Thread: Steel for Lathe Spindle

For the amount of stuffing around trying to get so hollow bar the right size, I suspect that you would be better off getting some solid and then drilling/ reaming it out. Quickly the closest I can see is a piece of low carbon material 1" ID, 1.75" OD. A hydraulic cylinder manufacturer may have something hollow (or make something for you) perhaps. If you pick right alloy, do you really need to harden it? A previous employer used to make parts out of 4140 and not harden them - the increased strength was enough to do the job. Remember that steel properties and alloying abilities have advanced significantly since that lathe was made.

Michael

Just musing I'll check the steel bible latter today:

My instincts are pointing me to a chrome-moly type steel, but here are the metics I'm musing over:
1. Tempered hardness in the low 50's RHC
2. Preferably air hardening or slow oil. ie less shock distortion/less prone to cracking
3. High toughness.
4. Excellent wear resistance.
5. Dimensionally stable

-Josh

Originally Posted by Ueee

Hi All,
I need to make a new spindle for the 715. The question is from what?

Preferably something that is not going to distort too much when hardened, i have to thread both ends of the spindle, the nose for the L-00 nut retaining ring, and the tail for the locking ring. Both threads are 24tpi. I don't like my chances of being able to grind them, although with a die grinder set at the helix angle with the right shaped wheel.....maybe.

The spindle in just under 12" long, 1.625" largest dia with a .950" bore. I'm wondering if any steel is available in tube rather then solid?

Right now o-1 sounds good as it has very low distortion rates.

The other option would be to braze a new nose back on the existing spindle. It is just the tapered part of the L-00, and the seat for the 4C collets. The thread for the retaining ring is still there.

Machine O/S and then grind in situ is the plan for the nose either way, and the way Rivett did them originally.

Thoughts?


Cheers,
Ew

Thought of a truck axle Ewan or maybe a drive shaft from an earth moving machine might be worth a trip to an earth movers yard checck out his grave yard scrap pile. always a good source of material. ''fridge currency '' works. John ps take a triangular file with you i you cant nick it with a file is too hard truck axles work ok and are good steel and lots of 2 inch dias out there have often used it but usually drop the blank in a hot bed of coals in fire and let it sit over night covered usuall y case is not too deep it turns ok. 0.02 cents worth.

Originally Posted by j.ashburn

Thought of a truck axle Ewan or maybe a drive shaft from an earth moving machine might be worth a trip to an earth movers yard checck out his grave yard scrap pile. always a good source of material. ''fridge currency '' works. John ps take a triangular file with you i you cant nick it with a file is too hard truck axles work ok and are good steel and lots of 2 inch dias out there have often used it but usually drop the blank in a hot bed of coals in fire and let it sit over night covered usuall y case is not too deep it turns ok. 0.02 cents worth.

Thanks for the tip I have a few axle shafts that are to bloody hard to turn I will put them in the fire and try again

A couple of possibilities from the alloy steels, well more than a couple but depending on where you wan't to balance.

4340 (probably most available hence cheaper) and thin sections can be air hardened.

The other notables are
8645 (used for high stress shafts)
A6 (Lowest heat treatment distortion, less than O1)

-J

I would just use 4140... It is easily available... I think unless you have a cylindrical grinder in good order and know how to use it, there is no point is using some exotic expensive steel..

Reasons being you are not going to be able get the precision you will be expecting...

Not a put me down on anyone's abilities, but a spindle is one of the the most important parts of a machine tool.. any inaccuracies there will immediately translate to the workpiece...

As an example, A few weeks ago I was trying to measure the ID runout of an ABEC5 angular contact bearing....

I did this by putting a machined weight on top and with an indicator on the ID, spinning the bearing, trying to find the high spot..

What I found was that the results were not consistent, because if I put any weight on the bearing, even though I had it lightly preloaded, the runout went all over the place... What that told me was for a bearing to run true, all the weight applied to it, has to be dead nuts square...

If I was to install these bearings in a lathe and say some part of the spindle the bearings mount against was not machined proper square, the bearings will have immediate runout... That includes any adjusting thread for a nut...

Can a spindle be made on just your normal shop tools with care.... Sure it can... Just I would not expect what I would expect to come out of a manufacturers shop that has full grinding facilities at their disposal...

As such I would just use 4140 hollow bar... or something like that....

Lathe spindles are hardened for durability. Good quality lathes have hardened spindles. But many Chinese made lathes have only soft spindles, and yet seem to last many years of hobby use, too. It probably depends what you want to use the lathe for. A hardened lathe spindle is a lot more expensive than a soft one, lots more work to make. If you go hardened, you have to precision grind all important surfaces. Unless maybe, if you could find and get access to a place that can do nitriding (I do not know of any in Australia, but there is bound to be some place that does this?). Chris

4340 is about 50% more expensive per kg than 4140. But as RC said you can 4140 get in hollow round bar and that could be another significant saving in time and money. Main benefit I see of 4340 is that is a lot more forgiving with the quench.
-J

Originally Posted by .RC.

