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Rostok 3D Printer Build

I’ve put off start­ing a 3D print­er for a long time, mostly because I couldn’t think of any­thing par­tic­u­larly use­ful to do with it. But over the past year or so I’ve run off a few parts, and the list of things I’d like to have has got­ten longer. So for my birth­day a couple weeks ago, in a fit of delin­quent irre­spons­ib­il­ity I pulled the trig­ger on a Ros­tok Mini delta print­er kit from 3d Print­er Czar. Took just over a week from order to the deliv­ery arriv­ing, and it’s been tak­ing up most of my free time since Tues­day after­noon.

Part 1: mechanical build

I man­aged to com­plete the basic mech­an­ic­al build in 3 – 4 hours in one even­ing. The dir­ec­tions online are a little rough in parts, but mostly pretty thor­ough. The kit includes most tools needed, which was nice. But a hex key for the M8 bolts on the top belt bear­ings was miss­ing, and my hands were very glad to have decent-sized pli­ers.

Assembled Rostok Mini frame

First minor issue I had was with bolt­ing things to the prin­ted parts. It’s import­ant not to over-tight­en these — I man­aged to crack one part slightly along the print grain tight­en­ing it a little too much. I’m not too con­cerned about it because it has oth­er bolts nearby to take up the strain, but I was much more cau­tious after that one.

Second was with the two prin­ted parts attached to the hotend. One seemed to warp slightly insert­ing the hotend, leav­ing the end tilted slightly to one side. Not really a showstop­per, and worst case I’d be able to print a replace­ment part, pos­sibly with a slightly wider insert for the hotend..

I only had one major prob­lem after the build was fin­ished. The build instruc­tions don’t place any­where near enough emphas­is on how import­ant it is to make sure the car­bon fibre delta arms are the same length. Fol­low­ing the dir­ec­tions to the let­ter I eye­balled the rods to make sure they were about the same length, cut strips from a leftover screw bag­gie, wrapped them around the lead screws on my u-joints, and jammed them in to the ends of my rods. That left me with a cent­ral effect­or plat­form that was vis­ibly a few degrees off level. And shortly after­wards I dis­covered that the rods were also pretty fra­gile — the u-joints liable to pull out of the rods with too much force.

I sup­pose this could be improved by pack­ing the lead screws with thick­er plastic, and then I’d be able to match the lengths of the rods more care­fully by screw­ing the u-joints in and out. But decided to scrap that idea, and go with a more per­man­ent solu­tion. I’d build a jig to hold the rods in place and glue them.

Part 2: fixing the arms

Yes­ter­day I unscrewed the arms and meas­ured the rods more care­fully. Found a good 1.5mm dif­fer­ence between the shortest and longest arms, which in hind­sight is pretty ridicu­lous. With the effect­or plate in my hand though I was able to real­ise that the bolts hold­ing it togeth­er were still barely fin­ger-tight. Tight­en­ing them up held the whole struc­ture togeth­er prop­erly and straightened up the hotend nicely.

Build­ing a jig to hold my arms while they were glued was simple enough. I took the length of the longest arm, added 34mm for the two Traxxas 5349 u-joints (they’re 22mm long and 10mm wide, so it seemed logic­al that the centre of the hole would be 17mm from the end), and an extra mm for luck. From there one could prob­ably bang a couple of nails in to a block of wood and use that to make a series of arms the same length, but I star­ted to over­en­gin­eer a little. Start­ing with Lib­reCAD I quickly drew up a block with six pairs of screw holes the right dis­tance (uh, 187mm for my arms).

B8gNylwCAAAXUCqThis even­ing I wandered down to Robots and Dino­saurs, a pretty great maker space in Sydney, and used the laser cut­ter to cut a chunk of 8mm acryl­ic to shape. Then added longish bolts and fixed them in place to make my jig. Filed the insides of the car­bon fibre rods a little, then used extra strong, slow set­ting Araldite epoxy to glue the u-joints to the rods. Placed the joints on to the rods, fixed them down with anoth­er set of nuts, and then looped rub­ber bands over the ends to make sure everything stayed togeth­er.

I gave the glue a few hours to set, then took the arms off and tested them all on the same pair of bolts to make sure I hadn’t done any­thing too stu­pid. Not sure why, because I don’t know what I’d do if the arms were dif­fer­ent lengths at this point. But they all slid over the bolts with the same amount of play, so I’m pretty con­fid­ent I’ve got them accur­ate enough, and right now I’m pretty pleased with how well it worked.

So, next is to leave the arms overnight to fully cure. Tomor­row I’ll reas­semble everything then get back to work on the wir­ing and elec­tron­ics.

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