On 09/04/2016 04:10 AM, Gene Heskett wrote: ... snip
To continue this thread about G76 and E, I note that it says its an error if E is more that half the drive line length. All this time I thought, and have observed, was that it was the fraction of a full turn. Then I grokked that programming a taper of K height would appear to be a matter of speccing the drive length way out in the air, and programming E to be 49% of the drive line length. So all the taper would be done on the workpiece. Longer tapers by moving the starting Z position in units of the pitch P, and the starting X in K increments and running the same line of code again. A time killer, but when in Rome...
I tend to think of the end tapers as chamfers. They allow a gradual start or end. Fiddling with the parameters one can fool G76 to making an end chamfer look like a tapered thread, but it is not ideal. Half of the thread length becomes a chamfer, and half becomes wasted in air. Extra I is needed to drive K into the stock so that the end of the chamfer is still into the stock by one thread depth, when it really wants to just break free. I gets really complicated in a hurry.
I attached a rough graphic of what I think needs to be fiddled to get a tapered thread from the current G76.
When I get the little monster operational again, I will need some help in arriving at a 7 degree included angle, eg 3.5 degrees at the workpiece, as I think this is worth exploring. The solution to my tapered thread requirement may have been right under my nose all the time! Cheers, Gene Heskett
If you can compile and run the LinuxCNC source it should not be too hard to try out the G76 with taper and chamfers version.
-- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/
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