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Threading on lathe issues
« on: March 01, 2015, 02:05:51 PM »
Hi guys, Need help!

Been searching on the forum for  a couple of weeks on threading on the lathe to solve my issue but I have had no success. My issue is that the timing on threads are off on each pass. Question is how do I correct this issue. My thinking is that Mach 3 is not picking up the timing correctly.

Hardware:
C35 board,
C3 board for indexing. board set on active high with Mach3 also set on active high for the pin.
100 mm disc with one 3mm slot
VFD (Teco N3) controlled by a C6 board.

Mach 3 version: R3.043.066

RPM reading on Mach 3 is correct. (meaning that rpm might be off by 1-2 rpm at most)
Debounce set at 0

X and Z axis movement and backlash are perfect.

Any advice will be helpful.
Thank you,
Raul M

               

Offline RICH

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Re: Threading on lathe issues
« Reply #1 on: March 01, 2015, 02:22:38 PM »
Have a read of Threading On The Lathe which can be found in Members Docs.
http://www.machsupport.com/forum/index.php/topic,13017.msg85313.html#msg85313

May need to set your rpm manualy as that can interfere with the threading cycle.
Not sure about version .066 infulence,as i have not used it, and others have gone back to earlier version
due to problems with it.
Make sure you have 3- 5X pitch of movement before actual threading to allow for axis acceleration

I'll let others reply about .066 who have tried or used it.

RICH
Re: Threading on lathe issues
« Reply #2 on: March 01, 2015, 03:20:17 PM »
Rich,
Thank you for your response. I have read the thread and manual but still can figure it out.
What version of Mach 3 works for threading?

Re: Threading on lathe issues
« Reply #3 on: March 01, 2015, 03:55:27 PM »
I use .057 and have threaded successfully on easy stuff.  I think Mach is OK but my machine lacks the spindle power & stability needed for doing steel over 16mm dia.  I'd kill for 1 - 2 rpm variation under load.;)  I have a 3/4 hp Baldor DC motor that's belt reduced about 4:1 and it's still too puny.:(  Maybe one of these days I'll stumble across a 1.5kw servo drive real cheap.  That'd fix it.

Fortunately I don't really HAVE to do CNC threading much since I have another lathe that'll do the jobs I HAVE to do.  
Milton from Tennessee ya'll.

Offline RICH

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Re: Threading on lathe issues
« Reply #4 on: March 01, 2015, 04:29:22 PM »
Dickeybird,
Have you  ever tried doing the other methods of threading? ie; Alternate Flank Cutting
It helps when lacking power.
(see page 44 in the manual) In fact you can do acme threading using alternate flank with a sharp V cutter by adjusting the depth. ;)

RICH
« Last Edit: March 01, 2015, 04:32:41 PM by RICH »

Offline BR549

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Re: Threading on lathe issues
« Reply #5 on: March 01, 2015, 04:33:30 PM »
Wow 3/4hp at 4:1 and you are having problems with spindle slowdown ??? 

Interesting, (;-) TP
Re: Threading on lathe issues
« Reply #6 on: March 01, 2015, 05:23:20 PM »
I think it's not so much a lack of torque slowdown under load but more of a variation around the set speed which shows up in the Mach spindle speed DRO as a small but constant up & down reading at all loads.  (No I don't have "Closed loop spindle control" checked.)  I also have a fairly slow Z-axis motor/drive.

 I think it's the KB DC speed control that causes it or my indexing disc slot width.  My disc/slot is very close to the OP's and is supposed to be OK.  I was going to try a wider slot or putz around with the KB but stopped trying to iron out the problem when the time spent/finished part ratio got too high to continue.

When things calm down a little around here I'm going to give it another shot or maybe just thread aluminum or acetal. ::)
Milton from Tennessee ya'll.

Offline Hood

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Re: Threading on lathe issues
« Reply #7 on: March 01, 2015, 05:30:53 PM »
Milton what is your max rpm?

Hood
Re: Threading on lathe issues
« Reply #8 on: March 02, 2015, 07:20:30 AM »
Dicky,
Thank you for your response. I will re-install the older version of Mach3 and do some testing over the next couple of days and I'll get back to you with my results.

Thanks again,
Raul
Re: Threading on lathe issues
« Reply #9 on: March 02, 2015, 09:04:17 AM »
Milton what is your max rpm?
1600 in direct drive, 400 in belt-reduction mode.
Milton from Tennessee ya'll.