Originally shared by Daniel F
Quadrap single gantry H-belt version
Finally I managed to post some pictures of my Quadrap adaption (CoreXY version). The CoreXY system seems to work quite well, the two nema 17 have enough power to drive the gantry/carriage combination. I didn’t take the weight but I can save the weight of the stepper on the gantry for the price of 4 bearings and two screws. Although I used toothed belts I tried to keep the design as simple as possible. The only issue I have is with the teflon tubing on the bearings, the wall thickness varies ± 0.1mm. Therefore the bearings run out of centre and I need to allow around 0.3mm play to allow smooth travel of the carriages. Not sure on precision yet…
The 12mm OD, 10mm ID tube is from eBay, any source for a tube with better tolerance values?
very clean work! wow! really impressive.
@Shauki It is two belts, each one is a little bit over 2m (need to measure the exact lenght). Toothed pulleys with 40 teeth are from ebay:http://www.ebay.com/itm/GT2-Aluminum-Timing-Belt-Pulleys-10mm-Bore-40T-RepRap-Prusa-Mendel-3D-Printer-/261459819301?pt=LH_DefaultDomain_0&hash=item3ce0383b25
Idlers are Cheap flanged bearings from Ebay as well (search for F636zz 6x22x7 mm Metal Flanged Ball Bearing). Amazing how cheap it is to ship items from China if you have enough time. Shipping and handling the Rollin bearings from Germqany to Switzerland cost me €13.5 plus €3 for monney transfer…
This is very nice ! Thanks for the good pictures.
I don’t have much experience with belt tension, practice have to show how much is enough. For the moment I tensioned them by hand and as each loop ends diagonally on the cariage, the tension should be the same on both loops. You don’t have to be sorry for the pollin bearings, they are perfect for the purpose you chose them and compared to igus slides they are still cheap…
Daniel no any nylon tube on long bearing?
Thanks Mauro, good hint, I might try it out. I think it dosn’t mater if it’s nylon or teflon,they are both resistant to wearing, the crucial point is mechanical tolerance, the wall thickness should be equal all around. I asked one of the chinese suppliers on eBay about tolerance of their teflon tubes but did not get an answer (which is an answer as well…)
@Shauki Yes this is very similar. Looks like you went Corexy not h-belt… which is good. Love the common pulley assembly on the Y-Carriage ends. Wish I had thought of that. It will help balance the forces even better than CoreXY already does. Belt tension is critical. And even more important is balance of tension between the belts. Since the belts are so long they are susceptible for stretch and harmonic vibration across the span. So even tension is the difference between round circles and ovals. It is worth the time to design an easily adjustable tension system. It could be as simple as another idler mid belt on the long run from the motor pulley to the corner idler. Something on a lever or slot would work. having it along this edge also has the advantage of limiting the vibration across the span.
One note is due to the double stepping required to turn two motors pulling at a 45deg into one motion along x or y, calibration can be a bit tricky to wrap your head around.
ah ok, so I mixed the names up, H belt is the design with just one belt, core-xy with two, is that right? If so I should rename my post to Quadrap CoreXY.
Thanks for the input with the belt tensioner, I’m thinking about an L profile running below the belt, it could be fixed with the M6 corner screws. The idler could sit in a slot half way between motor pulley and corner idler.
@Daniel_F is there something keeping the belts apart on the common idler post?
Edit: never mind I see the flange now.
Eric, as you already noticed it is flanged bearings, see picture 6, it’s a bit hard to see. The flange is on the lower side, between the to bearings is a little washer that keeps them apart and adds some room for the lower belt. There is just an air gap between the lower belt and the flange of the upper bearing, but I checked and the lower belt newer touched the flange of the upper bearing. Plan B would have been to use 2 bearings per idler with the flanged sides on the outside, but this would have made everything higher. I think it’s better to have the lower and upper belt as close together as possible because of tilting force on the carriage
yes but due to the not-so-precise covering tubes there is bit of play, about 0.2mm in each direction I tilt. It still runs on the rail.
I measured the belt length, they are 1.94m each but I see potential to shorten them for 16cm each so they would end up to 1.78m. I’m just not shure if it is worth the effort.
was quite busy, but there is some progress, I’ll post an update soon.