Hi folks I would just like to horn in on this one. I have probably turned at least a thousand rotors and brake drums as an auto mechanic for over 50 years as well as automotive machinist for most of that time in one form or another. First let us look at turning brake drums. In the proper machine you would have a solid shaft through the spindle with a thread and nut on each end. On a dedicated machine the nose of the spindle would have a slight tapered seat in the end of it and the shaft a matching taper cone on it which would seat against a shoulder on the shaft. On the other end, outboard end that will be, you have a similar situation. This guarantees that the shaft is running true to the bore. In the case of a rear drum we would have a cup that would fit on the shaft with it's mouth facing out away from the headstock. This cup would be about 5" or so in diameter and would have 4 or 5 sections cut out of the rim about 1/8" or so deep leaving about a 3/4" section of rim intact between each cut out section. These would be faced off to be at perfect right angles to the shaft. This would support one side of the flat surface of the drum. You need two of these, one for each side of the drum. Now the other thing you would need is a cone to centre the drum on the shaft. These cones can have a taper on them of about 10 or 15 degrees and only need to be about 1 1/2" long. Usually you would have about 4 different diameters to cover the various hole sizes in the drums. I had them up to 6" diameter for truck drums. You would place a spring something like a Chev starter solenoid spring inside the cup and then the cone. Set the drum over the cone and then the other cup and spacers as required to bring the nut up tight. The spring holds the cone in the centre of the drum. In our case the boring bar would come in from the headstock side of the drum with a tool bit set in the end at an angle. In the case of a drum lathe the spindle moved in and out not the boring bar. And finally you need to have a rubber chatter belt wrapped around the outside of the drum or in most cases you will render the drum useless when you start turning.
Now how can you adapt that to a regular metal lathe?
First let us visit the previous writer idea. Yes you could take a piece of axle and cut the end off. However this leaves a serious problem. How many axles are you going to cut up for all the various drums you will encounter and where would you find them in the first place never mind the cost. Second, an axle is only turned true and parallel for a very short distance where the bearing rides, not enough to support drum turning. Third, the raised portion on the end of the axle must match the hole of the drum exactly to keep the drum concentric to within .001' or better. With only this short portion of support you would also need support from the tail stock centre.
Now I must remind you that Southbend had a series of booklets covering the automotive trade and one of those covered turning brake drums. I have a set of these bought from one of our venders but can't put my fingers on the just now.
I will make some drawings later as to how you might proceed to turn drums on your lathe.
Then there was the subject of turning rotors, flywheels also fit into that category although they may have so many hard spots in them that you would need to grind them most of the time using something like a tool post grinder.
To hold a rotor or for that matter a front brake drum you would use much the same method of holding the part. Early machines just used cones but later machines used a sphere shaped cone. Remember that the early drum hubs used ball bearings where later hubs used tapered roller bearing. Although dedicated machines cut both sides at the same time this is not necessary. It won't make any difference. And we always ended up having to cut more off one side than the other because of groves etc. The only thing that is extremely important is that you do not make them thiner than the safe limit specified for each make and model of vehicle. VERY IMPORTANT.
The same goes for brake drums. You will also need a chatter band for the rotor.
The one for the rotors are usually about 1/2" wide by 1/8+ thick and usually has some pieces of lead attached to them and are made from rubber. These prevent chatter or squeal marks from forming on the surface. For drums they can be 2" wide by 1/4" thick with a flat hook attached to one end for slipping under the belt which is about 3-4 feet long and stretch wound around the drum. So I hope you folks got some help from this and not found it too intrusive.
I will be back soon with some pictures of how I would set up for these jobs.
Regards, Nick
