[WayneC]

I'm getting ready to upgrade my Shopbot PR machine, and I need help to decide between Bishop Wisecarver wheels and rails, or HiWin rails.

The issue that may decide for me is the installation. If HiWin guides have the kind of tolerances they do, will this cause the blocks to bind if my rails are not perfectly parallel or coplaner? How far out can I be before I have binding problems?

To mount the rails, I plan to use tensioned piano wire as a guide, so that a spacer will complete a circuit and light a bulb when I just make contact with the wire. Will that get me close enough to prevent binding?

I'm sure lots of people here have experience installing HiWin or similar rails and bearing blocks. How accurate do I have to be? How do I get this sort of accuracy?

I'm wanting to use the HiWIn, but if they require more precision than my skill and equipment can provide, I'll back up to BWC wheels and rails.

Thanks in advance for your help.

[Zumba]

You can use hiwins but they will require extensive shimming.

I'm not sure why you're upgrading the linear motion though... the weakest link on a PR model is the motor and drive system.

[WayneC]

I'm upgrading the linear motion AND the control stuff. I have an Ascension 1000 control box upgrade coming. I'll be upgrading to Mach3 software from the PR's DOS based control program.

The linear motion part is really an equally weak link on the PR. The Z axis in particular is susceptible to loosing steps if dust control is not very good, and the entire gantry is easily moved out of square. Also, as you may be aware, the PR uses Bishop Wisecarver wheels that ride on the corner of steel unitstrut.

It does surpriseingly well as it its, but I tried to 'improve' the rigidity of the gantry, and did so badly at the weld job I warped the unistrut. Since I'm gonna have to replace that, I decided just to upgrade the linear motion at the same time.

I'm now thinking I'll just install some BWC rails and use the existing PR wheels. I'll build a new gantry with BWC rails and a new Z axis. That should make things more reliable and get faster and smoother performance. At least thats the plan.

Thanks for your input.

[cbass]

Some linear rails are designed for applications where perfect allignment is not possible. They can operate within a range of non-allignment. I know THK makes these and I'm pretty sure HiWin does too. Of course you trade off linear accuracy (and rigidity). I'm not sure how much this would affect your application, but I think the results would be better than the wheel system you described.

You might want to give them a call....


Carlo