Witch Wanding to Change Rear Space

[jclay]

Has anybody here done enough witch-wanding to have a good idea of how much it can change, say, the rear space of a frame. Is changing a 130 rear space to 135 within it's capabilities (the bridges haven't been installed)?

Any other tips, like how hot (color), do you do it in steps, that sort of thing. Do any videos exist? I have the witch-wanding article in BQ V12, No. 4 but I thought I'd seen a video somewhere, too.

I'll report the results of a test I've set up, and plan on doing today, with a BB shell and a couple of chainstays but if anybody else has experience to share it would be helpful.

Hat tip to Freddie Parr who mentioned this technique a long time ago. He was a good guy.

Thanks in advance.

[e-RICHIE]

You can wave the flame inside the RH chain stay and watch the RH dropout move outboard; same with the LH side. But after the metal cools it comes in. The operation is mostly if not all myth. You're better off muscling the dimension.

[jclay]

You can wave the flame inside the RH chain stay and watch the RH dropout move outboard; same with the LH side. But after the metal cools it comes in. The operation is mostly if not all myth. You're better off muscling the dimension.

I muscled it and now I'm off to the bridges.

Thank you Richard.

[jclay]

I muscled it and now I'm off to the bridges.

Thank you Richard.

Curious about this, I brazed a CS into a shell and witchwanded it about 40 times, taking before/after measurements and qualitatively describing the heat applied (e.g. diameter of hot spot, more (or less) orange, a little bit long/short dwell). Of course the metal moves, the trick being to have it move the amount you want in the direction you want, absolutely reliably. I allowed the metal to cool between iterations and I worked both sides of the stay.

I quickly discovered that I needed to support the DO end so that it couldn't move away from the side being heated but was free to move towards the heated side. Heating an unconstrained stay didn't generate even reliable direction of movement (relative to the side being heated), never mind amount. Once I constrained movement as described (before iteration 10) I started to get reliable movement in the desired direction but the amount varied between nothing and several mm. Around iteration 30 I converged on a standard heat application with small changes to size, color or dwell, and started to get the amount of movement I desired most of the time but still had some results being a couple mm off.

The upshot is that I didn't get to the point of being reliably able to move the DO, say, 0.5mm vs 1.5; about half of the last 10 iterations were successful in that way but that left the other half off in the weeds. The experimentation was performed before I corrected the rear space for the contraction due to bridge installation; thought I might try it if the results were good enough; they weren't. I cold set it and don't see attempting witchwanding on real frames but it was an interesting and useful side trip.

[e-RICHIE]

Braze up the rears such that, when bridges are added, the assembly contracts into the desired O.L.D.

[jclay]

Braze up the rears such that, when bridges are added, the assembly contracts into the desired O.L.D.

Used to do that but thought I could finesse things so I wouldn't need to; a time or two it turned out that way.

The contraction that occurs when the chain stays are brazed in but before the bridge is added: I never added extra rear space to account for that, just bent it back to the desired rear space and fit the bridge, which will now be back to OLD +2 or 3mm.

Thanks.

[e-RICHIE]

Used to do that but thought I could finesse things so I wouldn't need to; a time or two it turned out that way.

The contraction that occurs when the chain stays are brazed in but before the bridge is added: I never added extra rear space to account for that, just bent it back to the desired rear space and fit the bridge, which will now be back to OLD +2 or 3mm.

Thanks.

Witch wanding, and even cold-setting, isn’t finessing. Develop a sequence that yields the desired result after brazing. Points end up/will end up in a predictable, repeatable spot.

[jclay]

Witch wanding, and even cold-setting, isn’t finessing. Develop a sequence that yields the desired result after brazing. Points end up/will end up in a predictable, repeatable spot.

I meant finesse with the brazing.

[e-RICHIE]

I meant finesse with the brazing.

Repetition. Routine. Relentlessness.