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  1. #1
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    Default Help please with cutting a thread on an Aluminium Rod

    I'm new to metalwork, and certainly new to cutting a thread on a rod, and need some help please. I am building a Radio Antenna to the design attached. The design calls for a thread to be cut on the bottom of three aluminium rods.

    I have two questions, and the first is this:

    Q: The internal thread on the Stud Mound into which the 'Driven Element' rod must screw is 3/8". ( https://www.thunderpole.co.uk/mounti...tud-mount.html )

    The attached design appears to call for 10mm diameter Aluminium Rod. But I can also buy 9.52mm (3/8") diameter Aluminium Rod. 3/8" equates to 9.525 mm, not 10 mm. Should I buy 10mm diameter rod, as called for in the design, or 9.52mm (3/8") diameter? I am assuming that 3/8" is the outside diameter of the thread, and I don't have a lathe to reduce the diameter before cutting the thread.

    I don't want to cast doubt on the obviously well-drawn plan, but logic suggests that I should cut the thread on 9.52mm diameter rod for all three rods, which won't require any preparation or reduction of diameter before cutting the thread.

    Second Question:

    Please forgive the dumb question - this is all very new to me - but 'measure twice and buy once' is good advice. I vaguely remember (55 years ago) being shown how to cut a thread in a school metalwork lesson.... and will need to buy the necessary die and hand tool from ebay! But what die should I be buying? Just a 3/8" thread die? Or do I need to be more specific?

    Thanks in advance... both for reading, and hopefully for answering....

    Richard
    Attached Images Attached Images

  2. #2
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    Default

    Hi Richard. First of all, let me welcome you to our MetalWork forum.

    Theres a great bunch of people here of every metalwork type you can imagine.
    To explore what we have goto the FORUM box ant the LH top of the page.

    Click on the down arrow to get a pulldown menu.On the top you shall find Forum Home

    Click on that again and it will take you to a scroll page with each of our sub-forums and special areas like the Welcome Wagon and lots of others.

    Please take the time to read the the rules (Terms of Service) at very top of the page the top and have a look at what is on the long list below that.

    Looking at the drawing it looks like it won't make a damn of difference if you go ahead and a 3/8 x 24 thread straight on the 3/8" (9.52 mm ) diameter. That is unless the step down diameters effects some other factors.

    To make it easier to start your thread I would file a small taper on the rod ends to allow the die to start.You must take care to keep the die perpendicular to the shaft axis as its very easy ( in aluminium ) to start crooked and end up with a wonky thread. Possibly some practice pieces are required.

    Welcome again
    Grahame

  3. #3
    Join Date
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    You could either buy 3/8" rod and thread it 3/8 as called up in the drawing or buy 10mm rod and thread it for M10. It does not matter which provided you have matching nuts for it - that may be a better place to start - what is easiest to get. You will need to buy a die that matches the nuts you intend to use.

    When cutting threads on Al, use a suitable lubricant (WD40, CRC or alternatively rub a wax candle against the area to be threaded)

    Michael

  4. #4
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    Looking at your drawing it appears that the rods are turned down to suit the 3/8" unf thread.

    Does anything need to clamp to the rods, if it does you may not be able to use the 3/8" rod unless you have clamps or fittings to suit the smaller rod diameter.

    In regards to the stock and die , I would suggest buying a good quality die ( either split or solid ) and a stock ( the part that holds the die to suit ).

    You will need to hold your rod securely to cut the thread, preferably in the vertical position, most quality dies will have a lead or taper at one face of the die to make starting the thread easier, the cheaper dies may not and this will make it harder to start the thread.

    As has been said a short taper on the end of your rod will assist in starting.

  5. #5
    Join Date
    Sep 2012
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    York, North Yorkshire UK
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    Hi Richard,

    Welcome to the forum ! As you can see I am also in the UK, just a bit North of you

    You might have a problem sourcing a 3/8" X 24 tpi die. As far as I'm aware it isn't a very common thread. As is an SO239 which is 5/8" X 24 tpi. Non of the tool suppliers stock them. Tracey Tools down your way might be able to help.
    Best Regards:
    Baron J.

