The Home Machinist!

As far as cutting/tooling goes I should have what's needed I think.
I've got the disc and drum tooling/bits from an actual brake lathe,I've used them to turn down distributor shafts in my drill press

But as you guy's said I'm also worried about whether the machine can turn the drum appropriately.
To clarify,I have no desire to turn a rotor-only a brake drum.

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.

I'll try and get a pic of some of the cutting fixtures and bits i've got,and maybe just experiment with mounting the drum and getting the speed lower.
How do you guy's calculate the speed?
I'm sure i've got something laying around the shop,be nice to know the correct tool though.
I'll post up a couple pics in a few of the tooling I have available,thanks for the tips.

It only costs me $8 per drum/rotor to have my guy do them,but it would be worth a couple hours of my time if I can get them done at home.
Not regularly,I like giving my buddy the business-just this exception.
I figure it's at least worth trying to get it running true,even if I don't cut it.

Always fun to play. If it works, more power to you! If it doesn't, then you had a learning experience.



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.

Thanks for the formula,i'll put it on the machine where I can get to it fast and easy.
I already have a good calculator in the toolbox

I do know that i've got alot to learn about different grades of hardness etc..
Everything I want to work with is fortunately much softer than the bits i'm using (Al mostly).

I did chuck up a very small peice of lead pipe in it and took a bit out of the interior and smoothed it out.
I was rebuilding my air compressor head and upgraded the intake manifold with it.
The manual feed takes some getting used to but I got it nice and smooth.
I can already smell the purchase of a bigger,nicer machine once i've got a good handle on it.
If for no other reason than it doesn't need to be babysat,though it's fun eyeballing the cut and seeing the fresh work shine.

You mention both charts and the machinist's handbook,i'm assuming the charts are in the handbook?
I've seen mention of the machinist's handbook but have yet to look it up for purchase.
Is there a place to get the charts online until I can purchase the handbook?

What other books,articles or online references would you reccomend?

Some softer metals and plastics need different angles on the tool bits compared to steel -- either blunter so the bit doesn't dig in too deep or sharper to cut rather than scrape. Hardness is not the only factor: there's a balancing act between "hardness" and "toughness" too. Aluminium cuts nicely with a keener edge than used for steel, but brass requires a much blunter edge.



There are some good primers put out by the US military:
Army Training Manual
Navy Version

Do a bit of searching in the "General Discussions" forum on this board and you will find a wealth of other recommended titles that you can buy, but those two are a great starting point.

"Machinery's Handbook" is so named because it is (or at least was originally) published by the magazine "Machinery". It is copyrighted. The latest edition that can be freely downloaded because the copyright has expired is the 15th edition, if I recall correctly. A google search will pop that up in short order. They are up to the 29th edition now. I bought a used copy of the 27th edition on eBay for considerably cheaper than the current one! However, while the 27th goes into considerable depth regarding modern carbide tooling, I was disappointed to discover they have dropped much of the older info regarding HSS tooling.

For quick references, just google what you want to know. Here's a good one on sharpening lathe bits

I have a nice one that I downloaded from somewhere but I can't remember where and it doesn't contain any identifying info, so I'll just attach it.

Thanks for all the info!

I will add them to my favorites,find that free copy and see what I need to do to get ahold of a newer copy.

I should mention that this aluminum I am wanting to machine has yet to be casted.

I'm putting together a foundry since I have plenty of scrap aluminum and used oil hanging around.
I want to attempt casting several things including TB adapters for small V6 engines and even a small easy barrel manifold.
The machine is needed for facing,boring etc.. on the tb's,adapters,throttle plates.
Nothing big,just some stuff i'd like to experiment with at the track.

I should have all the materials to build the foundry today hopefully,and hoping to have a couple badly casted parts that need remelted in the next few days

Thanks for all the great advice!