I would just use 4140... It is easily available... I think unless you have a cylindrical grinder in good order and know how to use it, there is no point is using some exotic expensive steel..

Reasons being you are not going to be able get the precision you will be expecting...

Not a put me down on anyone's abilities, but a spindle is one of the the most important parts of a machine tool.. any inaccuracies there will immediately translate to the workpiece...

As an example, A few weeks ago I was trying to measure the ID runout of an ABEC5 angular contact bearing....

I did this by putting a machined weight on top and with an indicator on the ID, spinning the bearing, trying to find the high spot..

What I found was that the results were not consistent, because if I put any weight on the bearing, even though I had it lightly preloaded, the runout went all over the place... What that told me was for a bearing to run true, all the weight applied to it, has to be dead nuts square...

If I was to install these bearings in a lathe and say some part of the spindle the bearings mount against was not machined proper square, the bearings will have immediate runout... That includes any adjusting thread for a nut...

Can a spindle be made on just your normal shop tools with care.... Sure it can... Just I would not expect what I would expect to come out of a manufacturers shop that has full grinding facilities at their disposal...

As such I would just use 4140 hollow bar... or something like that....

Hi Richard,
That is a very good point. With the mars as it is the best I could hope for might be in the region of 5-10um. No doubt the LeBlond could do much better, but that's a ways off.
I was thinking about talking to Phil about getting it ground, the other thing that occurred to me is MTA In Sydney may be able to do it. I know you have used them, do you know if they grind spindles? Surely they would since they do full machine rebuilds.

I actually have some 4140 here, it is case hardned but I could fix that. Mind you the price for a short bit is cheap enough anyway.

Cheers,
Ew

You cannot case harden 4140.... I tried then when it failed I did some research and no, you can only case harden low carbon steels...

SAG180 recently did some spindle work on his SAG180 lathe... He posted about it over on the PM forum..

He reground the spindle bearing areas (it is a plain bearing spindle) on a Makino TC grinder using made up tooling to hold it...

Of course is the spindle is running you could machine the nose in situ...

There are ways and means and tricks around when time is not a factor to consider..

I think once you start talking about taking it to a commercial shop, it is time to open your wallet wide... But happy to be proved wrong there...

Originally Posted by .RC.

You cannot case harden 4140.... I tried then when it failed I did some research and no, you can only case harden low carbon steels....

Yes, it's probably flame hardened or induction hardened. That can leave a hard surface but softer as you cut deeper.

Originally Posted by Ewan

Machine O/S and then grind in situ is the plan for the nose either way, and the way Rivett did them originally.

I think that sounds like it will work, I wonder how good those little air grinders would do on a job like that?

As .RC. says spindles are the single most critical part of any machine tool, and everything else flows from there. Should be a good exercise.

Regards
Ray

Re 4140, .4% puts it in the low carbon range, it should still be able to take up carbon and get a harder surface i would have thought?

The stuff i have is hard in the middle....its unmachinable (with my machines) on the outside......

Maybe the best thing to do is make a "test" one from what i have, leave it soft and grind the nose in situ as i suggested to start with. That *should* leave me with a nose that has radial run out as good as the bearings, but axial run out only as good as i can machine (and lap?) my shoulders. But then i guess any axial runnout will also lead to some radial runnout?

Depending on how that goes at some stage i can make a new one and get it ground, or own a cyl grinder by then that is "good enough" (is there such a thing?, there always seems to be a smaller unit of measurement to chase.....)

Ray, the Waldown will be far too big for the Rivett to swing, it will have to be something smaller.....

Ew

Annealing 4140 looks like it is a pain.

Heat to 750 cool to 665 at less than 6C /hr .
or
Heat to 750 cool rapidly to 675 and hold for 9 hr

:S

I'll admit to being a little confused here; why case harden 4140? as it through hardens all by itself nothing fancy required heat to light orange and quench in oil.

-Josh

Originally Posted by Brobdingnagian

Annealing 4140 looks like it is a pain.

Heat to 750 cool to 665 at less than 6C /hr .
or
Heat to 750 cool rapidly to 675 and hold for 9 hr

:S

I'll admit to being a little confused here; why case harden 4140? as it through hardens all by itself nothing fancy required heat to light orange and quench in oil.

-Josh

Dunno, they are old backhoe pins, they are as hard as all getout on the outside maybe 2-3mm thick. I'll throw the pin in the fire next time i have it on, then load it up with coke and let it cool all night (it will still have embers the next morning normally). If that doesn't work the pins are pretty well useless except maybe to grind into cyl. squares.

Who can get 4140 locally? I can't, i didn't even know it was available in tube.

Ew