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Author Topic: How many pulses for a lathe spindle encoder is really needed?  (Read 7340 times)

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Offline tjhj

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How many pulses for a lathe spindle encoder is really needed?
« on: October 29, 2009, 02:47:53 PM »
Hello All,
I have recently converted my MicroMark 7x12 to CNC, I have been happy with the results so far, but I want to add threading and have hit a hang up on the best way to do that.

I am debating between using a slotted wheel directly off the spindle with 50-60 slots in it, or placing pulleys to speed up the speed of the encoder disk relative to the spindle in the range of 3-27 times. (Happen to have some small pulleys and needle bearing that give that range, 3, 9, or 27 times) And one index pulse per revolution.
So the big question how many pulses off a spindle encoder do you really need to make accurate two cut direction threads? I saw one encoder that had almost 2,000 PPR, so I figured more is better, but does it even matter? Will 1350 PPR make any difference than 50 PPR? If so is there a threshold and where is it?

I saw someone say that they were cutting threads with just an index pulse? Is the whole multi-pulse encoder necessary?

Thank you for your time,
TJ

Offline Hood

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Re: How many pulses for a lathe spindle encoder is really needed?
« Reply #1 on: October 29, 2009, 03:03:44 PM »
Single pulse per rev is what I use.
Hood

Offline tjhj

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Re: How many pulses for a lathe spindle encoder is really needed?
« Reply #2 on: October 29, 2009, 04:17:11 PM »
Is there type of threading you cant do? Or any limitations you have found using only 1 pulse per revolution?

Thank you,
TJ

Offline RICH

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Re: How many pulses for a lathe spindle encoder is really needed?
« Reply #3 on: October 29, 2009, 04:42:27 PM »
TJ,
I also only use a single index pulse. That is what i would suggest you use at this time.
We have been, and continue, to test a number of different impulse combinations, but
nothing has proven to an be advantage at this time or is implemented strickly for testing purposes.

RICH  

Offline RICH

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Re: How many pulses for a lathe spindle encoder is really needed?
« Reply #4 on: October 29, 2009, 04:55:01 PM »
TJ,
The limitations will be due to  the "Lathe System" you have.
Threading is actively being reviewed and tested for modification. Hopefully it will be all sorted out
in the very near future ( like a week or so/ never know ). 

Don't get hung up on the single pulse per rev. Threading is way more complex than just the single index pulse.
RICH
Re: How many pulses for a lathe spindle encoder is really needed?
« Reply #5 on: October 31, 2009, 05:52:18 AM »
TJ,
I also only use a single index pulse. That is what i would suggest you use at this time.
We have been, and continue, to test a number of different impulse combinations, but
nothing has proven to an be advantage at this time or is implemented strickly for testing purposes.

RICH  

Hi Rich,

I've been searching the forum for teh answer to this question...so one slot it is.
re: the slot width, should I use the calculation in the lathe manual, or have you used another "formula"

I guess the main thing is that the slot is not too narrow.

ATB
Derek

You can "chop it off" but can't "chop it on"

Offline RICH

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Re: How many pulses for a lathe spindle encoder is really needed?
« Reply #6 on: October 31, 2009, 08:20:41 AM »
Derek,
Use the calculation in the manual. The slot width can be bigger. You may find that you don't get a DRO indication of your rpm range. If so, make it wider to increase the signal time.  I widened one of mine from a calculated 1/8" to 1/4" wide to get full DRO readout.

BTW, there will be something posted in the Members Docs on threading using MACH3 Turn. It will cover a lot of territory and is in the making.

The threading looks to be better than ever ( we have been tweaking it for over a year now ). The latest changes may be incorporated into the next version of Mach in the near future.

Is there some kind of specific threading / cutting that you are interested in or have concerns about?

RICH

Re: How many pulses for a lathe spindle encoder is really needed?
« Reply #7 on: October 31, 2009, 01:33:45 PM »
Derek,

BTW, there will be something posted in the Members Docs on threading using MACH3 Turn. It will cover a lot of territory and is in the making.
Is there some kind of specific threading / cutting that you are interested in or have concerns about?

RICH
Hi Rich,

Thanks for te reply,

I have no specific concerns but having recently converted my Colchester / Anilam lathe to Mach, I now need to get the screw cutting working.
First job will be a M20 x 15 long internal thread in Ali and brass..

The massive post on screw cutting problems makes interesting reading, so I guess I want to set up the spindle feedback in such a way to be "compatible" with the final findings you and Art are working on.

Thanks
Derek
You can "chop it off" but can't "chop it on"

Offline RICH

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Re: How many pulses for a lathe spindle encoder is really needed?
« Reply #8 on: October 31, 2009, 03:25:50 PM »
I haven't done much internal threading. Can get away with tapping most of the time......

M20 x15 long ( i am an imperialist ) is about equivilent of 3/4-24 x 5/8" long ( around a sharp v depth of 0.036 ).
Shouldn't have any problem. You may want to try just an external thread thread first to gain some experience and see how it goes. Don't know if your lathe is punney or robust.

The big difference to CNC, is that with a manual lathe, you can always adjust the depth cut , ie; some brass will work harden, to suite how things are going.
Let us know how you do,

BTW, why not hang on for say a week  if you can, and waite for the improved version of the threading to be posted.

RICH

Offline RICH

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Re: How many pulses for a lathe spindle encoder is really needed?
« Reply #9 on: October 31, 2009, 03:30:31 PM »
HMM...... just noticed.
 ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D


Come on out Brett wherever you are!
 ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D