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Author Topic: Problems threading on the lathe  (Read 330275 times)

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Offline Rieks

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Re: Problems threading on the lathe
« Reply #110 on: March 01, 2009, 03:33:16 PM »
Hello Art,

In my case, the Z-axis was out of position during the "walk away" of the X-axis.
At this moment , I can't tryout anything, my PC is out of order, but I remember that Z-axis was out for 1 cut,
and than looked to be back in the right position.
I didn't gave it any attention than, because I taught that it was the result of the Z-axis problem.

Rieks

Offline Graham Waterworth

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Re: Problems threading on the lathe
« Reply #111 on: March 01, 2009, 05:07:07 PM »
Hi Rich,

what is the spec of the thread you are trying to produce and have you a sketch of the part.

I do not understand why you have two G32 lines for each pass

Graham
Without engineers the world stops

Offline ART

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Re: Problems threading on the lathe
« Reply #112 on: March 01, 2009, 05:41:16 PM »
Hi Guys:

  Hmm, those are interesting test results. Im not sure I understand all the comments on the first one.. Im also real confused as to how this can happen but I think Im getting closer to
maybe coming up with possible reasons, if so I can test them and see.

  First, so the axis never go out of position.. thats good, it measn no loss of information at any rate, so there must be a scrambling going on somewhere.
The 3 seconds does match an internal number I use I think.. its the threading wait for stability and index.. weird that its being waited for though..

 OK, so I need to understand a bit better, you say if its slowed down to 50, then slowly worked back to 100, its OK? But not if you stop it for
more than 3 seconds? Or is it ok only if stopped for 3 seconds, but screws up otherwise? Im not sure if Im getting that right.

  So if it slows less than 50% and then speeds up is all OK? The error you get woudl be the spindle speed being sensed as zero on start of next pass calculations..

 Can anyone tell me what happens if a G32 is single stepped? And you slow it down and back up during the pass, then do the next line.. Does it taper then?

We'll track it back.. :)
Art

Offline RICH

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Re: Problems threading on the lathe
« Reply #113 on: March 01, 2009, 07:01:41 PM »
Graham,
That code is as generated out of the wizard. It's a 1-13 just for the convenience of monitoring the axis moves
as i changed spindle speeds for testing. Two G32 lines??, well that goes back a long time, 8 months ago when i first tried threading. Normaly just use the G76.
RICH
Re: Problems threading on the lathe
« Reply #114 on: March 01, 2009, 07:27:44 PM »
 Art, can the problem be seen while running the code one line at a time, The simple answer is yes, but only if you do it just right.  I tried to run the exact same g32 routine that I have been working wit one Line at a time, and at first I thought the problem was not present.  I could it the single button, then the cycle start button over and over watching one move at a time.  I would manually change the spindle speed during the cutting pass, and at first I would wait a couple of seconds in between moves, and the problem did not appear.  Then I tried again this time clicking the mouse button over and over as quickly as I could again while varying the spindle speed, and to my suprise the problem appeared again.  I did this a few times since I found it quite interesting.  All of this was done while just cutting air, maybee I should try it while actually cutting?  Let us know if you want some other specific tests done, and I am sure that one of us can do it for you.  Thanks for the help.

Offline RICH

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Re: Problems threading on the lathe
« Reply #115 on: March 01, 2009, 07:48:07 PM »
Art,
The first group of comments ( 1st threading pass) was info about each line of code and and just confirms that all
is  working.


The 3 sec is the total elapsed time of "no spindle rotation" /  no spindle index would be recieved by MACH.  
It would be the equivilant of a cutter jammed into the stock. When i turn the spindle back on, Z will continue to move down the threading pass and then return to the start point, but the program just stops and you get the
error message. And the axis locations are right where they should be.

The rpm change ( I can't tell exactly, it's probably from a 100 dn to 30 and back to something near 100),
Did numerous different speed changes, and note that i wasn't interested in some "transition %" ,but rather
trying to see if i could consistantly create the goofy x/z move.
It would be the equivilant of the cutter gradualy slowing down the spindle and then the spindle speeding back up
while cuttiing a thread. It dosen't matter if after the slow down you don't bring up the spindle speed as you will get that goofy x/z move in the next pass. The Z velocity will track / increase or decrease along with the spindle increase or decrease and there is no x change of movement during this period.
If you stop the spindle for 1 sec it just seems like the equivilant of a spindle slow down and speed up.

Note that the spindle speed changes were only done during the actual threading move, after it started and beforee it ended. So those changes have nothing to do with a G00 or G01.  

I'll go a line by line and see what happens. ( ii see Trevor has already done so)
RICH

 
Re: Problems threading on the lathe
« Reply #116 on: March 01, 2009, 07:53:30 PM »
Here is another related, but dangerously general question.  Just how much hp do I need to cut a 1/2-13 thread in 6061 at 400 rpm in lets say 20 passes or less.  Assuming that everthing else such as tool geometry/ rigidy and such are assumed to be ideal?  I am considering the purchase of a VFD and motor, so I would like some opinions.  Do I need 1hp, 2hp, 3-5hp?  Let me know as if I am going to buy one I would only like to do it once.  I realize that I have asked a question whose answer could be dependent on alot of variables, but some educated guesses, or better yet pieces of practical experience would make my descision easier.  Thanks.

Offline RICH

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Re: Problems threading on the lathe
« Reply #117 on: March 01, 2009, 08:54:11 PM »
TrevoH,
May i suggest you just hold off and don't buy anything.
Calc's can be done, heck there are books books written, there are studies by companies for years.
Add a different cuttinig fluid, or cutter and the calc ain't worth poop ( ok, maybe ball park).

RICH

Offline RICH

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Re: Problems threading on the lathe
« Reply #118 on: March 01, 2009, 09:03:17 PM »
Here is a G32 code which you can use for testing and it's much easiier to duplicate the
X&Z goofy pass over and over again and variations on the theme without stepping one by one
thru a large program.

RICH

(TEST OF SPINDLE SLOW DOWN)
G0 X1.1 Z-0.1
G0 X1
M98 P1000 L10
M30
O1000
G01 Z-0.1
G32 X0.999 Z-0.0997 F0.076923
G32 X0.999 Z1 F0.076923
G4 P5
G01 X1.1 Z1 F0.076923
G00 X1.1 Z-0.1
G00 X1
(Min decremant being used)
(Decrement = 0.001 pass 2)
G01 Z-0.1
G32 X0.998 Z-0.0994 F0.076923
G32 X0.998 Z1 F0.076923
G01 X1.1 Z1 F0.076923
G00 X1.1 Z-0.1
G00 X1
M99


Offline ART

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Re: Problems threading on the lathe
« Reply #119 on: March 01, 2009, 11:24:31 PM »
Ill give this program a shot tomorrow and jam my spindle a bit to see if I can repeat this one... sounds more liek an application fault somewhere, but Im not sure yet..

Art