[romihs]

Hello,

I am looking at spindles and their designs.
I know that a good spindle design needs to take temperature and COE (coefficient of expansion) into account.

I read that high-nickel steel alloys are the best material for spindles as this alloy has a low COE.

Which steels (designation or code) have high concentrations of nickel?

I am assuming that the high-nickel alloys are difficult to machine.

Thanks to any who do respond.

Regards

Sandi

[scadvice]

Are you going to heat treat and grind the taper and bearing journals on the spindle? A2 is very stable during HT, but depending on the size and sectional thickness of the spindle, you may want to consider other materials possibley going to a case hardening steel. I would look for steel alloys with a carbon range of .40 to .50 %. These are best suited for that kind of application.
Steve

[keebler303]

I am using 4140 PH (pre hard) for the spindle on a small CNC lathe I am working on.

Matt

[romihs]

Thanks guys for your responses.

There is one thing I am also trying to figure out; Is it required to harden surfaces on the spindle and housing components or not?

If hardening is required, does one only harden surfaces that contact tool holders, or does one also harden the areas where the bearings are situated?

Regards

Sandi

[clovenedhoof]

hardening the surfaces will result in a stronger and longer last part. If it's practical to do so.
-Chris

[jmorris@mailmds]

We have had great results with S7, steel. You can machine it oversize, heat treat and then grind the bearing journels. it holds up much better than A2, in our demanding spindle applications.

[romihs]

Thanks jmorris for that bit of handy info.

Regards

Sandi

[scadvice]

...correct, S7 is also a good Tool Steel to use. It has a very high shock value compared to other steels when hardend and resist chipping, ect.

Steve

[NC Cams]

A perhaps more reasonably priced spindle steel is SAE8620. Get the AQBQ variant if you can as it is much cleaner and has less stringers. Heat treat via carburize and harden. If you want to selectively harden, copper plate the areas you don't want hardened. The way we do it is copper plate the whole piece and then grind off the copper where we want it hard prior to H/T. Shallow case of 1.25mm is fine for most surfaces, do 3mm case on areas that will see lots of traffic or "ding" potential.

Don't even consider 9310, you can use 4820 as an option but why bother, 8620 is plenty good.

A more rigid, tougher spindle can be made from 4140 hardened and drawn to Rc 40-42. PHT is OK but no where near as hard and tough. PHT is machineable, Rc 40-42 is probably not.

As far as I'm concerned, tool steels can be used but they are over priced when you know how to use less costly steels that are properly heat treated.

BTW, it is usually beneficial to "double draw" any of the the above prior to machining and heat treating. This involves first annealing the steel then once back at room temp, normalizing the steel. Noticeable difference in machinability and part stability.

Regardless of the material, do a 1250 deg F thermal soak after machining and prior to H/T for at least 2 hours. Again, this eliminates residual stresses from machining.

Finally, make sure the H/T guys quench the part AXIALLY as in dunking. They must NOT dunk the side of the spindle into the quench bath as this will warp the part. After doing all the above, you don't want to have to screw around with warped parts. The best way to deal with warped parts is to NOT WARP THEM from the get go. We always cryo stabilize when we do our shaft work.

[romihs]

NC Cams,

Thanks for that info!
You have gone and nailed my question square on the nail.

And you have given me some VERY valuable info, which I never thought of before but is logical when I think about it.

I see that you have considerable experience working with steel, creating machine tools.

Thanks again.

Regards

Sandi

[js412000]

NC Cams- Have you ever tried 52100 ball bearing steel for a spindle?

I once ground some 52100 shafts on a cylindrical grinder. The customer wanted a extra smooth finish, so I left .0002" on the diameter for polishing.

It took what seemed like forever to polish even .0001 off. I had to put them in a lathe and spin them at 1500 rpm (1 1/2" diameter) to remove the material.

I want an alloy that is the most wear resistant for the spindle internal taper part.

I am guessing that 52100 or 8620 will be cheaper than a tool steel, like A-2.

[scadvice]

A perhaps more reasonably priced spindle steel is SAE8620. Get the AQBQ variant if you can as it is much cleaner and has less stringers. Heat treat via carburize and harden. If you want to selectively harden, copper plate the areas you don't want hardened. The way we do it is copper plate the whole piece and then grind off the copper where we want it hard prior to H/T. Shallow case of 1.25mm is fine for most surfaces, do 3mm case on areas that will see lots of traffic or "ding" potential.

Don't even consider 9310, you can use 4820 as an option but why bother, 8620 is plenty good.

A more rigid, tougher spindle can be made from 4140 hardened and drawn to Rc 40-42. PHT is OK but no where near as hard and tough. PHT is machineable, Rc 40-42 is probably not.

As far as I'm concerned, tool steels can be used but they are over priced when you know how to use less costly steels that are properly heat treated.

BTW, it is usually beneficial to "double draw" any of the the above prior to machining and heat treating. This involves first annealing the steel then once back at room temp, normalizing the steel. Noticeable difference in machinability and part stability.

Regardless of the material, do a 1250 deg F thermal soak after machining and prior to H/T for at least 2 hours. Again, this eliminates residual stresses from machining.

