Adding an Openbuilds Openrail Y axis to a Taz 3/4/5

Here’s the build thread for the Z axis, it has a few more pictures in it:

Basically, the stock Taz Z endstop target uses an M5 bolt with a thumbscrew cap and a spring to set the bed height. The Z endstop mounted on the X carriage comes down, hits that and stops. The issue I found with it, and it isn’t nearly as bad on the 4/5’s as it was on the 3 and earlier, was that repeated impacts, vibrations and heat cycles would cause the spring to push up on the target and raise it slowly over time. That’s why a lot of 3d printers, the Taz in particular have at least a partial reputation of needing to readjust the bed frequently. To eliminate that entirely, and give myself greater starting layer height control, I replaced that M5 screw and spring arrangement with an actual Mcrometer body as an option. You can also still use the M5 bolt approach, which isn’t bad these days, but for ultimate precision where you will never have to change the bed level again, the Micrometer is the way to go. The tricky part is finding the micrometer body, and then finding one that doesn’t cost an arm and a leg.

As far as the anti backlash module goes, that particular unit will not fit the Taz leadscrews. You would need to switch them out for a less accurate threaded rod, which means firmware changes, etc. There is actually an anti backlash nut designed for use with those leadscrews from the factory, but it costs $234 per leadscrew from Mitsumi, and I haven’t even seen anyone else who carries them.

I’ve thought about building an anti backlash nut into my anti z wobble nut mount, but there isn’t enough room to do it without losing 20mm Z travel at least. On my leadscrews anyways, I don’t seem to have very much detectable lash at all, so it hasn’t been a high priority for me. The easiest way to add one would be to get a second leadscrew nut, trim it down, run a compression spring between it and the main one, then lock the second one to the main one via some pins. I’ve tried that before with my AO-100 and it works really well, just takes up space.

One thing with this that I would like to see is a bracket between the 40x20 rails both in the front and the back to help keep them square with each other. I believe there should be enough room for them to not get in the way of anything, but in the back they would need to go over the motor mount. It might be possible to add it to a modified motor and bearing mount. Keeping those rails level and square is probably one of the hardest part of this mod, except for me being an idiot and screwing up while drilling the holes. I would try to make ones myself but I really suck at CAD.

I was contemplating something along those lines. Ideally a modified aluminum plate with a couple of extra bolt holes would work. That or some sort of overlay plate. Anything inboard of those plates would have to be pretty thin to avoid moving things. Once I get the last of the anti wobble parts finished ill see if I can work something up.

I’m assembling my Y Rails now and also had to cut 5mm off each rail.


I had the extra 5mm on my Y rails also. I didn’t cut it off though.

Ill add a note to the instructions. I wonder which rail set is off, are the lulzbot ones short, or the openbuilds ones too long? I started with a taz 3 chassis, so my extrusions may have been a different lot.

The Openbuilds Rails are 505mm.


So you order a 500mm rail and they send you a 505mm? That would annoy me. :smiley: People generally don’t want to have to hack it down when they ordered it a specific length.

Whats even wierder is the prototype set I ordered was 500 exactly. They must have recieved a new order in after I built mine that were all chopped ioncorrectly.

I went ahead and posted a thread in the openbuilds forum asking that they check their inventory of those particular rails and correct them. I would encourage anyone who recieved an incorrect set of rails to post in there as well so they can get you a corrected set.

For me it’s not a big deal since I mounted an aluminum blade to my Miter Saw knowing that I was going to have to cut the X Rail.

But I can imagine it would be annoying for anyone expecting exactly 500mm.

I should measure all the ones I bought from Misumi and see if they are on spec.


Open rails answered on their forums that they generally leave the parts a little long.

With that said, what are the correct lengths for the x and y rails? It seems like the Y rails should be 500mm but I have never seen an actual length posted for the x. There is a length posted that needs to be removed from the x rail but that will not be accurate if the original rail length is variable.

I will measure the length when I get home.

I am printing parts now for a holiday upgrade. I can cut the rail at work if I have a length. Otherwise, I will have to use a hack saw.

I attempted to assemble my Y rails today and got as far as trying to mount the bed with the Wheels installed and there is no way the Bed is going on.

I used the Drill Guides and the holes for the wheels are perfect since I used a Transfer Punch to mark the centers of the holes and a Drill Press to drill them.

With the stationary Wheels installed, I placed the Bed on the rails and then manually held up one of the wheels under a 7.2mm hole, pushing the wheel up against the rail. It is off by a few milimeters.

Do you have a drawing with distances for the holes? I can’t imagine how the holes can be off since the guide plates mount perfectly to the bed.

Further investigations tomorrow.


My X rail is presently 435.5mm long, with a 2MM gap to the end of the X idler end mount to allow for plate adjustment. The 3 T nuts and bolts hold the end plate itself in position just fine without the end pressure , and I could be 7mm shorter than that and not have any issues if necessary.

Here are a couple drawings showing the full plate
The drilled holes end up being 189.95mm apart from hole center to hole center. You might check if your rail assemblies are pushed too far out on the Y end plates or too close together depending on how it is off. Worst case scenario you can drill additional holes inboard or outboard of those holes without affection motion or structure too much as long as you keep at least 10mm of Aluminum between large holes.
bedmodification.dwg (63.6 KB)
bedmodification.dxf (408 KB)
Bedmodification.stl (181 KB)

Thank you!

X parts are printing right now.

What i discovered is that even using the guides, there is enough slop in the 3mm bolt / hole assembly to throw it off. You have to ensure that the guides are precisely centered on all 4 bolt holes.

Got the Bed on.

My Eccentrics are at the extreme outside, so the wheels are as far away from the rails as they can get.

What I’ve noticed that towards the end of the movement (front of machine) one of the stationary wheels slides against the rail instead of turning. For the rest of the movement, the wheels all turn.

Also, Openbuilds says to lube the rails. What are you all using for this?

On my upgraded Linear Bearing rods, I was using Super Lube. Would Way Oil (like what is used on Mills and Lathes) be a better choice?

On to the X-Axis :ugeek: