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Author Topic: Problems threading on the lathe  (Read 116034 times)
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RICH
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« Reply #560 on: October 16, 2009, 08:32:42 PM »

ART,
Thanks for the info as now i know how to interpret the data better.

I delibrately increased the rpm in the wizard becuase you could see the rpm float  in the threading diagnostics.

Yep, focus  on the crazy passes. They are the killers, since on a punny lathe you could "spiral down into the black hole"  and the resulting thread becomes hard to measure.

If the lead error can only be corrected within some tolerance, then a decreasing thread may be a better choice.
This way it starts out meeting some standard. The nut will go on and becomes loose. I will to post something practical as an example and think about it more.

Will try few with the last posting. That gives flavor to the tests i did were i varied the pitch some to get the lead error to zero.

BY the way, those crazycuts are really bad. ie; all of a sudden you go from just a a few tho cut to cutting
cutting .030" to .040" deep / full V cut. The force on a 1/4" dia rod is realy great including the carriage also.
If the material was hard you would probably break the insert.

Again thanks for stayng with this,
RICH

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ART
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« Reply #561 on: October 16, 2009, 09:41:53 PM »

Rich:

 Thanks, we'll see what the numbers show. Ill add soem code , hopefully tomorrow, to see about monitoring the high and low rpm during the thread run.
Im coming to the conclusion the actual rpmis slowing during the cut, and we're simply not correcting for it. Im not sure why it only slows on some passes, not others
but Im getting convinced its slowing enough to make the pitch elongate. Its possible simply turning on correction may solve it, but Id like to see the numbers prove its happening.


Art
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SteinarN
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« Reply #562 on: October 17, 2009, 01:23:01 AM »

Art,
If I read the debug correctly it is 4 rpm measurments or 4 full rotations before each pass starts. If these rpm measurments differ, what rpm is the motion planned for? The last rpm measurment or an average of the 4 rpm measurments?
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ART
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« Reply #563 on: October 17, 2009, 08:32:14 AM »

Hi:

  Actually, you get only one report per move. The reason there are four entries is the approach moves or any other G1 motion after an initial G32.


For example, if you use a g32 move to approach the start of thread, then do athread, then retract with a g1, that would be three entries in the log.

Art
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RICH
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« Reply #564 on: October 17, 2009, 07:34:13 PM »

ART,
Not sure what you posted on page page 56 reply 559 is valid report. Here is the readout i get from dry run.

RICH


* NEW REPORT.jpg (24.45 KB, 704x57 - viewed 97 times.)
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ART
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« Reply #565 on: October 17, 2009, 09:07:38 PM »

Rich:

 Ooops..my bad.. Ill fix that up..

Art
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ART
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« Reply #566 on: October 18, 2009, 08:30:58 AM »

Rich:

  Its assuming the S word has been commanded. Is it possibel since your manual that the S speed is set to 0? That woudl make it read #.inf

Thx
Art
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RICH
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« Reply #567 on: October 18, 2009, 08:23:53 PM »

ART,
All tests V.028  per posted MachSpindleOct16 on  page 55 - reply 559.
--------------------
Test #1 was out of curiosity doing a thread test at 404 rpm using the following code:
M98 P0001 L20
M30
O0001
G32 Z-1.9 F.1
G4 P2
G01 X.1
G01 Z0.0
G01 X0.0
G4 P2
M99
M30

So i just did 20 looped passes. Pass #6 and #17 were bad, and the lead increse was .003" / inch.
--------------------
Test #2 used code from the wizard.
404rpm/ .1P / 20 passes@.0002"
Pass #14,19 & 20 were visualy observed as bad. I have attached a file which icludes the report for test #2 and test #3.The first pass had a decrease in lead of .0008" /1"  and .001" /  1.4" inch. Then there was a correction after pass#1 and pass #14, 19, & 20 were bad visualy and changed the lead to a increase, namely .0035" / inch.
Picture TEST#2 shows the passes at 1.4" along the scribing.
----------------------
Test #3 was the same as test #2.....EXCEPT..... I decided to try correctng the pitch and see what would happen.
So instead of a .1P ,  the modified pitch used  was 0.09965 ..... (0.1000 - .00035=.09965 ). So the first 13 passes
showed a decreased lead of 0.001". Pass #14, 19, & 20 were bad and cause an increase in pitch.
This is shown in picture TEST#3.

Picture TEST#3MAG shows a maginfied view at the 1" point of scribing.

---------------------

SO three different tests and all had a common .0035" total "range" of lead error. I could shift the location of the error relative to a perfect pitch. Note also that each test had a screwy pass all occuring at around pass #14 or #19 or so. Those screwy passes al seem rather close to what happened n other tests. In the other test that went to 40 passes they seem to occur around pass #15,30,and near  40.

--------------------
BTW: I did one additional test. I hate to compare apples and oranges.....but for info ......... It was manualy done on my 30 to 40 year old Rockwell 11" MANUAL lathe. Pitch was .1 @ 10 passes and the change in lead was 0.0003" in 2" of scribing, no variance between lines, single scribed line. Hmm....
all those old belts and pulleys /gears / gearbox, lead screw, half nuts and 23 times more accurate than my CNC lathe!

RICH


* TEST#2_56 559 HCIR.JPG (106.34 KB, 850x505 - viewed 104 times.)

* TEST#3_56 559 HCIR.JPG (97.96 KB, 796x493 - viewed 100 times.)

* TEST#3MAG_56 559 HCIR.JPG (63.44 KB, 826x663 - viewed 99 times.)
* LastErrors TEST#2 &#3 56_559_HCIR.txt (18.71 KB - downloaded 90 times.)
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ART
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« Reply #568 on: October 18, 2009, 09:55:04 PM »

Rich:

 Numbers seem to still show good. This version will output spindle speeds during the thread as well as what its planned at.

You know, if the spindle actually is slowing down..we have correction turned off, so Id expect a advancing pitch.. Perhaps
after this test its time to turn on the correction..

Art

* Mach3SpindleOct18.zip (1161.17 KB - downloaded 68 times.)
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RICH
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« Reply #569 on: October 18, 2009, 11:24:11 PM »

ART,
Will do a few tomorow to get some data.
I don't know about the spindle actualy slowing down.Your cutting air with these tests. The 60 hertz AC is rather highly regulated to the motor. The only thing, motor / pulley / belt / pulley/ belt tensioner / gears as a "system " may change but it would be repetative in one revolution. What ever that varience, would be quite small and the sensor if acting repetatively, probably wouldn't pick it up. Or with my driends instrument, you know your measuring the system, but have no clue as to which component .

What bugs me is the occurance of the screwy passes. They "seem" to be patterned somewhat. If 40 passes are done, then keep your eyes around pass 15-20 to get a bad and then 30 and finaly towards the last 38-40.
So it's in terms of threading cycles 20-10-10. Reduce the passes to 20 and it looks like 10-5-5. The real bitch is you can't "see" it by dry running.

I didn't try it opticaly. I need that G4 pause in there to take a measurment. Need to play with that some as that would allow a lot of testing and save a lot of time. Figured i could do the subroutine, put a dwell in to mimic the time, and see if i can catch bad passes. That was part of test #1, since at one time, you couldn't put a G4 into a threading cycle.

My question is, using that subroutine, is it an apple and not an orange relative to doing the scribing via code out of the wizard?

RICH
 
 
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