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SpiderMonkey Posted - 08/20/2019 : 09:06:04
Discovered we have a 3d printer at the office, and a pretty decent one (Prusa MK3).

First order of business was some jigs for the different sized tubes to be used for the upwrong I'm building for the wife. These ensure the tubes are centered, and the angles for the frame are correct.

Next, I realized I could probably go faster and get more precise and regular joins for some of my common tube joins if I made a mold to get that done.

Next up, an idler cog that will fit a 608 bearing. I'm not sure how well it'll do.

According to this site, (https://www.makeitfrom.com/compare/Acetal-Homopolymer-POM-H/Polylactic-Acid-PLA-Polylactide) many of the characteristics of PLA are fairly similar to POM-H (Delrin) so I think it may be OK. Replacements would be cheap and easy to acquire.

From there, the mind spins. I can make a nice mold/mandrel for doing a replacement head tube (or just the ends) for my NoCom to straighten up the front... Proper jigs for the 50mm main tubes of the recumbent projects would eliminate alignment problems...

Should I stop joining the tubes wet and make molds for those joins, bladder-press CF into them and make custom lugs instead? Would let me add a couple of cm to the frame lengths for the grownups (tube lengths limited by what ships from China, so a free couple CM from a lug = savings of an entire tube, or $25-$50).

25   L A T E S T    R E P L I E S    (Newest First)
Balor Posted - 03/09/2020 : 08:05:14
My point exactly (and esun PA GF claims to be even better). As for stiffness - that's what 'sandwich' construction is for.
Filled materials are more easily printed due to massive decreased warp factor, though require a hardened nozzle of course... still needs many hours of drying before printing unfortunately.
strayray Posted - 03/09/2020 : 07:49:35
>better strength to weight then aluminium
Call me surprised. A quick lookup of 6061-T6, to pick a random alloy, has an ultimate tensile strength of 310 MPa, but a fatigue strength of 95 MPa.
Meanwhile Matterhacker NylonG is claiming a tensile strength of 95 Mpa. Derating that by 30% for fatigue (rough guess from googling), and again for 3D printing it, it is somewhat weaker. But if you scale by the 2.7x density advantage of PA-GF, PA-GF looks competitive.

I've read nylon's properties vary widely with humidity, and some with temperature. For example, straight from the mold, nylon it quite brittle because it's so dry (IIRC 0.1% humidity is a target for injection molding feedstock). It recovers after re-humidification. But that's really dry. I don't know how its properties vary across real-life biking conditions. (I do expect my days of sub-zero Fahrenheit biking are over. so I can discount those temps.)

For stiffness, (modulus of 69 GPa vs 4 GPa in NylonG), aluminum still has the advantage, even when scaled by weight. But because the plastic is less dense, you can increase dimensions to make up for much of that.
Balor Posted - 03/06/2020 : 04:39:13

I think I'll try replicating that some more, for actual frame joints.

I'll need to experiment with annealed PLA (unannealed will not work for sure - low creep resistance), annealead CF-pla, ABS/ABS-GF, PETG and CF-petg (annealed), and maybe I'll try polycarbonate and GF-filled PA (this one is CRAZY strong, better strength to weight then aluminium (and better than PA-CF)! http://www.esun3d.net/UploadFiles/Download/MSDS_eSUN_ePA-GF%20filament.pdf though, obviously, there is anisotropy inherent in 3d printing and needs to be dried before each print)

Too bad there are no 3d printable PC-GF filaments I can find, that would be *ultimate* 3d printing plastic! I already have an all-metal nozzle and I've made a diy enclose that works well (no warpage of ABS parts at all).
Balor Posted - 01/05/2020 : 17:23:08
Thanks, I've bought a used convection oven and it worked nicely (as well as apping temperature).

Also see this:

If that works... why not print it from CF-filled PLA? I think I'll make my own BB :).
strayray Posted - 01/01/2020 : 17:52:41
Balor, see https://ultimaker.com/en/resources/52682-how-to-dry-pva

If you go the silica gel beads route (5-8 USD/lb), I prefer color changing indicator beads, so you can tell when they need to be recharged. I prefer the orange-green beads over the blue-pink beads. The blue-pink beads have cobalt chloride - a known irritant and suspected carcinogen.
Balor Posted - 12/31/2019 : 15:23:01
There is still downside of course - prone to buckling failure. But when printed with bare minimum of infill, it can be fixed as well!
Btw, PLA is really tough and rigid. If you shield it from the sun, (it has HDT of about 55 C) it is an excellent material, I've printed some COGS and they stood up to serious watts (hundreds, actually).

