On Sun, 2013-07-07 at 23:21 -0500, John Morris wrote: > On 07/06/2013 04:28 PM, Jon Elson wrote: > > Chris Morley wrote: > >> I am not an expert, just interested. I don't follow your reasoning. > >> Jerk limiting is about having the TP ask for movement that is possible > >> for the machine to actually produce. > >> infinite jerk is impossible for a machine to produce movement for. > >> While we can ignore it in relatively slow and small machines, I can not > >> see why you would want to turn it off in some cases. > >> > > G33 (lathe threading) assumes the spindle is mostly maintaining constant > > velocity. G33.1 (rigid tapping) assumes the spindle reverses fairly quickly > > at a certain point. The Z axis must follow the spindle quite closely, or > > it will break small taps and muck up the thread on larger ones. > >> It seems if you have the TP request infinite jerk, then you are must > >> realize > >> that your are asking the machine to NOT follow the TP command for a small > >> instant. > >> I don't see how G33.1 is any different then other machine movements. > >> > > Other than spindle synched moves, ALL axes are under TP command, and > > that should always keep them synched so they are all at the correct > > coordinated position. With a spindle-synched move, the tool must > > follow the spindle, which often is NOT a servo axis, and is just > > generally obeying a velocity command. When the G33.1 gets > > to the point of reversing the spindle, it can reverse fairly quickly, > > depending on the particular machine setup, and the Z BETTER > > keep up with however fast it reverses! Having any interpolation, > > jerk limiting, etc. between the spindle encoder and the Z axis would > > apply strain to the tap, and be very undesirable. > > Restating, to see if I understand: > > Conditions: Z axis needs to be slaved to the spindle speed; at the same > time, Z axis jerk needs to be limited. > > Complications: Tapping operations have problems with friction and > grabbing, causing uncontrolled and rapid spindle deceleration. Also, > spindle acceleration and reversal control is not as precise as other > motion components. Nothing we can do about the uncontrollable! > > My naive impulse (don't be polite about shooting it down ;) : Translate > maximum Z axis jerk into maximum spindle jerk, and then just do the best > we can to keep spindle jerk within bounds, given whatever complications. > (This can be generalized, for example when the spindle is at an angle > and multiple axes must be slaved.) > > John Hi all, I'm guessing that for machines with gearing and a constant speed spindle motor there is usually plenty of power to cut threads for even form threads if the hole is the correct size. I suspect that Jon when tapping Al panels never runs out of spindle power.
The next problem is that of lube. I once asked a well known manufacturer of tapping heads what he recommended for lube and his answer was NGLI 2 grease. I've used it a few times for essentially hand taping but since I don't have a synchronized spindle I don't power tap. :-( Just a question; on proper sized holes wouldn't a form tap give more even torque? Dave > ------------------------------------------------------------------------------ > This SF.net email is sponsored by Windows: > > Build for Windows Store. > > http://p.sf.net/sfu/windows-dev2dev > _______________________________________________ > Emc-developers mailing list > Emc-developers@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-developers ------------------------------------------------------------------------------ This SF.net email is sponsored by Windows: Build for Windows Store. http://p.sf.net/sfu/windows-dev2dev _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
