Myford ML7 turning Stainless – optimistic?

[Matt Nolan 1Participant @mattnolan1]

Beginner question ahead!

Doing a bit of reading around, I am becoming increasingly convinced that I might not get away with one of the things I hoped I would be able to do in my "new" ML7. Don't worry. I will still find plenty of uses for it.

What I would like to do:

Turn 2-1/2" diameter 316 bar into a T-shaped cross section. Keeping the full diameter at one end, less a bit of cleaning up and some radii, but taking another inch or two of the length of it down to around 1-1/2" diameter. The finish on the smaller diameter section doesn't have to be pretty. It will be an interference or adhesive fit into some aluminium tubing so some roughness would actually be a bonus.

Is the ML7 sturdy enough? I read that deep and fast cuts are needed, and lots of coolant. Though, when drilling 316, I find that slow drill speed and high pressure works the best, with cobalt bits.

So, questions:

Is the ML7 rigid enough?

Is the current 1/4 HP motor strong enough? What can I upgrade to? 3/4 or more?

What is a suitable coolant that I can splash all over the Myford?

Is there hope or should I give up?

This is for very small runs. Ones and twos. At a later stage, if I wanted lots of these parts, I would get a 3rd party machine shop to make them. But I still may then need to skim down the 1-1/2" diameter a bit. The aluminium tubing ID seems to have a fair tolerance / varies in supplier.

Would this be a more feasible prospect? Or is it worse as I'd be taking a lighter cut?

An alternative in this latter scenario would be to make some bed-mounting stands for the aluminium tubing (it is LONG!) and ream out the top of the ID on the lathe instead.

Thanks in advance for your advice and wisdom,

Matt.

[Matt Nolan 1Participant @mattnolan1]

Can I turn 2-1/4″ stainless bar?

[Martin ConnellyParticipant @martinconnelly55370]

Your low horsepower will limit the depth of cut you can do but you need to run at a lower speed for stainless which will help. Do not take too shallow a cut or the tool will rub in places and work harden the stainless. Stainless can work harden if you pause the cut so you need to keep a constant feed on, power feed is best if available.

Have you considered sawing away most of the waste to reduce the amount of turning you have to do?

Martin

[JasonBModerator @jasonb]

Can't comment on the Myford but does it have to be 316? could you get away with an easier machining grade such as 303.

[Mike PooleParticipant @mikepoole82104]

Good advice from Martin, it will do the job but it will take a while. I think 1/4hp is about the smallest practical motor for the ML7 1/2hp is probably optimum, the super 7 had 3/4hp as standard but is is a different headstock.

Mike

[HopperParticipant @hopper]

Only way to find out is to try it. There are many variables to try, such as tool bit geometery, HSS vs Carbide, speed, feed etc, there aer no hard and fast answers.

Yes a quarter horse motor will do it. It just means you won't be taking .150" cuts at 800rpm. More like .050" cuts or less at 200rpm or less.

For tough jobs on these small lathes it can help to run a tailstock centre even on short work so that it gives a more rigid set up, allowing deeper cuts and faster feed without chatter. You will need to keep the feed up to the tool so that it does not rub and work harden the stainless.

[Ian S CParticipant @iansc]

If a Super Adept can cut about a ten thou depth in a 1" bit of stainless (think it's 304), then a Myford should do it ok, but 3/4hp would be a great help for this and all other work you do on the machine.

Ian S C

[Matt Nolan 1Participant @mattnolan1]

Thanks Gents.

I need 316 for the hardness. Otherwise 303 would be a better choice. 416 could be an option, but may be harder to source in small amounts, and more expensive. I need to do more digging around.

I don't have a power saw, though my Evolution chop or table saws *might* manage to take the bulk of the material off with a bit of jigging.

Ian S C – are you running that cut dry?

[Neil WyattModerator @neilwyatt]

Worth using a carbide tip tool, less likely to blunt if you do work harden a patch.

Don't be too timid, very shallow cuts will leave a work-hardened layer and the next cut may look like a ploughed field.

Neil

[john brennan 1Participant @johnbrennan1]

Matt, any austenitic stainless will be as hard as 316 for any given strength which is imparted by the cold working needed to form it into bar. So unless you need the superior corrosion resisting qualities of 316. 303, with its kinder machining characteristics should be ok Beware however that if hardness is a required condition austenitic stainless steel can be supplied softened and, as such, may not be suitable

[Matt Nolan 1Participant @mattnolan1]

Posted by john brennan 1 on 23/09/2016 15:26:38:

Matt, any austenitic stainless will be as hard as 316 for any given strength which is imparted by the cold working needed to form it into bar. So unless you need the superior corrosion resisting qualities of 316. 303, with its kinder machining characteristics should be ok Beware however that if hardness is a required condition austenitic stainless steel can be supplied softened and, as such, may not be suitable

Thanks John.

I had looked up the hardnesses here – http://offroadtoys.com/technical/materials/stainless/ – but you make a good point, those are the annealed hardnesses. If the 303 in bar form will be pretty close in hardness to 316, then that would be fine.

[john brennan 1Participant @johnbrennan1]

Thank you, Matt, in an increasingly familiar senior moment the term 'annealed' was a hole in my memory

[JonParticipant @jon]

World of difference between G303, 304 and G316.
One I wont touch again is the Duplex stuff unless have to, beefy machine or not, coolant or no coolant, tipped or not and drilling a lot worse.

