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Author Topic: Problems threading on the lathe  (Read 330253 times)

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Offline RICH

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Re: Problems threading on the lathe
« Reply #490 on: October 06, 2009, 10:47:38 PM »
ART,
All i can do is try to give you info that is repeatable here and measured quite accurately. If you want to try something, just send it to me.

It would be nice if the threading diagnostics would "capture" the info it's displaying as that may give you a look at
each complete threading cycle for comparison. 

The only other thing we can do on my end is, maybe, is to capture the spindle  triggering tiiming and also put an encoder on the end on the Z axis and capture it's movement relative to the spindle. I can't do that, but  i know
 a friend who would probably do that  and has the expensive o'scope that would do it. But not sure it would be of value and that takes some time to do it right.

RICH
 

Offline ART

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Re: Problems threading on the lathe
« Reply #491 on: October 07, 2009, 10:14:11 AM »
Rich:

  Dont think we need to go that deep. The numbers appear to be telling  astory.. Im just trying to decipher what it is. :)

The fact teh accuracy increases as rev speed increases seems to show that the long time of correction between rev's is allowing an error
to creep in, the lower the time between rev's the less the error.

   Ill generate a driver with no correction to see.

Art

Offline RICH

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Re: Problems threading on the lathe
« Reply #492 on: October 07, 2009, 10:29:59 AM »
Sounds good to me.  I am very curious.
RICH

Offline Hood

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Re: Problems threading on the lathe
« Reply #493 on: October 08, 2009, 04:47:36 AM »
I am not sure how relevant a test using the SmoothStepper is but its all I can test with due to no parallel port on the Pico mobo.
Lathe has 12.5 Kw AC Servo on spindle and Index pulse from encoder is used via the SmoothStepper.
First test was a scratch test  2 mm pitch 200 mm long 24.5 mm dia and 1000 rpm. Measured the full 200 mm with digital calipers and also laying a 200mm mic along side and could not see any error.
Second test was a scratch test 2 mm pitch 200 mm long 29.5 mm dia and 200 rpm and again measured as above and again no error detected over the 200mm.
Also put both threads alongside each other and again could not detect any errors.

Hood

Offline ART

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Re: Problems threading on the lathe
« Reply #494 on: October 08, 2009, 09:06:08 AM »
Hi Hood:

  Well, it proves the feedrate and such are all being computed properly. Thats a help. Any error must lie in th edriver.


Rich, heres a driver that has no correction, its turned off, otherwise all is the same.

To load it, you need to simply remove the driver using control panel, then copy this into your mach3 folder, and run drivertest.exe.

If you get the message "Driver is loaded , Reboot", ( you dont have to reboot), then install worked. If you dont, you didnt remove the old
one properly. ( Id back up your old one just renamig it mach3.sys.old

Good luck
Art
 

Offline RICH

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Re: Problems threading on the lathe
« Reply #495 on: October 08, 2009, 09:25:40 AM »
Thanks a bunch ART,
I was waiting for it and will do a few tests today.
RICH

Offline RICH

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Re: Problems threading on the lathe
« Reply #496 on: October 08, 2009, 11:28:27 AM »
ART,
First test with no correction. I was  just interested what the lead would be like.
Test done at 115 rpm / 40 passes at .1 pitch / .0001" depths same as all the other resting.

There was a single scribed line and the pitch decreased by .007". Now i measured two quadrants  of the scribing and that was the average since one was .0055  and the other was .008. So a small change maybe not worth considering.

There is something interesting, maybe:
Ran driver test for 25000khz and pulses now at 24802.
Chips screen shows kernel at 24933.

I rebooted after the threading  test and got the same same exact kernel as above. Those are different than  what was shown in the other tests.
The other driver showed 25455 and Chip's  screen reported 23654.

I didn't see any reason to do some more scribing tests figuring if that one was off the others would also be off.

So what do you think?

RICH
« Last Edit: October 08, 2009, 11:32:05 AM by RICH »

Offline RICH

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Re: Problems threading on the lathe
« Reply #497 on: October 08, 2009, 12:31:40 PM »
Hi All,
Just a little info on the visual inspection and pictures that i am posting for your reading pleasure.

Here is a picture of the scribed line located at about 2".  The test was done with a new sharpened pointed tool.
The intent of checking the end of the scribbing is just to confirm that there is a single scribed line that i am measuring to for checking the lead. If there are multiple scribed lines then something mechanical, electronic / electrical, or even software can be causing it. So there is consistentcy here. I will remark that the line is .002" wide and .002" deep after 40 passes. The picture is taken with a camera through the fical micrometer eyepiece at 40x .
So you can measure directly to 0.0001".  

During the threading cycle, the actual cutting / scribing is being monitored via a 30x microscope mounted on the lathe  carriage. You can see the actual scribing cut and watch the width as the passes increase. Should any "tracking" of the scribed line vary , then the  pass that created it is noted.

Now up to this point,  most of the error that's been noted is over a 1" distance. If you have error at 1", the error will continue on down the thread. So if it's .007" at 1" of threading then it will be .028" at 4". No long threads have been done because it would just be wasting material and taking a lot longer to test.

I'll try and post something to put the error into "practical" perspective later on.

RICH

Offline ART

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Re: Problems threading on the lathe
« Reply #498 on: October 08, 2009, 02:59:08 PM »
Hi Rich:

  Wow, thats pretty clear. SO the lines are pretty good, the pitchis decreasing by .8% or so ..


>>I rebooted after the threading  test and got the same same exact kernel as above. Those are different than  what was shown in the other tests.
The other driver showed 25455 and Chip's  screen reported 23654.

  Not important. What happens is that as the kernal starts up, it measures the number of interrupts per second, and vary's a few internal variables that
control the operating system, when it figures its close enough, it locks them in so they dont fluctuate. Mach3 takes into account what the number is when
planning, so the differing kernal numbers should have no effect, and they dont seem to.

   So we're left with a variation, .8% at 115RPM, lower as we go up.. Ill crunch some more numbers tonight to see if I can see where that may be at,
though Im off the mind that its the RPM reading thats off, .8% of 115 woudl only be a bit less than 1RPM, so thats likely where the error is. The error
seems less at higher RPM's, but that may make a twisted sense of logic happy in the driver..

   We're thrust next on trying to make the RPM more accurate to see if that helps. The smoothstepper counts the RPM internally on a firmware clock,
and the tests you have done don't. Id like ot know though if a set RPM reads differently in the advanced threading plugin as opposed to the standard rpm ,
the advanced plugin tells you both I think, the ratio between them may be interesting ....

Thx
Art

Offline RICH

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Re: Problems threading on the lathe
« Reply #499 on: October 08, 2009, 04:47:54 PM »
ART,
I'll do the advanced timing test.
I will say that the Threading Diagnostics screen always shows that the Real Time rpm is higher. It will float from 195.5 to 196.1
Till then,
Rich