cold setting - need reassurance!

[GazK]

I just discovered the rear fork on my summer project is 120mm, not 126mm as I had (stupidly) assumed. I have a 130mm hub arriving any day. So I'm into cold setting the frame. Has anyone undertaken this terrifying-looking process? Sheldon says its ok but I need reassuring! PS frame is 531

 

[Gerry Attrick]

Chill. The proces is brutal-looking but is in reality straightforward providing you take your time and use only the gentlest of pressure.

I used this method on my old 531 BSA Prima and found it much easier than I thought it would be. You need very little weight on the plank to effect the required bend, but you must check the you bend each side by an equal amount to avoid your tracking going out of alignment. Use Sheldon's method of checking this with a string tied from one rear dropout to the other around the headtube and measure the distance from the string to the seat tube.

Start by using the smallest pressure and measuring, then increasing the pressure very gradually until the correct bend is achieved. Good luck.

 

[GazK]

Thanks gerry - more good advice. Should I do a string check after the first fork is bent or wait till I've done both? And did you bind the bridges to prevent them popping? I've heard some people do this but Sheldon doesn't mention it

 

[GazK]

Ps derailleur fits fine. It's the only thing that does!

 

[Gerry Attrick]

I bent both sides and achieved the spacing I needed before worrying about track alignment. After all, it is relatively easy to correct that afterwards. I never gave the bridges a thought as if they popped then the brazing was poor and IMHO the frame unsafe anyway. And even if they had popped, it would be no great shakes to get them re-brazed.

 

[TheDoctor]

Bending steel is a morceaux de gateaux. It'll be fine.
It's exactly what a framebuilder would do, except they'd charge you for it. I've cold-set 531ST from 126mm to 135mm and it was easy. No problem at all

 

[GazK]

Bending steel is a morceaux de gateaux. It'll be fine.
It's exactly what a framebuilder would do, except they'd charge you for it. I've cold-set 531ST from 126mm to 135mm and it was easy. No problem at all

Thanks both of you - just the reassurance I need. Now where's that 2 x 4?

 

[delstron]

Thanks both of you - just the reassurance I need. Now where's that 2 x 4?

I used the alternative 'threaded rod' method with success. Did need to exceed the target dimension quite a bit to ensure it sprang back to 130mm

 

[chillyuk]

I have never done this job, but thinking about it do the drop outs have to be adjusted to keep them square with the wheels, or is the actual amount of deformation so small it is not an issue.

(Is it square with the wheels or parallel).

 

[TheDoctor]

I don't think there was enough difference to measure, plus I wasn't sure I could get them parallel, so I left them alone.

 

[Gerry Attrick]

If opening out the drop outs by 10mm or so, then the divergence from parallel created is insufficient to cause problems......provided they were parallel in the first place!

 

[hubgearfreak]

Should I do a string check after the first fork is bent or wait till I've done both?

use brickalyers line, it's stretchy enough to be on the job throughout.

 

[GazK]

Well I finally got up the courage, and after a couple of overshoots, its all sorted. I was using almost my whole weight though!

A couple of tips for anyone else thinking of doing this:

- use a pair old old bar grips, cut lengthways and wrapped round the seat tube, to protect the paint

- use a digital caliper. Much easier to gauge small movements