On Jul 7 2013 10:45 PM, dave wrote: > 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?
I never thought of using grease before. Sounds interesting, useful and cheaper than tapmatic juice. I will have to try it... Also remember that if you periodically reverse direction to break the chips, that stresses are seriously non-linear only vaguely predictable. I'm liking all the discussions... EBo -- ------------------------------------------------------------------------------ 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
