October 14, 2009

Random thoughts on frame fixtures

First off, for those of you who are interested (ie, those folks in line!) I’m on the mend. I got a solid 4 or 5 hours of work in today and should be back on track full time soon here. Still coughing and wheezing a bit, but the antibiotics seem to be killing the secondary infection I (always after I’m sick) have in my lungs.

Some random fellow posted some pictures of his new frame fixture on flikr recently, which made me think a bit about the fixtures that are out there. For folks who are in the market for one, this might be useful. For those of you who just like bikes, not frame fixtures, it still might be interesting.

The fixture does several things for you – it lets you produce a given geometry (ie, it holds the tubes in the position you want them to be when the frame is done), it sometimes serves as a way of holding onto everything when you’re welding, and it can be used (assuming it’s accurately made) as an alignment gauge as well.

Full-time/professional framebuilders are mostly concerned about ease of setup – if I have to spend half an hour with an angle finder and pieces of string to get everything where I need it, that’s a half hour in which I accomplished, well, nothing, really. Time is money for the pros, and most of them, consequently, use Anvil bikes fixtures, which are meticulously made and thoughtfully designed – they have all the features you need, and none that you don’t.

Here’s a shot of the fixture I used (though mine is a much older version) – the Anvil Journeyman.

This sucker retails for about $3500. A couple others (which I don’t like as well) are the Henry James (about $2500, I think) and the Bringheli fixture ($1300). Some shots of those:

You can see just from looking at them that the Anvil is quicker to set up (everything is clearly marked in terms of angles/heights/distances, and you’ll never need a tape measure, protractor, or angle finder). But is that worth an extra $1000-2000? Figure the quick setup saves you just 5 minutes a frame, and that you do 50 frames a year that you sell for, say, $1500. In a year, you’ve saved a little over 4 hours. Assuming building a frame takes you around 10, you’re already well on the way to paying for the extra convenience in just a year.

If, on the other hand, you just want to make one bike, or a few bikes each year for yourself and your friends, you can go the homemade fixture route. There are a lot of ways to do this, many involving a nice form of aluminum extrusion called 8020. Here’s a link to the instructables page (with other links) for your convenience.

A common misconception about jigs and fixtures is that if the fixture is straight, the end product that comes out of it will be. In fact, the fixture’s only role in alignment is to make sure everything is straight to start out – if joints don’t fit tightly, or the welding/brazing isn’t done well and in the right sequence, the frame (or fork, or whatever) will spring right out of alignment as soon as you take it out of the fixture. It’s the quality of the mitering and the joinery that really determine alignment – while the fixture has a role, it’s not nearly as important as many people think.

So the bottom line is that while I wish the flikr fellow the best of luck, he’s entering a pretty competitive marketplace. Anything requiring that much material and machine time is probably going to have to be pretty pricey – and the Anvil is very hard to beat in terms of convenience and accuracy.

Oh, and if you really want to break the bank, the Anvil Super-Master is the way to go – for a cool $7200, you can be the envy of all the other builders on the block!