How To Make A Disc Mount Adapter

From TrialsWiki

[edit] How To Make A Disc Mount Adapter

I have had a couple of people ask me how to do this, so here goes.

For whatever reason, you want to mount a disc onto a bike without a disc mount. This is fairly easy, you just need to be OK at engineering fabrication.

Using one of these mounts means you can experiment with a rear disc brake without changing your frame or rear wheel, (as long as the hub has disc tabs). I did it for about £120, including the wheel and brake.

I also made a small spacer to extend the axle slightly, as the disc mount takes up 3mm of your axle. I don't know how effective it is, but it might give it a bit of extra strength. Don't have any pics though unfortunately. It's a small brass cylinder, with two flats on so it would fit in the dropout.

There are several things to sort out, before you can think about make the mount.

The rear wheel. The mount needs to fit in between the rear wheel and the frame, so you need to have a gap big enough for the mount. I did this by using a Monty TI rear hub. Monty hubs are designed to run in Monty frames, which for some reason, have a smaller spacing between the dropouts. This means that when used in a frame with standard spacing, such as any Deng or Onza, there is a gap of 3/4mm in between the frame and the hub on the disc side. (Snail cams on the inside).

You also need to take into account the amount of dish needed on the wheel. Because the hub needs to be set over to the drive side to get the mount in, the rim needs to be dished to the non-drive side in order to stop it rubbing the frame. This is easy if you know how to build wheels. See Here.

---

Step 1: Setting Up Your Work Area.

Sounds really fussy, but it's important. You need all the tools, a vice and your bike ready to go.

The bike needs to be strapped up or down to something, so that you can whip the rear wheel in and out while you are making the mount.

You will need these tools:

• A Drill. I used a bench drill, which is best as you can clamp your work down to it in order to get a nice, round hole.
• Drill Bits. You will need a 5mm and a 10mm, possibly a few others, you may wish to drill the mount later to make it lighter.
• Hacksaw.
• Various files. A flat, half round and a round file. Large, medium and small versions are good, as you will be filing many different radius curves. Also a set of Micro/Swiss files, these are fairly essential.
• Vice. Can't be done without.
• Scriber. Needed to scratch the surface of the metal so you can make a mark which you can see.
• Angle grinder. Very useful for working the metal down quickly. Although a bench grinder would be even better, I did without.
• Centre Punch. Made for making indents for the drill bit's to locate to, so the holes are exactly where you want them.
• Big Hammer. For hitting the centre punch with and bending the mount. A plastic ended one would be best, as it doesn't damage the surface of the metal.
• 3mm Stainless Steel. The material for the mount. You might be able to get away with using some thicker aluminium, but the wheel would need to be dished a lot more, and I had enough trouble with mine.

---

Step 2: Making The Axle Hole.

Take the steel sheet, and make a centre punch mark in one of the corners, a bout 25mm in from either side, then drill a pilot hole with a 4/5mm drill bit, then the final hole with a 10mm drill bit. The best way to do this is to use a bench drill, and bolt the steel to the table/shelf.

Step 2: Making Cutting The Basic Shape.

You should now be able to mount it into the frame. Put the wheel into the frame with the snail cams in, and nip the bolts up so that the frame is pulled in, but you can still rotate the mount around.

You need to start chopping it away, to get an idea of the shape you’re aiming for, here is a picture.

Step 3: Bending it to fit the frame.

As can be seen from the above picture, the mount needs bending.

The two end sections need to be kept in line at all times, so bend them both a little at a time. The bends also need to be parallel, otherwise the two end sections will not be parallel.

What you need to make sure of, is that the end section runs up the inside of the 4 bolt mount.

AFter you have this, you need to bend it over at the top so it has a 90 degree angle so it goes over the four bolt mount, then you need to mark out the holes to bolt it to the 4 bolt mount, then drill two holes and file them so that they are both oval, so that the mount can slide up and down.

You should now be able to set it up in the bike, but not fit the caliper. To do this, just keep grinding and filing it away until the caliper will fit in the right place, then drill the holes for it and it should work fine.

The last step is to smooth it off, if there is a file mark or a hacksaw cut mark left across the edge of the metal, it could start a crack, so I draw filed the edge all the way round.

You can also drill it out to make it lighter as I have done. Good luck.