Vintage Workshop
Services for Brough Superior motorcycles and their contemporaries

Enfield 8" brake drums  last update: 2/2006
Above, you can see the raw casting.

I built the pattern with a thick ring around the brake drum, so I can machine 3 types of brake drums from it:

* the "Norton" style with 3 cooling fins
(casting the 3 fins would make for a very complex pattern including a core box)

* the late 30's style with one central fin,

* the early style, which has no fins at all.

However, cutting the 3 fins with a parting tool proved a critical operation. Diameter, i.e. cutting speed, is the enemy here. You need a big and sturdy lathe to drive in a parting tool on a 240mm diameter, and then the tool has to stand it!

In the end, the only way seemed to use an indexable tungsten parting tool. With this, however, you can only produce square fins.

When most of he material has been removed, I use a radiused HSS tool to make the fins look nicer. This means very slow revs and lots of patience (and frequent sharpening of the tool...)

Machining the rear side of the drum is relatively straightforward then.

Next I do the inside...

... and a preliminary cut on the brake surface. I finish this only after mounting the drum on the hub, as otherwise you will always find the surface slightly triangulated due to the pressure of the chuck jaws.

This is an early style hub without fins, which will receive the glorious aluminium cooling ring (of debatable technical merit...)

I leave a small ridge near the front of the hub: it stiffens the drum and gives the shrunk-on cooling ring a positive location.

So here is a finned drum next to a raw casting. A couple of hours at the lathe and another hour to clean up the lathe and yourself...

I found it is a waste to cut off all of the thick ring for making the un-finned drums. So I made another pattern for the un-finned drums now.

Unfortunately the foundry who used to cast these drums for me has let me down now, so I am, once more, searching for a foundry who will cast a small batch in good quality at an acceptable price...

Any kind of feedback to is appreciated
(sorry, this is not a clickable 'mailto:' hyperlink. If you want to write me, please type my address in your mailer. )

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