I need a way to properly dissicate the PVA, cause it came wet out of the box, literally steams when printed and when printed has no layer adhesion whatsoever :(
Patrick Bateman Posted - 12/31/2019 : 14:55:35
Not sure if it came up in the thread, but you really want to avoid using PLA on a bike. Basically it will melt in the sun. It's made of corn and it has a very low melting point. One of my 3D printed speaker projects melted in the sun, during the *winter!*

Another "neat" thing to keep in mind, with 3D printers, is that you can make ridiculously stiff shapes by making them large in diameter with thin walls. When I was first making 3D objects, I was making them with walls that were about 1/4" thick, but after some time I realized I might as well "go big" since there's not much downside to doing so. (IE, with aluminum or steel, there's a limit of how thin the walls can get, but with a 3D printer you can make walls that are a fraction of a millimeter thick if you feel like it.)
Balor Posted - 11/03/2019 : 18:45:42
Originally posted by harv

If you can print polycarbonate, acetone will make it craze into tiny easy to break pieces. Even though PC is expensive it has double the modulus of HIPS so you can make the shell thinner. Also has a higher heat distortion temp than HIPS, so if there is heat from the epoxy curing the PC mandrel should distort less than HIPS.

Interesting! But I'll need a full metal nozzle to print PC, something I don't currently have, plus likely a heated bed with temp above 120 - something my printer does not support at all :(.
Plus, I'll have mess with anti-adhesives (otherwise 'crazing' it will not help much, it will remain stuck to the laminate).

It seems that cheapest way is just printing with ABS and dissolving it in acetone. It is not even *that* bad compared to most other solvents, just smells. PVA is also highly hydroscopic (duh!) so some filament enclosure with dessicant will be required...
harv Posted - 11/03/2019 : 16:18:29
If you can print polycarbonate, acetone will make it craze into tiny easy to break pieces. Even though PC is expensive it has double the modulus of HIPS so you can make the shell thinner. Also has a higher heat distortion temp than HIPS, so if there is heat from the epoxy curing the PC mandrel should distort less than HIPS.
Balor Posted - 11/03/2019 : 13:41:02
Yea, I know. It is pretty damn expencive though, and not stiff at all (so will need to be prined with a lot of material to avoid distorting during vacuum bagging). But it does seem like the best option if you want to avoid aggressive solvents - I've bought some lemonene, and brand of hips I have refused to be dissolved in it, only becoming kinda 'gooey'. Damn polymer chemistry...
alevand Posted - 11/03/2019 : 11:56:57
You can by PVA filament that dissolves in water.

Tony Levand
Balor Posted - 11/03/2019 : 10:14:14
Btw, experimenting with TPU bladders is more or less a failure: It is extremely hard to make them airtight, and even dunking into dilute glue does not seem to really work in the long run (and is stinky).
I think a better idea is to 'paint' it with a liquid latex, or two-part polyurethane/silicone. Plus, 3d printing TPU is pretty stiff by itself (shore 90Aish) so even a thin wall is rather resistant to being stretched/compressed, will only truly work for larger bladders where forces are much greater I presume.
Balor Posted - 10/31/2019 : 14:36:13
Did a test of carbon 'lug'- printed an ABS shell, vacuumed a few layers of carbon around it, than dissolved it in acetone (took awhile, process is rather stinky). Turned out pretty good, except inner diameter somehow ended up smaler than the 'mandrel' - I presume due to print lines. Good thing I've had some leeway! Should have printed it bit larger and polished it first I presume - maybe acetone-polished, by brand of ABS is pretty damn resistant to this stuff.

Next try - HIPS and lemonene (damn expencive though, not exactly mountain dew either, but at least does not stink as bad).
Balor Posted - 10/08/2019 : 08:59:32
Prusa (the printer I've got access too) recommends shore 90-ish filament, so fairly stiff.
Hmm... Bowden or direct extruder? Yours look like direct one, should handle any filament provided you turn off retract (better print in 'vase mode') and keep speeds slow and steady.
Admittedly, I think it is easier to simply buy vibration isolation mounts from amazon, they come with mounting bolts attached, and I think that their rubber has better compression set then printable TPU. On the other hand, you have much more design freedom that way, may print it hollow for instance for 'air suspension' :).
SpiderMonkey Posted - 10/08/2019 : 08:03:45
Wondering how to get a good valve seal on the end of one. Maybe just Gorilla Glue a valve in the end. Probably a better idea for a mold that doesn't get smaller at the ends.

For straight stuff, forgetting about air, thickening it up, and squeezing it at the ends with a couple washers on a long screw should do the trick to push it outward. (IRRC That's how Garrie H. does custom head-tubes, headset-ready.)

Prusa (the printer I've got access too) recommends shore 90-ish filament, so fairly stiff.

Didn't realize until you prodded me that one could print custom elastomers for seat mounting, etc. to try to take out a little road buzz. I'll have to tuck that away for the future.

Balor Posted - 10/07/2019 : 07:18:07
That's where 3d printed bladders may come in handy. If you wrap it PE bags first - fully reusable as well. TPU filament is relatively expensive, but not by much.
You may leave the bladder to be cure inside the mould though, it should *really* add some vibration damping to the part (vibration damping properly of carbon is massively overblown if you ask me) at expense of some weight (and having to print more bladders).
SpiderMonkey Posted - 10/07/2019 : 06:54:53
Interesting. I'm getting closer to done with the wife's upright bike, and then back to the homebuilt recumbent(s). I need to test my inner lug molds. I bought a yard of unidirectional and a yard of 45-degree biaxial to go with some plain weave to make these.

