Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: kdoney on August 11, 2009, 10:21:48 AM
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Everytime I setup .05 pitch for 20/inch I continually get 24/inch. I haven't checked any other pitch but I have check my screw specs and pulses per inch and they are correct. 20% off would certainly show up even with my measurements. I slowed the rpm's to 70 and have tried 3 other settings. The actual spindle dro is saying 203 at 200 and nothing at 70 but the pulses are showing up correctly on the scope. The automatic setting in pins settings still show the spindle index is correct at 70 rpms too.
Come on guys. It doesn't have to be right. Just guess, I won't say anything. I'm out of ideas.
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Do the threads look good otherwise?
Tried running the threading plugin to see if it catches any problems?
Do you have "Use Spindle Feedbac in Sync mode" checked?
Hood
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No the threads don't look that clean. More of a U than a V. I thought that was from the tool bit. I don't have a threading plugin. I have Version R3.042.020. I am using synch with spindle speed averaging.
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I would test the z for correct setup. Use a dial guage and do the G1 z1 test to make sure the steps per unit are correct.
Just a thought, (;-) TP
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I don't have a threading plugin.
It should be there, think its call Turn Diagnostics. If not let me know and I will attach it for you.
Hood
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Under config plugins it is there and I have it green checked but under plugins it isn't there.
Nevermind. I needed to reboot. It's there now.
I just checked with the scope again and it looks good. Strong 5V signal about 2mS every rpm.
When I run threading I get 86.28 rpm. Threading in effect. Rpm variation running from 0 to .04. Highest variation .06.
That's kind of strange since the spindle is suppose to be running at 70 rpm. That's my 20% variation.
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Hood
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kdoney,
Some commments on threading in general:
1. LATHE - Threading requires a lathe with properly adjusted backlash compensation or better yet almost no
backlash.The motor should not slow down during the threading pass, even though the porgram will account for it
within reason. The lathe should be tested for accuracy before trying to do any threading.
I would suggest that you turn down a piece to diameter, color it with say a blue permanent marker, and then do
a number of fine passes ( say 10 or 20 at 0.0001" ) and inspect to see that each pass follows the same scribed
line. The thread will only be as good as the lathe axis system is.
2. Code - I don't recall any problem with using G32 or G76( single start thread - for multi start you better have a good
system !) If you want, you can change the wizard so that it outputs G32 ( no canned cycle and all passes are coded
individualy ). The only comment is that you should have a Z movement equal to, say 3 to 5 times the
pitch, so the axis has time to ramp to and maintian speed before the threading actually starts. So there is
a relationship here in that your motors must be able to accelerate, but, the wizard informs you if things are not right
for the selected spindle speed.
3. INDEX- You should have rpm display for your range of spindle speed. You may need to adjust slot width
to get it. It can vary some 1 to 2 maybe at a particular spindle speed, the more stable the rpm reading the
better and it should be fairly close over your range.
If you don't have an rpm, I am not sure what the program is using to trigger the the start of the thread cycle,
in fact it may never start it.
In config>ports& pins>spinde setup - check / use - spinde feedback in sync mode and spindle speed averaging.
In config>ports & pins> input signal - make sure you use index for a single slot ....or timing for a multi slot disc
4. Monitoring - You can use the turn diagnostics to monitor the threading cycle.
SO............................................
Make sure your index is working properly and then do the lathe test.
As far as making "U" instead if a sharp "V", i think it's a setup problem also, if the steps per unit are correct then it's
mechanical problem, and the lathe test will show it.
Hope this helps,
RICH
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After checking my electronic system again and testing the mechanics coupling, I find the machine is rotating at the speed indicated by the electronics. It starts off about 20% fast at slow speeds and changes to about 10% at higher speeds. Since this is the case, should the threading still be correct since I have the threading movement synch'd with the feedback?
The cheap chinese lathe has been retrofitted with good ballscrews and adequate mounting and motor coupling. There is no measurable backlash greater that .001. I believe the gears in the lathe are crap and don't indicate what they should be but the electronic gearing should solve that.
It is a new cheap chinese lathe. :-)
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Using steppers or servos? I don't have experience on servo's, Hood or someone else will know if there are any
quirks.
