Welding jig evolution

Well, my shop space has changed a couple of times since my last post here, but the project is still the same, and has been making some interesting developments in this long time of silence.

My primary interest is in creating human powered vehicles, and the current project is building my next long john style cargo bike.

This one has served me well for about ten years now, but it's quite long in the tooth and there are things about its construction I was never happy with.  

...Like the fact that the basket is crooked, because I just Did it, by hand and by eye without any kind of fixtures at all. It tracks straight and rides really well, but the sides of the basket were kind of an afterthought. i was so impatient to ride it  by the time I go to that point that I rushed through it instead of taking the time, and the results have irritated me a bit since then.

To be more accurate, the current project is developing a System for creating cargo bikes from the available resource of older bicycles, recycled and repurposed. 

The efforts of the past six months have been intensely focused on creating a welding jig for ensuring straightness and accuracy. 

It’s taken a couple of different forms as I thought about it and tried things out,  I have photos documenting the things I’ve tried, but now I think I’ve finally hit on something that will work, and work well.

I’m almost ready to try it out, I the basic structure is finished, and now I only need to create the specific attachments for cradling the tubing and mating up with various shapes.

 

The first idea I had was... Interesting.

I used a flat base and drew a 1" grid on it, intending to use it as a layout tool.

The idea was pretty basic, Use the grid base to keep everything relatively straight, build fixtures to hold all the tubes,

 These blocks were just place holders, of course. They were the only things I could make with enough precision at the time. I didn't have a drill press or any effective means of clamping, and I really wanted to at least mock everything up to get a better idea of what I needed to do for it next

 

I hadn't worked out anything for securing the blocks to the board, or securing the tubing inside the blocks, I was really just playing around with ideas at this point. I decided to actually do the grid and start thinking seriously about using this design because i came up with somehting I liked while playing with the parts:

I do still plan to use scooter frames for putting together a longjohn front end at some point, but this was just an idea I didn't get a chance to complete. Some of the basics of this idea have carried through, though. I figured out how to cut a BMX fork in such a way that the curved shoulders of the fork legs will form a 90 degree angle:

That's something I've kept working with.



That was about 2012 or thereabouts. As it often does, life got in the way, and the parts of this project got scattered.
The next thing I tried took a different route. Instead of the wooden graph base, I decided to build with steel:

The base was made of metal sawhorses and angle steel from bed frames.

I bolted the whole thing together with 5mm cantilever brake hardware, but only at the very ends of the angle steel rails. Each rail was two pieces of angle steel with a spacer between them to create a channel. The clamps in the picture about were for applying pressure on that channel to lock things into place.

I switched to wood for the blocks, as now I had better tools. I used small cut ends of the angle steel itself to create the tabs on the undersides of the blocks, which then slipped into the channel created by the two long angle steel rails. Then the clamps come into play.

This jig worked fairly well at holding the parts in place, but it wasn't as precise as I was looking for. The tubing pieces were now securely mounted into the blocks, held on by screws, but in drilling and cutting the blocks, I was still working by hand. The mounting holes for the screws didn't line up right, making the caps want to go on crooked, the tabs in the bases would want to move around, and it was difficult to get them positioned precisely in the center of the block, so they'd be just slightly off, but when all the parts were bolted in that "slightly off" would turn into "Way off" where the tubes were supposed to butt together.

Cutting the forks by hand was tricky too. It was very difficult to keep everything straight.
And this design fell out of favor as well.

I still have all the blocks from this stage. I'm thinking about ways to integrate them into the system I have now.

I didn't continue working on this for long enough to get past the initial basket shape for the long john and start thinking about how the rest of the bike would interface into it, I just took it apart. I had a better idea anyway.

A couple of years before, someone had shown me a design for a wooden sawhorse.

 I immediately saw the potential, but at the time was sure the bed frame welding jig was going to give me what I needed, so I just put that design on the back burner. I changed work spaces a couple of times, too, so it was all I could do to keep all the parts of my various projects together.
Time passed, and the idea finally came around again. I decided to try it.

It's double layers of 3/4' plywood, so it's pretty hefty. I have more images of how it went together,
but I won't post those right now. It went together okay, with some slight adjustments needing to be made to get the pieces to fit. i had trouble with the notches, because i wasn't sure how to cut them in order to get straight, clean edges that locked without play...

                                                                      Mind the Gap...

I eventually fixed all that with shims and figured out how to keep it from happening again. I had tried to use power tools to cut the first slots, but just couldn't get enough control to keep things straight and tight, so I eventually switched to a hammer, chisel, and wood file for making the various slots and cleaning them up to be able to function.

The finished structure is completely slotted together, everything comes apart and the major pieces all pack flat.
The fixtures that connect the tubing and the donor frame to the jig won't pack flat, but they don't take up too much space. This time I started with the donor frame instead of the basket area, and worked forward.

The fixtures are designed to cap over the main rail, so they can slide up and down for height adjustments.
The vertical slots on the fixtures correspond with horizontal slots cut into the main rail itself, giving the fixtures back and forward to give length adjustment, for dealing with different sized donor frames.

I used bike axles for the threaded shafts here, but as you can see the wheel nuts are too small to properly deal with the width of the slot, so I'll be putting some big old 1 1/2' washers on either side as well.





The fixtures holding the rest of the tubing, the load area, etc,are oriented a bit differently, and so are harder to clamp.

I plan to secure the tubes into place using really long hose clamps looping around the bottom of the main rail. The fixtures pictured and are not the finished article They have an additional block on either side to keep the fixture perfectly upright. I managed to cut and dress the slots for all of these so there is no slop or play.

 With all the rails being the same width, I can position the fixtures anywhere on the rectangle to support the tubes securely without being too close to the heat, except in one place, where the wood will be protected by copper sheets nailed into place on it:

This is the bottom bracket area, It's critical, because it's where the Cargo portion primarily interfaces with the donor bike, as in my previous long john. 

Not the best looking weld beads in the world there, but they were among my very first, and they've held strongly for nearly a decade now, and seen much hard use.

The photos of this area are kind of dark, and the paired horizontal tubes for the load beam have not been cut or coped yet, so it takes a minute to see the relevant details. Sorry. about that. Lighting is an issue in the shop I'm in now. Hopefully you can see just how the bottom bracket shell is contacted.

So that area is going to be capped in metal, because whether I decide to fillet braze or weld for that particular joint, there's no way the wood of the fixture is going to be more than a half inch away from the arc, or be bathed in flame.

I might end up having to find a different material for that bottom bracket shell cradle anyway, but I'm going to try copper sheets and little tiny nails first, because i think it might work.

I don't have enough fixtures made to fit everything up yet, or even to outline the bed/basket area.

That'll be what I'm doing tomorrow.

This catches the project up to the present. 

The first photos in this post were taken in 2012. Most of this work happened this year. This represents me thinking with my hands and working to figure out what I wanted with the actual parts instead of writing very much down, although by the time i got to the sawhorse stage, I'd pretty much given on Documenting vs. Doing the Thing, and started making proper drawings. 

I've actually got a bunch of drawings of my ideas for bike design, but I kept viewing the jig itself as simply a means to an end, to be handled quickly and not dwelt upon, so the real work of building the bike could begin. Once I got over that and started treating the jig as equally important, it was a lot less frustrating to be doing carpentry instead of metalworking.

Soon I'm going to have to publish that stack of drawings.

Anyway, we're caught up to the present. Thanks for hanging in through the whole process here, and I hope you found this interesting, and that perhaps some of this is useful to you. Feel free to ask questions.

More as this project progresses...