I've got some 22mm x 19mm ID handlebar stock coming, with a 19mm mold for making join lugs to be one of the first tests.

The biggest savings for me will be if my lug mold works for seat making corners. I'd have to make up to a dozen hand joins per seat with a 2 x 45 degree turn, which is a PITA. Lugs from this will hopefully be faster, stronger, and a lot easier. I need to find a skinny inner tube, though. The diameters on those ends are 15mm OD.

I need to stop at REI. They've got a busy cycling shop and they've been happy to let me root through their box of popped inner tubes to find salvageable ones for this kind of thing. Re-use before recycle and all that.

Balor Posted - 10/07/2019 : 06:39:18
Next step in 3D printer assisted composite manufacturing :)

Seems extremely cool if you ask me. I don't think you even need to design any means to inflate the bladder - Just print it "airtight" using close tolerances to inner geometry (plus composite layers) and put it under vaccuum.
You will not get very high compression this way, but I don't think that is really important for a homebuild - still tons better than hand layup.
SpiderMonkey Posted - 09/19/2019 : 08:46:40
I have made dozens of designs for tooling, so it's been a good learning process. I'm going to try a couple bearing drifts next. Those are usually expensive, and I never have the ones I need. I think solid plastic would be plenty good for pressing into hubs, etc.

I've got some improved bike jig bits printing right now, lolz.

strayray Posted - 09/17/2019 : 20:13:25
Looks like you're putting that 3D printer to great use!
SpiderMonkey Posted - 09/13/2019 : 20:46:50
Getting the hang of this 3d printing thing. I needed a little rotating v-block to help support the wife's upwrong frame for tacking on the chainstays and seatstays. This little 2-part design I made was quick and easy and works really well.

This BB shell holder is sturdy enough, but it's PITA to thread the rod through the cones, crews, shell, ends, etc. Next time (if I get ambitious and print another version) I'll slot the hole and print a block closure for it that just snugs down with an M5.

SpiderMonkey Posted - 09/12/2019 : 07:45:15
Finished the disk stick made with a hunk of scrap aluminum tube and some 3-d printed parts.

SpiderMonkey Posted - 09/10/2019 : 19:49:29
Originally posted by Balor

That's great! Can you point out at some materials you've found particularly educational when it comes to 3D desing, or maybe even make a few hints yourself?
So far I find that tinkercad maxes out my ability to model in 3d, and using 3d printed jigs with carbon tubes will REALLY come in handy in my next project.

I watched a couple of youtube videos by a guy named Lars about Fusion 360, then I just dove in and started making stuff. I use Fusion, export the components as STLs, slice them in Prusa slicer, and I print at 0.15 or 0.20mm layers.

You can insert McMaster-Carr parts right info fusion, so, for instance, when I needed to quick design a rotating piece of jig for my aluminum extrusion jig, I could just grab a couple of lengths of the extrusion I bought from them and work up my part right there on the same stock:

That might not be news to the engineers and machinists here, but it was a cool thing for me to get using. Those extrusion pieces are the ones I'm using, so I just built that rotating fixture (circled) and I'll print it in 2 pieces tomorrow, and it'll be pre-drilled to go together with M5s. I tap the PLA, making the pilot holes 4.25. It taps well and holds just fine for these purposes.

The jigs really are the best thing I've made. These made it simple (and it likely would have been impossible without them) to put together my wife's upwrong on the kitchen island with no swear words.

SpiderMonkey Posted - 09/10/2019 : 19:37:45
My 50mm tubes are supposed to be 46mm ID. They're pretty close. They're a lot closer than I could print and mold. But I'll stick with bonded in aluminum. I've got a lot of CF over aluminum in the stable, and I've never had a problem with any of it. (Fork ands, BB shells.) The one time I froze an aluminum mandrel inside a CF tube (and it had separator film) and swapped it back and forth between hot and ice water to try to get it to loosen up, it gave me plenty of confidence that CF over glass over knurled aluminum in epoxy isn't likely to loosen up in my use.

I've had problems with black CF just heating up so much it heats up the steel screws holding stuff and they loosen. I park black CF in the shade all the time as a result.

Listening to the Fancy Boys and their Incredible Creaking $6,000 Carbon Upwrongs on the trail means I'm not a fan of any press-fit BB systems, and even less so considering the crankset hoops I'd have to jump through to work with that product. I have more than half a dozen cranksets sitting around already for british threaded BB shells.

If I didn't maybe I'd experiment.

Balor Posted - 09/10/2019 : 13:20:06
By the way, by using a 46mm id carbon tube (it has to be very smooth though... or you can print the mandrel and make it yourself using carbon sleeves) and using a interlock BB like this:
You can get rid of aluminium insert in the frame (which is prone to delamination sometimes, due to thermal expansion coefficient mismatch), and save some weight.
I've heard that such a system indeed eliminates creaking and allow the cups to be pressed directly into carbon.
I'll try to do it myself.

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