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Well I'm running 1250 steppers on a 12X36 lathe. I just input 86 RPM in the wizard and am now getting 20 threads per inch. I don't understand why I have to enter any rpm in the wizard or need it if the threading movement is synch'd with the spindle index pulse.
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Ok, backlash should not be a culprit.
Can you confirm that the steps / unit are correct.?
Do the lathe test i mentioned.
I do recall threading where my actual spindle rpm was higher than what i told the wizard ( say 101 / 102 instead of
100 ) and the pitch was still ok. Also i will note that , the program will modify the the feed rate if the rpm is lower
but not higher on the next pass based on what it interpreted in the prior pass.
I assume you have one of those lathes that have the rpm readout and you know it's off by 20%.
I assume that the a slotted index is being used for the basis of determing the DRO readout.
Now if you are using something downstream from the Chinese readout / electronics that is incorrect to begin with
then that's a different story as the spindle to feed per revolution just is not right from the start.
Just somne thoughts,
RICH
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The wizard only checks to see that the acceleration and max velocity are within your configuration settings for your motors. And warns you if not. it doesn't change the feed rate. Look at the code ( better yet change it over so that it's generating a G32 and you will see what i am talking about.
So you slowed the speed down, the contoller then was able to compensate the feed rate based on a slower spindle speed. SO the feed per revolution was correct for the feed rate.
You need to fix what / where you are getting the index pulse from so the rpm is correct to Mach.
It is not Gcode problem, it is not a Mach / threading problem, it is bad rpm input to the program.
RICH
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I did not slow it down. I tried 70 RPM (geared on the lathe) yesterday and it did not work. I got the plugin today which told me I was actually running 86 RPM when the gears told me I was running 70. When I plugged in 86 rpm in the wizard the only difference was the insertion of S86 into the code. The point I am trying to make is somehow the Mach3Turn engine is synchronizing the spindle index to the threading movement of the lathe, right? If this is so, then the only thing the wizard is doing is commanding the spindle speed. The Mach3Turn engine (software) is taking the gcode for threading and adjusting it for the actual spindle index, right?
So why does putting in 86 into the wizard all of a sudden change my lathe movement to 20 threads per inch? Since my spindle is not really controlled by the gcode S86, I assume the Mach3Turn engine uses this to adjust the threading.
So one question is, does Mach3Turn use the spindle index to control the movement of the lathe during threading and does it take into account any S commands?
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When you run you rcode are you in G94 mode or G95 mode? IF the calculations were done for G94 mode then the feed will be based on the programed Sspeed not the indicated spindle speed.
Same with G95 mode IF you do not check" sync spindle" on It has to go by the programed NOT the indicated.
NOW IF your programed and you actual speed is off SO will your thread pitch.
Just a thought (;-) TP
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"So one question is, does Mach3Turn use the spindle index to control the movement of the lathe during threading?"
YES
Yes, it will adjust the Z axis movement, within some range, and try to correct for variations in the spindle speed.
So if the spindle were to slow down during the threading pass as compared to a feed rate it will try and fix it in the next pass. During the threading it will try and slow the axis, but if, out of range too far then the thread is
beyond repair practicaly speaking.
It won't' correct for higher speeds, since that should not be possible if i remember correctly... during the threading.
Now the "trigger" so to speak , going from G94 to G95 is based on seeing a stable rpm. If "green light is given", the axis will ramp in speed and the controlled point should hit the material in sink and based on the gcode.
What is not clear in my memory, is, the basis / control of what exactly happens during the ramping ( lot going on!).
My lathe is simple, no BOB's, no spindle speed control so there are no complexities to deal with. Just a dumb index
saying to Mach, this is the spindle rpm and here is a spot / trigger you can use to start threading. The true spindle rpm ( as measured measured with a independant indicator ) is close to the DRO display over the whole rpm range.
RICH
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Is it a licenced or demo version of Mach?
Hood
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Kdoney,
If the lathe is set (geared) to 70 rpm, but it runs at 86, maybe you are running a 50Hz lathe motor at a 60 Hz frequency ...