Jon, thanks, very good. This is the long term plan. Now, if I wanted to do it with a floating tap holder, I could just measure accurately the speed of the spindle with a handheld tachometer, match the downfeed rate as carefully as possible, and just do it with G code. Note that right now I set RPM manually by operating an air motor to change speed.
I just wrote a sub to do it. It is untested. O<tap_with_floating_holder> sub #<depth> = #1 (Hole Depth) #<tpi> = #2 (Threads per Inch) #<rpm> = #3 (RPM of the spindle, EXACTLY MEASURED) #<safez> = #4 (Safe Height) #<frate> = [#<rpm> / #<tpi>] M3 (Forward) G1 Z#<depth> F#<frate> M4 (Reverse) G1 Z#<safez> F#<frate> M3 (Forward again) O<tap_with_floating_holder> endsub M2 As the quill reverses, the tap will lag the movement and offset itself in the floating holder a little bit, but that is what floating holders are for. On Mon, Sep 27, 2010 at 12:04 PM, Jon Elson <[email protected]> wrote: > Igor Chudov wrote: >> I have a possible job to do to drill and tap 200 holes. The more I >> think, the more it seems that I would be served well if I get rigid >> tapping to work. >> > Having done exactly that - a fixture plate with 288 holes - I am sure > you are right. > Either a tapping head or rigid tapping. Otherwise, very sore arms and back. >> My question is, how does rigid tapping handle spindle reversal? >> > When the depth specified in the command is reached, the spindle speed is > reversed. > If your spindle direction is by relays only, then it is a pretty abrupt > reversal. if you > have spindle speed set by analog output to the VFD, then it can be run > through the > HAL component lowpass (how I did it because I understood the component) > or limit > (recommended by others). You set the filtering rate-of-change so that > your Z axis > servo can follow the reversal without excessive following error. >> How does EMC know so well how speeds acts when the spindle is stopped, >> then reversed? >> > It is constantly watching the spindle position. "Speed", in fact, isn't > really monitored, it > is position. The spindle's encoder counter is zeroed at the index mark > when entering > spindle-sync'ed motion, and then the encoder is a count of rotation. > 1.00 equals the first > full turn, 2.00 is the second full turn, etc. The Z axis is slaved to > the rotation times the > thread pitch. As the spindle stops and reverses, the Z just stays in > sync with the encoder, > all the way in, and all the way back out. > > There are a couple things that have to be right for this to work. One > is that the trajectory planner > must be run at the same period as the servo thread. Otherwise, the > position interpolation of the > T.P. introduces a delay which causes Z to lag one way going in and the > opposite way coming > back out, dragging the tap. So, you would have something like this in > the .ini file : > > # Servo task period, in nanoseconds - will be rounded to an integer multiple > # of BASE_PERIOD > SERVO_PERIOD = 1000000 > # Trajectory Planner task period, in nanoseconds - will be rounded to an > # integer multiple of SERVO_PERIOD > TRAJ_PERIOD = 1000000 > > Your spindle encoder needs to have minimal backlash in however you attach it > to the spindle. You have to check with air cuts and Halscope to make sure the > Z following error is within a reasonable tolerance during the spindle > reversal, > at the thread pitch and spindle RPMs in question. Once you have this figured > out, > you can probably come up with a table that threads finer than X TPI can be cut > at 2000 RPM, threads down to Y TPI can be done at 1000 RPM, and the threads > coarser > than Z TPI must be done at 500 RPM or below. If your following error limits > are > set tight, then exceeding that rule would cause a following error on Z, > requiring you > to back the tap out manually - not a lot of fun! > > The tradeoff on the VFD acceleration is that the tap will go deeper than the > commanded > depth. The slower the acceleration of the spindle, the more the tap will > coast in before > the reversal happens. When tapping thick material or blind holes, the amount > of this > overrun can be a concern. > > > Jon > > ------------------------------------------------------------------------------ > Start uncovering the many advantages of virtual appliances > and start using them to simplify application deployment and > accelerate your shift to cloud computing. > http://p.sf.net/sfu/novell-sfdev2dev > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > ------------------------------------------------------------------------------ Start uncovering the many advantages of virtual appliances and start using them to simplify application deployment and accelerate your shift to cloud computing. http://p.sf.net/sfu/novell-sfdev2dev _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
