I fired up the printer today, to experiment with some detail parts for some 5" gauge logging flat cars I'm making.
Some tie-rod washers, which take some 7BA studding in them, a queen post, stake pocket, plus a ratchet, pawl and handwheel
I'm also playing with a knuckle coupler. I have my doubts that even in PETG, it would have the strength to pull me - the intention is just to see whether it would function well enough for unloaded or log-loaded cars. That said, PETG is surprisingly tough, at least in compression: I built a small, dual-rail bender for G scale track with it a while back and it could bend the track into a semi-circle with ease.
I've produced two coupler types - one is a closed knuckle, the other is a slotted one to take a chain or bar
I've also printed a set of axleboxes. They take 22x7x7 sealed bearings and will fit between some 12mmx3mm steel bar, bent into an archbar frame. I don't have access to a hydraulic press so I'm hoping my vice-mounted press jaws will be up to the task if I heat the steel first
The axleboxes are a strong design - tested with bearings and 8mm steel axle fitted, a force of several hundred Kgs (there was no pressure gauge available to get a precise reading) was applied to the top of the axle boxes, with the shaft supported beneath. The shaft deforms before the axleboxes do.
Thanks Connor, Your Crab really is a thing of beauty and I can't help wondering if you'd have been able to design bearings into the axle boxes without having to change their dimensions? If you're not planning on running it, as you say I don't suppose it'll make too much difference. It's coming along beautifully by the way, It's going to be a real credit to you when it's done!
I've been experimenting with some resin-printed versions of the knuckle couplers.
I'm pretty pleased with the functionality. The locking pins are working under gravity here but are spring-loaded to auto-lock in the finished version. I'm experimenting with some textured rust-effect paint for them.
The flat car itself is under construction. Im currently trying veraious stains for the decking
I've been doing a bit of statistical research on tensile strength of various printing materials. Resin is pretty much the weakest - weaker than PLA filament unless you invest in the tougher variants.
A PLA hook in testing can support up to 285 lbs but its tensile strength decreases over time and particularly with UV exposure.
Orientation between the print and pull forces plays a part as does the fill type.
Nylon is a step up from PLA in tension and the same hook can withstand a 485lb pull, without the time-based degradation.
Polycarbonate is the best printing filament for this kind of application and able to withstand a 685lb pull.
Both nylon and polycarbonate would be unlikely to print successfully on a consumer printer without modifications to cope with the necessary print temperatures (250-300C). Nylon filament also usually requires drying prior to printing as its hygroscopic.
Post by choochooenthusiast on Dec 28, 2022 23:07:16 GMT
Darren, your research on filament properties is much appreciated as I’m about to stock up again and don’t know what to get! Polycarbonate would be ideal. Prusa sells a Polycarbonate blend capable of being printed on Prusa printers. Might be worth trying.