Steel Forks

[S1m0nR]

Re: Re:

thanks kieth ..they must pin the fork legs in also.i wish i could see some photo's
of the method of fork building and how they get it exact.

kevin the gerbil wants to know HOW :xmas-cool:

Hi there,

I made my first set of forks last year at Downland Cycles in Kent. There's less mystery to it than you might think!

The forks are made on a jig which holds the assembled dropouts, blades, crown and steerer in place and then the whole lot is brazed together. The thing that ensures that everything lines up is the crown lug. The steerer tube is a very tight fit in the top and likewise so are the fork blades.

Fork blades (or at least the Reynolds 631 ones that I used) come pre-bent, so you adjust the wheel offset (how much in front of the crown the axle sits) by trimming off metal from the bottom of the blade, then you adjust for wheel/mudguard etc clearance by lopping the relevant bit off the top with a hacksaw.

To get the dropouts straight in the blade, fit the blades into the crown lug and run a file ove the top and bottom - that gives you the correct line. You then cut a slot to accept the dropout.

Next, braze the dropouts into the slots, then you're able to flux it all up and assemble the whole thing into a jig before brazing it all together. The lug us a really meaty bit of metal, as are the fork blades and steerer so it takes quite a lot of heat to get the rod to melt.

Once you've brazed it, allowed it to cool and washed all the flux off with hot water you've probably got quite a lot of filing to do to tidy up. When that's done you trial-fit a wheel into the dropouts and find.... that it's not straight! Things tend to move and buckle a bit with the heat when brazing (especially if you're a beginner) so to get everything precise, you get a bit of wood between the blades and lever them until it all lines up. If you cut everything to the right length and got your dropouts straight then it'll eventually line up.

I'll stick some pictures up in a bit, when I've found them!

Hope that's what you're after. You can see my blog about building the frame here: http://srframebuilding.blogspot.co.uk/ I've yet to update it with the fork building day.

 

[shed]

Re:

so in reality once i file the brazing off if i heat the crown around the steerer it should pull out

 

[S1m0nR]

Re: Re:

so in reality once i file the brazing off if i heat the crown around the steerer it should pull out

Impossible to say for sure without a picture but if the fork crown is the same as the one I used then yes. You don't even need to file off the braze - it'll melt very easily.

As you probably know, repeated heating and cooling of the lug will weaken it so you're probably better off getting a replacement steerer tube ready and then fitting it at the time you remove the old one.

Also, you'd probably better remove the bearing face from the top of the crown lug before heating. It'll act as a heat sink but also you don't want to distort it. Easy to remove using a vice and mallet.

 

[S1m0nR]

Re:



Fork jig




Dropout Trial-fitted before brazing.



Trial fitting blades to crown lug




Steerer tube fitted to crown lug before brazing - note that it passes right through. You have to file the extra bit off after brazing.




Brazed, prior to filing.

 

[oonaff]

thanks s1 r' the jig is a solid beast heavy as hell.truly bomb proof,,chances of finding at a car boot..slim
i wonder if the old fork and stearer could be set in a fire proof mould like fine concrete/plaster of paris? prior to
steerer removal with a grease release agent as a one off for diy.then re applied[new stearer] pinned and brazed ?that way no fear of fork blades moving.or misallignment :idea:[which would be great
the existing steerer was in the right place ]

 

[S1m0nR]

Re:

No need to go to those lengths - just clamp the blades gently in a vice somewhere near the top (but far enough out so that you can get access to the bottom of the crown lug) and then heat up the lug to get the steerer out. The problem you're going to have and it's the only big risk is that you may end up damaging the top of the lug and burning off the area that's been machined to accept the bearing. To try to avoid this, make sure you get plenty of heat to the underside of the steerer - i.e. work upwards between the fork blades if that makes sense. You can afford to burn a bit of metal off from there if you have to.

I've seen this job done and unfortunately that time although care was taken, the lug got damaged. That's why I was recommending having the replacement steerer tube ready to go in as you'll only have to heat it once.

Good luck!

 

[shed]

Re:

thanks mate