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making a grade 8 bolt

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  • DR
    replied
    FWIW, long time ago we had a job using some high strength bolts, USA made. The job was to drill a number of small axial and cross holes. We needed to have the bolts annealed for the drilling. Called the manufacturer, Unbrako, to ask what they were made of, info the heat treater needed for annealing and re-heat treating. The company said "none of your business". They said they could use any material they wanted as long as the bolts met the strength specs. We sent them to a metal tester to determine the alloy (which I don't recall now).

    Another job we made wheel studs for a vintage Maserati, different thread pitch on each end. The customer spec'd the material . We machined to length with the important end chamfer angles specified by the thread rolling company. The chamfer angle is important so after distortion from rolling the thread starts easily. The thread rollers have to centerless grind the roll area to precise diameter, then roll. Off to the heat treater to complete the parts. I recall they were well over a hundred bucks per stud.

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  • Willy
    replied
    Some of you may find this short series of videos very enlightening and interesting.
    The three part series of videos consists of a tour of ARP Fasteners and covers all steps of how these components are made.
    This company is probably not only the largest manufacture of high performance automotive fasteners but also thee go-to source for extremely high grade mission critical fasteners for various industries. Need something special? If they don't already have it they'll make whatever you need. They claim higher than aerospace industry standards!

    I've used them numerous times in the past and have always been impressed with their quality. Their downloadable catalog is also a fantastic wealth of information regarding some of the finer points of fastener design and metallurgy.
    Be sure to watch all 3 videos.

    https://www.youtube.com/watch?v=WYnyIu7GCJ4

    https://www.youtube.com/watch?v=ubb7hhRehsc

    https://www.youtube.com/watch?v=rfLQTvy0NPw

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  • garyhlucas
    replied
    Originally posted by Richard P Wilson View Post
    You guys can slag off McMaster all you like, but you don't know how insanely jealous it makes me here in the UK to read of this one stop store that seems to sell EVERYTHING a machinist needs. We've got nothing like that over here.
    They have been doing a great job for about 125 years too! I have only been dealing with them for a little over 50 years. I am super impressed at how well they made the transition to the internet too. I have the luck of having one of their warehouses right in my backyard and I got a personal tour of the place when I contacted them about some suggestions. This also means same day delivery or pick up there in an hour! They told me a lot about their operations while I was there and it is amazing to say the least.

    We are very lucky!

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  • MattiJ
    replied
    Originally posted by Mcgyver View Post

    I think you'd heat treat afterwards to save the rolling dies. I won't go to the mat (haha) on this as I haven't enough direct knowledge, but what you says is contrary to what I've read and contrary somewhat to experience in that metal does have a grain that doesn't start to go away unless you normalize. Cutting threads interrupts the grain, rolling does not.

    whats your source that that rolled is only stronger if heat treated after, and why? A friend runs a good size fastener manufacturer, i'll see if he has any insight
    you lose the cold work hardening and only benefit is the better ”grain flow”

    Some source that I was able to come up in a hurry:
    https://www.globalfastenernews.com/w..._Threading.pdf
    edit: better source https://citeseerx.ist.psu.edu/viewdo...=rep1&type=pdf

    Based on quick look 150ksi yield is the practical upper limit for thread rolling so grade 8 would be borderline possible but no doubt more wear and tear for machines. https://www.portlandbolt.com/technic...threads-bolts/

    Last edited by MattiJ; 09-15-2021, 12:58 PM.

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  • BCRider
    replied
    Originally posted by Mcgyver View Post

    Would you know how to dress the wheel? The wheel obviously has to be tilted to match the helix .....but thread profiles are not tilted, i.e. they're in a plane aligned with the axis. So how do you dress the sides of the wheel, to what angle? I've pondered grinding threads but wonder about the wheel geometry and dressing
    I read a little on such a thread grinding machine at one point. The machine being described had a full time "crush dresser" that rode against the wheel to maintain the shape. I guessed at the time that this meant a roller with the thread profile.

    The grinding wheel would need to be presented at an angle to the work that matched the helix angle of the thread pitch. And the work turned and fed at the thread pitch rate much like single pointing.

    At least that's what I got out of reading that paragraph or two about thread grinders a few years back. The reference to the thread grinding being for use in making taps. Using the grinder allowed for some amount of relief being ground into the threads so when the gullets were ground away that the teeth had the proper cutting clearances.

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  • J Tiers
    replied
    There are two issues.... One is the potential stress riser unless you cut rounded threads. That can be fixed by using a full profile threading insert for the thread concerned.

    The other is the grain and the increase in strength due to work-hardening from rolling the threads. That is not as easily handled for cut threads. Rolling is somewhat like forging in how it works with the "grain", and some sort of heat treatment may be needed to attain the same added strength.

