If you have a small stepper driven machine then homing may not be all that important, but if you have a large high power machine you really want to put the controls in the proper context before running programs on it. In other words you really want to have it know where the soft limits are. Big machines do drastic things to stop fast when a limit is made. In the case of my lathe, the drive enable is dropped, a contactor between the drive and the motor opens and a secondary contactor shorts out the motor hopefully stopping the machine before the hard stop is made. This isn't easy on anything.
If you have good home limit switches (not cheap) you can get within a couple mils pretty easily assuming your tools are set properly. So for a lot of work, that is good enough and that can eliminate manual touch offs. Anyway, that's my take on it. Dave >>>>>>>>>>>>>>>>>>>> David Braley wrote: > Hello all, > > Working away at researching my Anilam 1100 mill retrofit. Started to > read the EMC2 Integrators Manual V2.3. Seemed like the most useful > document for me at the moment. Figured I might learn something, so I > don't ask too many noob questions. So far so good. > > Did get to an interesting part of the manual in the early chapters on > the concept of Homing. The idea and how to do it is straight forward > enough. But this is the thing that really bugs me about the whole > concept of homing. Why? I mean really, why. The limit switches keep your > machine from crashing. So why home it? > > The developers of EMC, original and present, are obviously a bunch of > smart dudes. A lot of effort and coding goes into the hole homing > subject/feature. I know the homing feature must be there for some > important reason. I also know you can disable the homing feature in EMC. > I actually learned that by reading the manual! Ha! (note: I'm no where > near finished with the Integrators Manual!) > > I've been a precision handle cranker now for over 35 years. The two-axis > Anilam milling machine I've been running for the last year or so is the > first automated machine I've ever had my hands on. It has no homing > feature, but it does have table limit switches for obviously reasons. > > I need help understanding why a CNC needs to home itself. If your reply > is simply so that the machine can know where it's boundaries are so it > will NOT run a program off the limits of it's own travel, then I still > ask why? Why does a machine need to know it's work envelop before it > gets to the limits of table travel. How does this help the machine run > better, or be more productive? I ask because you don't have to be a > rocket scientist to position your vise or work-holding fixture on a > table to run a program on a machine without it running into the limit > switches. > > There must be some other REALLY important reason behind all of this > homing stuff that I just don't get.... yet :) > > Just a guess, but does the need for homing have something to do with > some kind of nesting feature in EMC? Then I could see a need for the > machine to know exactly where it's at relative to it's boundaries. In > the nesting programs I've seen, the machining envelop is know so the > program can populate the space with parts for cutting. More common on > Plasma, Laser, WaterJet type machines, but I guess I could also see some > kind of nesting feature useful for a milling machine. Well, maybe not a > milling machine. > > Thanks and take care, > > David > > ------------------------------------------------------------------------------ > Come build with us! The BlackBerry® Developer Conference in SF, CA > is the only developer event you need to attend this year. Jumpstart your > developing skills, take BlackBerry mobile applications to market and stay > ahead of the curve. Join us from November 9-12, 2009. Register now! > http://p.sf.net/sfu/devconf > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > > ------------------------------------------------------------------------------ Come build with us! The BlackBerry® Developer Conference in SF, CA is the only developer event you need to attend this year. Jumpstart your developing skills, take BlackBerry mobile applications to market and stay ahead of the curve. Join us from November 9-12, 2009. Register now! http://p.sf.net/sfu/devconf _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
