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Author Topic: Opinion and advice - explain relationship of encoder to kernel speed  (Read 17021 times)

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Offline Hood

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Re: Opinion and advice - explain relationship of encoder to kernel speed
« Reply #10 on: April 11, 2009, 12:03:30 PM »
Oh and as for the servo driven spindle, that wouldnt help unless you set it as an A Axis because Mach can still only use a single index pulse rather than full encoder. The threading is a mystery but it all seems to boil down to either computer stability or spindle power at the moment, I have never had an issue with threading on the lathe, previously it had an induction motor and now it has a servo. With the servo the spindle speed in mach is rock steady  and even when I had the incuction motor is was as well (as far as I can remember) I have also had two different mobos in this. I am sure Art will get the better of it at some point in time.
Hood

Offline simpson36

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Re: Opinion and advice - explain relationship of encoder to kernel speed
« Reply #11 on: April 11, 2009, 01:31:21 PM »
I'm not a fan of the single point threading scheme used by Mach and it does not surprise me that it is and has been problematic. I have been following the discussion on threading and frankly I don't see how threading will ever be reliable when trying to compensate for spindle speed deviations using a single pulse per rev when the variable speed controllers also have built in compensation that Mach is unaware of, but that's another topic altogether.

I considered your solution of two Mach setups using one to turn and one to index, but that will not suit my purposes. YOu would understand if I explain what I want to accomplish.

The part I have in mind has numerous steps requiring several setups and several programs. One of the problems is (speak of the devil) threading, but that's easy to resolve. The unresolvable problem come sin turing down stock from 3/4" to .4" for about .6" from one end and then cutting flats 90 degrees apart on the OD at the end.

With a turning tool, a drill bit and a tap setup in a plate attached to the mill head, I can turn down the OD, bevel te end, drill a hole and tap the end. Then, with the same setup and thesame program, continue on to index and cut the flats with an end mill in the mill spindle.

There is one last operation that I could also do with the setup, which is cut a slight crown on the other end using a cut-off tool, but I know I will n ot have enough power or rigidity to do that. BUt I'll settle for doing the other stuff in one swoop. It now takes several setups and several programs and manual tapping of the hole. 

This is a hobby for me, but I like a challenge and making a 'mini machining center' of sorts would certainly serve that purpose  :o

vmax549

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Re: Opinion and advice - explain relationship of encoder to kernel speed
« Reply #12 on: April 12, 2009, 10:27:10 AM »
YOU can do what you want with what you have with the 4th as is.

The problem you will have with code is once you start the a to rotate NO other moves can start until the A completes its move.(;-)

But you can program it as one move but it is not conventional in any manner of code.

Yoou can also run the spindle and rotate the A to mill the shaft down to .6 same as cutting with a singlepoint tool. Then to do a finish cut and change to a 60deg v bit  thread in the same manner.

It is the way you have to code that will be very different but possible.

(;-) TP
« Last Edit: April 12, 2009, 10:30:48 AM by vmax549 »

Offline simpson36

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Re: Opinion and advice - explain relationship of encoder to kernel speed
« Reply #13 on: April 13, 2009, 01:49:51 AM »
I'll try cutting the barrel down with the end mill next time I get the rig set up. That's an interesting idea. In this case, the threads are internal, but your idea about the v tool in also interesting.

What I am confused about are the comments that the A axis has to complete before any other moves. That's not how it works for me. When I program G1 A360 X.1 for example, BOTH moves happen simultaneously.

That's how I single pointed these (external) threads on the rig:



Originally, I built the rig only to be an indexer, and in that capacity, it works perfectly. Driven by a 900 oz-in stepper, it  just does not have enough power or speed to do other tasks like threading (it stalls easily) and turning (not fast enough), hence the idea of repowering it with a servo motor.

This is how the drive is arranged except that I have since installed a wider belt:



« Last Edit: April 13, 2009, 01:55:51 AM by simpson36 »

Offline Dan13

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Re: Opinion and advice - explain relationship of encoder to kernel speed
« Reply #14 on: April 14, 2009, 05:39:39 AM »
Terry,

How do you use that SwapAxis approach for rigid tapping? I have now a servo motor on my lathe's spindle and I would like to try this approach. I have pins 7 and 8 set as the spindle's step and direction signals respectively.

I tried to set the same pins for the A axis and thought I could program either the A axis to move or the spindle to rotate. But the SS doesn't support setting twice the same pin.

I also tried setting different pins for A (14 and 16) and connecting them to the servo drive as well (in addition to the 7 and 8), but didn't work neither.

Thanks,
Daniel

Offline simpson36

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Re: Opinion and advice - explain relationship of encoder to kernel speed
« Reply #15 on: April 14, 2009, 09:56:10 AM »
I'm not sure who Terry is, but I'll take a crack at an answer.

The idea, I believe is to have multiple Mach setups and use the one appropriate for what you ware doing.

For example you would have one setup where pin 7 and 8 are the spindle and a second setup where 7 and 8 are the 'A' axis.

I'm not sure how to accomplish starting Mach with different configurations. It may involve starting the program with an argument, renaming the configuration file prior to launching Mach, or simply having two installs of Mach.

Incidentally, I have now probed Mach's limits (software only) with 'A' as a spindle. The 'A" axis went to around 40 MILLION before I stopped it. Should be plenty for any normal work, I should think.

Offline Dan13

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Re: Opinion and advice - explain relationship of encoder to kernel speed
« Reply #16 on: April 14, 2009, 11:35:53 AM »
I remember Terry once said on another thread here that he had used this approach successfully, that's why I referred to him.

What you suggest is using different profiles, one for rigid tapping with A axis and one for turning operations. I don't think that was what Terry was using, as this is not very practical. I remember he said he was using SwapAxis, but how particularly?

Daniel

Offline simpson36

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Re: Opinion and advice - explain relationship of encoder to kernel speed
« Reply #17 on: April 14, 2009, 12:01:49 PM »
Yes that is doable and is what I will be doing to get rigid tapping if the SS doesnt support it when I eventually get the mill finished. It would however be a lot of working out and coding. The easiest option would be to set up two profiles, one a mill and the other a Turn and when you wanted to do lathe work just start up the Turn profile, the A axis would be set as a spindle in it.
Hood

Again, I don't know who Terri is, but I was remebering the above comment from earlier in this thread from 'Hood'

Two profiles seems like a viable solution to me. What would make that solution impractical in your opinion?

As to the axis swap, I have written one program that does this sucessfully, but it was a real mind bender to get it right. Up is down, left is up, right no longer exists, that type of thing . . LOL!

Art is hard at work modifying the threading code for Machturn, so maybe the objective can be met more easily with whatever new capabilities he manages to stuff in there.




Offline Dan13

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Re: Opinion and advice - explain relationship of encoder to kernel speed
« Reply #18 on: April 14, 2009, 12:24:08 PM »
Different profiles approach is not practical since my goal is not just to rigid tap, but rather do the rigid tapping as part of the gcode program to produce a finished part. I want to turn, drill and tap with the same gcode.

Here is the link to the thread where Terry mentioned he had used this approach successfully:

http://www.machsupport.com/forum/index.php/topic,9582.0.html

Daniel

Offline Hood

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Re: Opinion and advice - explain relationship of encoder to kernel speed
« Reply #19 on: April 14, 2009, 01:31:43 PM »
SwapAxis is, as far as I know not implemented in the SmoothStepper.
Hood