I was gearing up to build a frame with no jig. I have a flattish plate, which is actually the hot-rolled steel base of a Park double-sided repair stand. Not aerospace-flat, but definitely bike-frame-flat. Then I started buying Brown & Sharpe V-blocks when they were cheap used on ebay, collected enough (namely eight) for two blocks per tube (front triangle only). V-blocks work as well as the aforementioned Paragon blocks for jigging, but are useful for other stuff, and they work for any tube diameters, with appropriate shims under them. But if you're buying enough Paragon blocks to hold both ends of each tube, then you don't need V-blocks. Maybe get whichever is cheaper. I settled on a particular, common model of B&S blocks so they'd be matched in height despite buying onesy-twosies from different ebayers. Chineseum might be cheaper but I try not to buy crappy tools.
I wanted to build a frame with trad tube diameters, e.g. 1" TT. So, to hold all the tubes in the same plane, I needed two tricks:
- A couple 1/16" thick shims to put under the V-blocks that hold the TT, to bring them to the same height as the DT & ST. I have stainless "welding coupons" that work perfectly, a bit over a dollar each in packs of 10 here. (OK those are too thick by .0025". If you care about such precision, you can sand them down that much easily enough.)
- a 1-1/8" tube or bar to go through the HT, with sliding 'shim' tubes that fit between the 1-1/8" bar and the 30 mm inside diameter of the HT. There's no tube made with those exact dimensions so you might need a lathe or a friend with a lathe to get those shims made. I would make them with a slight taper so they tighten on a HT that's a little bigger or smaller on ID.
With ST, DT and both ends of the HT holder all being 1-1/8", only the TT blocks need shims.
This method depends on tacking or pinning the ST to the BB shell and confirming it is square. A frame stick (flat bar with a screw pointer at one end) is all you need to confirm squareness.
A BB post can be made to hold the BB square to the plate, but it would have to be custom-made to be the exact right height to match the plane established by the height of the tubes in your blocks. And different BB shells come in different widths, which would require shimming the height of the BB post to match. Probably better to just let the BB shell height float, and confirm squareness with the frame stick, tacking and adjusting as necessary.
The hockey-stick frame assembly method is not a requirement but probably best in this scenario. That can be DT/HT, or TT/HT.
I say I "was" gearing up to do this, with filed miters, but then two things fell into my lap: a lathe, which I adapted to mitering the tubes, and a pretty decent jig, made by a local amateur/hobbyist FB. He was taking a machinist training course at community college and this was his class project, so it was made quite well and precisely, though not to my liking in some ways. So I have modified it fairly heavily. But it had "good bones".
Overhauling the lathe, getting it in the basement and set up the way I like, then all the work on the jig, has consumed a year or more of my hobby time that I could have spent building frames. That was fun for me, but you see the trade-off — I still have yet to make the first frame with this lathe and jig. If you'd rather build a frame or three than have all the "fun" of setting up a framebuilding shop, then just wade in. Make like a Nike and
just do it.
Even some long-time pros built without a jig. Didn't the Taylors (Jack Taylor Cycles) just set the tubes on fire bricks with a heavy weight laid on top of them to hold them in place? I saw them doing that in the video, I think it is called "Bicycle Brothers", though I don't know if they
always built that way.
I think the quality and alignment of the frame made this way can be excellent, it's just a lot slower. A jig pays for itself if you're going to be making dozens of frames. I don't know where the break-even point is, could vary by a huge amount depending on what jig you're comparing. A DIY, for example made of 80/20 extrusions, might be cheaper in materials but will consume your life for (probably) a month or more, and you definitely can build a frame faster than you can build the jig. But if you have access to a cheap but adequate jig that you can use right away, then
maybe.
Oh yeah and you need a place to store the jig when not in use, which is non-trivial for most designs, they're bulky. So overall, most beginners should not consider a jig until they're really sure (1) what they like and need in a jig, and (2) whether they really like framebuilding and want to keep doing it, for long enough to justify the jig.
What I'm saying is, do as I say, not as I do.
Mark B