Mendel - X-ends upside down?

I've acquired a partially built mendel kit and I'm planning to take it apart and start over (just enough things not up to my standards :-)).

In looking at the basic frame I've been trying to find ways to maximize the print area. One of the big problems was the size of the Y base plate that limited the Y-travel to ~140mm. Looking at other designs I've found that if I replace that with a smaller base plate and move the print bed support poitns in (and convert to 3 support points for easier leveling) I can increase the Y-travel to over 200mm.

But I also noticed that the Z travel is quite limited. I assumed that the extruder drive would hit the frame top first and figured that sometime in the distant future I could redesign the frame vertices to have a wider space at the top. But I was surprised to find that the first thing to hit was the X belt against the back risers. In looking at this I came up with a simple idea that may solve this...

Could I just invert the X-ends? Currently the X motor and belt are above the plane of the X smooth bars. By inverting the X-ends and running them "upside down", the motor, belt and pully would be below the X bars, but not anywhere near as low as the extruder tip. This would allow another ~30mm of Z height at the top but doesn't seem like it would have any issues at the bottom.

Has anyone tried this? Do you see any problems with this? Is there a reason the X ends need to be right side up?

Thanks,
Bret

Someone posted pics of it on G+ a few weeks ago. Yes, it works fine.

First printer? Make sure to build it so your Z axis screws can wobble all they want.

Thanks Dale. I'll turn them over to get more Z-height :-).

This is my first printer. Thanks for the tip on the Z axis screws. The kit came with the plastic couplers but I've seen others that have metal ones with spring sections and the reprappro kit uses flexible tubing and clamps.

Why do you need this flexibility on the Z-axis drives? (Please just post the link if there is a big discussion on it or somethign on the main reprap page). The generic build instructions include the plastic couplers so I assumed they would work.

Thanks!
-Bret

Flexible tubing and clamps works fine.
The important point about Z wobble is that all Z rods will have slight curvature - they are never perfect. The rods will be clamped to the Z motors at one end but, as Dale says, they should be left to wobble at the other end. Trying to put clamps or bearings on the free end to stop them from wobbling actually makes the problem worse by transmitting any slight deviation into the X axis. This WILL be visible in your prints.

Ah, I get it now. Line up the motor shaft and the threaded rod, but don't pin down the lower part of the rod. That makes sense as the X-axis linear bearings should keep it aligned at the point of the print, but the bottom of the rods might wiggle around. If you pin them down then any warping in the threaded rods will be forced to shift the print bed around.

Thanks for the great newbie advice :-)
-Bret

I just played around with turning the X ends upside down and it would work but it will take some modification of the extruder carriage settup. The belt attachment needs to go down a little farther and and then those conflict with some of the structure of the carriage. It's certainly doable but it'll take more fiddling than I want to do right now. So for the initial build I'm going to stick with the standard way.

There are several plastic pieces from this kit that are "iffy" and one of the first things I'm going to print once it's calibrated is a new set of printer parts so that when something breaks for good I can rebuild. Then I'll start thinking about Z-height modifications.

Is there an extruder carriage which is already setup for this upside down operation somewhere on thingiverse?

Thanks,
Bret

Dale, can you provide a link to the example of someone doing this from a few weeks ago? I'd really like to do it on my system but I'm not sur what to do with the main carriage piece.
Thanks,
Bret

I think I found a post about this on Thingiverse: [www.thingiverse.com]

In this case he had a different setup which had a symetric extruder carriage so I think he just flipped it over to get the mount points for the belt. My carriage (I believe the standard Prusa2) isn't symetric so I need to rework the belt clamp setup to be on the bottom without conflicting with the X-rods. I'll play with it when I get to that point and see what I can work up. Let me know if you have any ideas.

Thanks,
Bret

I analyzed the standard carriage for the prusa 2 that I have and it looks like I should be able to shorten the belt clamp blocks just up to the first hole, then drill a new hole for the M3 bolt and use the original bolt hole for the outside. Of course, moving the blocks to the underneath side with the carriage still on top. With the belts I have there still should be sufficient room for the belt ends between the bolts and with the shorter block it will be out of the way of the X-rods.

I don't know if this is worth it to risk my only extruder carriage with drilling and such modifications, but it really would increase the Z-height considerably. The link on thingiverse indicated it was a 40% increase in Z-height.

I'm seriously considering modifying my base print bed plate so that it rests directly on the linear bearings held on with zip ties. I have some pretty good metal working tools (my last project was building a car in my garage) and I think I could make the modifications without too much risk. The setup would have great Z-height with both of those modifications.

But I do need to get my printer up and running so I can print out a new set of parts for backup because the ones that came with the kit are pretty iffy (had to glue one of the X-ends back together already and I need to spend 3-5 minutes to widen every M3 nut hole in order to get them to fit. Not great quality).

-Bret

Must be differences in individual setups, but on my Prusa i2 the limiting factor is the extruder large gear and motor hitting first the triangle rods at the ends of X travel and eventually the horizontal top rods in the middle of the X travel. So flipping the X ends and/or carriage would do absolutely nothing for the maximum Z travel, since the extruder would hit the frame at the same Z as before (since the height from the nozzle tip to extruder's highest points still stays the same).

But if there is any unnecessary gap between the heat bed and the lower frame rods, that's one place to get more Z travel. I have a printed Y carriage traveling on smooth rods mounted below the frame rods and adjustable alu plate over that, so I can adjust the bed as low as possible.

I checked with the exruder in place and the big gear was close to one of the top rods but actually went between the rods if the belt didn't hit the side bar first. That's for my setup anway. I'm not sure but I think it's a greg's modification to the basic wade's extruder.

I'm also playing with the print bed to get the maximum Z-height. I think the configuration I'm going with is the smooth Y rods above the frame but then have the base plate attach directly to the bearings (with square holes for the bearings to fit part way through). This looks like it will get the bed as close to the frame pieces but still be able to pass over the top. Then the PCB with short leveling screws and some small insulation to keep that distance down as well. Then glass clipped to the top.

Thanks for the tips. I'll play again with the extruder in place to make sure it really fits like I think it does before going off and drilling and cutting.
-Bret

Your find on Thingiverse may be what I was remembering. I couldn't find it on G+.

I would definitely recommend getting it working in the normal configuration first, so you can make parts to experiment on. You could even just abandon the MG carriage for a Prusa i3 carriage and x axis. Or design something that works the way you want. Once the printer is working, the possibilities are nearly endless.

Thanks Dale. I think I'll take your advice about getting it working in the normal configuration, but there's always the temptation to fiddle with things :-). I think there are some X designs that will make it easier to do the flip so I'll probably just pring those and then do the flip.

Since you'll be taking it apart, how about designing some vertices that move the frame out of the way?

Yeah, I was thinking about doing that at some point too. You would have to replace all of the vertices so that the upper bars are at a different angle, but then the whole extruder could fit between the top bars and get another few cms of Z height. But taking the X ends off is easier and less of a back track that taking the whole frame apart. Maybe just redoing the extruder to be a bit thinner would be easier :-).