Compact 5 pc running linuxcnc - no circuit board mods (plug and play)

we managed to get a few of these 'compact 5 pc' from a local school. As most of you I started searching the internet for info on the lathe. I found an article in summer 2007 issue of digital machinist. The digital machinist article explained how to remove the octal latch from the interface board, Jumping it, then switching the board to step/dir and setting up mach. I did a search for the 74ls374 chip discussed in the article. It looked like I could use linuxcnc to send the clock signal to the board. So after some figuring and searching I found figured out the printer port pins..

x step pin 2
x dir pin 3
z step pin 4
z dir pin 5
index pin 12
estop pin 11
100 ppr sensor pin 10
74ls374 enable pin 14
74ls374 clock pin 1

So I hacked together a hal file that used the 'reset' function of the printer port driver to send a clock every base period to latch the 74ls374 chip. After not remembering to set switch 1 to on on the emco interface board (sets the interface to step/dir) and scratching my I got linuxcnc communicating. The performance was not stellar. The article above talks about setting your max velocity to 19ipm. This is what I was seeing. Just pretty poor performance. Sounded crappy. Now it could be that I didn't have the timing perfect but read on.. (according to the article above - the original software did around 30ipm)

When I forgot to set switch 1 on the emco interface board - I had decided (by twiddling bits on the printer port with linuxcnc) that the default setup must have been phase drive. The original software controlled the 4 phases of the stepper drives/motors. I didn't have much to lose so I modified the linuxcnc hal file to do 4 phase drive for each axis and set switch on on the emco board back to 'off'. (and maybe there was a reason why they did it that way... who knows)

http://www.linuxcnc.org/docs/2.5/html/hal/rtcomps.html#_stepgen_a_id_sec_stepgen_a

So pins 2-5 ran one stepper and pins 6-9 ran the other.

xphase-a pin 2
xphase-b pin 3
xphase-c pin 4
xphase-d pin 5
yphase-a pin 6
yphase-b pin 7
yphase-c pin 8
yphase-d pin 9

the stepgen in linuxcnc will do a bunch of wave forms - I was interested in - 5 through 10. (4 phase patterns)

I started with pattern 9. This is Unipolar Half Step
-This acted the same as the step/dir I started with. 19ipm max and sounded crappy.

Next I tried pattern 10. This was a long shot as it is Bipolar Half Step
-I don't think it worked at all - or at least it was way worse..

Then I tried pattern 5. Unipolar Full Step (one winding on)
-I had to half the steps per inch obviously - but it acted the same as the above. around 19ipm and sounded bad.

finally I tried patten 6. Unipolar Full Step (two windings on)
-Wow. This sounded nice. We started pushing it and it started sounding rough at around 40ipm. (didn't seem to be losing steps but I think I might be just fine with 35ipm max)
We still have to up the acceleration as that could be pushed a bit also. this is around .0005 per step - very usable. Actaully have been playing with it for the last few days - 45ipm seems to be repeatable. (indicated) but we have been running it at 40ipm.

Very happy.
With this performance initially - I don't know if I will change the drives/steppers until they fail...

one last thing I would like to try is putting the interface back into step/dir mode and from what I have read - you can put it into full step mode.

So - Again - this is without modifying the emco electronics in any way. Setting up linuxcnc to output the 'clock' to latch the chip. All 4 switches off on the emco interface board.. Plug and Play.

Unmolsted emco interface and stepperdrive
http://electronicsam.com/images/emco/interfaceanddrive.JPG

Picture of one of the lathes.
http://electronicsam.com/images/emco/emcoclose.JPG

Videos of threading.
http://www.youtube.com/watch?v=ERMizV-yy8U
https://www.youtube.com/watch?v=_7skJhKzU7Y

Initial version of the config files here
http://electronicsam.com/images/emco/linuxcnc_configs/
I would like to add a spindle rpm meter and a at-speed setup within hal so that the machine won't cut unless the spindle is on.
(use at your own risk)

sam