Heavily modifying an old frame vs building from scratch

Check out Paul Brodie’s videos. He’s got some clever rear triangle fixtures that are much simpler than a full frame jig.

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i have devoured brodie’s videos over the years haha. i definitely should go back and revisit them though, thanks!

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I’ve done some minor mods of older steel frames as well. Totally worth doing and a great way to keep old bikes on the road (or trail). The flat surface fixture is the simplest and most flexible for your purposes and the tubing blocks can be re-used in the future for clocking the tubes for mitering. A basic 80/20 fixture is also not too expensive and there are many designs out there. But most would require some parts to be machined on a lathe.

I vote flat surface and tubing blocks. Too bad your in New Mexico, I have one I could loan you if you were closer.

-Jon

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Oh, and www.geometrygeeks.bike is a good source for geometry info. But buyer be ware, it is user generated so may not be super accurate. One thing you could do is buy a cheap digital angle finder, that way you can get relative angle for all the tubes. Or put some wheels and tires on it and get actual angles. From there you can figure out miter angles too.
-Jon

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my cheap digital angle finder showed up in the mail today actually! i picked up a miter jig for my drill and while it’s a pretty solid piece, it’s angle scale leaves lot to be desired. i figured the best fix was a digital angle finder.

the more i think about it, the more i agree a flat surface fixture might be the way to go. my biggest hold up is space, my shed is 10x10 and some of the space has to double as storage so it’s gonna be tight but i think i might be able to make it work.

i’m insulating the shed this weekend and putting a sun shade over it to hopefully cool it down in there. currently it’s an oven when the sun’s up!

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do ya’ll think a torsion box workbench will work well as a flat surface, this plus a tube block set? it would take up a good chunk of my 10x10 shed, but it could double as my general work bench/desk for the other stuff i’m planning on doing in there.

i’m having a hard time finding anything local, i had considered building my own bench and using a t slot top, like this one from rockler - https://www.rockler.com/rockler-t-track-table-top-28-x-40
but that top alone cost more than this torsion box bench.

currently still working on getting the shed to be less of an oven when the sun’s out.

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I think it’s good enough. +/-3mm of frame flatness is as much as you can expect without investing thousands into a professional setup. If you have good fabrication skills, you don’t need a certified flat table to get a tighter tolerance.

This video from Paul Brodie does a good job showing two different methods of allignment:

The surface table and the feeler gauge had different results, which probably means both methods are inaccurate.

Where are you located @floppywonka ?

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i’m in santa fe, new mexico.

the torsion bench i was looking at sold shortly after i asked about it so i’m gonna keep looking for now.

i really need to go through brodie’s videos again, the man is such a wealth of knowledge.

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