Problems threading on the lathe

[ART]

Rich:

  In theory, the code should do the same out of wizard or G32 coding. Should be no difference.


  The numbers are telling a story, and your next test of rpm during thread will be interesting. My problem is envisioning where the driver coudl possibly make a screwy pass. Its a bit banger at a steady frequency, so it shoudl be impossible since correction is turned off to make a screwy pass. Only a slowing or speeding up soindle could explain it to me.. I guess well have to calculate just how much a speed up or slowdown must ba happening. Its either the spindle RPM OR the actual output slowing since we KNOW the planning is correct via your numbers from all the tests. We're zeroing in on the crazy passes, but Im having trouble envisioning how it can happen.. so far anyway.

  After the next series of testing Ill turn on the correction and see what effect that has.. Im a bit stumped..but thats typical till you get to the Ahha moment in these types of things.

Art

[RICH]

ART,
Three tests for your review. All tests are identical and reports attached for
each. All done with posted version from page 57- reply 568.
402 rpm @ 20 passes / .1p
Note that test #3 was stopped after pass #9.

Test#1   
It was the last two passes that did a heavy cut and i just assumed it was 19 shown in the TEST#1 PIC.That was done wth the unaided eye. I KNEW THaT PASS #8 OR 9 WAS BAD AND THEN 10,11,12,13,14,15,16 AS A GROUP SEEMED OK. BUT THEN 17 & 18 WERE BAD. ( MAY BE OFF IN MY COUNT OF PASSES BUT THAT'S MY NOTES ).

TEST#2
Ths one was monitored under the microsope.

Pass 1 to 8 - looked right on as group

Pass 9 was bad and moved the lead to an increase over 1-8 scribe. As a group 10,11,12,13,14,15 followed in pass 9 scribe.

Pass 16 decreased the lead from from 9-15 scibedline.

Pass #17 inceased / moved the lead back to pass #9

Pass 18 and 19 moved the lead.

SO it oscilated back and forth ( i believe that is what happened in test #1 also ) All within the .0035" total lead error / two scribed lines.

I show all the above summarized in TEST#2 pic.

TEST#3
I figured i would try and catch the bad pass by itself and it looked like
#9.......Could be wrong. No pic but i d have an error report.
Under 40x and a side view you can barely see the .001" deep marks.

--------
I didn;t have a chance to compare the above visual descriptions to the reports but they should be close.
 
RICH

[RICH]

ART,
TEST #3 ATTACHED

RICH

[ART]

Rich:

 When you take a microscope shot like that, how far into the thread is it?

Art

[RICH]

ART,
Your only looking at 0.002" total depth. The lighting when taking the picture can skew the actual outline.
I am going to post another / revised picture  for test # 2 with some info to refine the information. I think it's important.
Should take  about 15 minutes.
RICH

[RICH]

ART,
This picture better shows what was actualy seen. The shift is more logical based on the report ( 8 & 9 ) pass.
I don't understand why #10 to 16 stayed on this side but they did. The report dosn't account for what actualy happened.Now 18 seems logical as it would be deeper and was on that side. Pass #17, 19 &20 are somewhere on the other side, not necessarily as shown ( that's my guess) since all i could see was that they shifted over to that side.

The only way i can take a better shot of the marks would be at 100X and would probably need to cut into the tube and look at a cross section or get my other microscope working.

BTW:  Chucked up about 10 lbs of weight to load down the spindle some and ran some dry runs. Yes , the rpm dropped from
402 to 401, but there was no change in the in the error report. Just figured that maybe adding mass to the rotating spindle  / inertia would make a difference.

RICH

[ART]

Hi Rich:


  My bad.. I meant how far into the thread ( as in 2" from start..1" from start..ect.. ). I was wondering if it went further and further out.. or if it is the same amount out 10 pitches in as it is 5 pitches in..

Art

[RICH]

ART,
Progressively decreasing. For TEST#2 at the 1"/ 10 pitches 1line (#18) @ -.0018" and the other line at - .0048".
At 1.5" / 15 pitches  #18 @ - .002" an the other @ -.007"
RICH

[ART]

Rich:

  OK, begs the question.. if you do a .2pitch , does it scale or does it stay the same runout as a .1 pitch..

Art

[RICH]

ART,
Will try one out. You don't know what you have when you get multiple scribe lines.
RICH