disc mounts on to a retro frame? am i out of order?

[Uncle Grumpy]

Further to the above... here's a bit of process related stuff...

I used a wheel and clamped a cable disc caliper to the rotor, "bolted" some cardboard to the mount to give me a rough template. Also did the same for the support brace to get it roughed in. In the photo below, it's been cut and trimmed to make it a little sexier than a squared piece of steel.



I transferred the cardboard template across to some steel to make the mount, also using some international standard dimensions that you can track down on the interwebs.



I also made a jig to mount the mount so the mount could be mounted. There are commercially available ones available, but I used threaded rod, nuts and also a rotor to check alignment.



Then comes the marking, trimming, test fitting, trimming, test fitting, trimming... etc. Measure twice, cut once? Bullsh*t. Measure once carefully and trim dozens of times until you get it sitting right. Grind off a little at a time. I should point out that this is all done with fairly basic tools, scribe, rule, angle grinder with cutting wheel and another with a flap disc, disc sander, bench grinder, various hand files, pedestal drill, proper drill bits, emery paper, centre punch and hammer, and a solid vise.

These are of course what I consider to be basic tools. I own lots more tools, but owning anything less than the types of tools listed above indicates a character flaw and I would be wary of you if we passed on the street.

Oh, and a brazing set up. You could also use a TIG welder. You could get away with a MIG if the frame was made out of chunky 4130 - not so anything thin walled. I'd try to avoid using a stick welder. I used a Bullfinch torch and BBQ gas.

Part 2 to follow...

 

[Uncle Grumpy]

Part 2...

Eventually, you get the mount sitting flush with the frame, and at the correct offset to the axle. Also, you'll need to hack out some space for the caliper to sit.

I should add that you should continue to check the alignment of everything as you go. Like, make sure the jig is sitting in the dropouts correctly, all that sort of palaver. I also had to knock off the higher of the 2 rack mounts to fit the mount.



Eventually, you'll get the mounting alignment and then you can fire up the torch, put on your brazing goggles and pretend you're Tom Ritchey.

You'll get it brazed up. I know you can. If I can, you can, because I'm average at everything so you'll likely do far better than me.

Do a test fit, and find that everything works just as it should with no rubbing of the disc*.



*Okay... I had to shim the caliper across with a couple of washers - big deal. Moral of the story is "yes, by all means add a disc mount and don't be afraid to do it yourself if you have the tools.

If you don't have the tools, get the tools. Tool ownership is the correct way to live your life. Do things with your hands, people. Build character.

 

[nodding dog]

Nicely done and some proper shed engineering!

I was wondering how you were going to keep the disc tabs perfectly aligned whilst still allowing access for the flame and brazing rod but that picture illustrates it nicely.

 

[bikeworkshop]

Disc tabs are quite cheap and save a load of work and calculations.
For the bracing tube I use a length of seatstay - that way the thickness and alloy match reasonably well so the heat and braze flow quite evenly.

Using Tubes from a scrapped frame should be ok if you clean them up well

 

[markoc]

Happy to send pics/measurement of the OE disc tab on my P7

 

[Uncle Grumpy]

Nicely done and some proper shed engineering!

I was wondering how you were going to keep the disc tabs perfectly aligned whilst still allowing access for the flame and brazing rod but that picture illustrates it nicely.

Thanks. I enjoy that kind of stuff. Even better when it involves learning new skills and problem solving... and buying new tools.

There's plenty of space to get the torch into the inside of the triangle, wasn't a problem. The way I did it was probably a lot of overthinking things, but that's probably just how I'm wired.

Disc tabs are quite cheap and save a load of work and calculations.
For the bracing tube I use a length of seatstay - that way the thickness and alloy match reasonably well so the heat and braze flow quite evenly.

I agree... but I made mine myself because the doctor said I needed more smugness.

 

[Skülly2]

I've had a Thorn eXp converted for disc by Winston Vaz, he added a brace too and some hose-guides (I left on the V-Brake posts because I liked the idea of it being un-converted, so to speak). Again a not super-special frame, just a nice frame. It was totally worth the effort, the bike is a dream to lug camping gear, on-off road, steep descents etc. My Dreamboat-bike now.

 

[novocaine]

Part 2...

Eventually, you get the mount sitting flush with the frame, and at the correct offset to the axle. Also, you'll need to hack out some space for the caliper to sit.

I should add that you should continue to check the alignment of everything as you go. Like, make sure the jig is sitting in the dropouts correctly, all that sort of palaver. I also had to knock off the higher of the 2 rack mounts to fit the mount.

View attachment 992152

Eventually, you'll get the mounting alignment and then you can fire up the torch, put on your brazing goggles and pretend you're Tom Ritchey.

You'll get it brazed up. I know you can. If I can, you can, because I'm average at everything so you'll likely do far better than me.

Do a test fit, and find that everything works just as it should with no rubbing of the disc*.

View attachment 992153

*Okay... I had to shim the caliper across with a couple of washers - big deal. Moral of the story is "yes, by all means add a disc mount and don't be afraid to do it yourself if you have the tools.

If you don't have the tools, get the tools. Tool ownership is the correct way to live your life. Do things with your hands, people. Build character.

This is how I made my disc brake adapters to run 210mm rotors on IS mounts to IS caliper (Formula B4) when the brake was designed for 180 front and 160 rear.

obviously without the brazing. I made the cardboard template in plywood though, so it could be tested (ish) before milling it from aluminium.