Does EN19T or EN24T respond well to burnishing?
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  1. #1
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    Default Does EN19T or EN24T respond well to burnishing?

    I'm going to make a milling spindle for my lathe and would like to use angular contact bearings in the rear, and a needle roller bearing at the tooling end - inspired by the Deckel vertical spindle. I'd like the needle rollers to ride on the spindle.. I'm pretty set on this layout for milling.

    I'd like to make it from EN19T or EN24T and wondered if either of these would be reasonably hard wearing (as a bearing inner race surface) if lapped then burnished where the needle rollers ride?

    The milling spindle would be used only occasionally, driven by 1/3hp motor, ISO20 taper.

    Thank you

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    IME (of seeing others attempts ) nowhere near hard enough for needles to run on, if you can use needle rollers with an inner track

    FWIW, with a milling spindle you will be far better off with taper roller or angular contact, etc etc bearings.

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    Taper rollers look much more suitable but needle rollers at the front end will fit..

    The housing needs to be small enough to fit on a Myford type vertical slide and I wanted to use ISO 20 for the taper - ISO 30 would be nice but too big and MT1/MT2 isn't really a milling taper.. I'll use 8mm watchmakers collets via an adaptor too.

    I could use a different grade of steel and send it off for heat treatment but pre-hard is pretty straightforward to machine. Is there something else machinable which would be better?

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    Have you thought about using ER Collets direct on the spindle,.......... I built a 1/3hp milling spindle nigh 30 years back and went ER (1/2'' or 13mm Cap) direct in the end, and have never regretted the choice.

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    Figure out how to use something like this as your spindle:

    Techniks CNC Machine Tooling | ER Holder Extensions

    Essentially as per Citrus Sam above.

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    The ER spindle is a good idea but I'm fancying also being able to use some bits of tooling from my watchmaking lathe, and would make a couple of arbors for the ISO20 taper..

    Will see if we have anything hardened at work nowadays, might just give it a go in prehard - a housing can be reused with a new bearing spacer.

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    Neither of them will be hard enough in the T condition. If you don't want to risk re-hardening+tempering them with heat/salt bath+quench+temper then the cost of gas nitriding is quite reasonable.

    I'm going to be sending out a gear and a splined milling machine spindle drive collar for this in the near future for my milling machine that I'm still rebuilding. Both are EN24T, but can be surface hardened significantly with the nitriding process.

    The alternative is either inner tracks or angular contact/taper roller bearings at the tooling end. Presumably you are constrained by the available inside and outside diameters? If that is the case, then google for nitriding near you.

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    Recommend you hit up ebay and find a driven tool for a cnc lathe to adapt for your purposes. Not as interesting as making your own, but if you don't have the facilities to do it properly you will at least have a functional milling spindle at the end.

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    A thought on bearings - have you considered magneto bearings ? for their size they'll take some good loads .....here's a taster Magneto Bearings: Magneto Single Row Deep Groove Ball Bearings

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    Thank you to everyone for the suggestions and discussion, some of the solutions were likely better or more sensible than my intended direction but I wanted to keep the existing design.

    I called a couple of companies today to get a quote for nitride hardening, it was cheaper than expected - usually I tend to think of all that stuff as a higher class of work so it doesn't enter my mind.. seems I should be able to get a few things hardened and still stay within their minimum price too.

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    plasma nitriding?

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    Just two maybe-relevant points ... I put a fair amount of effort roller burnishing on one project. It wasn't as great as Cogsdill says. It was hard to hold size and the finish wasn't that great. For a fairly large number of parts it might be worth the trouble but difficult to get good results on a onesy-twosey project.

    The other point is, there's been a large amount of research into roller bearings. Life span below 58 Rc is poor. Above that is good. So that's another thing to consider ... burnished is never going to be that hard.

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    You want a decent amount of depth for any case hardening, otherwise you can still create a "standing wave" of flexing of the surface, which can fatigue and spall off material fairly quickly when a rolling element is running on it.

    Just a quick guess, but for smaller, light duty direct rolling shafts I'd like a MM or so of ~RC60 hardness. Maybe a bit thinner will work, but I'd be cautious if the case is less than 0.25mm.

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    Quote Originally Posted by Milland View Post
    You want a decent amount of depth for any case hardening, otherwise you can still create a "standing wave" of flexing of the surface, which can fatigue and spall off material fairly quickly when a rolling element is running on it.

    Just a quick guess, but for smaller, light duty direct rolling shafts I'd like a MM or so of ~RC60 hardness. Maybe a bit thinner will work, but I'd be cautious if the case is less than 0.25mm.
    The other method there is a harder core - say 40 or more - and a thin surface like nitriding that's only a couple thou deep. Some gears are done that way because of distortion, but not usually heavily-loaded ones. Nitriding will get you up to about 70 Rc, which is kinda nice for wear resistance. 4130 is better than 4140 for that.

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    why is that? cr/mo is the same.

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    Quote Originally Posted by dian View Post
    why is that? cr/mo is the same.
    This isn't (IMHO) a well written article, but it does point out the benefit of lower carbon content in a steel that's to be nitrided:

    Nitriding, Process Methods and Metallurgy | The Monty
    [near the bottom, titled "Alloy steels"]. Basically, lower carbon reduces the deleterious effects of the compound layer.

    Again, I wasn't super-impressed with the writing clarity, so you may want to find further sources to confirm or deny this statement.

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    Why not just use a needle bearing sleeve pressed onto the shaft.
    Not enough room?
    Bob

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    Quote Originally Posted by Milland View Post
    This isn't (IMHO) a well written article, but it does point out the benefit of lower carbon content in a steel that's to be nitrided:

    Nitriding, Process Methods and Metallurgy | The Monty
    [near the bottom, titled "Alloy steels"]. Basically, lower carbon reduces the deleterious effects of the compound layer.

    Again, I wasn't super-impressed with the writing clarity, so you may want to find further sources to confirm or deny this statement.
    thanks, however my table lists 4130 (1.7218) as hrc 60 max and 4140 (1.7225) as hrc 64 max. similarly i see hv 500 for ck45 and hv 550 for ck60. is that just theory?

    (interstingly grey iron goes up to 62 hrc.)

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    Quote Originally Posted by dian View Post
    thanks, however my table lists 4130 (1.7218) as hrc 60 max and 4140 (1.7225) as hrc 64 max. similarly i see hv 500 for ck45 and hv 550 for ck60. is that just theory?

    (interstingly grey iron goes up to 62 hrc.)
    If you're speaking of basic response to nitriding, it may be that you can achieve higher hardness, but with a thicker "white layer" with the higher carbon content. But I'm not sure, as I mentioned I'd want to see more references before I trusted anything...


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