Hi Robert, On May 9, 2008, at 7:21 PM, rtwas wrote:
> Hello, > > Being new to g-code and cnc I've been trying to learn the best way to > think about > the coordinate spaces and offsets etc (for a cnc mill). I'm not certain there is a 'best' way to think about coordinate space. One must home to where ever the home switches are but can offset from there. I home LL (lower left and spindle up) for G54 and do not offset. Some machines home UR (and spindle up) so all moves are negative. The Mazak at Galesburg offsets (X and Y) to middle of table. > > I'm thinking I should use a *fixture* plate with alignment pins etc to > mount to the > table. Some kind of pallet plate to hold the work (plugs into > fixture). I've seen used Boeing machines with a 1" aluminum plate drilled and tapped in a 2" or 50 mm grid. Lots of flexibility for mounting. For 90% of what I do I use UL of my vise as G59.3 and clamp fixtures in the vise. I simply draw my parts with a 0,0 UL corner. That point is pretty well fixed. ;-) > > My current thinking is that I would home x and y to the lower left of > the table. For z I'd use a spacer block > off the table to the end of the spindle. I keep thinking about making a tool length gage mounted on the table with a piston and a prox switch. It should be a very fast and accurate way of setting length. So far the round-to-it has eluded me. > > From there I'd use global offsets use a global offset (G92) to > align to > the fixture. From there I'm guessing > one whould use the users-selectable coordinate systems to align to a > theoretical x, and y starting point with > some kind of z plane somehwere over the part. > > Tool tables looked kinda fancy so I was going to defer using them > until > I had a better mental foundation of > the system, using some kind of programatic offsets instead. Tool tables exist because they are really nice. You need the diameter offsets to do G41/42 so you might as well learn to use the tool length G43. I break fewer tools using tool length. For me part Z (0) is the upper surface of the part. This makes canned cycles for drilling really easy. One gets used to setting R a certain distance above the part and then the machine rapids to there and goes to work. All of this does take some time to set up (and then to verify) but you have to do that with a new program anyway. The learning curve may seem steep but it is worth it. Dave > > Any input appreciated. > > Thanks. > > Robert W. > > > ---------------------------------------------------------------------- > --- > This SF.net email is sponsored by the 2008 JavaOne(SM) Conference > Don't miss this year's exciting event. There's still time to save > $100. > Use priority code J8TL2D2. > http://ad.doubleclick.net/clk;198757673;13503038;p?http:// > java.sun.com/javaone > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------- This SF.net email is sponsored by the 2008 JavaOne(SM) Conference Don't miss this year's exciting event. There's still time to save $100. Use priority code J8TL2D2. http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
