DIY steel hardening

[BevelParticipant @bevel]

Hi All,

 

Need advice on which steel I can succesfully harden at home.

I have couple of live centres which are decent enough but the actual centres haven’t been hardened sufficiently, obviously chinesium lol. I want to replace them with own but I’m not clued in to which steel I can harden myself without fuss? Looking at 17-20mm dia bar roughly 50mm long.

Your advice and expertise will be greatly appreciated many TIA.

 

 

[noel shelleyParticipant @noelshelley55608]

The traditional material was silver steel, though other modern types may be better, some one will come up with better info ? Noel.

[BevelParticipant @bevel]

Thx Noel

[bernard towersParticipant @bernardtowers37738]

EN8 is easy to machine and harden

[JasonBModerator @jasonb]

Don’t be too quick to blame Chinesium. The ctr that is intended to go into the headstock known as the “Live ctr” is usually left soft so that it can be skimmed perfectly true in situ which removes the possibility of any run out of the spindle taper. You can’t do that if it is hard.

If by “Live” you actually mean a rotating ctr then they are not usually that hard, even my brand name one will score if you run the cutting tool into it.

You really only need a dead ctr that goes into the tailstock to be hard as that has the work rotating against it.

[Thor 🇳🇴Participant @thor]

EN8 is a medium carbon steel, the lathe centres I have are hardened tool steel with approximately 1%C and may be some Chromium. 20mm silver steel should be OK and isn’t that difficult to machine when it is annealed. After hardening and tempering you may have to grind the centre, if you don’t have that why not by a centre?

Thor

[JohnFParticipant @johnf59703]

Yes EN8 or EN9 or Silver steel, all are easy to harden and machine.  Silver steel is easier to harden –more carbon also fairly stable

For hardening you need a hearth,  a good sized gas torch and say a gallon of oil for quenching.  You can use a water quench but oil is better.

The hearth can be a few fire bricks piled up — Note fire bricks NOT ones from storage heaters !

Heat to a “cherry red” and quench then polish & temper to a pale straw colour in subdued daylight. Or temper in the domestic oven to maximum temp usually about 250/260*C soak for say 1 hour. Not perfect but it should be OK for this.

Or for this application you might try “spot” hardening — just heat the tip to cherry red and quench, the rest will remain soft .  You could even try this with the existing ones and see what happens for hardness — difficult with “unknowniuum”

John

PS where are you located ?

[John HaineParticipant @johnhaine32865]

If they are getting hot enough to soften in use then perhaps there isn’t enough grease or pressure is too high, or both.  If they’re soft then just skim ’em with a carbide tool to restore/recentre the point.

[noel shelleyParticipant @noelshelley55608]

Check on the quenching  medium specified. Could be water, brine or oil. Tempering can be done in oil, in which case use vegetable oil, NOT mineral oil. Noel.

[BevelParticipant @bevel]

Thx guys all very much appreciated.

Replying to Thor’s question ‘why don’t I buy one’, good question but obvsly that would be far too easy lol, I’ll most probably spend more money and valuable time ‘fixing’ the 2 I have then end up buying a branded one anyways bone head that I am. I’m a slave to false economy gents I’m afraid lol

Just annoys me when you buy something that for the sake of pennies could be best bargain you ever had. 2 centres I have were bought from Warco and were only 20odd quid, absolute steal I thought but first one stopped rotating for some reason and thats were the trouble began. As pointed out the centre then developed an annoying step. No amount of oil/grease could make it turn whilst under pressure. I complained and got sent another, exactly the same unfortunately.

Bearings run smooth but theres a crudely cut piece of pipe acting as a spacer between the 2 and like I said the centres are not very hard. Shame cos they would be more than adequate for my needs I’m only m/c to thousands not tenths.

 

[duncan webster 1Participant @duncanwebster1]

As others have said, no need for a rotating centre to be hard, so why make life difficult

[JasonBModerator @jasonb]

If they are not hard then why not just pull it apart and remachine the point with a carbide insert. neW set of bearings and a better spacer which sounds like you need anyway then put it back together

[not done it yetParticipant @notdoneityet]

Bevel,

Please take note of JasonB’s replies.  They are both spot on – and the rest who are suggesting hardening were either incorrect or were thinking it was a fixed centre in the tailstock.

No need, at all, for a hardened part.  They were manufactured that way because there was never any need for a hardened part – because the bearings do the rotating duty.

Any centre in a chuck jaw should be machined (skimmed), in situ, every time it is mounted.  More taper centres are often assumed to be dead accurate – but that assumes the socket, into which the centre is mounted, is perfectly true.

The best centre is always going to the one machined (skimmed), in situ, every time it is mounted.

[BevelParticipant @bevel]

 

Ok guys point taken, just one small point before closing the thread both centres are tailstock centres on MT3 arbors so I presume they have to be disassembled to machine lips out anyway?

[David George 1Participant @davidgeorge1]

On my tailstock centers I have a live centre which is hardened toaround 50RC which is made from silver steel.  I have a toolpost grinder which is used to grind the tip after it is disembled for grinding. My fixed centre from new was fairly soft and kept picking up on jibe so i drilled the point out and insreted a round piece of tungsten carbide wuichwas brazed into place. This was also ground to a nice point with my toolpost grinder and a diamond grinding point. The carbide doesn’t pick up or wear.

David

 

 

[JasonBModerator @jasonb]

Yes you need to take them apart so you can hold the pointed bit without it rotating.

[HuubParticipant @huub]

In general I use silver steel for hardening tool bits and C45 steel for larger parts that need to be hardened. Both are heated to red and than quenched in water. After hardening, Silver steel is a bit harder dan C45 steel (0.45% carbide).

[BevelParticipant @bevel]

Thx again gents

[Huub]

On Huub Said:

In general I use silver steel for hardening tool bits and C45 steel for larger parts that need to be hardened. Both are heated to red and than quenched in water. After hardening, Silver steel is a bit harder dan C45 steel (0.45% carbide).

Is C45 a typo?  New to me so I looked it up and the spec says it’s a medium carbon steel with low hardenability. Many other virtues:  “good machinability, high tensile strength, and versatility, making it suitable for various applications like gears and shafts. It is commonly used in engineering and automotive industries due to its balance of strength and workability.”

Low hardenability might be just what Bevel needs!  A centre that resists wear, but isn’t so hard it damages the job.

Building on that thought, I usually prefer work-holding to be a bit softer than the workpiece.  For example bench vice jaws tend to score  jobs, so I usually put a pair of DIY aluminium protectors on before gripping anything.     In the same way, I occasionally slip Copper protectors over lathe chuck jaws, less often because the Copper reduces accuracy.

So I don’t mind fixed and live centres being on the soft side.  They’re less likely to damage the job and are easy to resharpen etc.

Another thought: Bevel has written off two live-centres.  Maybe they were poorly made from a bad batch.  Or could it be they were forced too hard into the job?  The tailstock only needs to be wound tight enough to support the workpiece.

Dave

[JasonBModerator @jasonb]

The C grades are often used in Europe and are the ISO designations and been around a long time..

C45 is about the same as the old EN8 which many here have suggested. You are not looking for cutting edge hardness, just something that is likely to be a bit harder than the metal the ctr is supporting so no need for much more.

So certainly NOT a typo

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