How to increase the inner diameter of a plastic knob

[Jack_TriPpEr]

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.

 

[Ayrton]

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?

 

[ehdwuld]

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

Yeah be careful

 

[Jack_TriPpEr]

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?

Yeah be careful

Glad to hear that drilling seems to be a safe and effective way to go. Thanks guys.

 

[GuitarDoc]

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.

 

[DavidRavenMoon]

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


Sent from my iPhone using Tapatalk

 

[Jack_TriPpEr]

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.

No threads involved. Solid shaft pot, knob is meant for aolid shaft - has a set screw.

 

[DavidRavenMoon]

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

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.


Sent from my iPhone using Tapatalk

 

[NegativeEase]

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.

 

[GuitarDoc]

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.

 

[NegativeEase]

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.

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.

 

[Jack_TriPpEr]

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

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.

 

[ehdwuld]

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

 

[Mincer]

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

Yes, by hand seems like a logical and safe way of doing this.

 

[Ayrton]

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.

 

[Mincer]

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

Or, bit in a vise and slowly spin the knob by hand.

 

[GuitarDoc]

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

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.

 

[GuitarDoc]

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

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.

 

[ItsaBass]

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.

 

[GuitarDoc]

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.