Best way to make control cavity deeler

[arav87]

I’m having trouble finding a concentric pot with the values I want that has a bushing long enough to stick through the body of my bass, so I’d like to remove some material from the inside to make a normal CTS 250/500 fit.

What would be the best tool for such a tight space that I could use to slowly make space for the pot? I believe the top is 1/4” thick so I’d ideally like to remove 1/8” from a spot about the circumference of the pot itself to not impact the integrity of the top.

Thanks in advance

 

[Matt Liebenau]

A drill press and Forstner bit a little bigger than the body of the potentiometer would be my first thought. Carefully line up the body on the drill press table after padding the table to protect the finish, clamp the body down with a padded clamp and slowly work up to the depth you want. If you’re going that thin I’d probably try to find a fender washer the threaded part of the pot will fit through with the outside about the same diameter as the recess you’re going to drill and use that to reinforce the top of the control cavity if possible.

 

[arav87]

A drill press and Forstner bit a little bigger than the body of the potentiometer would be my first thought. Carefully line up the body on the drill press table after padding the table to protect the finish, clamp the body down with a padded clamp and slowly work up to the depth you want. If you’re going that thin I’d probably try to find a fender washer the threaded part of the pot will fit through with the outside about the same diameter as the recess you’re going to drill and use that to reinforce the top of the control cavity if possible.

I don’t have access to a drill press, do you think a power drill wood be ok to use?

 

[Matt Liebenau]

I don’t have access to a drill press, do you think a power drill wood be ok to use?

You’d have to be very careful. You’re drilling into an already existing hole and without something for the tip of the Forstner to bite into it will want to chatter or wander. Get some thin scrap wood or MDF and cut a piece small enough to fit in the control cavity then drill a hole through it with the Forstner bit. Position the wood scrap exactly where you want it and clamp or double stick tape it into the control cavity and use that as a guide. Remember, go slowly. It’s easy to remove too much and very difficult to put it back.

 

[Aloe]

careful: thinning the wood around pots might make it fragile. I've seen basses with cracked top after the pot knob had a bump. and I've seen basses with extra armor (like a metal plate) for preventing this very thing.

what are you trying to accomplish with a 500/250 pot: volume+tone? go two 500s. I think, a dual 500/500 MEC would be more compact than a CTS one.

 

[arav87]

It is a warmoth body with p bass control holes and a rear cavity. I have 2 p bass pickups, stacked vol/tone and a blend.

The only concentric pot I could find from CTS that fits is the one warmoth sells which is a CTS 500/500, but the pickups are a bit brighter sounding than I’d like so I thought maybe the 250k would mellow them a bit.

I just can’t find a 500/250 stack with a bushing that is long enough

 

[Dirk Diggler]

I would NOT suggest using a hand drill, you really need a drill press for stability.
And a Forstner bit is best no doubt, though it's possible to use a router, again though stability of the router is important.

 

[Aloe]

The only concentric pot I could find from CTS that fits is the one warmoth sells which is a CTS 500/500, but the pickups are a bit brighter sounding than I’d like so I thought maybe the 250k would mellow them a bit.

just in case: a 500k tone dialed half way sounds exactly the same as a 250k pot wide open. no other magic is there.

there's also an option to add a resistor to the circuit, kinda making a 250k pot from a 500k one.

 

[turf3]

I'd use a sharp 1/4" chisel, NO mallet, just push by hand and check frequently.

 

[groovaholic]

the pickups are a bit brighter sounding than I’d like so I thought maybe the 250k would mellow them a bit.

First off: that double-reverse P looks COOL.

Second: adding a loading cap on each pickup would be MUCH easier than removing wood from the bass.

Solder a 680pF cap across where each pickup connects to hot and ground - it'll tame the brightness and it's completely reversible...and you can experiment with cap values to get the right amount of treble reduction.

 

[sawzalot]

I'm not a luthier but I am a woodworker, I'd never use a hand drill for something like this. WIth a forstner bit if you're even a tiny bit off of absolutely plumb you'll be removing a lot more material than you want. You can't put it back once it's gone, and you're running a relatively high risk of ruining the body. If there's a reversible electronic way of solving this problem I'd 100% go that route.

