Are you talking about this madness on the right? 
6 Likes
The fat ones were just to see what it looked like. Two outer hubs back to back. Only went to 20 psi for fun.
The rim that ripped apart earlier had several points of failure I introduced:
-nylon with fill (CF or GF) is hard to gauge layer adhesion visually when printing. Nylons without fill almost look translucent in areas with 100% infill and good layer adhesion. Fibers break up that visual cue and I got fooled into thinking it was solid in the z dimension.
-outer, wide half of hub was not annealed.
-the wide half of hub was also warped so that the inner radius mated perfectly with thin hub and spun true on the axle. The outer diameter of hub, near the bolt pattern, curved upward off build plate a little bit, leaving a 1mm gap where the two halves of the hubs most distant from axle should have mated seamlessly. When I tightened the hub fasteners down, I think they might have been uneven and pulled the hub apart. I used a star pattern and did final torque by hand.
It failed here:
I never found the ejected part. I did look. Bad pic, and even worse testing jig, but hereās my swing set.
14 Likes
Reprinted, increased temp 10c, expoxy around lines that delaminated. Annealed.
I really like the Y spoke design. I did a little tinkering, I havenāt printed them, they arenāt the pictured print above.
Just some thoughts. Probably doesnāt matter for a good PETG print.
I would recommend against filaments with fill unless you are experienced. I do feel extremely confident in printing your Y design in dry, Taulman 910 nylon. Good prints will fracture along stress lines that ignore layer lines, and I feel like I can judge adhesion by looking at the part while still printing.
6 Likes
Anyway, I popped a tire on my mountain board. Perfect time to swap in front hubs. I still need to figure out the rear wheel pulleys.
Yup, this looks consistent to my recommendation to not use filaments with additives such as CF. Did you do any pressure tests after annealing? Would definitely do that before you test them on a board.
I also fucking love that you made a swing out of them. 
Regarding the MBS pattern, I might make a set if there is demand for it. Would look a bit cleaner with just one hole instead of two. Idk if thats wanted though, as I have pulleys to go with the hubs.
1 Like
As in, āinflate hub and tire to X% above typical use pressureā ?
I roll at 30psi front. Filling to 60psi over night seems reasonable.
1 Like
Would be a good idea I think. Iām not sold on CF Nylon yet, would be a good idea to do some stress testing. When youāre driving the tire pressure will change dynamically, and will definitely exceed your 2 bar working pressure for brief periods at a time.
I got unsold recently.
Anyway the kids are tucked in at 60psi.
The glass filled polypropylene did not inspire confidence on smaller test prints.
I havenāt printed in Polycarbinate in awhile. Past prints in Polymaker polymax blends have had excellent layer adhesion, are significantly stiffer, and tolerate post print chemical and mechanical edits better than nylon.
I got a roll of red 3dxtech PC and it was the moistest filament Iāve ever put through a nozzle straight out of a vacuum sealed bag.
Id be embarrassed if I lent a buddy a length of filament that wet.
To be clear, Iām riding these hubs at reasonable speeds. Iām always the last one home when I skate with others. There are no notable metr logs to post. Iām slumming it in the 20s (mph) at most. Deep sand, ratchet bindings, 2wd, channel trucks, and new routes are not my ideal setup.
2 Likes
What diameter hole pattern is MBS and Trampa? Could do a 4.2mm slot, you should be using washers anyways if youāre clamping printed parts
1 Like
Trampa is 35,7mm
MBS is 40mm
I like trampa more because the hubs can be smaller. But itās not that critical. A slot is a cool idea, but might not work with all designsā¦
If there is a loud bang tonight donāt shoot anyone.
I once saw steam rising from a nozzle. But yeah, Iām recently dealing with a lot of wet filament too, the summer so far has been particularly damp.
1 Like
Itās actually a diameter of 80.3
Will matter for mating with gear drives
71.4mm and 80.3mm? Who makes these numbers 
I mean you have a fair point there
As a non engineer, Iād guess itās a cascade of competing constraints.
hubs design is governed first by bearings seats and tire lip diameter.
Then there is width of hub considerations. Some people arenāt happy with the manufacturerās tire contact patch.(see stoogeboards and etoxx)
If that all works out, then there is a legitimate long pause to think about the material the hubs would ultimately be made of. Metal, plastics, composites, mixed media construction?
Even within a single, general material, nylon filled glass for example. Injection molded, laser sintered, subtractive CNC, or FDM?
To keep this thread relevant, FDM. Who is printing ? Hewlett-Packard or rando diyer?
Diy? There are distinct tiers of what material and geometry is reasonably printable for a diy guy. I bet the average 3d print diyer has an printer without an enclosure. Maybe 40% to 20% have bothered with an all metal hotend that can print into the high 290s C.
There are only a few materials that fit these constraints if you are aiming community embrace.
Trace a circle of the inner tire diameter, mark the axle center. Pick an odd number of spokes (bc reasons). Design your little heart out. 3, 7, or 5 spokes? Now back track to the above considerations. How wide do those spokes need to be? You could model it in Fusion and other full features CAD suites like @dani did, but you know the home gamer (like me) is going to fuck it up if they can (also like me).
Decide on a safeish spoke width for your
manufacturering method.
Now, where would you like to place that bolt pattern? In the wheel spokes to allow for smaller wheel pullies?
This is making me anxious just thinking about designing for others.
1 Like
As an engineer I can assure you that a LOT of numbers come out of peopleās ass 
Almost all dimensions are based on another dimension or some physical property, but at some point a lot of it traces back to some number pulled from a range of valid numbers but that relatively arbitrary choice cascades through the project
5 Likes
Oh yeah sorry I ment radius. Also I measured the radius in CAD, and it was exactly 40mm. Looks like that model was not exactly right.
Yup lol. 40mm exact would have been perfectly possible. My bet is someone drew something up in CAD and because it was non-critical it was never looked at again.
1 Like
The trampa/summate spokes are great spacers for printed wheel pulleys that donāt have any stand off spacing built in. Itās plug and play. 3 printed hubs and a pulley in nylon taulman 910.
Iām 170lbs, tires at 30-35psi. Bunny hops, no real jumps yet.
6 Likes
Ooh genius idea, print hubs that use the Superstar insert in the print half way through the print so when itās done thereās no evidence of it but itās metal reinforced, just pause half way and press fit it in
3 Likes
Thatās an interesting idea.
Iāll stop hogging the air in this thread. I took the board out on a typical desert run but stayed away from the trails with lots of cactus spines.
3 printed hubs and a pulley survived 100f heat for an hour and deep sand that stalls my motors (Iām using wimpy vesc tool wizard recommended motor and battery currents).
Iām physically smoked from the heat but the parts are fine. Iāll post adventures on the āwar and piecesā build thread.
This was a net positive tinkering adventure.
15 Likes