Rear Triangle Fixture.

I think all I do is build fixtures. I have a fixture for just about everything. Having apprenticed in a prototype / tool and die machine shop back in the late 90’s and still working in the same field today, I guess I feel the need to develop a fixture everything. I built the frame fixture (jig) and that should cover everything I need to do on a bike frame. Or does it?

You see, due to the nature of working with lugs I have gotten decent at going without fixturing or with minimal assistance from fixturing. So, after I built a frame fixture I kind of started to feel it was over constrained. While I know this isn’t the case, I’m actually having a little trouble wanting to use it to finish a frame that I started a while back.

This fixture isn’t revolutionary or anything, heck, it’s probably hardly even evolutionary, but I got the idea on fucking Pintrest of all places. The idea is using the HT and ST from your front triangle to project the alignment of your rear triangle.

As with most fixtures, you need good straight surfaces. While there are probably straighter, a couple pieces of 1/4″ thick aluminum angle are lookin’ mighty fine for this job. Also, it’s cheap and easy to store.

I’ll be using my 2″ Paragon tube blocks with this fixture so I need a 2″ spacer with holes for a bolt and the dummy axle. Like this.

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Next is drilling holes in the aluminum angles. I used this block as a guide since it has the exact hole size and spacing I need.

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Trim the ends of the angle to clear the dropouts.

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Bolt it all together. Then using 3″ C-clamps to hold the aluminum angles to the tube blocks on the HT & ST I can align the dropouts and set the ST to chainstay angle.

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I can also use this fixture to align the front triangle for brazing the DT to the BB lug. Simply leaving off the rear triangle and clamping the HT and ST together in alignment. I have a feeling I’ll be using this one a lot.

Next mission is to finish this frame up. I’m looking forward to doing the triple triangle seatstays on this one!

Thanks for reading and PLEASE ride safe out there! Now that it’s dark at 5:15 you’ll need to light yourself up like a Christmas tree to be seen!

Allan Varcoe

EDIT!

Paul Ketelaar from Australia gave me some pointers on a way to really make this fixture more effective. There is 2 separate stages and I have only done 1. But I did make the parts for the second stage also. Stage 1 mod is basically adding a swinging arm to the end. This allows me to push the dropouts down (or up) without having to fiddle with the clamps that hold the fixture to the tube blocks.

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Stage 2 involves another segment between allowing articulation. This allows the use of traditional vertical road dropouts. You see with a horizontal dropout Stage 1 works fine because the dummy axle will slide in the dropout while the angle is being adjusted. Not in a vertical though.

Thanks Paul!

Check his FB out! He’s a badass!

https://m.facebook.com/steeltherideideal/

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