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Re: Problems threading on the lathe
« Reply #590 on: October 22, 2009, 09:53:30 AM »
I have lost some of the information here since long. If I remember correctly the RPM measurement is done before each pass but only ONE RPM is measured. In order to minimize the trigger deviation, if there is any, could it be an idea to measure the time of say 5 full revolutions and divide that time by 5 to get the RPM as accurate as possible?

Offline ART

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Re: Problems threading on the lathe
« Reply #591 on: October 22, 2009, 10:14:29 AM »
Hi Steiner:

  Actually, if averaging is turned on, its averaged over 8 rev's..

Art

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Re: Problems threading on the lathe
« Reply #592 on: October 22, 2009, 12:18:03 PM »
ART,
?- How many steps/inch is it set to.
X is 12700   Z is 20300
Out of curiosity i did a G01 @ F.01 for an .1 travel of the Z a few days ago.
While reading a book, was just like a Swiss watch listening to the stepper pulse, tic , tic , tic,

never missed a beat.

?-   Am I right in assuming the entry alwasys seems to look good on the crazy passes, but the

only thing you notice is the thread pitch is off, that it gets longer by  a set amount and gets more

out of position the longer the thread?

Yes. As far as i can tell @ 30x mag. Since your almost cutting air, ie; the scribe line is realy fine,  

but i would see if it changed by over .001".

?-seems your crazy pitches are advanced to the req. pitch

Yes, even when / if it oscilates, ie; it stays within say a range of .0035", may be multiple scibes
as i had shown in one of the replies.

?- you call for .2 pitch, your not quite double what a .1 pitch does
True, it is not linear along the thread, so if you take the longest length, then the error / " is different

than if you used the 1" mark. A single scribed line provides a definit measuring point. When you

have two of them, then you don't know which to use as one has a different error than the other,

small but different. SO you can play with the mean square root of those readings, but the average

measured between them is what i posted.  I would suggest you stay with the single scibed line

numbers and it is ususlay around .0035"/ inch as that has accured so frequently.

?- Can you do .5" at 115RPM? 1Inch pitch?
Hmm... using 115 rpm 0.2P=23 ipm
                                 0.5P=57.5 ipm
                                 0.8=91 ipm
                                 1.0=115 ipm (nope start skipping at 110 or so)

?- We may be too small in pitch to tell though.
Yep, only have a rather narrow range of data from tests.
I guess it would be nice to have data for the following:
RPM    PITCHES
-------    ---------------
100     .O125
200     .050
400     .1
800     .2
1600   .4
Thats 25 samples, and then should do at least 2 runs, which becomes 50 samples.
 I can't thread for that full range .

I believe the lead can be corrected or brought into some range, but again, i would go back to a

standard to quantify just what that error tolerance means.

Good to 0.8 P. I am limited to directly measuring the lead with the tool makers microscope  to

2" before i need to move the piece and start from another reference point.
So i introduce some error in lead the measurement when that is done.

As far as the screwy moves:
I want to try something, namely using Chips screen which has a large path display, also fool

around some while threading and monitoring Windows / MACH CPU usage. Basicaly i want to see

if getting more attention to it may have an effect on those crazy moves. Nothing ventured nothing

gained.


Comment on your post #589
That would agree with me changing the pitch in the wizard from say .1 to .99****************** or .100*********.

The rpm was fixed but the wizard did in fact create code with that  pitch , even though while in the

wizard it will round the number. The resulting thread lead error was reduced but still influenced by

the RPM change of 1.  

I'll run the OCT22-1 version.
Need to do a few things, so back in a few hours.

RICH
« Last Edit: October 22, 2009, 12:21:26 PM by RICH »

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Re: Problems threading on the lathe
« Reply #593 on: October 22, 2009, 12:28:56 PM »
Just a thought, trust that from a programing point of view, I am just plain stupid.
But, what if for a split second Windows was to divert and then the data would be recieved by Mach a little late,
and it continues and that causes a screwy move, because of Windows?
Or how about Mach not implementing a correction unless it's seen twice?

