Re: [CAD_CAM_EDM_DRO] Re: Sherline Spindle Pulse disk for threading

On Sun, 11 Nov 2007 13:57:24 -0000, you wrote:

Hi Glen

>Hi, I insert a tool change command to stop the program and check the
>thread. After the tool change I have another G76 with the full depth
>of thread as the first cut parameter in the threading wizard. I can
>then go over the thread as many times as I want with the finishing
>cuts only.

Yep - I can see where you are coming from, but that's exactly what
spring passes do (Q value in Mach G76).

>If you don't have a very steady "true spindle speed" reading in Mach 3
>it is impossible to cut a thread using G76.

Yep - that's absolutely essential.

Another important thing is to be able to command a speed, and know your
spindle is actually going to do that.

IF I used all my pulleys, I can do 10-2000 rpm. I don't bother. I stick
with 200-1100 rpm on one setting (there's 10 combinations). On that
setting I'm never more than +/- 2rpm across the range of commanded to
actual.

Personally I don't use G76, I use individual G32 passes, CAM controlled.
(Longer code, better thread)

BTW - There are a few strategies for cutting a thread, (very much
simplified)..

1 - you increase the depth of cut by the same amount each pass.

2 - you try to remove the same volume of material pass by pass.

My memory is dim on this, but there was a long discussion years ago in
the Mach group, I do remember that the wizards chose V2, dunno what Mach
chose.

Neither strategy is perfect, but V2 works better in my experience.

I still do my one or two spring passes and no matter how big or rigid
your machine is, if you take two passes at the same depth, you will
remove some material ;)


Steve Blackmore
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