The Big Think

June 21, 2015

JB Fillets

Filed under: The R2 Project — jasony @ 11:24 pm

More Skirt work. I went to TechShop tonight and took a look at the skirt brackets. The JB Weld I set up a few nights ago had cured and looked pretty good. Well, it actually looked like warmed over cow manure (grey cow manure), but it was on the underside/inside of the skirt and will never be seen. As long as the brackets hold and the skirt surrounds keep their shape I’ll be good.

I squeezed a whole tube of JB Weld into a plate and mixed it up and then used a plastic spoon to shape it into fillets on the underside where the pieces met. The brackets I’d JB’d into place a few days ago were holding everything in place while the fresh adhesive filled in and supported the fillets. It was a HUGE mess on the inside but, again, nobody will see that.

So then came the clamping. When we tried to weld the pieces a few weeks ago (and subsequently burned a hole in two of the pieces), we very slightly misaligned the pieces right as the welding bead took. It’s not much (about 2mm), but it’s enough to make the whole skirt a little crooked. You can force it into flatness but it takes some pressure.

Before the JB started to set up I got some clamps and a board and flattened out the slight warping in the skirt. Just as I was tightening the last clamp — **PING!!!** — the bracket that I’d tried to braze with the Alumaloy cut loose. Complete failure.


So now I had fresh, wet JB Weld drying and a structural failure. Well, the nice thing about being backed into a corner is that there’s only one way to go. Onward! I did my best to clamp things down and align all the parts. The nice thing was that, with the failed joint, things tended to straighten out a little bit. Here’s a pic of the failure point. You can also see the great big grey mess of we JB Weld on the inside:



I let the JB set for six hours and went back in to TechShop to check it. Once I took it off the clamps I still had some minor warpage and a few alignment issues but it sat surprisingly flat.

I took out the quarter inch mounting plate and sat it on top of the skirt and, except for the opened joint and some squeeze out (which I’ll deal with later), it all looked better than I thought it would.



I’ll clean up the squeeze out and sand down the scratches before powder coating but how to deal with the failed clamp? Well, there’s a product called LabMetal. It’s a little expensive ($35 after shipping) but basically acts as a moldable, powder-coatable filler paste. You goop it into place exactly like bondo and it fills gaps and adds some structural integrity. Then you can sand and grind the dried paste until you get a good surface for coating (again, exactly like bondo). My hope is that this will not only fill the crack but also add even more stability to the joints and connection points.

My only concern (and it’s pretty minor), is that so far every single opportunity for failure on the skirt has happened, and almost every solution has either failed or added additional issues that I’ve had to deal with. It’s been a constant matter of adjustment and readjustment and fixing problems that the last solution caused. For example, once I put the 1/4″ plate on the newly JB-welded skirt pieces I suddenly realized that I have no way to attach them together except to bolt them to the undercarriage of the frame. The problem is that I want to fill the gap between the two parts and smooth it out so that you can’t see the joint. BUT this means that the parts have to be connected. Before they get attached to the frame.

So. Extra step. I have to drill and tap more holes (probably six or eight) so that I can attach the two plates together. Once I do that and the entire thing is monolithic I’ll fill the gaps with Lab Metal and smooth everything down so that it looks nice.

If this doesn’t work I’ve decided that I’ll go back to square one and recut the parts and rebuild the whole thing. I have the waterjet files and know how to use the slip roller. All-in it’ll only cost me around $30. As a friend of mine at TechShop said, it’s not a failure, it’s just a first draft. I sure hope it works, though. I still have to make and attach the 12 vertical trim pieces but I’ll cross that bridge when I come to it. Or I’ll go back and build a new bridge.

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