Best way to change to linear rail system with minimum modification

Hi,

My actual printer setup has a problem with its vertical rods not being perfectly parallel. You can look at the picture to see how they look right now. I have 20x20 aluminum extrusion as chassis and plastic rod holders are used to attach 8 mm rods. A couple of Lme8UU bearings are used to link the rods to the Z carriage. A pololu motor with integrated leadscrew is used for controlling the height of the carriage. I want to change this system to a rail system to ensure that the rods are parallel. I have seen many alternatives, including MakerSlide, OpenRail, rail systems used in CNC machines, fully supported rods, etc.Which system would allow me to achieve my goal with minimum modifications? I have the STL files of the elevators but don't know how to edit them, so that's a factor. I was thinking about fully supported rods, which would be similar to my actual setup but I can't find this system for 8 mm rods (minimum I've found measures 12 mm). Any opinions or help would be appreciated.

Thanks.

I've not seen supported 8mm rails either and they might not be good on the Z, design looks quite nice, clean, especially with the white parts, you have the small 8mm bearings, maybe if you changed them for longer ones they might aid in setting up the rails to be parallel, or better still pity you couldnt print a plastic alignment tool, but I suppose there might be a problem with your mounts if they are out, not identical they will throw out the rails, and if the frame itself is a little out. I wonder if you where to get some 8mm metal rod supports and fix them to the very bottom extrusion rail, and at the top on the horizontal bar(space dependent, might need to rejig everything), but that could help to straighten things out. Is the problem showing up in prints?

Hi. Thanks for the answer. I haven't seen longer lme8uu bearings, do you have a link online for that part? A problem with this approach would be to find a way to fix bearings in place (the bearings have grooves on their ends and a metal piece goes into that groove to stabilize the beating.

About the alignment tool, do you have an example?

Fixing the rods to upper and lower extrusions is a good idea. However ^here are 2 technical problems: I need the upper and lower extrusions to be longer horizontally, as Metal rod holders I have seen online would be too long ( unless there are very narrow holders that I am not aware of). Also, the holder would need to have the same height as my current setup, as they wooildn' to be aligned with the Z elevator.

About problems, please check [forums.reprap.org] This could be part of my problem.

Thanks.

Search for LM8UU 45mm
[www.ebay.co.uk]
the problem is you couldnt use the circlips as your Z carriage is to short, but was thinking as you have a printer you could make something that works. The spacer/aligner I was thinking about is just a bar with two 8mm holes in it, slide it to bottom tighten, slide to top tighten, normally I just use the carriage assembly. Your rods would need to be longer to reach bottom rail, but I thought you probably have stuff in the way...thats the thing with design, change one thing and sometimes other things have to change with them,

If you used the metal 8mm rod supports, then rod centers would be about 20mm from extrusion, whats the current distance looks pretty close to that, if not, its a new motor mount, or shims/spacer for the rod supports.

Another option to think about would be to replace the Z plastic carriage with a short piece of 2020, get 2 8mm rod supports either end to slide on rails...no bearings...I've tried it and it doesnt have as much play as bearings, sure they might wear out but they are cheap.
Then if you add another 10mm rod support in the middle you can grip a standard 8mm brass helical nut, are you using 8mm dia lead?
Like in this picture but with 2020 profile in between, position supports where needed.


Edited 2 time(s). Last edit at 04/05/2016 03:23PM by MechaBits.

Thanks for the suggestions. I'll order longer 8 mm rails and fix them to the upper amd lower extrusions. This could help me for the parallelity issue.

My leadscrew is 8 mm.

Good luck, with 8mm lead your nuts same as above, so with a little pressure it fits in the 10mm rod support, no flex on that.

My rods have arrived yesterday. I replaced my actual rods with them and also changed rod holders with metallic ones. The first problem is with the holders: They don't hold the rods, they just slide in and out with ease. I had to use some Kapton tape on top of the rods to prevent them from sliding. I still have problems with the parallelity of the entire system. While the bearings are moving easily when the Z car is at the bottom position, one of them gets binded when the car goes upwards. Maybe the rods connecting the Z cars are not inserted equally into their respective slots. I'll try to use sanding paper to make the slots larger, so that they can accomodate all of the rods length.

They will tighten, maybe replace the cheap silver hex screws with others, insert a shim if its that bad or kapton tape around the rod. Then obviously tried loosening the rod mounts and using the carriage to align things(or loosen some frame screws)....but with plastic carriage there is no real way of knowing how straight those holes are? a little warp on that long'ish piece?