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Thread: How to increase the inner diameter of a plastic knob

  1. #1
    Toneologist kingswebe's Avatar
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    Default How to increase the inner diameter of a plastic knob

    I've got a plastic knob whose inner diameter is too small to fit the shaft of the potentiometer i want to use.

    Is it possible to increase the knob inner diameter by drill the hole wider with the appropriate sized bit? Or instead, use a dremel with a sanding pad fitting on the lateral surfaces of the dremel tip to sand the existing hole to be wider? Is one method more fool-proof than the other? Is there a third option I should consider?

    The knob is designed so that there is solid material all around the existing hole vs the hole just being a flanged design surrounded by empty space, so theoretically the knob should be able to withstand some drilling/dremeling without instant collapse.

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    Mojo's Minions Ayrton's Avatar
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    Default Re: How to increase the inner diameter of a plastic knob

    I have drilled out knobs before. You just have to be slow and careful not to drill through.

    Maybe just order some new knobs?
    -Chris


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    A Ficus ehdwuld's Avatar
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    Default Re: How to increase the inner diameter of a plastic knob

    Yeah be careful
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    Toneologist kingswebe's Avatar
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    Default Re: How to increase the inner diameter of a plastic knob

    Quote Originally Posted by Ayrton View Post
    I have drilled out knobs before. You just have to be slow and careful not to drill through.

    Maybe just order some new knobs?
    Quote Originally Posted by ehdwuld View Post
    Yeah be careful
    Glad to hear that drilling seems to be a safe and effective way to go. Thanks guys.

  5. #5
    Bacteriaolgoist GuitarDoc's Avatar
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    Default Re: How to increase the inner diameter of a plastic knob

    Are you sure it's too small? Or is it just a different knurl pattern? There are two different knurl patterns in knobs to fit the two different knurl patterns on pots...one to fit Asian made pots (Alpha, etc) and one to fit American pots (CTS, DMZ, etc).

    If your knob is a solid color you can get away with drilling it out. If it is transparent with the color coating on the inside of the knob you can't do it. In any case you need to be extremely careful because the drill bit will grab in the soft plastic and pull the bit all the way through in an instant and ruin your knob.

    It is best just to buy the correct knob for your pot.
    Originally Posted by IanBallard
    Rule of thumb... the more pot you have, the better your tone.

  6. #6
    Super Toneologist DavidRavenMoon's Avatar
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    Default Re: How to increase the inner diameter of a plastic knob

    If it’s a split shaft pot, you can gently squeeze the shaft a little to allow the knob to fit.

    Unless one is metric and the other imperial


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    Toneologist kingswebe's Avatar
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    Default Re: How to increase the inner diameter of a plastic knob

    Quote Originally Posted by GuitarDoc View Post
    Are you sure it's too small? Or is it just a different knurl pattern? There are two different knurl patterns in knobs to fit the two different knurl patterns on pots...one to fit Asian made pots (Alpha, etc) and one to fit American pots (CTS, DMZ, etc).

    If your knob is a solid color you can get away with drilling it out. If it is transparent with the color coating on the inside of the knob you can't do it. In any case you need to be extremely careful because the drill bit will grab in the soft plastic and pull the bit all the way through in an instant and ruin your knob.

    It is best just to buy the correct knob for your pot.
    No threads involved. Solid shaft pot, knob is meant for aolid shaft - has a set screw.

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    Super Toneologist DavidRavenMoon's Avatar
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    Default Re: How to increase the inner diameter of a plastic knob

    Quote Originally Posted by kingswebe View Post
    No threads involved. Solid shaft pot, knob is meant for aolid shaft - has a set screw.
    Yes, you cab drill those out. I do it with Hipshot knobs to fit on Bourns pots.


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    Mojo's Minions
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    Default Re: How to increase the inner diameter of a plastic knob

    If you have a highly tapered stepper bit or a Dremel with a jig/dremel stand it's a very easy job.

    But I'm guessing you are going old school -so mount the knob securely and move up in 64ths or 32nds with bit selection until it works.
    “For me, when everything goes wrong – that’s when adventure starts.” Yvonne Chouinard

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    Bacteriaolgoist GuitarDoc's Avatar
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    Default Re: How to increase the inner diameter of a plastic knob

    A "stepper bit" won't work, you need as close to a flat end drill bit as you can get.

    The ideal way to do it would be start with conventional drill bits and drill up to final diameter (NOT in 32nds" or even 64ths"...way too large, the bit will grab the plastic and destroy it). A couple thousandths" at a time, 128ths" at most. Then finish off with a milling bit (flat bottom) of the correct final diameter.
    Originally Posted by IanBallard
    Rule of thumb... the more pot you have, the better your tone.

  11. #11
    Mojo's Minions
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    Default Re: How to increase the inner diameter of a plastic knob

    Quote Originally Posted by GuitarDoc View Post
    A "stepper bit" won't work, you need as close to a flat end drill bit as you can get.

