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316 Stainless

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Steve35515/10/2021 10:30:39
215 forum posts
150 photos

Hi all

In the end I got on OK with turning brass and have managed to make a couple of components for my milling machine,

The next thing I need to make is one of these,

8d5c8194-089e-436a-81c4-e2a83f78c3a9.jpeg

I’ve had a 316 stainless rod lying around for ages, which I bought for a different project before I got my lathe. I thought it might be suitable. But when I tried to turn it, it basically rubbed out the tip of my HSS bit. So I sharpened it, and it worked for a while, even gave a reasonable finish. Then it happened again, and again…. And every time I grind it, the tip gets lower due to the back rake, now I can’t reach centre with it! I think I’ve ground 3 separate bits so far and the same thing keeps happening.

Any tips? Chuck away the 316 and get something else? I hear it is tough stuff.

 

thanks

Steve

 

e78f9313-4dee-4897-bc69-110029eeecbc.jpeg

Edited By Steve355 on 15/10/2021 10:30:58

Andrew Johnston15/10/2021 10:50:20
avatar
6574 forum posts
701 photos

Some stainless steels can be a pain, but 316 is lovely to turn. However, it work hardens at the drop of a hat. So one needs to use decent depth of cut and feed rate (4 thou/rev or more) and never let the tool rub. The tool shown seems an odd shape? i'd use a standard knife tool.

Andrew

Tony Pratt 115/10/2021 10:54:52
1929 forum posts
12 photos

Stainless IS completely different to brass, feeds & speeds need looking at also you need to keep the tool on centre height.

Tony

Steve35515/10/2021 10:55:31
215 forum posts
150 photos

Thanks Andrew

I made the tool that shape cos it will need to get into some shoulders.I actually tried several tool shapes.

What if the tool has *already* rubbed and hardened the steel?

steve

Brian Wood15/10/2021 10:55:44
2549 forum posts
39 photos

Try carbide tips Steve, not at high speed and keep the feed on, don't allow the tip to dwell as that induces work hardening in the material.

You should get a decent finish straight from the tool and stringy swarf, which is sharp and bitey!

Regards

Brian

Edited By Brian Wood on 15/10/2021 10:56:06

Steve35515/10/2021 10:57:09
215 forum posts
150 photos

It’s 1 inch diameter - ish and 300 rpm. Which is apparently 80 SFM.

Andrew Johnston15/10/2021 11:29:30
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6574 forum posts
701 photos
Posted by Steve355 on 15/10/2021 10:57:09:

It’s 1 inch diameter - ish and 300 rpm. Which is apparently 80 SFM.

That's a bit on the fast side, even the professionals only recommend 70fpm for 316 and HSS tooling. Drop it to 50/60fpm.

Andrew

Martin Connelly15/10/2021 11:46:37
avatar
2123 forum posts
222 photos

At work we tried chamfering 321 and 316L stainless with pipe bevelling machines with carbide cutters. Even then the slightest rub hardened the face and we always ended up resorting to grinding and latterly replaced a large double off-hand grinder with some belt linishers. I find the ground and polished carbide tips work well on stainless but always use power feed. I made something (the usual need for a tool to make something else) this week from a bit of scrap and only realised it was stainless when I couldn't pick up the chips with a magnetic sweeper. That included using a carbide threading insert to cut a 16mm thread on the end of it at 66RPM (middle pulley + back gear). The main bit of turning was from Ø20 to Ø16 at 106RPM (middle pulley direct drive).

Martin C

Edited By Martin Connelly on 15/10/2021 11:51:05

noel shelley15/10/2021 13:05:36
1281 forum posts
21 photos

316 is notorious for work hardening, you MUST keep the cut running. once hardened only carbide will work. Coolant is good if you have that luxury. Good Luck, Noel

Steve35517/10/2021 22:52:52
215 forum posts
150 photos

So… managed to find a bit more time for this today…..

Turns out that in fact I had miscalculated and previously I was turning at 600rpm = 152 fpm so way too fast for 316.

I dropped the RPM to 200 = 50 fpm and it is cutting consistently and properly, without wearing down the tool bit in seconds. Problem is ,now I am getting a nice screw thread. See pic.

I’ve increased the nose radius, made little difference.

I could increase the speed, but then I’d be back to where I was before.
if I reduce the feed rate but I’m concerned it would wear down the tool bit again.

In fact, my lathe doesn’t seem to have any other speed between 200 and 600. 600 is the slowest main gear speed and 200 is the fastest back gear speed, as far as I can tell.

Any thoughts?

Cheers

Steve

6d6af84e-11c8-468f-8cd9-56d117e46f3b.jpeg

Edited By Steve355 on 17/10/2021 22:59:28

Emgee17/10/2021 23:07:57
2404 forum posts
285 photos

Change your feedrate to something around .004" per rev, looks like your feed is on thread cutting rate.

Emgee

Steve35518/10/2021 05:53:23
215 forum posts
150 photos

Ahhh I get it. That’s why the change wheel chart has 114.4 and 171.6 TPI. I was wondering why on earth anyone would want to cut a thread that fine!

luckiky this is the beginners forum!

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David George 118/10/2021 08:11:07
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1808 forum posts
503 photos

This is a video to roughing out a stainless stem with a carbide indexable tool from JB cutting tools. On my 1950 M Type Drummond lathe.

https://youtu.be/vzrhyDr4JBM

David

Edited By David George 1 on 18/10/2021 08:12:34

Steve35518/10/2021 09:52:30
215 forum posts
150 photos

It never ends 🥺

So to do proper power feeding I need to use a full complement of change gears. But the little arbor to attach the second set of change gears to the quadrant is missing. It’s a Zyto lathe but uses Myford change gears - but I can’t obviously find a Myford part that matches.

Luckily it looks pretty easy to make, even for me. I can’t do the slot for the key, it in the short term that probably won’t matter.

Can someone please recommend a suitable type of metal to make it from?

fa534f11-a42b-42ee-ae6e-021daf6ecaec.jpeg

Tony Pratt 118/10/2021 10:49:23
1929 forum posts
12 photos

Mild steel will be fine, the key slot may be needed depending on your set up?

Tony

Tony Pratt 118/10/2021 10:49:23
1929 forum posts
12 photos

Mild steel will be fine, the key slot may be needed depending on your set up?

Tony

Richard Millington18/10/2021 10:50:35
61 forum posts
4 photos

If you are going to mount two gears on it for one to drive the other then you will need the slot.

You could file the slot for the keyway, or clamp the tube on the cross slide on a small V block and put a small milling cutter in the chuck.

Steve35518/10/2021 10:56:38
215 forum posts
150 photos

Good points, of course I need the key slot, what was I thinking.

Mild steel it is, I will order some.

thanks

Steve

Tim Stevens18/10/2021 11:20:01
avatar
1587 forum posts

You need to be a bit careful what you order, Steve. There is a lot of 'construction' steel about which is used for building roofs, etc, and it welds wonderfully but is difficult to machine in hobby workshops. If you order 'bright mild steel, leaded' you will pay a bit more but you'll get what you need.

And leaded means it has metallic lead in the recipe, so it machines nicely. Pronounced leddid, not leedid.

Regards, Tim

Clive Brown 118/10/2021 11:57:10
807 forum posts
39 photos

The slot isn't essential. All that's needed is a half-height key to connect the 2 change-wheels. Out with the hack-saw and files.

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