316 Stainless

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316 Stainless

This topic has 20 replies, 11 voices, and was last updated 18 October 2021 at 11:57 by Clive Brown 1.

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15 October 2021 at 10:30 #10988
Steve355
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@steve355
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15 October 2021 at 10:30 #566892
Steve355
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@steve355
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,

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

Edited By Steve355 on 15/10/2021 10:30:58
15 October 2021 at 10:50 #566897
Anonymous
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
15 October 2021 at 10:54 #566898
Tony Pratt 1
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@tonypratt1
Stainless IS completely different to brass, feeds & speeds need looking at also you need to keep the tool on centre height.

Tony
15 October 2021 at 10:55 #566899
Steve355
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@steve355
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
15 October 2021 at 10:55 #566900
Brian Wood
Participant
@brianwood45127
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
15 October 2021 at 10:57 #566901
Steve355
Participant
@steve355
It’s 1 inch diameter – ish and 300 rpm. Which is apparently 80 SFM.
15 October 2021 at 11:29 #566905
Anonymous
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
15 October 2021 at 11:46 #566908
Martin Connelly
Participant
@martinconnelly55370
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
15 October 2021 at 13:05 #566921
noel shelley
Participant
@noelshelley55608
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
17 October 2021 at 22:52 #567194
Steve355
Participant
@steve355
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

Edited By Steve355 on 17/10/2021 22:59:28
17 October 2021 at 23:07 #567195
Emgee
Participant
@emgee
Change your feedrate to something around .004" per rev, looks like your feed is on thread cutting rate.

Emgee
18 October 2021 at 05:53 #567199
Steve355
Participant
@steve355
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!
18 October 2021 at 08:11 #567201
David George 1
Participant
@davidgeorge1
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.

David

Edited By David George 1 on 18/10/2021 08:12:34
18 October 2021 at 09:52 #567210
Steve355
Participant
@steve355
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?
18 October 2021 at 10:49 #567217
Tony Pratt 1
Participant
@tonypratt1
Mild steel will be fine, the key slot may be needed depending on your set up?

Tony
18 October 2021 at 10:49 #567218
Tony Pratt 1
Participant
@tonypratt1
Mild steel will be fine, the key slot may be needed depending on your set up?

Tony
18 October 2021 at 10:50 #567219
Richard Millington
Participant
@richardmillington63972
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.
18 October 2021 at 10:56 #567220
Steve355
Participant
@steve355
Good points, of course I need the key slot, what was I thinking.

Mild steel it is, I will order some.

thanks

Steve
18 October 2021 at 11:20 #567222
Tim Stevens
Participant
@timstevens64731
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
18 October 2021 at 11:57 #567229
Clive Brown 1
Participant
@clivebrown1
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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