Manufacturing guy-at-large.

More workflow details

Added on by Spencer Wright.

The other day I got a nice email from Xavier Alexandre, which included a few good questions about my update from last week. His questions are here, along with my answers:

XA: It isn't entirely clear for me what guides your remeshing from a mechanical/strength optimization point of view. I get that you are trying to optimize for stiffness so you're trying to maximize the stem virtual hull volume. But this global shape is set at the beginning of your workflow in Inventor. Then you're trying to have an higher lattice density around the mechanical features but how did you set on edges length or thickness. Is it based on gut feeling? If so, do you feel that there will still be a lot of room for weight/mechanical properties optimization?

Yeah - you could definitely call my process "emergent." I know that my minimum practical beam size is going to be something greater than .6mm (the exact number is unclear and will require testing). I know that I want to minimize overhanging features, and that it'll probably be appealing (from a cost perspective) to build the main stem body on its end, so that I can pack more of them into a build plate. I also know that the clamp areas will need some significant surface area in order to not, for instance, damage a carbon fiber part that they might be clamped to. I also know that the threaded bolt holes (which will be M4, but which Inventor exports as 3.2mm diameter smooth holes) will need a minimum wall thickness of about 1mm, and will really want more than that. And I know that the heads of the bolts will similarly need a bearing surface of about 1mm, and that both the bearing surface and the threaded hole will need to be reinforced back to the rest of the structure in order to distribute the clamping load on the part.

In short: Yeah, it's mostly gut at the moment. But to be honest the biggest constraint right now is manufacturability; I need the lattice to be oriented so that it won't require support structures *everywhere*, and am focusing mostly on that at the moment. Once I've got that (and basic mass distribution in areas that I *know* will need it, e.g. bolt holes) mostly solved, then I'll move on to FEA. nTopology Element has an FEA solver built in, and you can feed the results back into the design so that overstressed areas get reinforced. I'm definitely excited to get there, but for now I'm focusing on making something that a job shop will be willing to make in the first place :)

XA: I didn't get the part with the interior Oct-Tet volume lattice at all. Is it gonna be merged with the exterior lattice? A lot of these beams will be surprisingly useful once the whole part is put together Huh?

Exactly - the volume lattice (which is an oct-tet topology - see this paper for a better description than I could ever give you) will be booleaned with the surface lattices to create one structure. If you look at that volume lattice on its own,  you'll notice that there are some stray beams that don't appear to be doing anything - they stick out into the middle of nowhere, and don't appear to be taking any load. But when you merge the volume with the surfaces, the situation changes, and those beams might be more useful than you would have thought.

As it happens, I've been focusing more and more on surface lattices in the past few days, as they're a bit easier to control explicitly - and the changes that I make are easier to immediately grasp the effects of. The "generate multiple individual lattices and then merge them at the end" workflow really isn't optimal for this reason: it takes way too long to understand what the finished structure will work like.

XA: You won't have skins in your design. I guess that for the stem to fit handlebars and steerer tubes you'll need the contacting beams to match the tubes curvature. Did you plan to design the beam shape for this or is it something you'll let for post processing. If so, do you plan to make those beams sturdier to account for grinding?

I'd *love* to bend the beams around the clamp area, actually. Right now I don't have a convenient way of doing that, but I'm looking into it. Either way I'll boolean out the clamp regions before printing, so I shouldn't need to grind away much. 

As you might expect, my thoughts on this workflow are changing as I use it more. It's a rather finicky process, and I'm eager to industrialize it a bit - and improve the areas that are most difficult to reproduce.

More soon!