Machining stainless

tcncj · Oct 16, 2017

Hello,
I need some advice about machining stainless. 99% of the work I do is Aluminum. But now I need to make some special nuts out of stainless. I never machine stainless. I will buy some new YG1 endmills specific for stainless.
But which type of stainless would I need? There seems to be allot of difference about the machining quality (303, 304, 316). Some are heat treated.
As far as I know stainless nuts are made out of 304.

rons · Oct 16, 2017

Every piece of stainless hardware I have ever purchased that was stamped 316. The way you listed the grades as machining quality is not something that makes sense. It is the hardness going from 303 (soft) to 316 (hardest). At the yard the owner calls 303 & 304 the machinable grades. You can make nuts out of 304 if they are not going to take a lot of torque for tightening. I usually apply some Optimoly paste when mating nuts and bolts are both stainless.

If you go for 316 then you had better get a few high performance taps.

tcncj · Oct 16, 2017

Thanks for your reply
The difference between 304 and 316 is the corrosion resistance. Where 316 is more corrosion resistant.
I didn't find anything about the hardness?
Nut will be tightened at +/- 100lb/ft

MattiJ · Oct 16, 2017

rons said:
Every piece of stainless hardware I have ever purchased that was stamped 316. The way you listed the grades as machining quality is not something that makes sense. It is the hardness going from 303 (soft) to 316 (hardest). At the yard the owner calls 303 & 304 the machinable grades. You can make nuts out of 304 if they are not going to take a lot of torque for tightening. I usually apply some Optimoly paste when mating nuts and bolts are both stainless.

If you go for 316 then you had better get a few high performance taps.

Plenty of A2 (roughly same as 304) fasteners available around here.
Strenght-vise not much difference between 304 and 316 fasteners. Both A2-70 and A2-80 grades are available as well as A4-70 vs A4-80

303 is the easiest to machine of the mentioned, 304 has a reputation of being real hit and miss.
If 416 has enough good corrosion properties its also nice to machine.

HuFlungDung · Oct 16, 2017

I'd suggest perhaps looking at 17-4 PH. Even in annealed condition it still machines pretty good, and will make a stronger thread. There may be a couple of heat treated conditions like H900 or H1150 available which I'm told would machine even nicer. 304 and 316 gall up when used in threaded applications unless you are very diligent with some anti-seize compound. Hell, they will seize up on your gauge when you're testing the fit!

DMF_TomB · Oct 16, 2017

tcncj said:
Hello,
I need some advice about machining stainless. 99% of the work I do is Aluminum. But now I need to make some special nuts out of stainless. I never machine stainless. I will buy some new YG1 endmills specific for stainless.
But which type of stainless would I need? There seems to be allot of difference about the machining quality (303, 304, 316). Some are heat treated.
As far as I know stainless nuts are made out of 304.

.
304 is often cold finished or work hardened. if you take too much depth and width of cut at a high ipt feed you just break the corners off the tool

Milland · Oct 16, 2017

Hardness will be more a function of the amount of cold working the material sees, rather than intrinsic to the alloy itself when talking about 304 vs 316. The addition of molybdenum to 316 will increase toughness and make it more prone work hardening during machining, so make sure to replace dull cutters asap.

The sulfur added to make 303 does degrade some of the beneficial aspects of 300 stainlesses: Making Stainless More Machinable :

Production Machining

FredC · Oct 16, 2017

I agree with MattiJ, if ultimate corrosion is not needed 416 HT, has a lot to be said for it. Easy to machine, resists galling, stronger than the 300 series stainless. OP said it would be tightened to 100 Foot pounds, resistance to galling may be important.
416HT is easier to machine, finishes nicer, and will be more gall resistant than the annealed 416.

azmachining · Oct 16, 2017

Between 304 and 316, 304 is not as hard on tooling and has a higher machinability then 316, but 304 may not machine as consistent as 316. As for threads if either of them are mating to stainless they will gall if cranked on enough and as previously said you will want to never seize the threads regardless of how often they're cranked.

tcncj · Oct 16, 2017

ok, so 416 heat treated is the way to go?

Limy Sami · Oct 16, 2017

tcncj said:
Nut will be tightened at +/- 100lb/ft

What size thread and what male thread material?

MattiJ · Oct 16, 2017

tcncj said:
ok, so 416 heat treated is the way to go?

Yeah, if you don't need to weld it and medium-good corrosion resistance is enough.

Stainless gun barrels are usually 416R steel. I was about to suggest visiting nearest gunsmith if you need only few short pieces of super heavy wall stainless tubing

Heat treated and extra high quality.
(But since you are located in UK that is probably easier said than done)

rons · Oct 16, 2017

MattiJ said:
Plenty of A2 (roughly same as 304) fasteners available around here.
Strenght-vise not much difference between 304 and 316 fasteners. Both A2-70 and A2-80 grades are available as well as A4-70 vs A4-80

303 is the easiest to machine of the mentioned, 304 has a reputation of being real hit and miss.
If 416 has enough good corrosion properties its also nice to machine.

4xx will rust.

MattiJ · Oct 16, 2017

rons said:
4xx will rust.

So does 304 and 316 if the environment is enough nasty.
But yeah, its not equivalent to even 304.

If it gives OP any scale the 416 is pretty close to 420, a common stainless kitchen knife material.
More alloyed 440 and 304 are around same ballpark in corrosion resistance depending on type of corrosion.

Bobw · Oct 16, 2017

So you can make them out of any "stainless" that you want????

303.. Cuts like F'n butter... You can't screw it up.
Pretty decent on the corrosion resistance.

If it needs to be "tougher".. 17-4 at an H1150...
You can buy H1150 off the shelf.
Has almost NO stainless type cutting properties, but is
nice and strong and very shiny... Cuts just like a
pre-hard 4xxx alloy steel.
Pretty darn good on the corrosion resistance also..

My 2 favorite stainless's.. Cuz they are Fricken Easy to machine, and they
are generally nice and consistent, and they won't break the bank. And
they are SHINY.. An annealed 416 can look like dull grey garbage if you
hit it wrong.

tcncj · Oct 17, 2017

Limy Sami said:
What size thread and what male thread material?

M24 / 1.5mm pitch

Milland · Oct 17, 2017

I would second using 17-4 in a condition 1025 to 1150. Good machinability, good corrosion resistance, better strength than 300 series SS.

tcncj · Oct 17, 2017

I just found out that most nuts for my application are made ouf 316 and polished afterwards.
Just for fun I will order some different types of stainless. Just to see the difference in machining and quality.
Thanks all for your advice

Limy Sami · Oct 17, 2017

Thanks tcncj

24 x 1.5mm, got that, but what's the male or bolt thread material? ....if by any chance it's also stainless, @100 ftlbs torque, there is every chance those threads will gall before you reach full torque, therefore not reach the clamping pressure required ????? ........and you will never / have one hell of a job getting them apart.

tcncj · Oct 17, 2017

The bolt is made of steel.

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