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Author Topic: Muti-start threading....  (Read 21998 times)

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Offline Tef9

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Muti-start threading....
« on: March 31, 2009, 05:18:56 PM »
Hello All,

I have played around with normal threading and I am starting to get some confidence, I am now looking at multi start threading via cnc and mach 3.

I last spoke to Hood about this here :

http://www.machsupport.com/forum/index.php/topic,10385.0.html

My questions are as follows:

1) Do I need to have controll of the direction of the spindle?

2) Do I need a special gear train for multi start?

3) Does mach 3 multi start thread by coming in at a different angle?  Will I need to vary the speed?

I am using a cnc Sherline.

The thread I would like to cut is a four way o.75pitch 9.5mm dia - straight, not on a taper...yet.

Thanks,

Andy

Online Graham Waterworth

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Re: Muti-start threading....
« Reply #1 on: March 31, 2009, 05:48:30 PM »
Program the thread 4 times each time start the z axis 1/4 pitch towards the tailstock. You will need and index pulse to do it.

Graham
Without engineers the world stops

Offline Tef9

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Re: Muti-start threading....
« Reply #2 on: March 31, 2009, 05:53:41 PM »
That sounds simple enough, however urm....what is index-pulse? is this the way the motor works?

Thanks,

Andy

Online Graham Waterworth

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Re: Muti-start threading....
« Reply #3 on: March 31, 2009, 06:00:59 PM »
It is a slotted disc on the spindle that sends a pulse to Mach3 to tell it the speed and position of the spindle.

Look in ports and pins for index , and see if it is set active.

Graham
Without engineers the world stops

Offline Tef9

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Re: Muti-start threading....
« Reply #4 on: March 31, 2009, 06:36:58 PM »
Ahhh I have set up an optical unit like Hood and rich with 1 slot in the disk, will that work?

Thanks,

Andy

Offline Hood

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Re: Muti-start threading....
« Reply #5 on: March 31, 2009, 07:06:12 PM »
Yes :)

Hood

Offline RICH

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Re: Muti-start threading....
« Reply #6 on: March 31, 2009, 08:49:28 PM »
ANDY,
Post a pic of the multi start thread.
BTW don't foget to make a nut also.
RICH

I only ever done one for kicks.

Offline Tef9

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Re: Muti-start threading....
« Reply #7 on: April 01, 2009, 03:38:01 AM »
Will give it a go over the weekend and post a pic, Thanks for all the replyes so far!

Andy

Rich - I dont have an internal threading tool yet, if it arrives in time I will give a nut go as well!

Offline bowber

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Re: Muti-start threading....
« Reply #8 on: April 01, 2009, 04:56:03 AM »
Hi

I've done multi start threads on my mill using the same principle, just move the start up or down the Z by the required amount, only down side is that on a mill it finishes short by that amount too so you end up with each thread finishing short by the offset.
There are a few solutions that come to mind but they all involve a bit of hand coding which i try to avoid as I nearly always make a silly small mistake.

Steve

Offline Tef9

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Re: Muti-start threading....
« Reply #9 on: April 01, 2009, 05:04:04 AM »
Surly you just change the G00 Z start value.  I have not tried yet but I thought it should only be somthing like:

(1/4 z move each time based on a 1mm pitch)

G00 Z0.0000 (start 1)

G76 <thread code here>

G00 Z0.2500 (Start 2)

G76 <thread code here>

G00 Z0.5000 (Start 3)

G76 <thread code here>

G00 Z0.7500 (Start 4)

Or at lease that is what I thought, it should not affect the Z end or am I missing somthing?

Andy