I'm confident that if I can get the drum mounted right and turning that I can get it cut.
I should have a spare drum laying around,it sounds like it might be worth mounting up and seeing if I can get the speed down.
Always fun to play. If it works, more power to you! If it doesn't, then you had a learning experience.
How do you guy's calculate the speed?
Ah yes, speeds and feeds. One of the great mysteries of machining!
The "optimum" machine speed (in RPM) depends on 3 things: diameter, material and tooling. Charts will generally give the cutting speed in Feet per Minute for a particular material. You must then calculate how many feet around your workpiece is and from that, how many RPM you need to spin it to achieve the correct FPM. Note that the word "optimum" means for a production shop -- it's a balance point between the cost of replacing worn out tooling vs labour costs of longer machining times.
In general, the faster the cutting speed, the shorter the tool life. "High Speed Steel" gets it's name from the fact it can last longer at higher speeds than ordinary tool steel. Similarly, M2 lasts longer than HSS, M35 (5% cobalt) longer than M2, M42 (8% cobalt) longer than M35, carbide longer than M42, etc. The odds of breaking the tooling on an interrupted cut or chattering machine goes up in the same order because the harder tooling is also more brittle. So: big, heavy, rigid industrial machines taking deep continuous cuts: carbide tooling. Little, shaky Chinese-built home machines taking interrupted cuts: HSS.
Of course, the tooling must be harder than the workpiece, no matter what. So if you have a brake drum with a work-hardened layer, HSS may just round off, gall and never cut into it. You may have no choice but to try the more expensive cutting tools.
Anyway, back to speeds. Not knowing the actual material and hardness, let's guess that it's moderately hard plain carbon steel (225-275 Brinell) and use 70fpm from Machinery's Handbook. You don't mention the diameter of the drum, so let's assume 10" for the sake of this example.
RPM = (12*FPM)/(pi*Diameter) This is not an exact science, so we can round pi off to 3 for quick calculations and simplify that formula to: RPM = (3*FPM)/Diameter = (3*70)/10 = 21 RPM
If you are using carbide, Machinery's handbook suggest a speed of at least 300FPM for that same material (bear in mind that there are all different grades of carbide and other grades can cut at different speeds!) This is typical of carbide tooling -- it can run much faster and produces a better finish when run faster. Unfortunately, it takes a lot more power to do so and carbide generally requires more pressure to cut so it needs a more rigid setup.
The amount of power you have available limits the amount of metal you can remove per minute -- the depth of cut and the feed rate at a given RPM. In the case of your brake drum, the depth of cut must be deep enough to get under any surface hardening. The feed rate must be slow enough so you overlap slightly and produce a smooth finish instead of a thread, but at the same time it must be fast enough to avoid further work-hardening of the material. Some materials work-harden just by looking at them sideways, other materials are very forgiving. With plain carbon steel, a feed of ~.015" per revolution would probably provide a decent finish without work hardening issues.
On your particular machine, you don't have an automated feed -- you have to hand-crank it. At 70RPM, you need to traverse the piece at about 1" per minute, and do so as smoothly as possible. Harold can probably hand-crank it and produce a good finish. I can certainly see the difference between my manual attempts and the automated results!
Anyway, those are some of the factors that come into play. Good luck with your experiments! Harold has obviously been following this thread and can be depended on to jump in and correct any mistakes I have made in the above. If his comments differ from mine, go with his advice! He actually knows what he's doing, I'm still pretty new.