Cargo Rack, Part 3

In this series: Part 1, Part 2, Part 3, Part 4.

Fillets!

I finally got around to doing the fillets on the rack.  I like doing fillets.  You can see what you're doing a lot more easily than you can when you're trying to flow bronze under a lug.  Something about there not being a sheet of metal between you and what you're working on.

Here's one that I started to clean up.  You can see that the fillet forms a nice smooth transition between the tubes.  There were a few spots where I didn't build up quite enough filler for that, but they're inconspicuous.  Considering how thick I made the fillets overall, I'm not worried about it  being structurally unsound.  

If I'm feeling especially neurotic I'll fill the little gaps in with J.B. Weld.  Since that particular epoxy has a bunch of powdered metal in it, the powder coat will stick to it.

Sneak Peak

In our next episode, I'll get into how I'm making the wooden deck for this rack.  It's all lasers and power tools!

In this series: Part 1, Part 2, Part 3, Part 4.

Cargo Rack, Part 2

In this series: Part 1, Part 2, Part 3, Part 4.

Yesterday I started brazing the rack, which was pretty exciting.  In this step, I just laid down a bit of bronze to hold things in place.  Later, I'll build up fillets.  A fillet is a meniscus of metal that joins pieces together.  When done properly, the metal creates a nice smooth transition between the two.  

Tabs

I cut the tabs out of some sample sheets of chromoly steel that I had lying around.  They're basically little metal guitar picks.  When the bike is done and all of the attachment points are installed, I'll drill them.  That'll let me level it out if something weird happens.  

I'm pretty sure, but not positive, that the sheets will be thick enough to resist bending when I'm carrying things.  If I was using it for loaded touring, I'd double them up.  I still may add a bit of reinforcement.  

Once the tabs were done, I slotted the vertical tubes of the rack, lined them up with the tabs on my basic sketch, and then squeezed them with a pair of pliers just enough to keep them from shifting (much).  

Brazing

I started brazing by securing the tabs.  I did each of the four connections one at a time.  The hard part was dealing with the last joint.  It kept wanting to spring free, as the rack widens slightly near the rear (for aerodynamic effect, or something).   I solved that with the sheet-metal vice grips that appear in one of the pictures below. 

Next, I attached the rails, where a bag will hang.  I clamped the first on one end, rotated it level, then tacked it on the other.  Then I was able to remove the clamp and tack the remaining end.  

The second rail was about 100 times harder, since it had to line up exactly with the first.  At one point I probably would have hurled it across the room if there weren't other folks around working.  Thankfully, after quite a bit of trial and error, it fell into place and I was able to tack it down before it slipped and hit me in the eye or something.

Here we go!  I need to finish the fillets and grind the ends a bit, but the look and geometry work.  

Next time: finishing fillets, adding tabs for the wooden deck, and making the strut to connect it to the seat cluster.

In this series: Part 1, Part 2, Part 3, Part 4.

Jigs and Silver

Jig

I put together my Half-A-Jig (tm) today.  I'm using one piece of extruded aluminum from 80/20 and a couple of v-blocks designed for drilling tubes.  One v-block is cut down to accommodate the lugs on the head tube, the points of which would otherwise keep the tube from lying flat.

The idea here is to help me align the head tube and seat tube so that they stay in plane, without spending $400 bucks and weeks on the materials to make a full jig.  Basically, I wanted a bit flat metal bar, but I didn't want to deal with the issues involved in clamping a round tube to said bar.  I had assumed that, in the process of getting it set up to work with the specific dimensions of my bike, I would have to shim things to get everything flat.  

I was pleasantly surprised to find that the two tubes ended up perfectly in plane!  I had a bit of wavering, but it was between exactly level and .1 degrees off... I think I'll live.  I may add some simple pipe clamps to hold things down so that I can tilt the whole structure to make tacking easier. 

First Silver Lug


I've decided to try my hand at doing lugs with silver.  Silver melts at a lower temperature and has a bit more surface tension and a lower viscosity when melted.  For these reasons, it can be a bit easier to work with than brass.

A practice joint mitered, lugged, fluxed, and ready to go!

Results: I burned some flux.  Having worked with brass mostly before, this isn't super-surprising.  Temperatures that would be fine with brass are way outside of the range that I should have the metal while working with silver.  I need to train myself to keep the flame back and moving more.  If I can spread the heat out more instead of focusing so much, I should be able to draw things through better.

When I cut it open, I found that things were fairly well filled in most places, but still had some voids that I wouldn't want in a finished product.  I'm going to do some more practice with random pieces of tubing and see if I can get past that point before I use the rest of my practice lugs.