Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Swarf-Boy on January 27, 2014, 09:41:08 AM
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Hi Folks,
I am still debating converting an old (but little used)small manual lathe to CNC, using stepper motors & ball screws.
I have worked out ( and had recommendations) on what direction to go mechanically.
I am however stuck on one point. I wish to do screw cutting on this lathe.
I have been informed that Mach3 can only handle 1 pulse per main spindle rotation. I understand that this may cause issues with screw cutting and make's multi start threads a no go area.
I have also been informed that the only solution to this, is to use a motion controller. I know the CSMIO plus the additional threading module will work. I realise that these are designed for industrial applications, but that is a bit out of my budget.
Are there alternatives, know to produce good results at a more affordable price?
Thanks
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The CSMIO is an excellent controller and definitely it conforms to Industrial practices such as 24vI/O etc but that is not to say it should not be used on a machine that is deemed not to be industrial.
As you say however the cost is more and if that is a problem then I do know the Smoothstepper threads very well, but it does just use a single pulse so your spindle motor would have to be fairly good at maintaining rpm.
Sadly the CSMIO/IP-M doesnt support threading at this time as if it did it would be a very economical controller for the smaller lathes as there is no need for breakout boards, spindle controllers etc that the other offerings really require.
The other option is to try the parallel port, lots of people have used it very successfully in the past for threading, me included. I have moved on from the PP now as my machines are mostly servo driven and the PP just could not give me the resolution and velocity that I required but for a stepper driven machine it is fine.
Hood
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I have been threading quite well with the standard PP set-up.
Like Hood says, I think the main issue is to have ample power at the spindle.
Maybe just over-sizing your spindle motor would be your most economical approach. ? ?
And, here is a cool post on multi-start threading.
http://www.machsupport.com/forum/index.php/topic,10385.msg64665.html#msg64665
Don't recall seeing anyone post any actual progress with footage.
Would be neat to see though.
Russ
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Russ, I tested out the multi start a long time ago but cant remember if I tried the method outlined in your link or not. Think I did and it didnt work but could be wrong.
I am sure the method I used was just to alter the start distance by the pitch amount. Now if I recall, say you were wanting a 2mm pitch 3 start you would code to have the pitch of 6mm and start maybe at Z10 then next pass would start at Z8 then final Z6.
Will have to test it out again to see if my memory is correct.
Hood
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Ok just done a search, here it is
http://www.machsupport.com/forum/index.php/topic,11064.msg72568.html#msg72568
Hood
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Thanks Hood, I wanted to try the #99066 method back when it was posted, but never got around to it.
Altering the start distance , , , just as simple, I guess.
But, you have to alter the STOP distances as well, right ?
#99066, Copy/Paste a few times ...... only need to change the angles. Might be easiest ... IF it works.
Might try it someday.
Thanks again,
Russ
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Good link ! ! !
Answers MY question.
Thanks
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Russ, end would just be the same, if that is what you are meaning by "STOP distance" Its the same Z position just 120 degrees further round on the material (assuming 3 start)
Hood
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Good link ! ! !
Answers MY question.
Thanks
Thanks Hood,
Russ
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Russ, end would just be the same, if that is what you are meaning by "STOP distance" Its the same Z position just 120 degrees further round on the material (assuming 3 start)
Hood
Guess I was loosely envisioning a shift, like a G52.
I hope to NEED this someday. :)
Russ
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I have been informed that Mach3 can only handle 1 pulse per main spindle rotation. I understand that this may cause issues with screw cutting and make's multi start threads a no go area.
That is not true and you can do multi start threads ...if...if .....your lathe "system" is accurate.
As noted by Russ and Hood, accurate / consistant spindle rpm will help along with adequate power so there is no slow down of the spindle.
For a single thread you can tolerate some small spindle change but with multistart .....the error will just show up and you'll have pitch problems.
You will find info on multi threading in the Threading on the Lathe write up in Members Doc's. see page 13 &14.
What i did know is in the write up.
I was barely able to do a good two start thread and three just didn't work for me here.
You want to see inaccuracy just scribe test and measure.
The # thing didn't work if I remember correctly and if you look at the code on page 14 you'll see that I just shifted the start point.
Been a few years since i tested.
RICH