The banana XY bushing block and belt tensioner. Drop in replacement for the ultimaker
by MoonCactus, published
This is a drop in replacement for the Ultimaker, though it should prove useful on other printers with belts with an X/Y moving head, such as the makerbot (it is all parametric: belt, rods, bushing etc)
It also embeds a novel and precise belt tensioner thanks to a sliding banana. No? Really!
Just have a look at the "exploded" STL view to know why!
Nb: these are for the Ultimaker gantry rods, so 6mm for the two central rods, 8 mm for the outer with a bushing of ~11mm (outside diameter). But the source can be adapted to other diameters (probably not smaller though).
One of my XY wooden block lost a leg and the head rod started to wobble.
As I had to design some replacement, I fitted a belt tensioning system by the way (have a look at the "exploded" stl file to understand).
- drop in replacement for the XY wooden blocks
- easily mountable/umountable (no need to remove your rods, except to get rid of the stock wooden parts the first time). This thing clamps the rods from the above and bottom, not from the side! If you do not want to disassemble the blocks you may be interested in http://www.thingiverse.com/thing:66866
- integrated screw- and banana-based precision belt tensioner :)
- probably lighter and easier to tune than the stock X/Y wood blocks (eg. I printed rev2 with rev1 faster than ever, my head moves better than before!)
- the belt is not bent out of the block (ie. it is kept parallel)
Bill of material and howto
Never force on the screws! A good practice is to quickly and progressively screw/unscrew so as to benefit from the heat when you carve the threads in the plastic (I use & recommend PLA).
a somehow working printer to print the block... Mine was still usable when I printed the first version (see the pic, broken leg on the bottom of the wooden block)
1x 30mm M3 screw + 2x 20mm M3 screws to clamp the axes vertically (screw them all progressively, with priority to the head rod and finalization with the rear long screw to clamp the bushing -- the latter almost does not have to be there so do not tighten it too much). I repeat: the bushing should not be over-tightened (no use / counter productive). Nuts may be added to secure the screws, but it was useless for me since the screw holes in the PLA were tight enough.
one M3 drill to widen the 3 holes of either the top or of the bottom part, according to the block you are printing. The screw must be able to move freely in the part closest to its head so as to clamp the rods properly.
2x 15mm (20mm is ok) M3 screws for keeping the belt in place (these are the horizontal screws). No real need for nuts there because the belt will push them aside... but:
I recommend 2 small pieces of bowden or PTFE tube to put on the previous screws, and to avoid ruining the belt on their threads with time(?). The pieces must be cut to the width of the belt of course. Only one of them is shown on my pics, but I definitely should add the second one. Update months later: still did not do it and still no wear on my belts, they are probably superfluous.
- 1 M3 screw for the belt tension (horizontal screw between the belt and the outer rod). Use the shortest length according to the tension you need. A 10mm may be enough (make absolutely sure it is not too long and does not scratch the rod!). Increase it for a longer banana :)
You may have to sand/cut a bit the banana so it slides enough in the curved slots. Then make sure the tensioning screw is able to push it, and that it goes back down when you press from the above as would the belt be doing. Once again, do not force on the tensioning screw, better cut more of the banana than ruin the PLA thread you'll be carving with the screw!
Also take care not to delaminate the walls when you screw the horizontal screws! I recommend you prepare the threads outside of the printer, then insert the belt, the tubes and slowly screw until you match the opposite hole. Then screw slowly again, keeping the bolt aligned. Quickly go forward and backward to heat the PLA by the way. You need a good print obviously for this part.
So... what to print?
Please make sure to use the proper parts for the proper location : they are not all alike as some feature the required tab to trigger the respective end-stop. Do not mismatch them just like you did not with the stock wooden blocks ;)
For the whole set, you will need to print:
3 x bottom + no tab
1 x bottom + tab
3 x top + no tab
1 x top + tab
- 4 x bananas
Obviously, forget "exploded.stl" which is there just to show how it works!
Note also that the banana versions labelled "long" and "huge" may be useful when the default banana is too short (with used and sloppy belts). It probably means you should consider buying new belts by the way!
Check the existing blocks to know what goes where. The most important thing is the tab! Of course, remove the thin oval skirts, as they just help to print the top parts (that tend otherwise to pop off the bed just before the junction and b/c of the overhang).
I recommend 0.15mm layer height or less for the top parts b/c of the overhangs. I used 1.2mm wall thickness. You may like to end the layers with the perimeters.
Top part better be 100% file, bottom part can be almost empty.
The banana could benefit from a high resolution (used 0.1), but the way its printed sideways so it may not have an impact. What is important is to print it at the lowest temperature possible and 100% infill.
The flat rounded tabs at Z=0 on the top/big raft should prevent them from popping off the bed before the layer joins with the other side. If it still fails, you can also use a brim or a raft to stabilize them further (I needed nothing of these).
The belt tensioner works by pushing the "banana" upwards in the curved side slots below the sidewalled belt (check the exploded view to see better). It works very efficiently for me. By default, this screw features no embedded nut: it is just tightly screwed in the plastic itself so be carefull not to ruin the thread. Embedding a nut there is tricky because of the lack of space, but the option is given (I did not use it).
Last file updates and revisions
Version 3d: there are m3-sized holes only anymore, and drilling is required for the proper top or bottom 3 holes. You may also simply drill all the way and use nuts. For me, they were tight enough and I did not need nuts.
Version 3.2: a smaller/tighter version towards the outside because the block in the back was hitting the vertical bed rods and Z-screw as hreedijk noticed it! oops... This time I did print this specific block and installed it on my own printer. It is tight but OK (<2mm gap).
At last I can tune my long belts with the same precision as with my short belts http://www.thingiverse.com/thing:40041 Please comment & feedback :)
This thing is Attribution - Share Alike - Creative Commons. I will not and I cannot waive my moral rights on this thing whatever the Thingiverse bozos ask for. It would be illegal in most of Europe anyway.