G316S11 Is doable if short length but will take an eternity reducing it by 1" dia, been there done it but did have a 1hp English motor on the old ML7, 1/3 HP standard. The only way I could turn it down was to use quality knife edged shaped Eclipse HSS 5% Cobalt though haven't seen any for 15 years or more just the cheap tat.
Used G316S11 like glass unless used a sharp tool and could take 1 thou off or 15 thou until cutter wears. If and when cutter dulls off it will work harden or just rub the job, just resharpen and take same cut as before no problem. Will have to sharpen even the Eclipse 12 to 16 times not forgetting the last cut sharpen again. By the way used to run it dry back then but not let build job build up excessive heat.

G316 215 Max HB Better corrosion resistance ie shipping
G303 230 Max HB Free machining, its harder much like a weldable steel upwards.
G304 215 Max HB A little harder to machine than 303.
**LINK**

[PeroParticipant @pero]

Matt

On the question of motors, I have happily run my ML7 for the last 35 years on a 1HP motor. However it is run with a slack belt so it is unable to transfer full power. The advantage is that if I do something wrong the belt slips before any major damage is done.

Most of my turning has been done on 316 stainless but in much smaller sizes than you are requiring. My tools are typically carbide for facing and turning and HSS for parting. No coolant but an occasional dab of Trefolex. As mentioned above the secret is to keep cutting. If you need to stop, back the tool off very quickly. It work hardens in an instant. Re-starting a hole after hardening can be very expensive on drills!

Pero

[Ian S CParticipant @iansc]

The stainless has a bit of undiluted soluble oil. I needed the part, regardless of the time taken, and I didn't want to disturb the work that was in the main lathe.

Ian S C

[HopperParticipant @hopper]

I would not be too worried about the 1/4 horse motor. There are horses and there are horses and there are ponies. My old Drummond has a great big old industrial-looking motor on it, labelled 1/4HP and it will take a .100"+ deep cut in mild steel at 400rpm all day long at a reasonable feed rate of 4 thou per rev or so. The belts will slip way before the motor will stall. (admittedly poly V belt running on the old flat pulleys but it still takes a pretty good deliberate effort to make it slip).

For 2" diameter stainless you will be running at lower rpm than that, hence lower gear ratio, hence more torque. And you could always gear down to top back-gear for even more torque again and proceed at a more leisurely pace if absolutely necessary.

I would try it before I discounted the 1/4 horse motor out of hand.

Edited By Hopper on 24/09/2016 13:07:17

Edited By Hopper on 24/09/2016 13:08:45

[Matt Nolan 1Participant @mattnolan1]

Thanks Hopper. I will certainly give it a go before getting a new motor. Right now the belt isn't tight enough (the second one, on the speed pulleys). I can turn the chuck by hand while holding the motor pulley. The lever is in the belts tight position, so I'll have to see how I can adjust this. Or maybe I need a new belt, or to put some belt dressing on. Rosin a good idea?

[Ian S CParticipant @iansc]

Get stuck in, put the lathe in back gear, start in low, next cut go up a speed, and so on till you find a speed that will cut well without chattering.

Ian S C

[Matt Nolan 1Participant @mattnolan1]

Posted by Ian S C on 25/09/2016 11:30:49:

Get stuck in, put the lathe in back gear, start in low, next cut go up a speed, and so on till you find a speed that will cut well without chattering.

Ian S C

I will! But first I need to build a table for the lathe. Just tossing up between making one and buying a proper stand. Time and more fun versus quick and more expensive.

[Nitai LeviParticipant @nitailevi73768]

Posted by Neil Wyatt on 23/09/2016 14:51:24:

Don't be too timid, very shallow cuts will leave a work-hardened layer and the next cut may look like a ploughed field.

Sounds like that is what happened to me (I'm guessing). I'm pretty clueless about turning stainless, need to do it once every couple of years or less. So far I've done it twice. I'm sure my small lathe and overall setup could have been more rigid, but it didn't just look like a rough finish. The only way I can describe it is a sharp fuzz. It did cut but got this finish on every cut and couldn't find a way to improve it. I did take very small cuts because my lathe couldn't handle anything more.

I'm about to replace my lathe with a much better one anyway, but also interested in any tips. With stainless what I need to do is turn approx 9.0mm diameter to 7.0mm.

[Ian S CParticipant @iansc]

In that photo of the Adept, a HSS tool is being used, but for a small(and not so small) lathe, a very servicable carbide tool can be made using the carbide tips from a circular saw blade, you will find that the tips alternately point left and right. I find old blades on building sites, there are usually a few tips that can be cut off, and brazed to a bit of steel to make a tool, these cut stainless nicely.

Ian S C

[Matt Nolan 1Participant @mattnolan1]

I finally got to having a go at this last night for an hour or so (what my spare time windows are like these days!)

I had to put the lathe in backgear and right down to the slowest pulley setting. Even then, the motor would stall occasionally. I was able to take off some diameter, nice scouring pad type swarf spirals coming off, but it was breathtakingly slow. I think a larger HP motor would be useful here, though I guess I risk pushing the loading limits of the bearings and gears.

I wasn't able to make a decent facing cut, no matter how I adjusted the gib strip on the second-hand top-slide. Time to get the dovetails re-ground methinks! The seller has offered a replacement slide, but I think it would be good to start from a known perfect situation.

It turns out that one of the bearing oil drippers has some kind of blockage. It filled up once, and emptied, but then wouldn't re-fill. Something else to take apart and have a look at.

So, I'm set-back but I have not given up yet. I need these parts soon though, so am off to see a local professional tomorrow morning with my 303 stock and some drawings.

Cheers,

Matt.

Edited By Matt Nolan 1 on 12/10/2016 15:49:03

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