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Author Topic: Muti-start threading....  (Read 19928 times)

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Offline Tef9

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Re: Muti-start threading....
« Reply #20 on: April 15, 2009, 03:54:57 AM »
Rich - I make pens so therefore I need a smooth multi start.

Hood - no not yet, will give that a go next.  The little lady has just gone back to uni so I now have some time now (i did not say that)  :)

Roll on the weekend !

Andy
Re: Muti-start threading....
« Reply #21 on: April 15, 2009, 06:55:35 AM »
 :)

Quote
Have you tried the angle offset way that I pasted details about in another thread you were enquiring about multi start threads?
Hood

Just thought I'd include the link to the "Angled Offset " approach mentioned by Hood in the earlier post.
http://www.machsupport.com/forum/index.php/topic,10385.0.html

RC

Offline Tef9

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Re: Muti-start threading....
« Reply #22 on: April 15, 2009, 07:53:24 AM »
Good Plan,

I might try and give it a go tonight, wont be able to make a nut to test it however if it looks uniform I will count it as an improvment.

Andy

Offline Tef9

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Re: Muti-start threading....
« Reply #23 on: April 18, 2009, 11:59:55 AM »
I have just spent 4 hours having a go at this in various ways, will post some pics and more info tommorrow night when I get back.

Andy

Offline Tef9

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Re: Muti-start threading....
« Reply #24 on: April 19, 2009, 01:40:12 PM »
Ok...trying to be a bit more scientific about this, I have done one single start and one double start.

The single start has perfect unform looking threads, the double start seems...messy!

This method was done using the 'move the z axis' method.

any ideas as to why the second start looks messyer that the first?

I have tried the angle approach however have no pics ... yet ... will upload results soon.

Andy

Offline RICH

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Re: Muti-start threading....
« Reply #25 on: April 20, 2009, 01:07:21 AM »
aNDY,
So how is the angled approach working for you?

RICH

Offline Dan13

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Re: Muti-start threading....
« Reply #26 on: April 20, 2009, 02:21:43 AM »
Hi Guys,

About a month ago I decided to try to cut a double start thread on my Emco lathe. I chucked a 15mm dia aluminum bar stock and gave it a go... and it worked perfect right on the first attempt.

I think that in order to cut multi start thread it's necessary to first understand the nomenclature and how it works. Pitch, P, is defined as the distance between two adjacent crests (for metric threads). Lead, is the distance the screw advances when it's turned one revolution. For a single start thread, lead and pitch are equal.

Thus, when you cut a (multi start) thread what you have to consider is the LEAD and NOT the PITCH. So if you want to cut a 1mm pitch double start thread, you have to program a feed of 2mm/Rev for each of the starts. Obviously, the two starts are 1mm apart, so after cutting the first lead you have to move the tool 1mm in Z and start the move from there for the second lead. Note that the depth of thread has to be the same as if you were cutting a single start thread with the same pitch (which is 1mm for this example).

Like was noted in the previous posts here, the end of cut (in Z direction) has to be adjusted for each lead so that that they end in the same point along Z.

Hope it helps ;)

BTW, Andy, both the threads on your picture above look messy. The single start thread looks awful - like mine used to be with the DC spindle motor that was not rotating steadily in the same RPM. Turned out my belt was worn out unevenly along the perimeter and was causing fluctuations in the spindle speed.

Daniel

Offline Tef9

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Re: Muti-start threading....
« Reply #27 on: April 20, 2009, 04:51:34 AM »
Hang on I think  I see you point, So if I set the pitch at 2.8mm and cut a four start thread is that an overall pitch of .7? (after increasing the z each time of course)

Andy

P.s did not think about the belt, will investigate a new one!

Offline Dan13

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Re: Muti-start threading....
« Reply #28 on: April 20, 2009, 05:17:30 AM »
Hi Andy,

Yes. If you set the pitch in Mach3 to 2.8mm (which is actually has to be called "lead") and advance the Z axis by 0.7mm for each start, then you would get a 4 start thread with a PITCH of 0.7mm and a LEAD of 2.8mm.

Prior to getting a new belt, check how it runs on the pulley - on mine I could actually see it going up and down when looking at a fixed point just above the pulley.

Daniel

Offline Tef9

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Re: Muti-start threading....
« Reply #29 on: April 20, 2009, 05:27:29 AM »
Thanks,

I will give it a go tonight, should have some brass rod ariving.

A