X-Carriage compatible with the MK3(S) Bondtech Prusa Extruder with the Revised X-axis
Compatible ONLY with the Revised X-axis or Bear X-ends
IMPORTANT: This carriage is compatible with stock frame only if you use "X-Carriage Back_Top (BondtechBear) (StockFrame)". The file is included in the downloads or LINK in case you are just after that specific part.
Assembly note for stock frame: Make sure to have the correct orientation when installing the X Carriage Back Top (StockFrame), the cutouts should be facing upwards.
While converting my printer setup to use the Bondtech Prusa Extruder I felt like the Bear X-carriage provided some well needed utility that previous ones didn't. However, I saw few things that can be further improved, hence this remix.
The belt path cutouts can be a sore point of the X-Carriage, because different materials, print settings and print artifacts can heavily influence the designed tolerances. Leading to cases where its very hard to insert the belt, damaging the belt in the process and possible poor alignment, or it was loose, tending to skip teeth under tension with the existing geometry of the cutout.
While I'd prefer a belt clamp of sorts, my interim solution to remedy this was to edit the belt path to closely match the published specs of the 2GT belt. This gives a lot more surface area that the belt is in contact with the carriage, while not necessarily attempting to compress the whole belt too tight. Only the last few millimeters compress the belt and need a tool to be pushed all the way in. This results in the belt being easier to insert (up to those last few mm), and those last few mm ensuring the belt can keep its positioning while under tension.
The rest of the changes to the carriage came along while analyzing the CAD files and printed parts, that at least in my opinion, needed slight optimization.
- Adjusted belt "holder" cutout to closely match the genuine 2GT belt shape (compatible with GT2 but not GT3). This allows for the belt to hold a lot more tension without slipping, while still being easy to insert in the carriage.
- Belt is accessible even when the whole carriage is assembled
- All X-Carriage-back screws are now the same length and are fixed on the X-Carriage in the same way. It helps with ease of assembly as well with some cases where the layers were failing (delaminating) above the square nuts.
- X-carriage-back clamps the bearings more uniformly
- The cable holder was edited to have far less aggressive bridging
- The screw for the cable holder protrudes deeper into the X-Carriage, giving it more layers to resist the cable holder appendix breaking off. This change eliminated one zip tie holder, edited the remaining ones to be split (2 for the top cables, 2 for the bottom)
- Added "ribs" to the cable holder, to help out with better constraining the nylon filament guide (tested it with stock ~3mm nylon filament , and ~2.8mm)
- Further optimized for 0.2mm layer height printing, added bit more clearance for the belt and cables, reinforced some thin features.
In case you are swapping parts around (MK2.5-MK3), the only parts that are different and version specific are: X-Carriage and X-Carriage-Back Bottom. The files affected have appropriate name tags.
If you prefer to have the cutout for the "old" optical sensor (MK3) closed on the X-carriage, I've added a version ONLY compatible with the MK3S add-on
X-Carriage-Back has two versions, although I recommend using this one, it allows access to all screws that secure the extruder, making assembly a bit more convenient.
STEP files are included for your modding pleasure and convenience. STL files were sliced and checked with Slic3r PE. Any constructive feedback is welcomed.
0.2mm (highly recommended)
I printed the parts from PETG, 0.4mm nozzle, 3 perimeters, 30% infill, 5 top/bottom layer which works quite fine for my prints. That being said, the 3D model isn't strictly tied to those settings, feel free to adjust them to your liking.
I would say it safe to stay within these limits:
5-7 bottom/top layers
Perimeters affect the strength of the parts the most, but also add weight the most. I would balance the amount of infill according to how many perimeters you choose. The number of bottom and top layers shouldn't be much of a factor for most of the printed parts, and its safe to use 5 regardless of infill/perimeters.
Please note this BoM contains only the fasteners used for the carriage and does not contain the ones used on the extruder side.
For detailed assembly instructions you can follow the guide Bear Upgrade has published.
The only change in the fasteners is 4 M3x18mm screws instead of M3x10mm, and 4 hex nuts (regular or nylock) instead of square nuts. Please check the pictures of the BoM for details.
However I would like to emphasize few key steps.
The X-Carriage Back is designed to exert slight pressure on the bearings (nominally 0.2mm). So, when assembling, don't aim to get the X-Carriage and X-Carriage-back to be in contact and leave no gap, rather tighten the screws (equally) only to the point when there is no slop between parts and has some slight pre-tension on the bearings. Overdoing it WILL cause binding of the bearings
- The belt should be pushed in all the way in the carriage, use a tool with a non sharpened edge to push it all the way in.
I used a metal nail file along the belt path, pushing from the position the belt enters the carriage up until the end of the belt, and repeat the process few times until the belt is fully seated.
Any similar tool with ~1mm thickness and dull edges will do the job (some people used flat screwdrivers), if in dire need, you can print a 0.8-1mm tall rectangle.
Avoid using a tool with a sharp edge to do this as it can damage the belt and try to push along the full length of the belt that is seated in the carriage (don't try to push at the same spot)
(17/04/2019) Added some more cable clearance on the X-Carriage-back Bottom (minor). Sorted the file names to have tags only for the files that are strictly compatible with their respective version (MK2.5-MK3)
(20/04/2019) Added a new version of X-Carriage-Back. Thanks for the great suggestion Anders Svendsen.
(19/05/2019) Added an optional version of the X-carriage compatible only with the MK3S sensor add-on
In no particular order I would like to mention the sources of the designs I got inspired from, or people who helped me in one way or another with the design. Thank you all.