Making my own custom parts

I've been thinking a lot about what it would take to produce custom crankarms.

I have researced backyard metal casting for a couple of years, with an eye toward figuring out how to make my own cycle parts when I need something for a project that doesn't exist in the size or the bolt pattern or general configuration I want.

I especially want to do hubs, for a few different reasons, but lately I read something about the mechanical advantage of longer crankarms, and I'm wondering what would happen with radically longer ones, I'm thinking 200mm to maybe 260mm, as opposed to the 180mm limit of what's readily available.

In Human powered vehicle applications, where you're designing the frame from scratch anyway, you can design around the longer cranks, so there's really no reason not to experiment.

I think it might be a way to get better torque for moving a heavier vehicle, and for my pedal RV project that will become important.

I know there's probably a way to use math to determine exactly what the difference in leverage would be, in each gear, even, but I don't know how to do it.

I kinda want to do it the hard way anyway, just for the experience of having done it.

Making the blank for the mold is easy, except for the square taper hole for the bottom bracket spindle. I'm not sure how to handle that, whether I want to mold it into the piece, or have it machined in after the casting process, like the threads for the pedal holes. I might be able to tap those threads in myself, too.

The spider portion is the next most difficult, mostly with keeping everything centered. It's embarrassing that I don't have the technique for dividing a circle into five equal parts memorized by now, because that's what I need to do. I have several sheets of thin wood, and I plan to build up each of these parts in layers, then trim and smooth for making the molds.

I have to form the spider by making it into one or two layers of that particular crank arm.

I can't wait to try this. I've been reading up on the process to the point that I think with the specifics close at hand for reference and enough time put into the preparation, I can create my own beginner's luck. 

This is another place where metalworking seems to begin with woodworking.

Metal casting becomes another carpentry project. You have to build special fixtures for holding the sand the part is in, etc.

I'm even going to have to build the furnace for melting the aluminum, including making my own refractory cement. 

Once my work space is ready. 

Feels good to be able to say even that. For years now I've been either using someone else's space or just not doing anything at all, besides getting frustrated. This past year has been really bad. I'm just not happy about Anything if I don't at least feel like something is Coming, that some opportunity is even Possible.

That's the thing that drove me craziest about living in Delaware at my mom's house.

In the Cities you're not allowed to do Anything- You need permits for this, there's fines for that, the neighbors bitch about every little thing, and when they complain it's usually to the city or the cops, not to your face.

I tried to build a little place to work at my mom's house, but there was just so much resistance from every possible direction that I got fed up with it and came back to Montana.

So anyway, Cranksets of unusual arm length.

It occurs to me, sitting here thinking about it, that the blanks don't have to be made of wood.

There's a 3D printing shop a few blocks from my house, and a crankarm is a relatively simple shape. I know the basic dimensions I need. This is a good project to learn that type of software anyway.