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I have a PDF a few pages back with torque specs and grease.
3. Production method. Given the 50mm-70mm of spacers and the use of FDM maintaining preload may be a challenge. Depending on your layer thickness and assuming you have the orientation controlled to prevent shearing, even a 100% infill part is likely 80% as strong as the equivalent injection molded part. It may even be less as it will be hard to get a part that size made without voids.
4. Load on the fork. I don't think there is an issue here with the overall load on the fork with that many spacers, but that will depend on how close to the limit you are pushing things with total system weight, fit, and stem length. Certainly worth checking.
The price of failure here can be high as the resulting bending moment can cause the fork to snap above the headset bearing.
I am really sorry if this comes off as rude, but I think it might be worth taking a step back on this project and clarifying your assumptions about the current design and limitations before proceeding. There are a lot of assumptions about how this will perform relative to the original design that could have serious safety implications.
1. Spacer stack height. 50mm is a lot of spacers to put under a carbon stem. 70mm is playing with fire IMO. Depending on manufacturer that's right at the upper limit of what would be recommended. Most like Trek and Specialized are in the 40mm range for the max amount of spacers. Cannondale is the exception where I think on some models they have said no more than 55mm of spacers. An extra long compression plug like the 90mm ones sold by Origin 8 might help, but the idea of that many spacers is already pushing the limit on designs in an industry that arguably is already playing with thin safety factors.
2. Design. Having a single, rigid, piece will help limit the steerer from bending but this is going to be dependent on getting a great fit to the steerer tube and the cone spacer under it. A split spacer will make that much harder to achieve.
3. Production method. Given the 50mm-70mm of spacers and the use of FDM maintaining preload may be a challenge. Depending on your layer thickness and assuming you have the orientation controlled to prevent shearing, even a 100% infill part is likely 80% as strong as the equivalent injection molded part. It may even be less as it will be hard to get a part that size made without voids.
4. Load on the fork. I don't think there is an issue here with the overall load on the fork with that many spacers, but that will depend on how close to the limit you are pushing things with total system weight, fit, and stem length. Certainly worth checking.
5. Material. I don't know what Velobuild uses for their spacers, but most of this type of stem spacer claim to be nylon or nylon/carbon. UV isn't an issue as most use stabilizers and the end product is considered UV stable. This is also true for many MJF and SLS PA12 based nylons.
The price of failure here can be high as the resulting bending moment can cause the fork to snap above the headset bearing.
3D-printed spacers above the stem are a whole different story. They are not loaded and therefore not critical at all. They are only loaded while you tighten the headset. Theoretical (I ofc do not advise) you could remove the spacers after you tightened the stem bolts.
However, a lot of Allez Sprints use 3D printed spacer adapter for the SL7 stem, as a loaded part...
Sometimes you don't want carbon.Also, I bought it as a frame set back when they still sold loose frames for really cheap.
I dont know if you will get right properties from a resin printer. Even 100% infill might not be enough. Might be worth looking at your material and see how samples lab test and make sure you have a good margin of safety. Or you can tighten a sample up to 4nm or something and see if it creeps enough that you need to retighten it after a few weeks.
My $.02: Once you have the fit worked out using the home printer, get the functional ones made by someone with a nice high end machine. MJF parts are cheap and while glass filled nylons are 2x the price of standard Nylon12, I believe MJF Nylon12GB (also Pa12gb) are what the 3d printed headset parts used on pro bikes use.
I hear ya. If you're set on using a consumer FDM printer, you can design in some holes for metal pins. Then you'd have some more solid material to take up the preload vs the plastic.
Best of luck!
I'm thankful for the two piece design. Can't tell you how many times I missed weaving the cables through dust cap which is one piece and then had to pull all cables out and route them through the cap. If spacers were also one piece one would have to pass all the cables thru them during the routing and before tightening the headset/stem. I wish the dust cap was two piece too. You can just pass the cables in the frame and later assemble cap and spacers.
Ive made some functional spacers. What do you mean one or two piece? Like split spacers vs. not? Or uses either a CF or metal insert for compressive strength?
Regarding the latter, if the spacers are under the stem they need to hold preload. It’s not a lot of force but its safety critical to prevent damage to the steerer. I am pretty conservative with this stuff but personally would only make spacers without an insert out of something like MJF Nylon12GB. It’s the 3d printed material closest in properties to the injection molded nylon 66 that OEM solutions seem to use.
Plenty of examples of 3d printed spacers from Extralite, etc failing.
More pieces means more adjustable, but structurally you'd want less (not that there was a meaningful difference).
However, typical plastics for consumer-grade machines may creep quite a bit under load (not sure if the ones filled with carbon dust fare better). You might have to retension the headset from time to time.
Is the frame one of those modern contraptions with headset parts and spacers being full of holes for cables and stuff? That might complicate things slightly. Other than that, it is doable. I've ridden a bike with a combined headset cone/collar* printed from pla for years.
*Not sure how those parts are called. I mean the conical ring that slips between upper bearing and fork shaft and then the usually more decorative part above that.
