Advice on making transmission shafts - Page 4
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  1. #61
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    Quote Originally Posted by CarbideBob View Post
    No smaller shop can ever hope to do this type fatigue testing.
    Bob
    I've designed parts for NASA where we were required to do fatigue and fracture analysis for critical parts, that would be part of a stress report, we proved analytically the part would be acceptable. Factors of safety were high (typically greater than 4) so there was margin for error that didn't result in a failure if either the analysis or material was sub-par.

    It's not that hard to do hand analysis of a part to assess fatigue/fracture life if you know the material, the heat treat,the loads (bending/torsion or both)stress concentrations etc, and what your doing etc.

    The only time we were ever asked to do a rotating beam fatigue analysis was on Aermet310. There was some concern of de-carburisation during heat treatment. We told the customer we were leaving .030" excess on the part before heat treat, and then machining that off after heat treat, therefore getting underneath the decarb layer. They said they would accept that if we made samples from the same plate, heat treated at the same time as the article, they would accept our analysis if backed up by acceptable results from the rotating beam test. Luckily the test went ok and we were able to prove that our approach was acceptable for the article.

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  3. #62
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    "Do you know enough to make a 'coherant' drawing? Do you know what the spline is, how to specify the splines including tolerances? Do you know what material you want to use and the specific heat treat callouts required? Do you know the tolerances required for the grinding etc?"

    No. But I could make a coherent drawing. I have no idea what a 'coherant' drawing is. But regardless, I don't need to get too in-depth with tolerances because anyone smart enough to cut splines will be able to take the sample shaft I give him and very, very quickly replicate it. A button-pusher machinist would indeed have a hard time...but that's not what I am after.

    Don't kid myself that aftermarket shafts are not stronger? Let's see...I never said OEM shafts are weak in the first place - but there's no doubt a good aftermarket shaft is stronger. I don't see a lot of the 2000HP drag car guys running stock shafts in their Powerglides.

    So anyway...after a little more digging I found someone who - get this - is a real machinist who actually makes shafts EXACTLY like I want. He makes them for himself and a few others. He didn't wet his pants over spline specs or any of the processes needed to produce a quality shaft. He has used these shafts with great success in his own cars that have way, way more severe duty than I'll ever see - so that passes my quality standard.

    Once he has his Financing group approve my credit he will accept an order from me for a minim of 5,000 shafts at $14,500 each, if I pay in advance. He will have his QA Metrology lab and his own metallurgy team begin the harrowing process of creating this part - I have come to learn that it is only slightly more difficult than a space shuttle rocket booster to produce - and the first of 5,00 shafts will be ready in 3.5 years. The school his kids attend will, however, name a gymnasium after me.


    Actually, he said he would make ONE, or as many as I want, for $500 each. I ordered three. End of story.

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  5. #63
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    Quote Originally Posted by GregSY View Post
    Actually, he said he would make ONE, or as many as I want, for $500 each. I ordered three. End of story.
    No, that's just the start of the next chapter.

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  7. #64
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    After a few delays (my fault), the shaft is in my hands....The shiny one is the new one, OEM is the other.

    I dropped the qty to one (1) as I decided to make sure all of my dimensions are spot-on. The PRACTICAL MACHINIST who made it was undeterred and seemed able and willing to produce this without making 2 million.

    Splines cut properly, diameters made larger where possible, and all out of 300M material with certs that was hardened, nitrided, and 'normalized'.

    Total production time of about a month.904-cf-shaft-final-r.jpg

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  9. #65
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    Thanks for update, the shaft looks nice.

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