    Leave a comment:


  • Mcgyver
    replied
    Originally posted by MattiJ View Post

    AFAIK rolled threads are not requirement for grade 8 per se. And the rolled thread is stronger than machined thread only if the thread is rolled before heat treatment. Many? manufacturers heat treat after rolling as it is cheaper….
    I think you'd heat treat afterwards to save the rolling dies. I won't go to the mat (haha) on this as I haven't enough direct knowledge, but what you says is contrary to what I've read and contrary somewhat to experience in that metal does have a grain that doesn't start to go away unless you normalize. Cutting threads interrupts the grain, rolling does not.

    whats your source that that rolled is only stronger if heat treated after, and why? A friend runs a good size fastener manufacturer, i'll see if he has any insight
    Last edited by Mcgyver; 09-15-2021, 08:31 AM.

    Leave a comment:


  • nickel-city-fab
    replied
    Originally posted by fxkl47BF View Post

    i agree 100%
    i repair/fix/upgrade old/antique devices/machines that will not be put to work full time
    none of my work is critical
    with a small lathe and mill i enjoy making the parts that i can

    it was stated in one of the post that o-1 is overkill
    but if one was to use o-1 what would the tempering temperature be to achieve the tensile strength of grade 8
    I would temper it at between 450 to 550 degrees F, basically a 45-50 RC temper.
    For a high strength application I would actually mirror-polish the threads, like a clockmaker.
    Last edited by nickel-city-fab; 09-15-2021, 09:02 AM.

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  • MattiJ
    replied
    Originally posted by Mcgyver View Post

    this. Rolled threads are stronger and that's what it'll need. Excellent coverage of that topic in Carroll Smith's "Engineered to Win"
    AFAIK rolled threads are not requirement for grade 8 per se. And the rolled thread is stronger than machined thread only if the thread is rolled before heat treatment. Many? manufacturers heat treat after rolling as it is cheaper…just like thread rolling is lot cheaper than cutting in large volumes.

    Original UN threadform is bad start anyways, IIRC whitworth threadform with rounded crests shows bigger improvement than rolling vs machined.

    best of the best is rolled thread after heat treatment with modified UN(xyz) thread form. But this is not your bog standard grade 8 hardware store bolt, more like costly aerospace fasteners or expensive head studs.
    Last edited by MattiJ; 09-15-2021, 03:12 AM.

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  • Richard P Wilson
    replied
    Originally posted by nickel-city-fab View Post

    Who was slagging off McMaster? I absolutely LOVE them for just those reasons... its one-stop shopping!
    I'm sure they would be happy to sell to you, but the shipping might be a bit much....
    Bear in mind they *are* a large industrial supplier after all..
    Not in this thread certainly, but theres been another thread on here recently complaining about them.

    Leave a comment:


  • JoeCB
    replied
    When I need a special high strength screw or bolt I make it out of a larger/longer grade 8 bolt. A handy source of pre-hardened material of known quality.
    Joe B

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  • fxkl47BF
    replied
    Originally posted by darryl View Post
    What others have alluded to- for anything critical it makes more sense to buy it. Critical meaning anything aviation, anything where failure could hurt somebody, or cause damage, that kind of thing. If you can buy gr 8 threaded rod you can make a custom length bolt, and it will most likely be stronger than what you will machine. Your decision must be tempered by the application.
    i agree 100%
    i repair/fix/upgrade old/antique devices/machines that will not be put to work full time
    none of my work is critical
    with a small lathe and mill i enjoy making the parts that i can

    it was stated in one of the post that o-1 is overkill
    but if one was to use o-1 what would the tempering temperature be to achieve the tensile strength of grade 8

    Leave a comment:


  • Doozer
    replied
    I think Brian at VersaMill has a thread grinder or 2...
    He might be able to give you the skinny on it,

    --D

    Leave a comment:


  • Mcgyver
    replied
    Originally posted by Doozer View Post
    I would really love to have an Excello thread grinder.
    So awesome. Maybe some day. Watch this space.
    Would you know how to dress the wheel? The wheel obviously has to be tilted to match the helix .....but thread profiles are not tilted, i.e. they're in a plane aligned with the axis. So how do you dress the sides of the wheel, to what angle? I've pondered grinding threads but wonder about the wheel geometry and dressing

    Leave a comment:


  • darryl
    replied
    What others have alluded to- for anything critical it makes more sense to buy it. Critical meaning anything aviation, anything where failure could hurt somebody, or cause damage, that kind of thing. If you can buy gr 8 threaded rod you can make a custom length bolt, and it will most likely be stronger than what you will machine. Your decision must be tempered by the application.

    Leave a comment:

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