Progress on the radial rack

December 22, 2010

My shipment of steel finally showed up last week, and I got down to work on D’s rack at last, and it’s coming together—with a bit of luck I’ll have it done this week!

After bending up the deck perimeter and the ‘hub’ circle, I pinned both joints with short lengths of tubing, split down one wall, and rolled into a diameter that would spring against the inside wall of the deck tubing, and self-jig the joints.

D's rack

Here you can see the deck and ‘hub’ compared to the drawing, and getting checked for squareness.  After a bit of alignment, I braze up the joint on the deck.

Once this is re-checked for squareness, I start brazing in the ‘spokes’, or radians, to connect the circle to the deck.

rack spoke

In this shot, I’m using a pair of stainless steel spokes and some duct tape as a makeshift jig to keep the short radian centered and in-plane with the rack deck during brazing. The spokes are resting on the outer deck, and are being tensioned by the tape, and acting against each other like a spring—the matched tension equalizes, and centers the radian tube perfectly.

Same routine again here with the circle. If you look closely, you can see that I’ve lined up one of the splices in the circle with the radian miter—I did the splices in the circle with some of the leftover silicon bronze that melts at a higher temperature, so that when I braze the radians, if I’m careful, the splice joints shouldn’t re-liquefy and flow out. Another way to tackle this problem would be to use silver for the radians, and bronze for the splices, the idea being the same—to have the higher-temperature material used on the first sub-assembly, and the lower-temp material on subsequent joints in the vicinity.

Brazed up and compared to the drawing again.

Here’s the second radian cut, mitered, and brazed in. Rather than working my way around the deck radian by radian, I’m adding every-second-radian first. This will allow me to check alignment at each stage and make sure everything’s lining up in-plane, and make corrections. Having a skeleton in place before adding the other radians should help keep everything aligned as I add the other pieces. If I added the radians one by one, the heat could have an incremental twisting effect, and things could end up veering out of plane pretty quickly.

Here’s another radian, mitered and ready to rock.

I’ve started fluxing and pre-loading mitered tubes with a bit of brass filler prior to brazing up the joint, which helps to both speed up the creation of an internal fillet, and acts as a good visual indicator of brass penetration around the perimeter of the miter. After the brass pre-load has all flowed around the joint, I build up a small external fillet.  Definitely getting much faster and cleaner.

And that’s it so far—time to get back into the shop!

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