Finally, make sure the H/T guys quench the part AXIALLY as in dunking. They must NOT dunk the side of the spindle into the quench bath as this will warp the part. After doing all the above, you don't want to have to screw around with warped parts. The best way to deal with warped parts is to NOT WARP THEM from the get go. We always cryo stabilize when we do our shaft work.

I agree with CN Cams. I stand corrected to what I said earlier, 8620 with a 3 mm case on the taper and bearing surfaces is the best option. I should have thought of that.
BTW - 40 to 42 is machinable, I do it all the time. You just have to follow certain rules. Steve(chair)

[romihs]

Steve,

Exactly which rules are those? :-)

Regards

Sandi

[scadvice]

I knew I would be called on that!! Heh..heh..:stickpoke
OK .... It's to much to cover all of it here, but give me a pratical example.

Tell me the material, its size, hardness, amount/thickness of removal. Operations,(turning, drilling, milling, ect. Will it be machine in an annealed state then hardend (RC ) for final machining or just hard? Single part or lots of parts?
Finally, the equipment available to do this on, size... HP...brand...ect.

Steve:cheers:

[NC Cams]

52100 for a spindle seems to be a bit of overkill, especially due to the reported machining issues with 52100. Another issue is cost, 52100 isn't as cheap as 8620. . Same with A2 and S7. After all, it is a spindle for a lathe and/or a machine tool. You are NOT supposed to be hammering and pounding on it.

A 3mm case should be plenty on 8620 If you want to make the surface even harder to prevent nicks and road rash, carbonitride the part AFTER you case harden it it. This puts a hard shell on it which really makes it less susceptible to road rash. Sort of super hard case on an already hard case.

This trick was done on 52100 to toughen up auto transmission bearings. Makes thru hardened steel act somewhat like carb and hardened steel.

Actually, you should be able to get 8620 up to an Rc 62-63 which is going to be hard to knick, scratch and otherwise damage. Use care in grinding as at this hardness level, you can't be ignorant and stupid when you grind it.

[romihs]

Hello guys,

I have "no" machining experience when comparing to you guys, and for that reason I 'prefer' what NC Cams has suggested.

I don't have the experience or know-how to do what Steve has suggested, so I would rather opt for the easier option.... (chair)

Regards

Sandi

[js412000]

Thanks, NC
How thick is carbon nitriding? I want to grind the taper after assembly.

[NC Cams]

Due to proprietary nature of the process of carbonitriding of pre hardened parts, I am not able to discuss the details of the process. It is not easy to do as the C/N part of process can/will soften the prehard part of the zone if you do it wrong.

Use 8620 AQBQ steel ONLY. Subject billet to double draw as noted above. Machine part to near net shape. Best bet is to copper plate the areas the you do not want carburized or do not need hard after machining. (threads, non support or non ground areas, etc). Be sure to leave enough stock in ground areas for following.

Stress relieve at 1250deg F for 1 hour per 1 inch thickness of material - prefererabley in neutral salt bath. Do this BEFORE H/T. Rough grind. Reason: the now stress free part should exhibit max warpage at thsi point from all prior operations.

THen go to carb and harden for 3mm case depth. MAke sure you have enough finish stock here as some minor warpage can still occur. After H/T, do all quenching axially - if you quench side of part, you will warp it.

Note, when you go to H/T, prevent warpage as much as possible, you must prevent H/T warpage as opposed to "fixing' it. IE: Stand shaft on end or hang in furnace, do not lay sideways. Quench axially as opposed to side first - side first quench WILL warp the part.

HOT straighten any warpage after HT to within 0.005" TIR. Cold stabilize via cryogenics,quench and temper. Hardness of surfaces should be Rc60-62. This should be plenty hard for service.

Use care with any grig blasting to clean the part after HT. Blasting can warp it. Better to tumble in finde medial to clean as this is less stressful and does a better job.


You can not make hard zones hard enough to prevent road rash from lazy, stupid or careless workers. IT is better to train workers properly than to try to make shaft bullet proof.

Reason: no matter how hard you try, the careless people will find bigger guns to shoot at bullet proof part.

[Ben Olson]

I agree that case hardened 8620 would make a good spindle ( this is the same steel that automobile ring and pinion gears are made from ) another alternative that I have had good results with is EN30b , a high nickel content steel that is air quenched ( it has similar properties to Astroloy ),,, when it is heat treated properly that is some tough stuff!

[noisy]

40 to 42 is machinable, I do it all the time. You just have to follow certain rules.

I know this is my first post and I'll have to hunt down the introduction post but don't hold that against me.

Have you ever tried to cut #1 stellight? Spelling?? I cut Hard Coat on our wear rings all day long, they test out at 49-62 depending on the Hard Coat material used. Please don't ask me a bunch of specs for the material because I don't know, I'm not a welder I just cut the crap. :lol: as for tooling we use ceramic tooling on all of our Hardcoatings. My rules are simple if the chips aren't coming off a nice multen red looking your not turning it fast enough. If you can get in under neith the weld that is best because all the intermitten cutting of the Hard coat weld will destroy your insert. I'll have to take some pictures of the equipment we have at work. I was cutting hardened 4140 steel plates 26" diameter and 2.250 inch thick. After all the work I do to them they get nitrided.