Kirk Wallace wrote: > I did my first CNC lathe thread today. I actually got a thread which, on > a first try, I didn't expect. I entered parameters for a 20 tpi thread > and got something like 23 tpi. When I setup the spindle parameters in > the ini file, I assumed that the encoder input scale should equal the > number of pulses per revolution (1250 cpr x 4 p/cpr = 5000 ppr). > > --- hnc-3a.ini --- > ... > [SPINDLE] > # Encoder > INPUT_SCALE = 5000 > OUTPUT_SCALE = 1 > # DAC output to VFD > DAC_SCALE = 320 > > ... > --- > > My thinking is that INPUT_SCALE should not need to be adjusted by cut > and try, so if the thread tpi is not correct, it must be an encoder > problem? Maybe missing pulses or noise adding pulses? Thanks for any > replies. It could be anything, so you have to investigate. First, put halmeter on the HAL pin ppmc.0.encoder.2.count, rotate the spindle to a known position, and read thhe halmeter value. (The above assumes you have the spindle encoder on axis 2, if it is on axis 3 use that number between encoder and count.) Now, turn the spindle exactly one turn and read again. The difference should be equal to the expected 5000 counts. If it is not, then you should do it 5 times, and see if you get wildly varying numbers or some consistent value. You should check your pulley and belts for slippage. One other good test is to set up halscope to look at ppmc.0.encoder.2.delta, which is the change in encoder reading every servo cycle. Run the spindle, and you should get a straight line, possibly with a lot of jitter, as the encoder is doubly quantized (can't count half a count, only whole integers, then it is sampled 1000 times a second by the servo update cycle.) But, if it shows sharp jumps or dips other than the +/- one count of quantization noise, that indicates a problem with the encoder. It is possible that everything up to this point was fine because the spindle drive was off, now that you've turned on the VFD it is creating noise in the encoder signals.
If the spindle encoder is working fine, then you have to look at the calibration of the other axes. A 1" travel dial indicator with magnetic mount is great for doing these tests. move to a place where the indicator reads zero, then move 1/2 inch away and see if the indicator registers a .500" move. You can also check your backlash this way. If you haven't done the servo tuning yet, you have no business putting a cutter and workpiece in the machine, it could be half an inch out of position and you wouldn't know. Jon ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
