On Tue, 17 Aug 2010 10:18:54 +0100, you wrote: >On 16 August 2010 05:24, Steve Blackmore <st...@pilotltd.net> wrote: > >> A "drive line" , as it seems to be called in past posts, should be able >> to have any value you want. It's a valid engineering technique to cut >> with a zero increment. > >I believe it is to define a safe return path for the cutter (and also >to let the interpreter know whether to cut an internal or external >thread). >Returning the tool along a line that skims the thread peaks does not >seem that valid to me.
Skimming the top at 0 removes flash edges, a common technique. >"I" defines the distance from the current tool position to the peak of >the threads, if you have just completed a turning sequence to finished >diameter then that doesn't mean that "I" is zero, it means that it >needs to take the value of the X backout you used for the return >rapid. > >> To put that in context, neither does G33, properly! I turn hundreds of >> parts per week. 30% have taper threads, they need to be in >> specification, to achieve that I need to fudge the pitch with EMC. > >You have complained of this before, but I have concluded that it is a feature. Nah - a PITA :) >It is almost no trouble at all to fudge the pitch to be correct, but >if you wanted to cut a spiral with only an X pitch (the scroll for a >three-jaw chuck, a face-cam, a camera iris control ring) then if G33 >always used the Z axis to define a pitch, you would have no way to >make it happen. A spiral or a scroll isn't a thread. By all means keep G33 for such things, but why not have a standard thread Gcode, preferably G32 with F for feed per rev ?? Almost no trouble isn't really good enough - Should be no trouble if implemented correctly. No CAM program I am aware of, or ANSI, ISO or DIN standard defines taper threads like EMC. You need to get out the calculator to work out the unique "EMC style" pitch. Both my favoured CAM programs have extensive inbuilt thread tables that allow you to define the thread without any entries apart from the start point and the thread length. Totally useless for taper threads, you have to manually enter all the parameters simply because EMC does not define taper threads correctly. The particular example I posted for John of a 2mm pitch thread would have to be fudged to 2.13mm, not an insignificant amount, and mistakenly done at 2mm pitch with EMC's non standard threading would have wrecked some expensive parts with 40mm 316 Stainless at £110 ($172) per metre. Steve Blackmore -- Steve Blackmore -- ------------------------------------------------------------------------------ This SF.net email is sponsored by Make an app they can't live without Enter the BlackBerry Developer Challenge http://p.sf.net/sfu/RIM-dev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
