The Taz Pro Fix Project - Hardware Endstops, Wider Chassis, Carriage fixes, and other fixes by magdong

Last crawled date: 3 years, 4 months ago

This is my personal repository for fixes I have made to the Taz Pro design. There aren't really going to be any instructions or how-to's with this, and use of anything here is done so at your own risk and voids your warranty.
The Taz Pro design seems to have some shortcomings. I attempt to address these shortcomings with various fixes.
Shortcoming 1 - The chassis seems to be too narrow to properly support single toolheads. So if you want to remove the behemoth dual head so you can print faster, and you install a single toolhead, keen observers may note that the toolhead just BARELY hits the front left pad. And sometimes, at least for me, the nozzle misses the pad completely and overshoots - because of Shortcoming 2 listed below (Software Endstops suck). And you can't shift the table or do anything else to address this, other than modify the back plate for the single toolhead - breaking compatibility with other machines. Fix? Widen the chassis. Instead of the horizontal 2020 rails being 530mm, I re-cut them to 540mm. This width still maintains compatibility with the original X rails and the Printed Solid enclosure. The rails only sit inset about 2.75mm on each end of the X-axis mounts, but that makes no functional difference and it still hits the set screws easily. The printed solid enclosure actually fits properly (rather than being wider) with this mod, as well, but you'll need revised "hangers" for holding the enclosure. I've provided those replacement parts. Widening the chassis also has the benefit of giving the dual head a bit more room to work without inappropriately ramming into things (particularly the right hand side overshoot) as well as giving a bit of a "filament dump" area on the left middle of the bed. You'll need to modify your firmware layout positions. I suggest using the DrunkenOctopus for a starting point, and modding from there.
Shortcoming 2 - Software endstops. My opinion - a major mistake. The Taz Pro often overshoots and grinds because of the software endstops, but, surprisingly, that's not why I've changed it. I changed it because software endstops are too inaccurate to trust for print resumes. There is too much variance between where it stops - it's not precisely repeatable, and that leads to minor layer shifts if the printer stops and has to rehome (out of filament, or if you try to activate power loss recovery in the firmware). So I added hardware endstops to X and Y. For the Y axis, I used the stock motor mount parts from the Taz Workhorse (I've included the parts here, but are not my design or mods and anything prefixed "lulzbot_original" falls under Lulzbot's license terms, not these ones). For X, I made a custom mount. This requires that you do some additional wiring, and that you tweak the interconnect housing. There is room to stack 2 connectors on top of eachother in the interconnect housing, so that makes life easier. There is a replacement interconnect housing included here to fit the extra wire for the X axis. No additional space is needed for the Y axis as it's only 2 wires on a tiny connector, so you can stack them. For the wiring, I ordered the proper IGUS flexible cable, the exact same wiring that the Taz Pro comes with. For the cable chain, fortunately, there is room in the cable chain for one extra wire. I have a suspicion that, between this (cable chain room) and the fact that the PS enclosure fits properly at 540mm leads me to ponder the possibility that the Taz Pro was actually originally designed @ 540mm with hardware endstops, but that they cut this out to reduce BOM cost before production. I don't know.
Shortcoming 3 - The X Carriage holders posilock nut holder is just marginally too small, at least for any of the posilock nuts I can find. So I widened it marginally, and thickened the top of the mount by 0.5mm. Why? Because without these changes, the damn top screw cracks the carriage mount when tightened sufficiently to remove the wobble from the top bearing, so these changes should prevent the crack.
Shortcoming 4 - The interface board mount screw that retains the bearing/bushing, when torqued to lulzbot spec, tends to crack, even when proper inter-layer adhesion is achieved with high quality ABS. While making room for the revised thickened carriage (revised to avoid cracking), I thickened the base that the screw seats on to attempt to mitigate this cracking.
Shortcoming 5 - The single toolhead can't reach the calibration cube. Wow. This, too? Makes you think about how well this printer was tested before release. The only way to fix this properly, while maintaining compatibility with both the single toolheads and the dual toolheads, without changing toolhead design, would be to increase the length of the 2020 rails on Y by 10mm as well. But that means I need larger 10mm rails, and I don't want to order those - I'm already too $$$ on a printer that was, IMO, designed broken, and I'm not willing to do that. So, with widening to 540mm horizontal 2020 rail, we are now able to reach and therefore leverage the front right levelling washer for the hysteresis calibration, rather than the "calibration cube". Functionally, it's the same thing, though we're not able to reach all 4 corners - only 3. Good enough, from my test results.
Shortcoming 6 - The horizontal cable chain (X) has the motor mount side 2.5mm proud of the double bearing holder receiving side, so the chain assembly gets slightly twisted, which is inappropriate. Fixed.
Other Fix - After adding an additional wire on the Z cable chain for the X min hardware end stop, the wires no longer stay in place at the end of the chain due to the short length before the control box. Created an alignment clip and a cable chain retainer pin to address.
There are other odds and sods in here and I may or may not add additional details regarding "why" - again, this is being posted primarily for me as a backup, but I thought perhaps other adventurous modders may want to try this too at their own risk.
Cheers.