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Author Topic: Problems threading on the lathe  (Read 330300 times)

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Offline John S

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Re: Problems threading on the lathe
« Reply #210 on: April 10, 2009, 08:59:37 AM »
Well my spindle speed sync is definitely ticked.

Hood, Your machine is probably the worse one to do any testing on. With 25 Hp at the spindle driving thru a mechanical gearbox it shouldn't alter speed by a tenth of a rev when threading. What are you using for an encoder ?

Has anyone other than Steve Blackmore tried using a normal encoder with Channel A and B on the Smooth Stepper ?

John S.

Offline Hood

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Re: Problems threading on the lathe
« Reply #211 on: April 10, 2009, 09:09:52 AM »
John, dont have that now, have an AC Servo on the spindle now and its a miserly 12.5Kw and it doesnt go through a gearbox. I am using the Index pulse from the encoder, well actually the buffered encoder output from the drive but the same thing. Dont think you can use the A and B channels yet for anything other than monitoring.
My revs are rock steady in Mach,they dont even jump one digit and I am not using averaging, they do read slightly wrong for example at 500rpm it may say 501 at 1000 say 1002 and at 2000 maybe 2004 but I think that may well be a smoothStepper calibration thing..
 As for the sync being checked, I was meaning Rich's test showed similar to what I have seen in the past when I forgot to check it after fitting the pico mobo in and was just wondering if it was possible that for some reason even if it was checked Mach was ignoring it.

Offline ART

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Re: Problems threading on the lathe
« Reply #212 on: April 10, 2009, 10:57:46 AM »
Hi Guys:

 >>My revs are rock steady in Mach,they dont even jump one digit and I am not using averaging

 Im of the opinion that THIS is the key to all of it. If the speed doesnt jump in non-averaged spindle, then it means
that computer is ROCK steady in cpu clock speed. In the old days they all were, but latest generations over past couple
years of CPU's vary the clock speed almost randomly even if your not power saving..

  I suspect this shows the real problem, random variance of the clock is slowly adding to an error that ccumulates over time.
Its why when I turn off correction, Johns machien actually looks liek a good thread..albeit it off flank cuts during the thread
on various passes, this coule be due to several different spindle speeds locking in as each pass changes the no-load RPM slightly
beofre taking off on its pass. The code assumes non-loaded is accurate prior to the pass and shoudl be the same pass to pass,
tru e on hoods, varying 1-2 on others, 5-6 on others.. Im coming to the conclusiogn this is the real culprit and explains why hoods is so
good.
   Im researching to see if I can take advantage of the system clock chip to better define "time" instead of using cpu clocks.. trouble is there
are technical challenges in such a thing.. but Im investigating. Keep up the good work, the testing is proving alow really, the linearity cal seems
unimportant and can be deleted, a new one can be made as a plugin to allow for better fine tuning for those that need it in future.

So it seems...
 The thread wandering over time is an accumulation of pass to pass errors caused by the divergence of "time" , and that length shows it best.
 Spindle RPM has an effect as the time variation affects the thread in a formula based on steps/pitch x lenth of pitch in some way, again, I suspect
this is accumulating error. Higher the RPM, the higher the variable speed sensed, and this affects them as you go up in speed..

   If I can hook into the timing chip in any meaningfull way this may solidify the rpm reading and we'll see what that gives. It'll take me a few days
to see how I may be able to do this..

  In truth though, the SS should be imune to this, Greg can read the actual RPM as exactly as it can be done. Rich: , how much fluctuation in speed reading do
YOU get?

Thanks
Art

Offline Hood

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Re: Problems threading on the lathe
« Reply #213 on: April 10, 2009, 11:15:03 AM »
One thing I would add which may confuse the situation is a while back I sheared a key in the headstock and never noticed until a thread had started cutting. The spindle slowed from 1000rpm at the start down to 300rpm at the end (or similar, it was a while ago) I heard this and was about to kill with the E-Stop but I noticed the Z axis seemed to be tracking so decided to let it go, it finished the 10 or so passes and I inspected the thread, it was perfect. It was a short thread if I remember, probably only 30mm long 20mm dia and 2mm pitch, this was with the SmoothStepper so thats why I was surprised to see Rich having problems with the SS, granted his is a longer thread.
 Just wish I could figure out a way to vary the servo speed to see what happens on a longer thread, maybe I can use an analogue signal  on the drives override inputs, will have to investigate.

Hood

Offline ART

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Re: Problems threading on the lathe
« Reply #214 on: April 10, 2009, 03:00:13 PM »
Hi Guys:

  This test is for experienced testers with PP test only. What Ive done is hook into the main 1,193,181Hz timing clock, and am measuring spindle RPM
with it. This clock should never vary no matter what, so Im interested in RPM readings only. Does this stabalise rpmp readings on your system , OR make
them more accurate. Test with averaging off to see if its stable and correct to your known speed. This method should read to a very high max frequency..

  YOu need to install this driver... and copy this new MAch3.exe into your folder.. save your old .exe and driver to get back to normal..

Thx
Art

Offline RICH

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Re: Problems threading on the lathe
« Reply #215 on: April 10, 2009, 04:18:41 PM »
Hi All,
Was off on a trip and just got back.

The "Use  Spindle Feedback In Sync Mode and also Spindle Speed Averaging is checked.

The RPM displayed in the DRO will only flicker once in a while and then only within 1 rpm and
I check the actual RPM with a good speed indicator and it says 300 RPM.
The cuts were 25 passes, but total depth was only .005" to eliminate any rpm influence and never once did I notice the rpm change.

I didn't use diagnostics to see what was happening in it's RPM reading ,and unfortunately, when using the SS you don't have a take on the rpm as when using the PP and can monitor with the Turn Diagnostics.

In the latest version of threading you can no longer put a dwell before or after the pass as you were able to do in prior versions. That allowed me to take actual indicated readings on each beginning and end of the Z moves for comparison.

Just for info, no need for comment,  I got a buddy who just CNC'd a lathe, has a two horse motor and when geared for like 600rpm it's probably like 5 or 6  hp,  for a screw he used a 1-8 tpi of threaded rod and has 0.046" of backlash ( hardware store threaded rod and nut ) . He uses backlash compensation and does small and large threads that look like they came off a high end machine. No i haven't checked the lead on his threads , but the point is, here is a machine that should turn out crap for threads and it dosen't! Mind boggling!

Have a few thinsg to do and then will fool around some more. Want to try ART's rpm test on a few different PC's.
RICH

Offline John S

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Re: Problems threading on the lathe
« Reply #216 on: April 10, 2009, 07:35:11 PM »
Will run first thing in the morning, midnight here and the bloody workshop is haunted anyway.

Last report of the 2HP motor geared for 600 rpm plus Hoods large spindle motor lead me to thing it's down to feed back from spindle speed.

Problem is most small modern machines use electronic variable speed of some description, unfortunately a reduction of speed will not give an increase of torque like the older pulley / gear driven machines.

John S.

Offline Chip

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Re: Problems threading on the lathe
« Reply #217 on: April 10, 2009, 08:07:05 PM »
Hi, Art

Not getting an RPM output hear until I put pulley ratio to .001, See picture bellow for details, Expanded RPM Dro display.

Using your exe and driver with simulated 555 timer setup hear.

Chip

Offline RICH

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Re: Problems threading on the lathe
« Reply #218 on: April 10, 2009, 09:05:22 PM »
ART,

- PP & AVERAGING "OFF"

         ---------------  RPM'S ----------------------------------        TURN DIAGNOSTICS RPM'S
PC     VERSION   MEASURED    DRO      DIAGNOSTICS  REAL TIME  APPLICATION
------   ------------   ---------------    -----------   ------------------   --------------   -------------------
DELL  3.042.024    299          299-302   299-302           299-302      299-302
         ART# 214    299             0               0               299-303     .119 - .120

NEC   3.042.024    300           300-330   300-330           300-340      300-340
         ART#214     300              0               0               298-301      .89-.9

- PP & AVERAGING "ON"

         ---------------  RPM'S ----------------------------------       TURN DIAGNOSTICS RPM'S
PC     VERSION   MEASURED    DRO      DIAGNOSTICS  REAL TIME  APPLICATION
------   ------------   ---------------    -----------   ------------------   --------------   -------------------
DELL  3.042.024    299            299           299-300       298-301       299
         ART# 214    299             0               0               300-302       0

NEC   3.042.024    300             300           300             299-302       300
         ART#214     300              0               0               298-300       0

Here is info on two of my pc's. I included rpms for all of the screens readouts and for both
on and off averaging.

Make sense?

RICH

Offline ART

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Re: Problems threading on the lathe
« Reply #219 on: April 10, 2009, 10:26:37 PM »
Hi Chip:

 Is it varying? Rich: Can you try a ratio of .001 as well as a test.. Im researchign why that may be so..

thx

Art