Help Please! Regarding Old Shopbot (96ish cable drive)

[John Rutledge]

SB v2.38 running in DOS on pentium machine. Vexta 266-02A Steppers Cable drive. I bought this for $300 from a guy in Austin who inherited it when he bought a business and had no idea how it worked and said it had been suspended up in the rafters unused for six years. I figured @ that price I couldn't get hurt too bad especially when splitting it with a buddy. Anyway, after four months of sitting in my buddies garage his wife got sick of it and he backed out. So the machine has been moved twice that I know of and I'm having trouble getting it going right.

Here are the issues I've run into so far:

1. The X was stalling and looked to be racking so I checked the rails for parallel. They were out as much as 3/16" so I adjusted them to within 1/32nd and diagonally within 1/8th for square. I also adjusted the parallelism cables for equal tension. It still stalls so my question is: Are those acceptable tolerances?

2. I tested the machine and the initial X travel was off by 6.375" but when calibrated it was within .25 inches over 71" of travel. Clearly not right, but better than it was. The Y is a different story. The Gantry is parallel within 1/16th but the stepper stalls quite a bit and over 48" it loses 9.5" traveling away and loses only 5.125" returning which causes it to hit the stop. This result is fairly repeatable within .25". I noticed that while against the stop and no longer traveling, the counter for the Y axis continued to tick down to zero. Does this indicate a problem with the encoder or does SB 2.38 count drive pulses to give that reading?

3. Diagnostic test on the encoder when looking at the stream goes as follows: 333332222000001111333332222000001111 etc. I noticed there are Five 3s in a row followed by Four 2s, Five 0s, Four 1s. I have no experience with this kind of equipment and no documentation with which to compare any of the diagnostics output and so have no way of determining if any of this is correct. What say you?


Thank you in advance for your patience with a newbie.

John

[Brady Watson]

John,
The cable drive tools are so few & far between at this point that you probably won't find the answers you seek here on the board. The best bet would be to contact SB Support and see what they have to say.

-B

[John Rutledge]

I was expecting that to be the case. I've seen some YouTube videos where guys are still using these old machines and was hoping there was a botter who had something to offer. I appreciate the reply.

[Still_Cable_Driven]

Well, I'll try to give you a hand. Brady pointed me at you, since I just posted a note about my cable-drive PR96 in the "shobbotter message board." Mine has been sitting idle for a bit too long, but I'm trying to get it back to work.

Do you have 3 X axis cables, or just two? The early system had 2 drive cables and a parallelization cable (fatter, with no covering) - and the only upgrade I've actually done was to apply the "two longer drive cables are the parallelization cable, too" modification. It removes some friction.

What speeds are you moving? One place you can get into losing steps on the oldsters is by running the axis faster than the steppers will go - especially if you are reading things from the modern drive era. As far as I recall I might cut at 1 inch per second and jog at 2.

Look for bumps and feel for binding of the stalling axes. With the power off, roll the axes by hand. A dent in the uni-strut can make the wheels bind.

Another issue with the encoders is running the encoder wires too close to the stepper wires - you can get interference.

The control software can (IIRC, and it's late so I'm not checking the manual right now - if the manual is even the same version as the software) be set to ignore or pay attention to the encoders. At some point the official word was to ignore them, as the newer tools moved away from using them. IIRC, I still look at them, as mine have not been problematic.

I also had some early movement issues from using a long unshielded serial cable between the controller and the computer.

I have no idea about the diagnostic output, though I can eventually check what mine says.

Take some pictures, I'll try to do the same. Off to bed for now.

[Still_Cable_Driven]

Old Stepper driver higher-voltage supply Is another upgrade I probably will do, though I cannot presently seem to track down the actual information on adjusting the limiting resistors. Gives a bit more speed.