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View Full Version : Machining 316 stainless, advice?



Willy
04-05-2009, 12:16 PM
I have an upcoming job to fabricate a propeller shaft for a client who is in the process of building a boat.
He has procured a piece of 316 stainless 6 ft long that requires a key way at one end and a taper at the other end, along with a slot and thru hole.

Although I've always had good success with stainless work in the past, and know that it can be a different breed of cat due to it's work hardening properties and gummy nature, I'm not familiar with 316 though.
I do know that it is a more difficult material to work with than the 303,304, and 416 ss that I've worked with in the past.

So any words of wisdom from those with 316 experience would be much appreciated. Just some general guidelines as to tooling types, (hss or carbide), cutter geometry, or any other tricks of the trade that would take the angst out of possibly ruining my day.

Thanks
Willy

lazlo
04-05-2009, 12:26 PM
I do know that it is a more difficult material to work with than the 303,304, and 416 ss that I've worked with in the past.

303 and 416 are Free Machining stainless. They machine wonderfully.

304 and 316 are really nasty to machine. They work harden in an instant, and produce nasty razor-sharp stringy swarf.

Willy
04-05-2009, 12:37 PM
Yes, thanks Lazlo, I know.
The 303 and 416 are nice materials to work with.
The 304, although I had good luck with, is nasty compared to the others.

So won't be in for too much of a surprise if I treat the 316 like 304?

lazlo
04-05-2009, 12:43 PM
So won't be in for too much of a surprise if I treat the 316 like 304?

That's been my experience. Take a healthy cut to keep it from work hardening, and coolant help a lot.

randyjaco
04-05-2009, 01:01 PM
There is a lot of art to cutting 316. Each situation requires different variables. I really hate having to work with the stuff. Keep the speed a little slower than the recommended SFM. Your feed needs to be relatively fast and constant. Use LOTS of coolant. If your feed is too slow, you will instantly work harden the material and burn up the tool. I would get some scrap and do several practice runs until you get it right. By all means use carbide if you can. Cobalt works in a pinch.

Scishopguy
04-05-2009, 04:16 PM
I had pretty good luck with 316L in all the odd parts I made for oceanograpic gear that we maintained and modified. The main thing, as Lazlo and others pointed out, is not to run the tool too fast and never let it sit and rub on a spot. I didn't have the luxury of a flood coolant system and applied cutting fluid from a bottle but still was able to get good finishes. I often had to cut o-ring grooves on case penetrators. The secret is keeping the tool sharp and using a good quality lube/cutting fluid. I had one brand, until it was discontinuied due to hazardous ingredients, called "Trim Tap heavy medium." It was extremely thick and clung to the part no matter how hot it got. THe down side of this product was that it fumed badly and would etch tooling with a brown patina. Probably not good on your lungs either. ;) When that was used up I tried the usual off the shelf fluids with little real success until I discovered Anchor Lube. Strange stuff to say the least. It is like some kind of paste type soap in a plastic squeeze bottle but really works good on stainless steel. MSC carries it. Good luck with your project.

Timleech
04-05-2009, 05:39 PM
I have an upcoming job to fabricate a propeller shaft for a client who is in the process of building a boat.
He has procured a piece of 316 stainless 6 ft long that requires a key way at one end and a taper at the other end, along with a slot and thru hole.

Although I've always had good success with stainless work in the past, and know that it can be a different breed of cat due to it's work hardening properties and gummy nature, I'm not familiar with 316 though.
I do know that it is a more difficult material to work with than the 303,304, and 416 ss that I've worked with in the past.

So any words of wisdom from those with 316 experience would be much appreciated. Just some general guidelines as to tooling types, (hss or carbide), cutter geometry, or any other tricks of the trade that would take the angst out of possibly ruining my day.

Thanks
Willy

I've done a fair number of 316 prop shafts, never had a real headache with one. Usual things as others have said, Use carbide, don't run too fast, decent feed rate, don't dwell, lots of coolant if it's a heavy cut or for parting. Neat oil for threading.
If the hole in one end is for the prop nut, I usually do those in situ with a hand held drill, no problem if you just keep going with a decent bit.

