I’ve been getting a lot of requests for custom forks from customers and as much as I love going to another builder in town and asking to use his fork blade bender, I think it’s time to make one of my own. I am likely going to be accused of over-engineering this, a fact which I proudly own, but I’m hoping to make something that will work well for my lifetime and can be adapted to my changing needs.
The design is missing a few things (fasteners in spots, means of attachment to a table, etc), but the overall idea is there. The die is CNC’d out of 6061 and the lever/clamp arms will be laser cut from 1/4" steel. The roller is currently modeled as a phenolic one from McMaster, but I might switch it back to the Polyurethane version other folks have used. It’s designed around a 225mm (~9") radius, but that’s pretty flexible.
The arm pivots on a bushings that are press fit in the die. I need to think a bit more about how to secure the arms without overly preloading the bushing.
I’d love to hear if folks think this design is sound or if people with more experience have ideas of features they’d implement differently.
Would the cost of the die skyrocket if you designed it to bend both blades at once? That’d guarantee bend symmetry and save time.
You’d probably need a longer lever to make both bends at once, which would likely require a longer clamp for the lever.
Perhaps you can add a little stop at the back of the blade tip clamp so every blade is positioned at the same depth.
The earlier you can start the bend the less of the tip you’ll have to cut off to have that curve continue into the dropout. Otherwise, it’ll have an ugly dog leg in the middle of the blade like the Surly forks. That might mean using a smaller diameter roller to get that point of tangency as close to the tip as possible.
Another consideration is to use a variable radius die. Maybe start at 8" and grow to 10". The narrow part of the blade will bend easier and it’ll get harder the further up you go. My hunk o’ junk bender does this for those tight and low rando bends. I think it starts at 4.5" and grows to 6". Works well for the rando specific blades but it flattens stouter blades.
It’d be great to know what your costs are once you get going. I’d love to upgrade my bender to something as nice as what you’ve got cooking.
I had originally designed around two blades at once, but even the raw stock was 3x as expensive. My machinist brother convinced me to go down to one. It would be possible to just get two dies made and use extra long axles to do two at a time.
Yes! Very good idea!
I had thought about this and my initial design was variable radius (based on this design). I know the rando folks like how that looks, but I think for v1 I want to keep it pretty simple. In theory, the whole design should be pretty modular for different radii.
I’ll keep you posted! Initial cost looks to be $200-250 for the main die and I’d guess another few hundred in hardware/small parts. If I can get my brother to make a few of them, I’ll probably sell a few!
Dunno about the other stuff but I spent a fair few hours recently trying to make a bender for 31.8mm top tubes, 220mm clr out of structural ply. Couldn’t get it to work, if it wanted to kink it would just dent the wood, more support required. That is pine, some hardwood might do the job.
Ended up dropping the tube off at the local bendery. The bender will live again though, probably for bending 25.4 or 28.6 once I have emotionally recovered from the failure
Delrin(acetyl) definitely works well. Vogeltanz made a beautiful bender that allows the die to be reversed. That way you have a tighter radius on on end for French versus Italian on the other. As long as the two curves are tangent I think it’s easy modeling.
His design also uses two side plates to sandwich the die which are steel. This allows you to pivot the big ass handle on a good surface, pressed in brass bushings in this case.
I would recommend having a set screw or something to pin the end of the blade in the clamp. If the blade slips, it will wrinkle.
In Seattle I use a hossfeld bender with a homebrew increasing radius die. It has the advantage of being useful for other things as well as opposed to a dedicated fork blade bender.
I’ll take some pictures tonight of the vogeltanz, and here is a shot of the hossfeld:
Hahn “fork rake is the first thing I look at on a bike” Rossman
I would love to do a segmented fork! That’s a long way off for me though.
If anyone is considering using the idler pulley I linked above, don’t do it! The groove is too narrow. Stick with one of the track roller wheels because they have a wider groove and 90 degree V. V-belt pulleys have a much tighter angle of around 34 degrees.