Andy Pugh wrote: <snip> An alternative might be to keep things much as they are, but to have a parameter in the G-code for how much "run up" it has. It then becomes a somewhat simpler trajectory planner issue to get to the thread start at the right speed next time the index comes round on the unloaded spindle and only then to enter the current position-feedback mode to stay on-pitch and allow for spindle velocity changes. I think that might actually be the essence of how Chris' patch works, though that just waits to get a better spindle speed estimate I think.
Greeting to all This may be another "data point". "Another PC based controller" produces pretty decent threads even on a low powered spindle like the Tormach Duality with only one pulse per rev. by not attempting to solve the general problem. The threading code (G32) watches index pulses until it sees several with a consistent timing. That gives the spindle speed and with the requested pitch (F word) gives the Z feed in units/min. Now the Z (and X for tapered threads) trajectory can be planned from the current Z position. On seing the next index the trajectory runs. To get a clean start one cuts a few threads in air over the acceleration period. So there is no exact thread position on the stock - it all depends of the acceleration - but multiple start threads work out fine by keeping the same spindle speed and starting with Z 1/2. 1/3 etc. of a pitch greater. The actual code does a running correction, if the spindle speed droops, effectively by using the feed rate override logic . I think it might be better to recognise a rise too as an overcompensated spindle drive can speed up on taking the cutting load - but that is a detail and was not done as FRO upwards could at one time violate the motor tuning parameters. This is by no means an electronic gearbox but needs no tuning and is surprisingly effective for turning even long threads. John Prentice ------------------------------------------------------------------------------ Come build with us! The BlackBerry(R) 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/devconference _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