Tim

MaxxLagg
04-05-2009, 07:40 PM
I had pretty good luck with 316L in all the odd parts I made for oceanograpic gear that we maintained and modified. The main thing, as Lazlo and others pointed out, is not to run the tool too fast and never let it sit and rub on a spot. I didn't have the luxury of a flood coolant system and applied cutting fluid from a bottle but still was able to get good finishes. I often had to cut o-ring grooves on case penetrators. The secret is keeping the tool sharp and using a good quality lube/cutting fluid. I had one brand, until it was discontinuied due to hazardous ingredients, called "Trim Tap heavy medium." It was extremely thick and clung to the part no matter how hot it got. THe down side of this product was that it fumed badly and would etch tooling with a brown patina. Probably not good on your lungs either. ;) When that was used up I tried the usual off the shelf fluids with little real success until I discovered Anchor Lube. Strange stuff to say the least. It is like some kind of paste type soap in a plastic squeeze bottle but really works good on stainless steel. MSC carries it. Good luck with your project.


As far as I know, Tap Heavy is still available. We have it at work. And Yes, it works EXTREMELY well on stainless. It is a tapping fluid but works well as a cutting fluid on stainless. The brown patina you describe is actually due to the hygroscopic nature of this stuff. You have to make sure that when you are done for the day to wipe off all surfaces that it touches (tools, vise, table, etc.) good with solvent. It will attract moisture out of the air and rust anything that is not wiped up! It doesn't show up until you come back to work the next day and, surprise!

All the other advise is good. I used to machine 316 all the time and it machines like 304 but just a little tougher. I has a better finish IMO if you get the speeds/feeds dialed in. The main thing we used it for was it's austenetic properties and it's performance in high heat tolerance in resistance welding applications. Good sharp tools, as much coolant/lubricant as you can throw at it, don't dwell on it or it will work harden like nothing else.

DR
04-05-2009, 09:28 PM
A couple points:

I don't let customers supply material if I can avoid it. They almost always buy the cheapest stock they can find. All 316 is not the same, most is not annealed. The chemistry of cheap stuff is not necessarily skewed toward machinability.

When I'm doing a critical part I always buy premium grade material. All the big names in stainless have a premium grade designed for machinability available in the common alloys like 304 & 316. Carpenter, Esco, Ludlum (sp) and others that don't come to mind now all have this type stock.


With premium material you pay more up front, with standard off the shelf material you pay on the other end in tooling and aggravation.

Willy
04-06-2009, 02:15 PM
Thanks guys for your input.
The machining characteristics of 316 are just as I thought, about the same as 304, just a little tougher. It's good to hear it from others though, gives me a little more confidence. Although I only have one shot at this and don't want to buy him another shaft, I will be using a test piece first in order to fine tune my turning and milling parameters.

Dr, yes I realize that there are versions of 316 ss available that are more machinable, unfortunately the customer already has the material so all I can hope for is that I'll get lucky.
Oh well if I screw it up I'll be able able to select my own material!:D

Oh, one more question...what would be the first choice for fluid, sulfur bearing cutting oil or a water and synthetic lubri-coolant blend whose name escapes me at the moment.

MaxxLagg
04-09-2009, 05:35 PM
Thanks guys for your input.
The machining characteristics of 316 are just as I thought, about the same as 304, just a little tougher. It's good to hear it from others though, gives me a little more confidence. Although I only have one shot at this and don't want to buy him another shaft, I will be using a test piece first in order to fine tune my turning and milling parameters.

Dr, yes I realize that there are versions of 316 ss available that are more machinable, unfortunately the customer already has the material so all I can hope for is that I'll get lucky.
Oh well if I screw it up I'll be able able to select my own material!:D

Oh, one more question...what would be the first choice for fluid, sulfur bearing cutting oil or a water and synthetic lubri-coolant blend whose name escapes me at the moment.

Well, if you can't get your hands on the Tap Heavy like you mentioned I'd stay with a cutting oil as opposed to a water based coolant, unless you can flood it ALL the time. You'll generate a prodigious amount of heat and a water based coolant, unless you're really laying it on, will just boil off on you. If you're using carbide it won't like that.