  6. #6
    Join Date
    Mar 2011
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    Southern Flinders Ranges
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    Default

    It doesn’t need to be solid. RF travels on the outside skin.. Make it all from tube. You could get some tube and tap it 3/8 and put a stud in it, like wise for the the reflectors, this is generally how commercial antennas are constructed. RF travels on the outside skin of conductors, that’s why larger coax cable like LDF 4-50 have a copper clad aluminium centre conductor, the RF only travels in the copper making it cheaper to produce.
    I make my living with RF, feel free to PM me if you have any questions about that part of what you are doing.

  7. #7
    Join Date
    May 2018
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    Brisbane
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    Default Help please with cutting a thread on an Aluminium Rod

    Round up a 3/8 UNF (United Fine) bolt and a 10 mm bolt and see which fits. Use the appropriate size rod for the job. UNF dies should be available from most tool retailers and ebay. You can get a 3/8 die to cut a thread on 10 mm rod with a bit of effort. Aluminum is pretty soft to cut although it work hardens. 10 mm rod would be about 20 thou oversize for 3/8.

  8. #8
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    Quote Originally Posted by jhillam View Post
    ... UNF dies should be available from most tool retailers and ebay...
    The OP is in the UK though. 3/8" BSF may be more easily borrowed/ obtained.

    Michael

  9. #9
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    Hi Guys,

    I've just checked with "Tracy Tools" here in Devon, UK. They have both taps and dies for 3/8" X 24 UNF

    Though I think the RF plugs and sockets may be 60 degree thread angle.
    Best Regards:
    Baron J.

  10. #10
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    Default

    That would suit the UNF.

  11. #11
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    Jan 2020
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    Nr Bristol, UK
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    Default Great! Thanks all... a real help

    Well, that was unexpected! A positive stream of help here. Thanks everyone - so far so good. What have I learned so far?
    1. That this is a great forum for help.
    2. I will take the suggestion of checking the internal thread of the stud into which the resonator must be screwed by trying it with a bolt of known size and thread. That way I will be sure I'm buying the correct die.
    3. 3/8 rod will work - my initial question. I don't want oversize and jamming issues!
    4. Yes, tube will work fine for RF, but I'd rather cut a thread on rod than tube! Newby doesn't want to complicate things....
    5. Once I know, and have checked, the size of the thread using the bolt method, I will buy a good quality die.
    6. If this works, then possibly the bug will have bitten!!

    Again, many thanks to everyone who has replied - and to those who took the trouble to read as well.
    Richard

  12. #12
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    Default

    Quote Originally Posted by racingtadpole View Post
    I make my living with RF, feel free to PM me if you have any questions about that part of what you are doing.
    . PM with associated RF question sent!

  13. #13
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    Quote Originally Posted by jhillam View Post
    Round up a 3/8 UNF (United Fine) bolt and a 10 mm bolt and see which fits. Use the appropriate size rod for the job. UNF dies should be available from most tool retailers and ebay. You can get a 3/8 die to cut a thread on 10 mm rod with a bit of effort. Aluminum is pretty soft to cut although it work hardens. 10 mm rod would be about 20 thou oversize for 3/8.
    The bolt test is brilliant!! Didn't think of that. I have already bought the insulated mounting stud, so have the thread into which the driven element must be screwed and therefore die cut. So the first job will be to check the thread size with a bolt. Then I can buy or borrow the correct die. If 3/8, then 3/8 rod. Don't want any oversize issues!!

  14. #14
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    Default Tapping the Aluminium Rod

    Quote Originally Posted by pipeclay View Post
    Looking at your drawing it appears that the rods are turned down to suit the 3/8" unf thread.

    Does anything need to clamp to the rods, if it does you may not be able to use the 3/8" rod unless you have clamps or fittings to suit the smaller rod diameter.
    No, nothing needs to be clamped. If bolt test proves, then 3/6 rod it is!

  15. #15
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    Default

    Hi Richard,

    Just a question, do you propose to transmit into this antenna ?
    Best Regards:
    Baron J.

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