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Author Topic: Questions on Threading With Turn on Sherline - From Yahoo SherlineCNC Group  (Read 28039 times)

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BOB,
POST#2 MORE PIC'S

RICH



Rich,


Thanks a million for this.  It's fantastic.  I am carrying the file out to the garage to give this a try. 


Bob

Offline RICH

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BOB,
I believe i was looking at your lathe on your site  and noticed that the wiring from your sensor was not shielded and ran under the motor. Not good as you'll get noise from the motor brushes getting into the pulse to MACH
Whip out that old specturm analyzer of your's and sniff around!  ;)  NY3P here! ;)
Shield wires as close as possible to the al box and ground the shield back at the controller.
You mess up the timing pulses and start the z too soon or late relatiive to what was prior cut  and your thread is history.
RICH
That may be the biggest part of your problem. The sensor is reading/reflecting off of a small radiused surface.
It might be better as illustrated so it reads on a flat surface.

How is yours RICH ?
Good luck ,
RC

Offline RICH

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RC / HOOD,
Is G76 all fixed up now? I havn't tried it in a while.

RICH

Offline RICH

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RC,
Pulse setup here is just like in the manual with a single  slotted disc and the opening width based on the calculation they gave in the manual ( slightly under ). For the thread test i just posted, the max variation in rpm was 1.46%  and the turn readout will just flicker once in a while from the 100 to 99 rpm in the display. I don't even do an rpm check anymore with the speed indicator anymore as I trust what Mach is telling me.

I can fool wiith my punny lathe manualy, by hand,slowi ng the spindle down and seeing what happens and must say that Art took care of the hobbiest. As you well know, when it comes to thread tolerance, we haven't gone there yet in this thread.

I tend to agree with you that Bob's problem may be the index pulse. I am only quessing, but if the pulse triggers Z start at say a diifferent point of the mark on the shaft, then you will see it by the change of the scribed line. Will need to waite for Bob to get back from the garage.
In the mean time wine and pitza, moma's nice, so i hope he dosn't take too long. ;)
RICH  
RICH,
  I'm using the slotted disc as well. I think the "Through Beam" type sensor is far superior to the reflective type.
It's more positive...ie: either ON or OFF.




I wouldn't wait for Bob if I were you !
I LIKE pitza !
RC
« Last Edit: January 23, 2009, 09:50:44 PM by Overloaded »
RC,
Pulse setup here is just like in the manual with a single  slotted disc and the opening width based on the calculation they gave in the manual ( slightly under ). For the thread test i just posted, the max variation in rpm was 1.46%  and the turn readout will just flicker once in a while from the 100 to 99 rpm in the display. I don't even do an rpm check anymore with the speed indicator anymore as I trust what Mach is telling me.

I can fool wiith my punny lathe manualy, by hand,slowi ng the spindle down and seeing what happens and must say that Art took care of the hobbiest. As you well know, when it comes to thread tolerance, we haven't gone there yet in this thread.

I tend to agree with you that Bob's problem may be the index pulse. I am only quessing, but if the pulse triggers Z start at say a diifferent point of the mark on the shaft, then you will see it by the change of the scribed line. Will need to waite for Bob to get back from the garage.
In the mean time wine and pitza, moma's nice, so i hope he dosn't take too long. ;)
RICH  

Rich,


I'm back.  

The final result looked like a frosted rod.  It did a thorough job of removing all of the marker, not a clean little spiral.  

Now to figure out why.

I readjusted my lathe Z axis and got it down to .001 backlash.  I take that out with backlash compensation.  My x axis had .0022 backlash (I'm in diameter mode - does that mean .0011 radius, or does diameter not matter in backlash??).  Whichever, I'm able to crank that out in backlash compensation so that a dozen back and forth moves on each axis (one at a time, of course) doesn't end up with the needle of my DTI off at all.  

But I did move the wires from the power cord and sensor apart and it was a noticeable difference.  The first few turns were everywhere, moving them made a difference and slowed down the wander.  It's still intolerable, but it did get better.  I did one wrap of the power cord on a big ferrite toroid I had lying around, but that didn't do much.  

I opened up the diagnostic panel, and it never showed my RPM off by more than 1%.  It never showed the pulse missing or anything.  It seemed perfect.  

Tomorrow, I'll re-wire that sensor.  I think I put a simple filter on the board, but I'll double check and add one if I need to.  


Thanks for all the help.
Bob

Offline DAlgie

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I had issues with my indexing on my lathe when I first got it going. I have the single slot type. I used to get rpm readings in the millions sometimes, and nothing made sense. Fixed it by; Adding a diode across the signal wires off the sensor, shielded the signal wire, and moved the signal wire away from the toroid transformer. It works flawlessly now, am very pleased with it, and have excellent results with the G76 wizard on version 1.84.001.
IMO, I think that your reflective sensor is a certain problem, and on a small diameter is bad as well. Go out to the machine and change all that out for a slotted type and I bet you'll finally be able to sleep nights for once....!
   DaveA.

Offline RICH

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Bob,
Backlash is just the non-movement of the axis. The value you use has nothing to do relative to radius or diameter
mode. So if the X has .0022 non movement then that's the value you input in the backlash screen.
My x axis has .004" also i also use 60% as a backlash speed.

Let me explain:
The z has done a rapid ( it is not returning at the F feed rate which was used to cut the thread) back to it's starting
location. In the program i think the distance is 0.1" in the plus z direction, so lets call it point "A". Now when it reaches point "A" the z comes to a stop. You defined to  Mach that there is non-movement via backlash in your configuration. So MACH is smart and thinks "before i let the Z travel to do another thread" i need account for the non-movement by macking the stepper turn some. Thus the stepper gets pulses to turn enough to take out your .0022 inches and lets call this "B". Now when the stepper rotates for that small amount, it can rotate at your max velocity or a percentage of the velocity. I just use a value of 60%, there is a setting in config>shuttle wheel setting>shuttle accel which affects how fast the stepper will rotate also. Now the Z is at point "B", it gets a signal  ( that index pulse ) from MACH to move and should arrive at point "C". Point "C" is a point realtive to the thread, and thus the next thread cut is done.

So, return to the start point "A",  squirt some clorox on the tires and smoke them soft and sitting at point "B",
rev limiter and line lock on......red-yellow- GREEN....., pop that clutch and let them horses go wild, off to and cross point "C" and the parachute opens  at "C" taking care of what needs to be done after the finish line.
OOPS, I lost the race, disqualified, and hit the dirt bank. What went wrong,  ??? dam i was running for brass pink slips.  >:(

The little vw bug beat me!  :-[ Think i need to look at what is happening on his end.  ;)

RICH