I am getting a little off track, but want to be open minded on the screwy moves.

RICH

Offline ART

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Re: Problems threading on the lathe
« Reply #594 on: October 22, 2009, 01:06:18 PM »
Rich:

  At the moment we have no correction, so that cant be it.. and if Windows was interupted then the pitch woudlnt start properly I think..
The more I crunch the numbers the more I think its the integer RPM.. Oct22-1 will be interesting..

Art

Offline RICH

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Re: Problems threading on the lathe
« Reply #595 on: October 22, 2009, 05:51:13 PM »
ART,
 :) :) :) :) :) :) :) :) :) :) :)
Now this is good news!

Tests all done with Ver.028 - OCT22-1 as shown below:
20 passes @.0002" / pass
Spindle Speed Averaging / Constant Velocity / Debounce Interval=600
Index Debounce=10 Z=60 IPM @ 6 accel  / X =80 IPM @ 8 accel

RPM  PITCH    LEAD ERROR AT LENGTH ( +=INCREASE -=DECREASE)
               0.5"         1"        1.7"     REMARKS
----  -----  -----         ------    ------    -------------------------
116   .1     N.A.          -0.0008   -0.0008
402   .1     N.A.          -0.0007   -0.0011
116   .5  +0.0000 /.0014"  +.0.0005 / 0.0014   Just measured at two  different places abt 180 degrees apart AT 1/2" and 1" lengths.

Attached are the data reports for each.

From a practical point,if actual threading was done and you could hold the diameter and cutting was good, then based on the lead errors above,you would produce a Class 3A thread.

There was a little of the "oscilating" seen but I think what i was realy seeing was backlash. The Z has 0.0008" and the X has 0.0003".

One of the things that come to mind is the acceleration and deceleration.
What i saw  was the "oscilating" starting to occur at about 2 threads short of the end of the thread and after 10 thread cycles. Could be wrong. As long as your in these kinds of tolerances who cares!
   
SO need to have additional testing to see if the above holds true over time.

RICH
« Last Edit: October 22, 2009, 05:53:06 PM by RICH »

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Re: Problems threading on the lathe
« Reply #596 on: October 22, 2009, 08:08:06 PM »
Hi Rich:

  Yes, I was thinking the number crunching was showing too many inferences to the RPM. I'm a bit embarassed
I didnt see it before, the lack of fractional component of the rpm measured seems the pitch culprit.

  Im going to turn on correction again after you run your tests, we'll see if that works as it should if you
apply a bit of pressure to the spindle while its turning..

Art

Offline RICH

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Re: Problems threading on the lathe
« Reply #597 on: October 22, 2009, 08:32:55 PM »
ART,
Will just cut some actual threads and see what happens. 1/4-20unc as that one is 0.0433 deep based on a sharp V . Should there be some slowdown and no correction it should show up rather quickly while threading.
In mean time post  one with the correction turned on. Then i can compare and comment.

RICH

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Re: Problems threading on the lathe
« Reply #598 on: October 22, 2009, 09:53:11 PM »
Rich:

   Hers a driver that turns correction back on..

Art

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Re: Problems threading on the lathe
« Reply #599 on: October 22, 2009, 10:48:42 PM »
Thanks ART,
 I cut four 1/4-20's,  three in AL all were good ( 40 passes) and the cutting. Two of them met Class 2 / 2A external thread.  

The fourth was C/S, just took one slow down of 1 rpm ( at around pass #18 ) and no correction and that was it
until it broke.  It was not supported in the tail stock and out about 1.25" which is too much. Even if it was supported the thread would have been poor. What happens is that if the lead gets off a little , you will catch the end were it just enters the stock, will deflect the stock, and that's  the beginning of the end! I call that lazy operator!

SO lets see what the correction does now.
RICH

MODIFIED: X axis gib was was  loose, so that didn't help with 1/4- 20 in steel.
« Last Edit: October 22, 2009, 10:58:09 PM by RICH »