Why don't all frame jigs have indices?

[steve garro]

I think they all have their own particular idiosyncrasies that you have to get used to.


So, I guess my point is that its not the fixture that builds the frame, its the framebuilder, and a good and straight frame can be built with any of them.

Dave

TRUTH

I've built on five different fixtures, and man………one day I said "Hell yeah, I've EARNED scales!"

It's faster - but yeah - you can make a bike or fuck up a perfectly good set of tubes on anything.

I have to say some jigs made certain kinds of bikes better then others, for sure.

- Garro.

[incepi]

I still do not understand how one jig assures that tubes are set in the same plane, and another jig does not provide that assurance. Which one does and which one does not? How do you know? Does it even matter if you are going to use heat and mechanical force to set the tubes into plane anyway?

[devlin]

I wouldn't care whose jig I used/bought (I don't have one) I would measure and 'zero' it before I used it. Meaning I would check it to see whether it was in fact in plane and adjust accordingly. Even Don's jigs I would check. As good as Don's in house QA is you just never know they might have missed something. Also I don't/wouldn't use the jig for that alignment. It would be tacked and taken to the table. One joint brazed at a time and checked that the geometry is still good against the jig and then back to the table. This I have learned from here, from Dazza and from my own work.

[Eric Estlund]

Don't assume that tools made with the intention of doing the same thing (holding bits in space) do it equally. I've used a number of fixtures, and the one I own is the best I have used.

Heat and leverage can change things, but the starting point is the starting point.

As others have mentioned, poor building on a great fixture will yield a bad frame. Building to a poor fixture is just a waste of time and materials. How accurate and how repeatable are based on your needs- I prefer to have the most accurate and easy to use tool I can for this.

[Mike Mcdermid]

I still do not understand how one jig assures that tubes are set in the same plane, and another jig does not provide that assurance. Which one does and which one does not? How do you know? Does it even matter if you are going to use heat and mechanical force to set the tubes into plane anyway?

Neither does anyone else

Learn to differentiate between precision and accuracy

It becomes very obvious why a fixture can get anything in plane, but can get stuff close enough

[incepi]

It's possible that a less expensive jig is as good as or better than a more expensive one. Nobody can be certain. There is no industry standard or certification. There is no independent study or test to refer to.

I wonder if large factories have a method for calibrating jigs. Something like a frame that has been determined to be in plane, with centred and perpendicular dropouts, bottom bracket, and head tube?

[bencooper]

You're assuming large factories build straight frames ;-)

I recently got one of Jim Stein's frame alignment jigs, and just to play with it I tried a bunch of production frames - some of them were way out. A Nicolai had the rear triangle over 10mm out of line.

Still rode well, however. What I think matters for alignment is that the steering axis is vertical when riding - on a diamond frame that's the same as saying that the HT and ST are in the same plane. That's something you can get good enough with practice and the Mk.1 eyeball. Other things it's nice to get straight, but does it matter if they're slightly off? For professional pride, yes - for how the bike rides, not so much.

[Mike Mcdermid]

It's possible that a less expensive jig is as good as or better than a more expensive one. Nobody can be certain. There is no industry standard or certification. There is no independent study or test to refer to.

I wonder if large factories have a method for calibrating jigs. Something like a frame that has been determined to be in plane, with centred and perpendicular dropouts, bottom bracket, and head tube?

of course there is anyone who served a toolmakers apprenticeship or is aware of calibration will tell you there are standards and tolerances , a good read so you have an understanding is moores "foundations of mechanical accuracy" it wont tell you fuck all about building bikes but you will have a much better understanding of how fixturing and accuracy are not mutually dependant

[Amaro Bikes]

mitering>sequence>fixture

[Doug Fattic]

Most professionals I know use an alignment table to get the tolerances they want. The fixture holds the tubes in the right relationship where it is spotted (and sometimes pinned) to keep them there and then on to the table where things are checked and adjusted to be put into the same plane. Where the accuracy of a fixture really comes into play is in the rear triangle. If whatever holds the rear dropouts is off by a millimeter that difference is magnified almost 3 times out by the rim. This is where the tolerances and robustness of a fixture really come into play and why the expensive ones made to a higher standard do a better job.

Classic builders with simple tooling got around the chainstay length problem by using horizontal long slot dropouts with adjuster screws. Verticals don’t allow that slop. Of course it is possible to build an accurate rear triangle without a fixture when a frame has a bottom bracket shell with sockets by using a dished and true rear wheel to dial in their length. The chainstays can be slid in and out until the wheel is right in the center and then brazed in a sequence to help insure they stay there. This method just takes a lot longer and is fine for hobbyists not concerned that time is money.

[mmoore]

from a non-framebuilder... just a bike hobbiest who built a bike frame...
plywood, an angle, some flat surfaces (not an alignment table) and a frame can be made.


its not fast, its only as accurate as you make it, but it worked.



indices on your jig are only going to be as accurate as you make them. know your jig and its faults and you will be better off than trusting a manufacturer to tell you that 73 degrees on the head tube fixture is actually 73 degrees.

[steve garro]

I still do not understand how one jig assures that tubes are set in the same plane, and another jig does not provide that assurance. Which one does and which one does not? How do you know? Does it even matter if you are going to use heat and mechanical force to set the tubes into plane anyway?

You are at the point where you are confounded by the realization that there is no limit to what you do not know - I suggest maybe building a few hundred more & reporting back with your conclusions.

Much shall be revealed.

Also, I think you are looking for affirmation, not truth.

- Garro.

[e-RICHIE]

It's possible that a less expensive jig is as good as or better than a more expensive one. Nobody can be certain.

It's not about the fixture, it's about the fixture-er. I am certain atmo.

[Amaro Bikes]

Why doesn't life have indices?

[EricKeller]

I still do not understand how one jig assures that tubes are set in the same plane, and another jig does not provide that assurance. Which one does and which one does not? How do you know? Does it even matter if you are going to use heat and mechanical force to set the tubes into plane anyway?

Last question first, you can't really use mechanical force to align frames any more, the tubing will not comply. Typical steel tubes are not straight. It's easy to pretend they just have a bow, but probably there is some twist too. So the fixture is really just a suggestion more than anything. I have considered trying to measure how far out my fixture is, but in the end a flick of the torch could change that. Take a tube, heat up one side to dull red, and see what shape the tube is when it cools

[incepi]

Why doesn't life have indices?

We'd still come out twisted and bent anyway, wouldn't we?

[Will Neide]

We'd still come out twisted and bent anyway, wouldn't we?

But we're still a blast to ride.

[Mike Mcdermid]

But we're still a blast to ride.

I knew a girl once she was a..............no ...no

[edoz]

I wonder if this will make Mike's head hurt.

[incepi]

I knew a girl once she was a..............no ...no

Was she twisted and bent?