Cannot lower bed to reach endstop

[illuminarti 18]

Now that you have more play in the nut/stage connection, is the z-screw centered on the coupler?

 

[Nicolinux 288]

Yes, the brass nut is centered on the z-coupler at the bottom and the banding/z-wobble artifacts are gone.

 

[illuminarti 18]

I think you're probably ok, then. I wonder if a modification to your design might work - extending the nut capture piece more along the front and back of the nut, so that it is free to slide left-to-right, but has less room to rotate.

You might also jsut try adding more lubrication to the z-screw. My nut seems to have quite a bit of freedom to rotate if I grab it by hand, but in practice when turning the screw it doesn't move. I guess the friction within the nut is less than the friction between the nut and z-stage.

 

[Nicolinux 288]

@owen: I thought a bit about it. I think this is not a problem at all. When the threaded rod turns, the brass nut turns until it hits an edge and stays there. Any subsequent turn pushes the nut against the same edge so it doesn't turn anymore. It would only be a problem if the z-stage would go down _and_ up while printing.

 

[illuminarti 18]

Also, in general, any effects from the nut rotating are only going to happen when changing direction... once the nut has rotated into it's maximum position in one direction, it will stay there for all future moves in that direction, so again, it probably doesn't harm anything in practice.

 

[Nicolinux 288]

Good idea I'll try both suggestions. Greasing is a no-brainer and a new part is easy to design in OpenSCAD. I thought about using the original wooden pieces again and just file a bit left and right.

 

[owen 19]

@owen: I thought a bit about it. I think this is not a problem at all. When the threaded rod turns, the brass nut turns until it hits an edge and stays there. Any subsequent turn pushes the nut against the same edge so it doesn't turn anymore. It would only be a problem if the z-stage would go down _and_ up while printing.

 

Yep you're right. Though all the effect probably happens at the start which could affect your start level and the first few layers. As Illuminarti greasing the thread would be a good idea.

 

[Nicolinux 288]

Another update on this issue. I took my Ultimaker apart in order to add the new high quality pulleys (from user foehnsturm) and thought that it might be a good idea to tackle the brass nut holder problem again. I took the original wooden parts and filed down a bit of material so that both holder (left and right) would move a few mm to the left. But this made the problem worse. Apparently the whole brass nut holder has now so much play and it allows the brass nut to also move front to back. The threaded rod wobbles like crazy - this can't be good

Here is an image of the changes I made. On the left the original part where I filed down some material. The green part is my replacement I made in OpenSCAD that was used up until now.

Video:

 

I deffinitely need to come up with something else. On the one hand I want the brass nut to slide horizontally but not vertically or front to back. I guess that the holes holding the brass nut holders show some wear and are a bit bigger now. That's understandable because I took this damned z-stage close to 10 times out to disassamble it...

I consider sourcing my own laser cut version of the front and back panel of the z-stage where I move the holes for the brass nut holders to the left hoping that the brass nut would then be centered on the z-coupler at the bottom. I need to find a laser cutter in my area first though.

 

[illuminarti 18]

The screw is only wobbling because it needs to... it's not centered in the coupler. If you focus on getting the screw held in the center and perpendicular, then the wobbling will be less, the nut won't need to move.

 

[Nicolinux 288]

You are right, this would be the best solution. But apparently my skills aren't adequate to make that happen. That's why I thought about sourcing new parts where the holes for the brass nut holder would be alredy in the right place (shifted to the left). I will try to print these parts myself but I guess due to warping they won't be straight/flat.

Another quick & dirty solution would be to use something like http://sugru.com and just jam the parts in place

 

[gr5 2,173]

Maybe you should just use some kind of glue. Maybe a rubbery glue like a hot glue gun (which if you don't like you can peel the glue off again). Or silicone caulking. With silicone caulking, you could assemble everything back together, put the Z stage 1 inch from the top and then insert caulking and let dry. This might be a bad idea - I don't know. But at least you can always take it apart and remove the glue later.

It sounds like you removed too much wood and now you need to add material back. Glue is usually good at this. Shims sometimes work also (thin slices of wood).

[Nicolinux 288]

Alright, last update (I hope).

