View Full Version : New Z axis on PR machine

06-06-2006, 02:54 PM
After the Boise Camp last Saturday I'm all ready to rework my PR and try to get some more performance out of it.

I think the weakest link in the machine is probably the Z axis. I'm wondering if I can install a new Z axis from say Tech Isel or some other company, with an upgrade ball screw and linear bearings, and of course a larger stepper motor.

1) Has anyone done upgraded a PR Z axis?
2) Is the Z driver in the PR controller capable of driving a larger stepper motor- like say a Y axis motor? That is, is the Z driver the same as the rest of the drivers in the PR controller?
3) Will I need to upgrade the Y carriage to handle a 3hp spindle? If I upgrade the Z axis, I'd like it to be able to use a spindle. If I need to upgrade the Y axis to accommodate the increased weight, I'd like to know that now.

I hope to get a bit more speed out of an upgraded Z axis, but more importantly, a little better performance for 3D work and better reliability. Are these reasonable expectations?

Still more upgrade questions, for the patient. I'm considering three more improvements:
1) replace the table base with sheet phenolic- I'm wanting a stable, always flat surface to mount spoilboard or plenum to. Wood changes thickness over the table size, adding to problems with spoilboard thickness. Will Phenolic cure this?
2) Y axis reinforcement- I want to weld triangles into the corners of my Y carriage so that it is much harder to get it to rack.
3) New X rails- I saw an excellent idea to install new hard rails on the outside of the unistrut, such that the bearings ride vertically. I expect this will make it harder to rack the Y carriage as well. ANy input?

All this is because I really want to get reliable performance out of my PR. If I can get that, I can justify a controller upgrade- something like the Acension or maybe a PRAlpha motherboard and Gecko/Mach3. WHo knows. But not until I have the mechanical part working as well as it can.

I'd appreciate any input before I start tweaking things.

Wayne from White Salmon

06-06-2006, 05:23 PM

I've made some of the mods you're talking about to my PR series.

I upgraded my z axis to R&P. I bought the upgrade direct from shopbot, the motor is similar to a Y axis motor (but I'm not certain that it is identical, I'm not at the shop right now to check).

I did NOT need to perform any mods to the Y axis (I'm running a router not a spindle, but I don't think that makes a difference for this question)

I've also upgraded my X axis using bishop wisecarver rails to have the rollers ride vertically.

I've been very happy with both upgrades.


PS: take a peek at this thread re: X-axis upgrade


Mike Windsor
06-06-2006, 10:09 PM
The best two modifications I did to my PR machine were : going to the PRT control box .I did change it when Shopbot offered the upgrade , but I've seen controls for sale on the forum . I did change the small motor on the Z axis to the larger pk 268 for a while , but dust in the ball screw was always a problem . The next best thing I did was to get a rack and pinion Z axis . The new router bracket is also far superior to the old hose clamp setup . ----You can use a dial gauge in the router and tram the router until it's perfect , but if the router isn't parallel to the movement of the axis you'll still be drilling oval holes

06-06-2006, 11:37 PM
Ed, can you tell me what model of Bishop-Wisecarver rails you bought? And how did you attach these to the Bot? Any tips on getting them exactly parallel?

And, what sort of improvement did you realize? Did you do anything to the Y carriage to stiffen it?

Thanks for your input!

06-07-2006, 10:28 AM

I used the "Dual-Vee" rails. They have a series of pre-drilled mounting holes. I attached these to the unistrut using bolts and standoffs. There are some fuzzy pics in a link here:


As far as parallel - my unistrut rails were already in good alignment, so the standoff technique required no additional adjustments.

I did not change a thing on the Y-axis.

The improvements were basically smoother moves and a more stable setup in general since the rails are now perpendicular to the wheels rather than a 45 degree setup in the original design.


06-07-2006, 10:42 AM
Now you have me thinking that this maybe something i want to do.
How did you do the hold down wheel on the bottom?

I was thinking of bolting an angle on the top of the unistrut similar to how the prt's are now, but couldn't figure out how to do the hold down wheel.
Any thoughts?


06-07-2006, 11:44 AM

I used a pretty crude technique (being a crude person). Simply a long bolt extending to the bottom of the unistrut. I'm sure that mechanically it isn't the most elegant solution, but it was pretty simple and works for my purposes



06-07-2006, 01:26 PM
Thanks for the Pic Ed helps me a lot.
Not sure if that is going to work for me though.
The more I try and fine tune my bot the more i realize how bent the unistrut is on the bottom flange where the hold down wheel goes.(Bought it used).
I have spent a lot of time straighting but still have some spots that i just can't seem to get perfect.