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Thread: How to double a thread size

  1. #1
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    Default How to double a thread size

    Morning everyone. Could someone on this site PLEASE tell me How to double small thread sizes, #2-56 / #3-48 / #4-40. i want to increase the size of some of Elmer Vertburg's model engines, but am having a hard time with small thread sizes. THANKS TO EVERYONE. telescope.
    Last edited by Telescope; 04-16-2018 at 07:40 AM.

  2. #2
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    I assume you want standard sizes. The easiest way is to get a Machine Screw Thread Chart. Double the major diameter of the thread you want to scale up and pick the closest screw size to that. A 2-56 would become about an 8-32.

  3. #3
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    To arrive at the diameter, start with #0, which is .060" then add .013" for each number larger.

  4. #4
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    The outer diameter of a #4-40 is 0.110", for a #5-40 is 0.122", for a #6 is 0.136" for a #8 is 0.163" and for a #10 is 0.190"
    If you double them, the closest you can get for the #4 and #5 and #6 is 1/4". A #8 doubled is 0.326, so the closest to that is 5/16". A #10 doubled becomes 3/8".
    Brian Rupnow

  5. #5
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    Don't forget that doubling the engine dimensions multiplies the volume by 8. Doubling the fastener dimensions increases their cross sectional area by 4.

  6. #6
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    Whenever I come up with something like this I find that a quick web search is the key. You need to know the physical sizes of the number series screws. So search for something like "number screw diameter table".

    The first item that came up took me to the right table for your needs but it was listed for "wood screws". Same info though. But the third item was the SIZE TABLE FOR MACHINE SCREWS.

    The other answers are right too. But I'm pretty sure a nice easy to read table like this is going to be easier by avoiding the need even for simple math.

    By the way telescope, I see that this is your first post! Welcome Aboard!

  7. #7
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    Quote Originally Posted by Telescope View Post
    Morning everyone. Could someone on this site PLEASE tell me How to double small thread sizes, #2-56 / #3-48 / #4-40. i want to increase the size of some of Elmer Vertburg's model engines, but am having a hard time with small thread sizes. THANKS TO EVERYONE. telescope.
    If you are looking to double the size of some of his engine designs, I would not worry so much about just doubling the size of all the fasteners he used.
    Let's face it, many of the engines we build are run relatively infrequently. "Steam" engines run on air, gas and atmospheric engines all run for minutes at a time.
    I'm not saying that you should use the same size fastener @ 2X that you would use @ 1:1. Many times just scaling up will look out of place. I have seen many models using, for instance, a 10-32, where a 6-32 (maybe even a 5-40 or 4-40) would look better aesthetically and certainly within the needed loading.
    I very much see the craftsmanship in a well detailed and proportioned model as much and more that just completing a model (as exemplified by George Britnell's model this weekend) Of course, there are times that you have to make compromises. Don't be scared to learn how to do something in this hobby, like tapping smaller threads. That's what its all about!

    Sid

  8. #8
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    Hardware store fasteners, especially nuts, are going to look grossly out of scale on most engine models.

    The rules I use for scaling fasteners look like this...

    D = bolt major diameter
    Across flats dimension of bolt hex head and matching nut = 1.5*D
    Bolt head thickness = 0.7*D
    Nut thickness = 0.9*D

    Also, remember that slotted, Phillips, SHCS screws will look out of place on Elmer's engines. Proper hex head miniature screws are available from numerous suppliers who cater to the miniaturist trade. For models like the wooden beam engine, square head hardware would be appropriate.

    Also note that Elmer uses screws in many places where studs and nuts would be more appropriate.
    Regards, Marv

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  9. #9
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    Clickbate is a sure way to double thread size.

    -D

  10. #10
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    From what I can see of his engine designs, I do not believe that there will be any great issues with the strength of the fasteners. I would just go to a standard screw size chart and look up the diameters of the screws in question. Then go down the list until you find a diameter value that is about twice that number and that is your screw. If you have a tight fit situation, you may have to go to a standard size that is a bit smaller than the exact 2X value.

    Some images of his engines:

    https://www.google.com/search?q=Elme...w=1529&bih=795
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

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