I decided to print the entire z-stage back/front panels. So I used my rapid prototyping machine to rapid prototype some panels I just needed to move the holes for the brass nut holder a bit to the left. In order to avoid warping I used a big tape (Orafol) that covers the entire bed and also set a huge brim for the object. It really helped and the warping was minimal:

After assembling, it looked quite nice but I had to do a lot of filing for the parts to fit on the left/right arms (a LOT!).

 

I installed it and well... it didn't fit :/. Oh the rage... Now that I disassembled this stupid z-stage more then 10 times, the wooden panels started to wear and small pieces would break out. There is now way I can do this for another 10 times. I was close to resignation and ready to accept the wobble problem but then I remembered that PLA softens when it gets hot. So I took a hairdryer and directed it on the brass nut for about 30 seconds. Then I could move the threaded rod around so that it fit easily in the z-coupler at the bottom. Man this brass nut can store heat... It took more then 10 minutes to cool.

 

It is working now. The z-stage back/front panels and the brass nut holders look like s*** - all bent and skewed, but it works. I don't see any wobble on tall parts. And the brass nut is locked in place and does not move. Still, I am not satisfied. Maybe I will try to find the correct position of the threaded rod and source my own laser cut parts that fit tightly. But I won't do this before Ultimaker releases a heated bed. I hope they re-design the whole z-stage while they are at it and I could replace the entire thing.

Just in case someone is interested in the process of exporting parts from the lasercut drawings. Here is how I did it. I can also provide the .svg, .scad and .stl files.

I just took the .eps file with the Ultimaker lasercut drawings, converted it with "Preview" on the Mac to .pdf and imported it in Inkscape (set view mode to "Outline"). From there I selected the parts I needed and created a new .svg document. There I connected some loose lines and moved the holes 2.5mm to the left. I exported the file to .dxf (each object on a different, named layer) and loaded it in OpenSCAD to extrude it upwards for 6mm. Then exported to .stl and printed.

 

[gr5 2,173]

I just took the .eps file with the Ultimaker lasercut drawings, converted it with "Preview" on the Mac to .pdf and imported it in Inkscape (set view mode to "Outline"). From there I selected the parts I needed and created a new .svg document. There I connected some loose lines and moved the holes 2.5mm to the left. I exported the file to .dxf (each object on a different, named layer) and loaded it in OpenSCAD to extrude it upwards for 6mm. Then exported to .stl and printed.

 

Just? Wow! Cool! You get the logo for free as a bonus! I am highlighting this post in my bookmarks for when I need to do this some day. I've used openScad which I assume is the hardest step anyway so the rest should be easy I suppose. Don't know inkscape at all but maybe I can use photoshop.

 

[gr5 2,173]

Earlier you said everything was too loose. I would have just used a hot glue gun and smothered the z-nut (and anything else that was moving) in hot glue. It would have been even uglier.

 

[Nicolinux 288]

Just? Wow! Cool! You get the logo for free as a bonus! I am highlighting this post in my bookmarks for when I need to do this some day. I've used openScad which I assume is the hardest step anyway so the rest should be easy I suppose. Don't know inkscape at all but maybe I can use photoshop.

 

I did consider to leave the Ultimaker logo out as a form of punishment for whoever designed the z-stage

Actually the Inkscape part was the hardest one. In OpenSCAD it was just one line. Regarding Inkscape - I guess you can do this in Adobe Illustrator too (that's what the Ultimaker folks used).

I also considered a hot glue gun but I thought that if I ever want to take it out again I shouldn't use it.

 

[msurunner 2]

I use a similar tape (another application tape) called ApliTape on parts that have difficulty adhering. It's relatively cheap and really quick to set up. Pull out ~8" and slap it on.

 

[Nicolinux 288]

So... continiuing my hobby (taking the z-stage apart) I have reverted back to the original wooden parts and only replaced the small brass nut holders. I fiddled with them until the threaded rod fit perfectly (and was centered) on the z-coupler at the bottom.

Since wobble is minimal (and inconsistent), I suspect it to be due to other factors. I have started a new thread here:

http://umforum.ultimaker.com/index.php?/topic/3084-inconsistent-z-wobble