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Re: thread problem
« Reply #30 on: February 09, 2009, 09:28:25 PM »
I have the same problem.My workaround is to add a dwell of a second at the start of each cut.
Kind of like waiting to engage the half nuts.Seems to work ok.I bought another ss for
the lathe but have not had time to install it.
Re: thread problem
« Reply #31 on: February 10, 2009, 10:39:41 AM »
Hi Hood, yep, that's checked and working - doesn't work without that - its all over the place without that checked. Z axis is near perfect no matter what happens with the spindle speed when checked, so I know that is working well.

Keith, I can't add that delay specifically as I'm using G76 (unless I change the macro??), however, this already has about 1 or 2 secs delay before each cut. Also, I feel the problem starts at the point the spindle slows, not before the start of the next thread cut. Its really counter-intuitive!

I'm starting to think it may be a bug in this version, either of the macro or Mach3...

As I said, everything is fine until the spindle slows more than about 5%. 3% or 4%, no issues but when the cut is sufficiently deep to slow it 5% then the very next cut exhibits this change in X axis, totally repeatably, in the next cut, and the next and the next but with no loss in actual position and no loss in steps. So it must be being commanded under Mach3 control otherwise the X DRO would be wrong, but it is absolutely accurate.

This is with and ORAC lathe and a 1/3hp motor (2000rpm) with VFD down to about 400rpm, so there is not much torque and no closed loop control of spindle speed - that is a future project...! With that in place I think this problem would not show up.  But, it should not be moving the X axis during a cut.

Thanks for your input!

Woody.

Offline Hood

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Re: thread problem
« Reply #32 on: February 10, 2009, 10:57:32 AM »
As a test it might be worth getting the macro to output G32 and see if it happens still.
Hood
Re: thread problem
« Reply #33 on: February 12, 2009, 07:13:49 PM »
did this get sorted out?
Re: thread problem
« Reply #34 on: February 13, 2009, 05:52:18 AM »
Not yet Keith, I have some homework to do to give Hood a little more info on my setup and a few experiements. Itching to get into the workshop... Day job just always seems to get in the way!

Woody.

Offline RICH

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Re: thread problem
« Reply #35 on: February 14, 2009, 10:34:16 PM »
HI All,
Did some thread cutting on my Punny  ( Sherline ) lathe today.
All the threads were done using the SmoothStepper, 20 TPI  @ 29 deg, varying the depth of cut,
and one case spindle speed also, using the wizard / M76. A single slot disc is used. You don't see a change in the rpm reading
when using the SS but you do see a change in the feed rate. The feedrate varies according to the spindle rpm.
Note the .009" passes made at 150 rpm and a change in feed rate of approx 18%. You could hear the spindle
slowdown and watch the Z change. The pitch dosn't vary as shown in the pictures and frankly not much
difference between the threads. During the 60 pass cuts i varied the spindle rpm more than 10 times  ( i can'y say
 how much because i prefer to watch where my fingers are ) and if you look at the cut / blued trace lines you can't even tell.
The threading works great.

When I  get a chance i will try the equivilent using G32. ( but if i remember it behaves the same way ). Never once did the x axis change movement.

RICH
« Last Edit: February 15, 2009, 06:47:49 AM by RICH »
Re: thread problem
« Reply #36 on: February 16, 2009, 04:46:00 AM »
Hi Rich, yeah, they look great - thanks for the info. I think your SmoothStepper is doing very nicely. What version of Mach3?

This is very cheeky of me but is there any chance you could try a metric 2mm pitch thread if you get a moment? Could it be a metric thing for me?

I've cut a few 1mm pitch threads, gently, with no issues over the weekend. It only seems to be with the deep, over 1mm pitch threads that problem shows up for me. When I get the time, I'll do more experimentation.

I'm stuck with my trusty parallel port...

I did look at the M76 macro code and that can't vary the X axis during a thread. It also outputs good G32 code when run in diagnostic mode, and the taper "bit" is set to zero. So, I'm still hunting for the reason!

Cheers,

Woody.

Offline RICH

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Re: thread problem
« Reply #37 on: February 16, 2009, 07:33:17 AM »
Woody,
A M6X1 is close to a 1/4-20 in terms of total thread depth cut
   M14X2      "          9/16-12             "                                 

I can try the m14x2 but think it's going to be a stretch for the punny lathe ( don't think the spindle motor
has the power to do it.  Maybe I'll try at a small pass like  0.002".

The m6x1 should be no problem though and just to check if it's a metric thing ( but frankly Hood would have
picked on somethnig like that a long time ago ) as i haven't had to do any metrics.

The PP works just as well as the SS. The reason for me using the SS is because my one computer can't be used
with the PP ( the PP pulse signal sucks / and the steppers just won't run correctly).

It's not cheeky to ask at all as i am sure others would gladly do the same.

Back some 7 months ago i spent a lot of time trying to cut thread's on the lathe. Threading was actually broke in MACH. Art spent a lot of time and in particular implemented in M76 and G32 the ability to adjust for spindle
speed problems. In the future ( maybe /whenever that is ) you will be able to use the SS via an encoder with steppers thus the Z would be slaved to the spindle down to a deap stop. Software can only do so much and
is just a comprimise for mechanical ills within reason.

I believe that there will always be threading problems for users. NOT BECAUSE OF MACH, but due to the users
mechanical / machine side of threading. Threading is one time which really shows just how good your overall machine is.Accuracy is important as a thread is sort like a go  no-go gage. Over all it will show up on either side of the spectrum
namely small / fine pitches  and the other end deep. If you can't do in between, you will never do the extremes. That's my nickle on threading.

MODIFIED: RUNNING MACH3 LOCKDOWN VERSION 3.042.20

RICH 
« Last Edit: February 16, 2009, 12:18:32 PM by RICH »

Offline Hood

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Re: thread problem
« Reply #38 on: February 16, 2009, 03:29:49 PM »
Its not a Metric problem, I can confirm that as I have only ever cut one non metric thread and my threads come out fine and I have done quite a lot :) Nowadays its all with the SmoothStepper but a lot were done with the parallel port.
 Below is a thread I did a few days ago, its the first one I have done since the servo went on the spindle, its working well :)
They are 18 X 1.5 and 16 X 2 threads, the close up is of the M16
Hood
Re: thread problem
« Reply #39 on: February 16, 2009, 09:40:46 PM »
I wonder if the problem is in release 42 20? I struggled today installed the smooth stepper
had a very frustrating time with every thing I touched.Oh well .Then I tried the newest release 43.000
and it seems to work fine.I also found that the c11 board from cnc4pc may have an issue.It would cause the computer
to freeze if I had it connected.I ended up connecting my pulse signal directly to pin 13 on the
ss port 2.As a side note a good idea to check the debounce value for encoders/index on the ss config.