HiWin rails on my modified PR

[waynec]

I'm trying to decide whether to upgrade another notch on my modified PR Shopbot.

I installed BWC rails and a new Extruded aluminum gantry, along with a new controller and Mach3 software. Things are much better overall.

But I can't get the performance I'd like from my new controller because of mechanical problems. I have two sources of problems:
1) The X rails (now BWC rails mounted on the sides of the old PR X rails) are not perfectly coplaner. The BWC wheels don't ride exactly right all the way down the rails. I can't get move speeds over 250ipm without skipping off the racks.

2) The wheel mounts on the gantry have too much flex. They are made of two pieces of aluminum angle iron. With the motors on there is no movement, but when the motors are disengaged from the rack the gantry becomes quite wiggly. The gantry itself is very rigid, but the sloppy wheel mounts don't seem to hold squareness very well.

I think these problems are what is limiting my jog and cut speeds, and causing the gantry to go slightly out of square from normal operation.

I'm thinking that I might upgrade to HiWin liner guides. On the PR, these will easily mount on top of the existing rails. Because they don't allow much slop in the pitch, roll, or yaw, they really reduce the variables that are behind my mechanical problems now.

Has anybody done this? I'm not great doing the mechanical stuff. I can't seem to get my rails exactly right, and I'm losing patience to keep trying. Same with the wheel mounts. I don't really want to go thru several attempts at fabricating brackets that work better.

I'm thinking that using the HiWin guides will eliminate the need to fabricate brackets or rework the rails.

What do you guys think? Anybody used HiWin linear guides?

Wayne
White Salmom WA

[scottbot]

Wayne,
I am still in the process of assembling my PRSAlpha and just about went nuts trying to get the rails aligned so the wheels would stay on the track for the ride from one end to the other. I literally spent about 3 days before I got it to work.

What I ended up doing was installing a precision washer that came with the Bot between one of the wheels and the gantry frame. The washer was in the "extras" bag but I didn't know about it until I talked to Frank at ShopBot. After the washer was installed I was able to align the tracks in about 2 hours.
After that life was good. I should be making dust by this weekend.
I can't help with the HiWin guides but you may be able to solve your track alignment issues with a precision washer.

Good luck.
Scott

[Brady Watson]

Wayne,
It sounds to me like you need to stiffen up your existing setup, particularly your gantry. Aluminum is a bad choice for gantry & mount materials unless it is constructed from stiff AL extrusions with the equivalent stiffness of steel. At the very least, I would try to gusset your existing AL gantry and stiffen it up. HiWin bearings are expensive & will NOT cure the problems that you are having. In fact, unless you have an absolutely SOLID & rigid gantry, I can almost guarantee that they will bind & fight each other. If I were doing it, I would WELD a steel PRT-style gantry together and be done with it. I have both BWC & HiWin bearings running on various machines in the shop. The BWC stuff is MUCH more forgiving than block/rail configurations and MUCH cheaper as well. I welded my original PRT gantry together & the days of loosening bolts & squaring/paralleling the gantry are long gone. If you still have your PR parts, use them as a template for a completely new steel gantry.

-B

[waynec]

Arggh. I have very heavy duty extrusions for the gantry, so I don't expect the extrusions themselves. I think the issue is with the brackets for the wheel mounts.

But I'll take your experienced advice, Brady. I'll find a way to stiffen up what I have before I buy an expensive set of new problems.

I may be able to add a gusset plate to my inverted T gantry, and mount both wheels to that. It will provide a stiff mounting plate for the wheels, and make the gantry ends more secure as well.

I've got an idea on how to improve the rail mount as well. I was trying to get out of the work, but from what you suggest, I'm not really gonna get out of spending time making sure the rails are as perfect as can be.

But, it helps to know. I was all ready to spend the money on rails.

Thanks for the benefit of your experience, Brady and Scott.

Wayne