The Big Think

April 20, 2016

R2 Update

Filed under: The R2 Project — jasony @ 8:38 am

It’s been a while since an R2 update. I probably need to write a lot more but I don’t have time right now (I’m actually building instead of writing about it).

About two weeks ago I decided to mill up the little leg “cups” that hold the leg hubs. It’s an easy part to overlook. Fortunately, I was able to find some aluminum tubing with an inside diameter (I.D.) that was close. I got a 12″ piece, chopped off a 5″ piece, and proceeded to very slowly mill out the I.D. on the lathe.

IMG 2003

IMG 2004

That wall is less than .125″ thick. It’s really delicate and I was worried about milling through it so this cut took me about 2 hours. I’m slow on the lathe but the tool scares me so I play it as safely as I can.

Once I got the I.D. correct I just cut off a piece that was the right length (two, actually). The part separated early before the cutting tool had cut completely through, which I was initially upset about (oh no! sanding a delicate part!)

IMG 2005

but it turns out that the little edge you can see on the left was pushed in a few thousandths of an inch and so it fits perfectly inside the mating hole and acts as a guide! I’ll have to chamfer off a tiny amount on the inside of the hub when the time comes so the hub will clear it, but since it’s inside the leg you’ll never see it. And besides, the little guide ring makes alignment and gluing MUCH easier. So an unintended mistake turns into a win! Happy accident.

In the past week I’ve worked about 20 hours at Techshop on the Horseshoe parts. Well, one horseshoe. I water jet cut out the 8 layers (out of .125″ aluminum 6061) and test fit them together.

Here’s a pic of the sheet of 6061 before and after water jetting

IMG 2007

IMG 2014

And here are the layers stacked up on the leg (which is itself just stacked precariously and not welded yet):

IMG 2015

Great fit. I had to file the tab from the water jet off of each layer (2 tabs actually)

IMG 2053

IMG 2052

I bought a set of files from Lowes since so many of the TechShop files are corrupted with steel or not in good shape. Add it to the budget.

IMG 2054

Once I’d filed away the tabs I sandblasted each part to give each layer a bit of “bite”. My idea here was to lay down a coating of aluminum epoxy to bond the layers together. However, once I got the epoxy and did a test run on some scrap, the scrap debonded (it broke) with very little pressure. So instead I VERY carefully aligned the eight layers and clamped them together, then spent the next three hours in the machine shop drilling and tapping some holes so the layers could be held together with screws. Somewhere during this process (power washing after the sandblasting, I think) some of the layers got very slightly bent. So now my perfectly flat horseshoe ends are flayed out. Ugh. I’m going to TechShop tonight to talk to a professional welder to see if it’s possible to clamp the layers together and tack weld them. In preparation for that I spent a few hours grinding a bevel on each layer so that when they’re stacked up there’s a little “V” shaped groove on the edges between layers. Hopefully if the layers can be welded this will give the aluminum rod enough “bite” to hold the layers together after grinding off the excess material.

Keep in mind that I’ve worked about 40 hours on just this one horseshoe. I haven’t even cut the parts for the second one yet. I’ll give the welding thing a try and if it works I’ll go ahead and commit to the second one. If, however, the welding is a total bomb then I’ll step back and rethink how I’m doing the horseshoes. I really really want aluminum shoes but if it’ll delay me too much I’ll do MDF now so that I can move on. Those parts are easy to replace in the future if/when I choose to revisit them. It’s been so long since I’ve seen forward momentum that it’s easy to get discouraged. So I’m considering making some temp parts and replacing them in the future if I get stuck at a certain point. Droid building is the Everest of Nerddom, as I’ve said. So there will be some parts of the journey that feel like you’re stuck. But I don’t want to get so mired up in one part that I get discouraged and wash out.

I’m frankly terrified to weld these things. I’ve spent a lot of time (and not inconsiderable money) getting the horseshoes to this point and if they warp under the heat (something I’ve been warned about) then it’s back to square one. But if I’m so nervous about messing them up that I don’t move forward then I’ll be stuck here forever. So I guess I have to do something. Hope I don’t screw it up. I might hire a pro to do these particular parts, or at least to just tack them in five or six places so that I can come back and Lab Metal them and sand them down.

Looking forward, there are so many aluminum parts that need to be welded that I’m almost certain I’ll have to learn to TIG weld. This project is about learning new skills but TIG is extremely difficult to master and represents a major detour while I develop the skill. Probably about 40-60 hours running a mile of bead to get good. In the meantime nothing will get planned, designed, or built. But there are so many parts to weld that hiring someone to do it doesn’t make much sense. My Techshop friend Bill May gave me a pep talk the other night that helped a lot. I was getting a bit discouraged thinking about the ridiculous challenge this project represents. Bill had some really kind and encouraging words for me and encouraged me to learn to TIG and keep moving forward. Frankly, I kind of needed it and appreciated it more than I think he realized.

It seems like at every single point in this project, from major design decisions down to where to clamp a part on the mill, there is some sort of little issue that crops up. For example, while tapping the holes in the horseshoe stack I discovered that my tap was about 1/16th too short. But since the stack was already clamped and the hole drilled I had to solve the problem right then. No coming back to it later since I couldn’t take it off the mill until the holes were drilled and tapped. I managed to figure out a solution but it took a lot of seat-of-the-pants thinking. The entire project is like that: nothing easy, everything fights you. So Bill’s words were really helpful. Keep pushing ahead. Eat the elephant one bite at a time. Don’t look at the summit– just look at the next step to be taken. This will take another three or four years (if I’m lucky!) and if I think of the whole project at once I’ll just get discouraged.

Okay, onward.

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