Pr32 x axis

[jseiler@bluemarble.net]

I bought a used pr32 benchtop that has screws on all the axes. The person who owned it before me moved the motor on the x axis up and put a hinge on the other side to allow some slop in that axis. I checked the threaded screw and it seems straight. This arrangement presents a slight problem, when the motor is pushing the carriage away from the motor, everything cuts smoothly, but when it is moving the carriage toward the motor, it leaves slight scallops on the cut (particularly obvious when cutting circles). In experimenting with this, I put a bungee cord around the hinge to hold it tightly and this seemed to help quite a bit. I then tried wrapping the cord such that it pushed the hinge toward the motor which caused it to bind when the carriage was near the x=0 position. I then tried wrapping the cord such that it pulled away from the motor and it seems to run ok that way. The original owner claimed this arrangement seemed to solve a binding issue, but I'm wondering if there is something besides the screw that might be bent. How much slop should be in the motor and how much slop should be in the "universal" that connects the motor to the screw shaft? I'm guessing none, but there seems to be quite a bit. I haven't disassembled it yet to see where the slop is. It doesn't seem to be in the ball nut.

I have found also about the fastest I can cut in insulation foam is about .7 in/s and jog at about 1 in/s. Is this about right for a machine of this age?

John

John

[jseiler]

The coupling is shot. This is a standard lovejoy model, so should be replaceable. The screw has a couple of small pits.

What I really need is to know how shopbot originally connected the x axis to the frame on the PR32. I checked the PR assembly manual, but since the PR32 came fully assembled, there is no information there. I want to put this back into stock or better condition. I'm seriously thinking about getting ball nuts with wipers if I can find some that fit.

Anyone have an benchtop PR32 that can send pictures of the motor mount and pillowblock mount for the x axis, or at least tell me if the pillow block is mounted directly to the rail and if the motor mount is directly on the rail? Any advice on getting the alignment perfect would be greatly appreciated. I have an email in to Shopbot support, but so far, no response. Maybe they don't support repairs of older machines.

On another note, Shopbot tells me I should not run more than 1.5"/s on the axes, but I can't get more than about 1"/s without the motors just stuttering (missing steps badly?). At lower speeds, everything seems pretty good as I can move to 0,0, drill a hole, move the 25,0, move to 25,25 and then back to 0,0 and fit back in the hole perfectly and the measurements are accurate as close as I can measure with a yardstick.

Please help,

John

[jseiler]

Anyone?

[billp]

John,
How fast is the computer you are using to run this machine?

[jseiler]

The computer that came with it was a Presario, I think it was 233 MHz. I replaced it with a pentium III at 800 MHz (I think). Does clock on the PC make that much difference over a serial link running straight line move and jog commands?
I've seen other posts about clock speed on 3d, but I was thinking on straight line moves, the control box was handling all the heavy lifting, but since I don't know for sure, I'm likely wrong.

[billp]

Your computer doesn't sound like the issue then. I asked because when the PR32 first came out some people were running really old 120 MZ units, and that limited their speed as well. It sounds as though you need a current owner to post some pix for you to get the details. Obviously if you CAN upgrade any of the questionable parts, you should. It would probably also help tech support if you could take some pictures of the issues you have mentioned, and e-mail them to support...This way if you call them, they will have something to work with..

[jseiler]

Ok, I disassembled everything. I found a thin (1/16" thick?) rectangular washer under the motor mount which I left in there (it looked original). I found the motor mount wasn't 90 degrees. I removed the hinge contraption and bolted the pillowblock to the frame. I loosened the ball nut mounting. I ran the axis toward the motor and that worked ok and didn't seem to move the ball nut mounting. I then moved it toward the pillow block. about 3/4 way over, it bound up. I added a set of washers to that side. I ran it back toward to motor, everything ok, back toward the pillow block, all ok. Must have lucked out. I tightened up the ball nut mounting and moved it back and forth. Sounds ok, seems to move ok.

How does one know everything is lined up really well besides..."it works and sounds ok."?????

I cut a small piece of lexan at .625 by 2.25. It was within 1/1000", so we're mostly ok.

[jseiler]

I got everything lined back up, and am trying to figure out how fast I should be able to cut without missing steps to know if there's anything else that needs to be replaced.

I cut several v-carved signs in hardwood at .3in/s and several trial runs in particle board at .4 in/s. Taking it up to .5 caused
missed steps in particle board. Brand new bit, 890 router. I can jog at about .7 in/s. The stepper motors hum and don't spin over 1in/s. Haven't tried it with the coupling disconnected yet. Question is...is this about right or would it be worthwhile to replace ball nuts, motors, output drivers, etc.?