    The ideal way to do it would be start with conventional drill bits and drill up to final diameter (NOT in 32nds" or even 64ths"...way too large, the bit will grab the plastic and destroy it). A couple thousandths" at a time, 128ths" at most. Then finish off with a milling bit (flat bottom) of the correct final diameter.
    I just did this with a stepper a few weeks ago. -On the GK style plastic knobs that have the gray cap so the stepper easily widened the channel and protruded out the other side with the gray cap off.

    Second, you can absolutely do this with 32nd or 64th bits . -I used to this in my sleep as a kid when adding weird knobs to solid posts.. I think the difference here is Guitar Doc is giving you the more correct Luthier approach, I was giving you the home solution because as indicated I said I'm guessing you are going old school without specialty tools.
    “For me, when everything goes wrong – that’s when adventure starts.” Yvonne Chouinard

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    Toneologist kingswebe's Avatar
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    Default Re: How to increase the inner diameter of a plastic knob

    Quote Originally Posted by NegativeEase View Post
    I just did this with a stepper a few weeks ago. -On the GK style plastic knobs that have the gray cap so the stepper easily widened the channel and protruded out the other side with the gray cap off.

    Second, you can absolutely do this with 32nd or 64th bits . -I used to this in my sleep as a kid when adding weird knobs to solid posts.. I think the difference here is Guitar Doc is giving you the more correct Luthier approach, I was giving you the home solution because as indicated I said I'm guessing you are going old school without specialty tools.
    Thanks, that makes sense.

  13. #13
    A Ficus ehdwuld's Avatar
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    Default Re: How to increase the inner diameter of a plastic knob

    Oh no not a step bit

    I used a normal drill set in 64's
    Found first the one that fit best the original hole
    Then next size up by hand
    Slowly
    No drill motor
    If you just do a small step wit each bit
    It is easy to drive by hand

    No running out into your other palm
    No running out the top
    None of that nonsense
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  14. #14
    Administrator Mincer's Avatar
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    Default Re: How to increase the inner diameter of a plastic knob

    Yes, by hand seems like a logical and safe way of doing this.
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    Mojo's Minions Ayrton's Avatar
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    Default Re: How to increase the inner diameter of a plastic knob

    If you attempt this by holding the knob in your hand, I suggest running the bit in reverse and move up in size gradually.
    -Chris


    Quote Originally Posted by John Suhr View Post
    Practice cures most tone issues

  16. #16
    Administrator Mincer's Avatar
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    Default Re: How to increase the inner diameter of a plastic knob

    Or, bit in a vise and slowly spin the knob by hand.
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    Bacteriaolgoist GuitarDoc's Avatar
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    Default Re: How to increase the inner diameter of a plastic knob

    Quote Originally Posted by NegativeEase View Post
    I just did this with a stepper a few weeks ago. -On the GK style plastic knobs that have the gray cap so the stepper easily widened the channel and protruded out the other side with the gray cap off.

    Second, you can absolutely do this with 32nd or 64th bits . -I used to this in my sleep as a kid when adding weird knobs to solid posts.. I think the difference here is Guitar Doc is giving you the more correct Luthier approach, I was giving you the home solution because as indicated I said I'm guessing you are going old school without specialty tools.
    Well, of course a step drill will work on a hollow cylinder!!! (And that's effectively what you have if you are working on a knob that has a removable cap). But I don't think that's what we have here.

    The suggestions that I gave, or the ones about doing it by hand are the most appropriate.
    Originally Posted by IanBallard
    Rule of thumb... the more pot you have, the better your tone.

  18. #18
    Bacteriaolgoist GuitarDoc's Avatar
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    Default Re: How to increase the inner diameter of a plastic knob

    Quote Originally Posted by Mincer View Post
    Or, bit in a vise and slowly spin the knob by hand.
    Yes, this is the best way to do it if the "correct" tools aren't available.
    Originally Posted by IanBallard
    Rule of thumb... the more pot you have, the better your tone.

  19. #19
    Mojo's Minions ItsaBass's Avatar
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    Default Re: How to increase the inner diameter of a plastic knob

    I would start the hole with a hand reamer, going as far as you can that way. Then finish it off with a drill (drill press, if you have one). The reamer helps to ensure that your hole doesn't drift off center.
    Quote Originally Posted by LesStrat View Post
    Yogi Berra was correct.
    Quote Originally Posted by JOLLY View Post
    I do a few chord things, some crappy lead stuff, and then some rhythm stuff.

  20. #20
    Bacteriaolgoist GuitarDoc's Avatar
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    Default Re: How to increase the inner diameter of a plastic knob

    The hole won't drift if you use conventional drill bits progressively wider in tiny increments. Certainly it can if you go right to the final size.

    That's NOT to say that using a reamer is NOT a good idea, but it is actually pretty easy to get the opening of the hole too wide using a reamer by hand.
    Originally Posted by IanBallard
    Rule of thumb... the more pot you have, the better your tone.

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