Thursday, January 21, 2010

Rackufacture: Rear Rack Jig

Glen was wondering if I might be interested in building a rear rack for one of his new Elephants. I'm pretty sure the Pope is still Catholic.

The timing was good because I've been thinking about fixturing and jigs and this gave me an excuse to get my feet wet. Glen gave me his construction drawing for the frame and I worked off of that to develop a drawing for a rack jig. It was supposed to be something simple and then it mushroomed into something way more complicated (my special talent), that could be adjustable so that you could build racks of the same style for different bikes, 'cause every one he builds is a little different. Not that he will ever ask me to build another one after he sees the kind of krap work I do, but it's not about that. It's about really wanting to do it and having half a reason to justify it. Hmmm, sounds like a lot of my bike purchases.

I don't have any machine tools, which limits how accurate the thing was gonna be and so I knew it probly wasn't gonna be a huge success this first time around but I also knew it was time to jump in, because you can only learn so much from reading and looking and then you have to learn from doing. I'll end up making lotsa mistakes, learning from them, hacking it up and itterating and making it better. So I guess that's my apology in advance for a C- on this first report card. Nuff said.

Ideas on paper . . .



Transferring the ideas from paper to steel . . .



A thousand hours later, all done . . .



This rack design uses that same two attachment points as most off-the-shelf racks: bosses on the dropouts and bosses on the seatstays. Here's the dropout end of the jig. It's adjustable for varying widths . . .



Here's the seatstay end, along with the feature that allows vertical adjustment relative to the dropout end (this will make more sense a few pics from now) . . .



Here's the feature that allows horizontal adjustment relative to the dropout end . . .



This is where the decks sits and is adjusted to the right elevation . . .



This is kind of a side note, but I have a problem with my method for making these large-radius bends. See the flat spot at the start of the bend? That ain't gonna do. I have some plans and parts for a home brew bender sitting on my bench . . .



Laying out the front struts . . .



Cut to length and ready to cope . . .



Another side note. I'm having a helluva time controlling heat with my new torch. Some days I wanna switch back to the bulky old POS. But the new one was a Christmas present to myself, so I can't, or I'll hurt my feelings. I have switched from a #1 to a #0 tip. That's helped, but I think I might have to go to a #00. Either that or develop some actual skills, 'cause I'm still getting things too hot. I can tell you're dying to know, so here's the diff between the #1 and #0 . . .



Front struts brazed on the topside . . .



Here's where this might start to actually make some sense. The deck and top struts are brazed in place. (Yup, same clamps, good eye.) The vertical strut assembly is brazed up and bolted to the jig. But the odds that I could braze this up and it would bolt to the frame are slim to none, so the vertical strut-to-deck joints will have to be brazed off the jig and on the frame . . .



As luck would have it, I met up with Glen at last night's bike hang and he told me that the frame hadn't been painted yet, but was going in tomorrow, which is now today and almost tomorrow. He said I could have it overnight. Found a 5-gallon can of midnight oil in the shop . . .









This pictures don't show it because I don't want them to, but things did not work out well. Nothing fit right. And since I was on deadline, I pushed too hard, which made everthing worse. I had to hack and re-work some stuff. And then I finally got it dialed in (so I thought), brazed up and finished off. Somewhere in the wee hours I closed up the shop and took the whole thing in the house with me overnight so it wouldn't get any rust blooms. I was exhaused but happy, and passed out sitting up, looking at it.



This morning, I drug my ass outta bed and before I could even get one sip of coffee in me, I took a look at the rack and noticed that it was badly misaligned. You can't really tell in this picture, but it's off in the left-right direction. Shit.



Glen say's he thinks it'll be alright. I'm not so sure. There's no easy fix. At this 5 minutes I'm not sure what went wrong, but I'll do the forensics and fix whatever the hell happened. You'll probably never know, because that would be the most boring blog post in the history of the universe. But if I do another one and get it right, you can be damn sure I'm gonna make you look at it.

5 comments:

Alistair said...

Pat,
very nice first attempt on the jig. Building a rack remotely from the bike (and having it fit well) is tricky. The only examples I've seen that were successful were jigs that Robert Beckman (the Sakkit touring racks) and Bruce Gordon built. Beckman's jigs were a combination of plywood (or maybe it was MDF)and De-Sta-co clamps. The racks were tig'ed so no risk of fire.
Here are a couple of links to pic's of Bruce's fixturing, http://www.bgcycles.com/pics9.96.html
http://www.bgcycles.com/pics9.97.html
Unfortunately, these don't show how the rack sub assemblies go together.
You'll notice that pro builders only make racks for customers who are also buying framesets. That way they can use the frame as the jig (and also make money, since there's clearly no money in racks).
I have no doubt you'll figure out your jig and get it to turn out accurate and repeatable results. Good luck!
By the way, if you're ever in Seattle we (you, me, Alex) should all get together for a rack making pow wow and share ideas.

Cheers.

glen c. said...

Pat- don't sweat it, I took the whole thing out back and smacked it on the bumper of the van as hard as I could. Looks perfect now.

Pat S said...

Alistair,
Thanks for the comments and info. The bender handle that moves from bend to bend on the BG jig is very cool. Yeah, it would be great to hang out with you and Alex and talk racks (and other bike stuff) sometime. I'll get in touch next time I'm headed your way.

Glen,
Now I know why you keep that van around.

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Anonymous said...

Pat
I don't know if this applies, but I read where you get things too hot whilst brazing. When I was in school, I was taught to braze with a slighlty carburizing flame. If you don't or haven't brazed in this flame setting fashion, it may be worth a try.