Milling Stainless?

[Muddy Creek Sam]

Howdy all,

I inherited a mill from my Dad, and have used it on mild steel. What do I need to know about milling Stainless? Not sure what differences might be.:confused:

Thanks in advance,

Sam :D

[jhrosier]

Sam,
Most grades of stainless will work harden instantly if your feedrate is not high enough or your spindle speed is too high.
The speeds for milling stainless are about half what you would use on steel.

Search for the websites of the companys who make milling cutters for feed, speed, and coolant suggestions.

It takes a really good, high pressure lube to tap stainless with a high speed steel tap.

If you machine cast iron with a cutter, don't ever try to use it for stainless after. Even though it may look perfect, the edges will be too dull to cut stainless.

It is not rocket science, unless you do it wrong.:)

Jack

[TCLouis]

is unique for those of us with little experience.

YES, it will work harden in an instant.

Other than that I know nothing about it.

[HeavyMetal]

A lot of the problems you'll face depend on the type of stainless your cutting.

300 and 400 stainless is gummy and you may look at coated milling cutters for that. A286 my require a whole lot more machine!

What is it your trying to make / cut? This may bring better ideas on board.

[Muddy Creek Sam]

I want to despur a SP101 Hammer for concealed Carry. Just thought I would try to do it with the mill. It is not a small nill, About 6 feet tall and was relled in on pipes about 20 yrs ago. Not a Bridgeport but can't remember the Brand.

Sam :D

[johnly]

Cutting fluids designed for stainless are well worth their cost. 303 cuts pretty well, as do the 400 series stainless. 316 is just plain difficult.

John

[JIMinPHX]

I want to despur a SP101 Hammer for concealed Carry. Just thought I would try to do it with the mill. It is not a small nill, About 6 feet tall and was relled in on pipes about 20 yrs ago. Not a Bridgeport but can't remember the Brand.

Sam :D

For that little job, I would just use a hack saw & clean it up with a file & some wet/dry paper afterwords. Hack saw blades are cheap. Use a 24 or 28 tpi.

As for milling stainless, that stuff about it hardening on the spot only applies to certain grades. Stainless actually cuts very nicely if you do it correctly. The biggest problem with milling SS is that it generates a lot of heat. Its the heat that kills your tools, not the hardness. recommended spindle speeds for stainless are usually around 1/4 or 1/5 of mild steel. The next step up from high speed steel tools when cutting stainless is cobalt tools. This is not because cobalt is harder, it's because cobalt takes heat better. Cobalt tooling is actually softer than straight hss tooling. Carbide is the preferred cutting tool material. Uncoated grades are usually recommended by people like Sandvik & Kennemetal.

There are basically 3 things to remember when cutting SS on a mill, or lathe, or saw, or even when you just drill it.
1 slow your spindle speed way down.
2 use very positive clearance angles on your cutting tools (like you would for aluminum)
3 use plenty of flood coolant.
If you don't have proper water soluble cutting lubricant in a flood pump, then trickle a garden hose on the work piece when you cut it. It's stainless, it ain't gunna rust. You need the cooling capacity more than the lubricity. You can wipe the tool dry when you are done.

As for tapping, I've done hundreds if not thousands of tapped holes in 304 & 316 with common cutting fluids & standard gun taps. I've probably single pointed more than that. The mean alloys usually tap better with roll forming taps & those do need a good high pressure lube.

That hammer on your SP101 is probably made from one of the tough grades of ss. I'd make sure to keep it cool when cutting, regardless of what tool you end up using.

The brand of your mill really doesn't matter. Anything Bridgeport size is plenty meaty enough for something like this. Even a half sized machine wouldn't choke on this little job.

[leftiye]

What little work on stainless I've done matches Jim's. I've seen it take out a bandsaw blade in about three seconds. I turned around and cut the piece by hand with a hacksaw. Overall, on a lathe my experience with 303 is that it is obstinate and tough to cut. Your hammer may already be hardened - abrasive cutting disc time.

[uncle joe]

One other thing with stainless, if you care wheather or not it looks good, don't use a tool on it that has been used on mild steel. This includes grinding wheels, sand paper and anything else used to shape it. This will contaminate it and cause it to rust where the tool was used.

[HeavyMetal]

If I was gonna de spur a hammer on a revolver, stainless or otherwise, I wouldn't use a mill.

Using a paded vise I'd clamp it in and get one of those re inforced cut off disc's you can put in a dremel tool. This would be the wheel you can actually see reinforcing fiberglass threads in!

This will cut that spur off in about 6 seconds and then you can use the cut off tool to rough shape your hammer area and then finish it off with a good 00 fine cut file and polish with 600 grit sand paper.

I've seen Pro gunsmith's do it this way and do it real fast!

[Big Dave]

Like several others have said, so much depends on what stainless you are working on. Most of the 400 series machine much like common low carbon steel. 303 machines quite well but must be done at a slower surface feet per minute rate. 305 and 307 get progressively nastier and you do not want to tangle with 347 and the inconel alloys without some really solid industrial duty machines and tungstun carbide cutters.

[Jon K]

Go slow, keep it flooded, and keep the carbide sharp.

You probably won't encounter 347, as it is a specialty application, mostly for high heat application, has good weldability.

Jon

[45caster]

Slow and easy lots of coolant

[machinisttx]

Low RPM, heavy feed. Use carbide if possible, but IME, most Bridgeport type machines aren't rigid enough to get good life out of carbide endmills.