On Saturday 07 November 2009, Andy Pugh wrote: >2009/11/7 Gene Heskett <[email protected]>: >> ; leave cutter parked in the hole to show off. >> ;Cunning ;-) >> G0 X[0 - #<Pitch>/2] >> #<Angle> = [#<Angle> + #<Step>] >> G0 C[#<Angle> - #<Step>/2] X0 Y[#<Radius>/COS[#<Step>/2]] >> G0 C#<Angle> X#<H_Width> Y#<Radius> > >Looking at the manual pages on G2 and G3 I noticed that you can do >Arcs with simultaneous rotary motions.> >With the code above you are dependent on having enough space round the >cutter for two straight-line paths to not foul the work. >This way is more elegant....
I turned off word wrap, is this what you meant? #<Angle> = [#<Angle> + #<Step>] G2 C#<Angle> X#<H_Pitch> Y#<Radius> I#<H_Pitch> J[0-#<Radius>] F[#<Feed> * 100] G0 X#<H_Width> F#<Feed> Great, I'll fix that. With the current sizes of things, there was room, and I believe the only artifact I saw in the one finished piece was one caused by the backlash in my table, which seemed to be being pushed a bit during the cut stroke from outer diameter to the inner diameter, and may have contributed to a grab and a broken bit as it started downslope of the 2nd tooth of the 2nd sprocket I cut this morning. In any event, the sprocket fits _very_ nicely, I can wrap 12 links of chain around a 13 tooth sprocket with no binding and no slop other than it could be a bit thicker than 1/8" for a hunk of #35 chain. I may have to go get my grin sewed back up, it went clear to my ears. :) >> Watching it cut electronic air I see another problem, the initial G2 >> move, half a turn for the initial spiral down of more than the bit >> diameter is probably going to clog the bit and maybe break it as I don't >> have a coolant spray to keep it power flushed, just a puddle of cutting >> oil, so wouldn't a G83 peck cycle be a better idea there? > >I suppose that depends on whether you have a slot drill or an end-mill >mounted. I was also assuming quite thin material. Another option would >be to do it in a number of Z steps. 4 flute solid carbide end mill, and the G83 is a peck drill cycle. At R0.015 and O.015, it kicks up some fairly serious chips for an 1/8" 4 flute mill. I have now ordered a 10 pack of 2 flute TiN coated, should work better in alu. >> I sure wish I understood those g2/g3 moves better. Those 2 pages in the >> manual need some clarification, I am just not getting it. > >I will try to make some clarifying drawings and put them on the Wiki >(as after a lot of head scratching last night I think I understand it >all now). As a precis: >To define an arc you need any three out of four of start point, end >point, radius and centre point. But what are those vars actually called? >In G-code you always define the start and end points then have a >choice of defining the centre point or the radius. >Defining the radius is the easy way. You define a radius, EMC solves >some equations and finds where the centre of that arc is, and produces >the arc. However this gives you no control of the arc centre, and very >small changes in start and end points can cause large changes in arc >centre position. When you are near 180 or 360 says the warnings. These cuts are about 90 degrees, so should be reasonably accurate, moreso than the backlash slop in my $100 4" table. :( >Alternatively you can define the centre point with I,J,K, and EMC >works out the radius. If the radius from the centre point to the start >and end points differs then EMC raises an error. Altogether too easily, but the error message needs heavy duty math to make an intelligent correction. >This means that some >maths is needed when the start and end points are not at cardinal >points. It is possibly easiest to solve by using a sweep angle and a >bit of trigonometry, though in this sprocket code I chose to use some >Pythagorus. (Note also that that line of the code keeps line-wrapping) I think I turned that off in this reply. >Note also that the centre point is defined _Relative_ to the current >position. That caused me a lot of confusion the first time, and maybe >you too. Yes. >The manual says that you can change that with G91.1. I wish I >had realised that much earlier. > >Cutter radius compensation would simplify the maths somewhat, and >would have made it easier to put a flat on the tooth tips. I >considered doing that with the current file, but the maths got tricky >because that means solving equations to find tangents. I was just going to cut a circle to trim them off in my original attempt. However, this works for this size chain & tooth counts. Smaller chain, and higher tooth counts help in this regard I believe. TAN is an emc function too. Cutter radius comp, I find cannot be used without canceling before changing tools. I was being lazy and using that to make emc stop while I was mounting and unmounting the workpiece, running the machine out from under the head, stopping the spindle and then restarting it for part2 of the operation. Beats having to load a 2nd program for me. :) Again, thank you very much Andy. Where should I put the working code, is my web page OK since I don't have perms to edit the wiki? -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) The NRA is offering FREE Associate memberships to anyone who wants them. <https://www.nrahq.org/nrabonus/accept-membership.asp> By golly, I'm beginning to think Linux really *is* the best thing since sliced bread. -- Vance Petree, Virginia Power ------------------------------------------------------------------------------ Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day trial. Simplify your report design, integration and deployment - and focus on what you do best, core application coding. Discover what's new with Crystal Reports now. http://p.sf.net/sfu/bobj-july _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
