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Old 07-06-2020, 01:29 PM   #1
BRENT in 10-uh-C
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Default O/T What material would you use for new axle shafts?

This is a little off-topic for a Model-A (-unless you want to consider the first-generation Model-As too ) but I am wanting some opinions from those who have some experience in machining some of these metals.

I have an upcoming project where I need to make a couple of new rear axles for a early brass-era automobile. I do have one to use as a sample so I am not starting totally from scratch however I am trying to determine whether I want to use 4140 or 4150, -or whether to use something like A6 or D6 to make these out of?

The hubs are not tapered but I will need to spline one end, machine a shoulder on the opposite end, a keyway for the hub, axle threads, and two bearing carrier surfaces, ...so there will be some machining involved. Whether to start with something I can anneal prior to the machine work, and then harden afterwards, or ???.

The other issue of uncertainty for me in this is it appears the sample I have is made from a mild steel based after drawing a file on it. Whether this one is an original axle from the factory, -or a 'blacksmith-built' one to replace a broken factory one at some point along the timeline I do not know. Since this is roughly a 20hp vehicle, maybe it does not need a tool steel strength axle but on the other hand, maybe they would have used something different had the metallurgy technology been better back then? Thoughts??
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Old 07-06-2020, 03:45 PM   #2
johnneilson
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Default Re: O/T What material would you use for new axle shafts?

Brett,
IMHO, I would stay away from the x6 tool steels as typically too brittle and cost prohibitive. I have used S7 for cams, broke one, heat treatment more than likely not uniform. (anneal after hardening)
4140 is probably good, another might be 1144, this is a "stress Proof steel" used very much in large calendar rolls and large shafting.
I would also stay away from anything with lead to assist machining such as 41L40.

Not being familiar with design of the axle, remember large radius fillets and avoid peak stress risers. (such as end of spline section)
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Old 07-06-2020, 05:14 PM   #3
fast150
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Default Re: O/T What material would you use for new axle shafts?

I agree with Mr. Neilson. The air hardening tool steels would be brittle. I would use 4140 as machined. It will work harden some in use and should hold up well in the splines, and less likely to break out a key way.
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Old 07-06-2020, 06:12 PM   #4
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Default Re: O/T What material would you use for new axle shafts?

4140 here too.
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Old 07-07-2020, 01:02 PM   #5
Dan McEachern
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Default Re: O/T What material would you use for new axle shafts?

Brent- use 4140HT, not annealed. 4140HT is 28-32Rc and is easily machined at this hardness. The ductility will still be sufficient at this hardness. You could use annealed 4140 and then have it heat treated after machining if you needed higher strength, but I think the pre heat treated material will work fine. I just made a new axle for our early sprint car out of this material and its tapered on one end and a spline on the other end.
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Old 07-07-2020, 01:27 PM   #6
d.j. moordigian
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Default Re: O/T What material would you use for new axle shafts?

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If you heat treat after turning / grinding it WILL move.

Brent,...talk too the guy that makes the axle's for your Son's race car...?

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Old 07-07-2020, 06:47 PM   #7
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Default Re: O/T What material would you use for new axle shafts?

1144 'stressproof" and do not heat treat it. You need to watch what you buy with 1144, as some of it is approx RC30, some as low as RC15. I would avoid anything supplied under RC20. Keep the feed speed down and flood it with water-soluble while cutting.

McMaster Carr carries several grades of 1144 and you can order just one foot of one inch stock for about $12 if you want to try it with your splining cutters and setup for machine-ability/ finish and fit.

I made plenty of replacement foundry shakeout machinery shafts from the stuff in the '90's and they never snapped like the original shafts they replaced.
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Old 07-08-2020, 10:28 AM   #8
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Default Re: O/T What material would you use for new axle shafts?

I have made many brass era car axles. As directed by the sprint car community, 4140 has been my choice of axle shaft material. Additional heat treating is not necessary. Pictured below is our 1916 Stanley Mt. Wagon that I have also made new axles for. Our kids and grand kids are aboard.
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Old 07-08-2020, 12:01 PM   #9
Terry, NJ
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Default Re: O/T What material would you use for new axle shafts?

Another vote for 4140 as is, no heat treating!
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Old 07-08-2020, 01:28 PM   #10
BRENT in 10-uh-C
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Default Re: O/T What material would you use for new axle shafts?

Thanks everyone. I just ordered two 5' lengths of 4140. I guess the older I get, the more I try to over-think things, so it's times like this where it is great to have friends to bounce ideas and thoughts off of.

Thanks again!!
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