Sorry! There is already an attachment with the same filename as the one you tried to upload. Please rename the file and try again.
Yes, you need to name the file something unique, then upload it.
Dave
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Thanks for your patience.
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Ben,
Can you post the xml that you are using for the lathe. The one you posted didn't even have Mach configured and was for a mill.
Was the pic attached done when your actualy running the machine or emulating the program?
RICH
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That pic is a actual run. Sorry about the xml, here is the correct one.
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More Info
It acted like the spindle rpm pulse was noisy or eratic. I then moved the signal wire (shielded all the way) from the
BOB directly to pin 15 on the DB25 cable. I checked the "Calibrate Spindle" and there are no spikes and the rpm
only varied < 1. The phenopy happens at the start of the thread but changes sometimes pass one sometimes
another pass and I can't run a threading operation without it happining. I'm using a OPB982 Slotted Optical Switch
and the disk has a .200" wide slot.
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You are using a very old version of Mach if you are using 3.042.038, there have been fixes to threading for the parallel port driver since them, so I suggest you try with the lockdown version.
Hood
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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
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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
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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".
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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
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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
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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
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I don't have VFD. I need to change belts. Right now I'm changing computers to eliminate one variable.
Ben
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Ok so what are you on about when you are saying calibrate spindle was used?
What are you using it for?
Hood
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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
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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
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I changed computers and so far the tool jerking in and out has disappeared. Thanks, I couldn't have done it without you guys. I only have so much hair--left. Now I'm going to cut some threads on 3/4" pvc pipe for practice. Is there an acceleration number I shouldn't go under for any tpi and spindle rpm ratio. ie a formula?
Ben
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Or does Mach use the acceleration listed in the "motor tuning" entries to calculate landing at the correct start point?
Ben
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Have a look at the Threading On the Lathe Writeup in Members Docs.
Try scribing lines on somethng. Can be used over and over again.
Mach will use the values you provided in motor tuning. Acceleration from a stopped position to some point in a time period
can usualy be addressed by allowing 3 to 5 threads ( general rule of thumb) in distance prior to actualy cuttting the thread.
Try scribing different tpi and rpm and don't ignore the wizard warnings if you are exceeding your settings.
If scribing is of good quality then do some actual threading in different materials to gain experience on using your lathe.
You'll be a pro in no time at all..... ;)
RICH
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Thanks Rich and Hood you've both been a great help.
Ben
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Glad we could help.
RICH