Hardened metal and home shops.

[Highpower]

What would you say is the maximum hardness (Rockwell C) that one should consider machining using the typical "inexpensive" carbide tooling that might be found in a home shop? Small solid carbide end mills for example.

How hard should too hard be for the average home shop to attempt?
There are hardness testing files that range from 40 - 65 on the Rockwell C scale. If you were to choose ONE file to use as a go/no go gauge for deciding to machine a piece of hard material or not, which one would it be?

[TomG]

Willie,

Rc50-55 is about the limit for standard tooling. Anything harder requires special cutters, machines and techniques.

Tom

[Highpower]

Thanks Tom. I'm in one of those between a rock and a hard place (no pun intended) once again. Do I spend the $$$ to buy some carbide cutters for a one-off project and take a chance of destroying them? Or do I anneal the part to allow for machining, but destroy the hardness the part needs to function properly? (No heat treat oven around here...)

So if I picked up a 50 C test file, I'm hoping that would be better than flipping a coin. If I can cut it as-is, that would be ideal. But I would rather not throw money down a hole buying carbide and then rendering it useless.

If I have to anneal it, the part isn't going to last long, which would also be a waste. Danged if you do, and danged if you don't.

[TomG]

Oops!

I really need to read my posts before hitting the "Post Reply" button.

I meant to type Rc30-35, not 50-55. Hope you haven't purchased your file yet.

Tom

[Highpower]

30???? Really??? Keep in mind I'm clueless about hardness scales.

At what point on the scale would a regular mill/finish file be able to cut?
All I know is a regular file skips right off of the shaft I want to work on.

[Hawkeye]

I don't have a good feel for the numbers, but if a regular file won't cut a piece of metal, I'm not cutting it.

If you have the heat available to anneal the piece, you should be able to harden and temper it. The methods would be more traditional, watching colours and such. Might be worth researching heat treating in the blacksmithing forums. I'd try it on a spare piece of the metal, or at least make sure you have enough to redo it if necessary.

Sometimes, heating the piece part way, then covering it with borax to keep the air off can prevent scaling.

[stevec]

Here's a thread on my recent experience at softening steel to a workable hardness.

http://www.metalworkingfun.com/showthread.php?tid=1237

[Highpower]

Thanks for that Steve.

But I was thinking about more of a "spot" annealing approach than doing the whole part. I only need to extend the parallel slots & grooves forward by 1-3/16".

   

I had an idea in my head for this shank, (SDS-Max) but it's turns out to have been a BAD idea. Oh well.

[PixMan]

I can easily turn or mill steels at 50 to 55Rc with the coated carbide tooling I have. Is it expensive? Not if you know what to buy and how to shop for it.

At hardness above that I have a CBN (cubic boron nitride) insert for turning that can handle over 70Rc. For flat surfaces, I have a surface grinder that makes all but the softest, non-magnetic materials cut like butter. ;)

[Highpower]

Yeah, but you aren't the average bear there Yogi.

I guess I should have titled it "typical" home shops.
I probably only have 3 - 4 tiny carbide end mills at most. And none of them are ball end mills which I would need for 2 of the 5 slots.

I'm sure I could buy another bit with the proper shank for probably less than what the end mills would cost. I should have known better.