How are "threads" made, any machinists out there?

Discussion in 'Archived Threads 2001-2004' started by Jay H, Oct 14, 2002.

  1. Jay H

    Jay H Producer

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    Just curious, to make a "screw" out of a bare extruded rod of some metal, how is it done? Is it a machine or a type of tool?

    I need to make some threaded metal rods for a custom bike rack using the tow hooks on my car. I have the tow hook itself and would need to copy the diameter and thread count for the rods. I have a brother-in-law who has access to machinists and welders so I'm curious what kind of info can I give him, besides the tow hook itself, to help...

    Jay
     
  2. Matt Whealton

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    There are specialized machine tools for thread cutting. Tapping is simple on a machining center but I think you'd need a CNC machine to do external thread cutting. (Pardon, my machine tool industry days are ,ahem, a bit in the past)!

    At any rate, you can buy threaded rod in all sorts of lengths, diameters, and thread gauges from fastener distributers. Why not do that? (You can also get choices of hardening and surface coating that way). Cutting them yourself, even if you have the equipment, may weaken the material or require a post machining hardening step.
     
  3. Bill Catherall

    Bill Catherall Screenwriter

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    To cut external threads you use a die. No need for any CNC machines. Hardened metals are obviously harder to cut, but will give you the strongest threads. But like Matt said, you can buy threaded rod in almost all sizes. Just check with McMaster-Carr online.
    There are other ways to create threads without cutting, like rolling the rod through a die that forms the threads, but that requires specialized machinery and is used for mass production.
    Oh, and to find out what size threads your hitch will take just measure the diameter of the hole and go buy some bolts with standard thread sizes in sizes close to that diameter and see which one fits (or you could buy a thread gage, but this is easier).
    If you measure the hole diameter to be approximately 1/4" then buy some #10-24, #10-32, 1/4-20, 1/4-18, 5/16-18, and 5/16-24 bolts.
     
  4. Leo Hinze

    Leo Hinze Stunt Coordinator

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    Threads can be made a variety of ways.

    External threads (like on a bolt) can be made by cutting. You can use a lathe, or you can buy a tap and die set. The dies are what are used to cut the threads.

    Internal threads are made by cutting only. You need a thread tap to make internal threads.

    The best way for you to match the threads on the tow hook is to give a tow hook to a machinist. They will have the proper guages and such to measure the pitch (number of threads per inch) and nominal diameter of the thread.

    Like Matt said, threaded rod is readily available. It is sometimes referred to as "all thread." Check your local hardware store. If you can't find it, it is easy for someone with basic machine tools to make a threaded rod for you.

    The strength difference between off-the-shelf threaded rod and a rod which you cut the threads yourself may or may not be a problem. Most off-the-shelf stuff will be made from high-strength alloys and properly heat-treated after the threads are made. The off-the-shelf stuff will probably have rolled threads, as that process works better with the higher strength alloy. Base rod for stuff you thread yourself will proabably not be as strong.

    That being said, if you are using threads that are large enough for towing the car, a 25 lb bicycle should be within the design strength.

    Good luck.
     
  5. Jay H

    Jay H Producer

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  6. Ryan Wright

    Ryan Wright Screenwriter

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    Jay, if you're putting your Spyder in a ditch, you've got more problems than the thread... [​IMG]
     
  7. Jay H

    Jay H Producer

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    Ryan: [​IMG] trying very hard not to!
    I just confirmed that the rod I have is non-standard! I've learned a helluva lot about Metric threaded rods and sizing and that it's size M22 x 2.0 which means it has an OD of 22mm and a thread pitch of 2mm. ISO/DIN standard of Metric rods says that all 22mm thread size rods have a standard thread pitch of 2.5mm which means my needed measurement is non-standard. Arrgh.. I will doublecheck my measurement of the thread pitch again to make sure. I'm told it might be more accurate to measure 11 threads and divide by 10 which makes sense, I guess a .5mm might be hard to determine by just sight alone and averaging the 10 pitches makes sense.
    Oh well, looks like welding a longer rod to two new or junkyard'ed tow hooks is looking better and better now [​IMG]
    Jay
     

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