 

[arav87]

First off: that double-reverse P looks COOL.

Second: adding a loading cap on each pickup would be MUCH easier than removing wood from the bass.

Solder a 680pF cap across where each pickup connects to hot and ground - it'll tame the brightness and it's completely reversible...and you can experiment with cap values to get the right amount of treble reduction.

Thanks, I’m psyched with how it’s turning out. This sounds like a great idea!

About these caps, so just solder it to the input on the blend pot? Would soldering a cap from input to ground on the input of the vol from the blend have the same impact, but evenly for both pups?

Also any rules of thumb about loading caps? Is it the higher the pF the darker the sound?

 

[Jazzdogg]

If you have yo ask, you may not be qualified to do the work yourself. Try the fix suggested by @groovaholic, above.

 

[GR7G5TER]

I don’t have access to a drill press, do you think a power drill wood be ok to use?

I'm no wood working genius and I free handed this mod on my Stu Hamm MIM using a power drill, be careful and you'll be fine.

 

[arav87]

If you have yo ask, you may not be qualified to do the work yourself. Try the fix suggested by @groovaholic, above.

I have no doubt I could do it, but I don’t own a drill press. I was hoping someone was going to tell me about some hand tool I could get inexpensive and use.

Definitely going to try groovaholics suggestion though, seems much easier

 

[Jazzdogg]

I have no doubt I could do it, but I don’t own a drill press. I was hoping someone was going to tell me about some hand tool I could get inexpensive and use.

Definitely going to try groovaholics suggestion though, seems much easier

As a retired college woodworking instructor I can affirm the job can be quickly completed using only hand tools.

I can also affirm that most of my students were amazed at the difference between their estimate of a task's difficulty and the actual difficulty after trying it; most overestimated their skill level, and underestimated the difficulty of the task at hand.

If I were undertaking such a task using hand tools, I would use a freshly sharpened mortising chisel and a router plane.

Because the difficulty of the work is directly proportional to the sharpness of the tools, your ability to do the work yourself is directly related to your sharpening skills; I have never found a new chisel suitably sharp to use out of the box.

My advice is to try to perform the task using a piece of scrap wood of the same species and grain orientation before attempting work on your bass.

Good luck!

 

[jglunt]

There are pots out there with longer shafts. Try Amazon. Try Ebay. Try amplifiedparts.com. Try guitarelectronics.com. Try allparts.com. Try stewmac.com. Even G&L Guitars sells long shaft pots in their online store. (See link below. I have no affiliation.) I highly recommend you do that instead of routing out the control cavity. These pots might not be CTS, but they'll be quality pots. Maybe Alpha. Maybe Bourns. I've used these pots with excellent results.

Pot - Tribute Series - Long Shaft

Mighty Might brand Long Split-Shaft potentiometer for G&L Tribute Series models where the pot is mounted through the body, not through a pickguard or control plate. Fits Tribute Series models include L-2000, L-2500, ASAT Deluxe Carved Top, Ascari GTS, Fiorano GTS. Will NOT fit USA models or any...

g-l-online-store.myshopify.com

 

[arav87]

I have no found a suitable concentric pot with a long enough bushing

 

[Matt Liebenau]

I have no doubt I could do it, but I don’t own a drill press. I was hoping someone was going to tell me about some hand tool I could get inexpensive and use.

Definitely going to try groovaholics suggestion though, seems much easier

If you don’t want to go the loading capacitor route you could try a Forstner bit in a hand brace instead of a powered drill. I’d still make and use a guide like I mentioned above.

 

[groovaholic]

About these caps, so just solder it to the input on the blend pot? Would soldering a cap from input to ground on the input of the vol from the blend have the same impact, but evenly for both pups?

Also any rules of thumb about loading caps? Is it the higher the pF the darker the sound?

Anywhere that the capacitor creates a path between hot and ground will bleed off treble.
You can do that two ways: either for each pickup or the whole circuit.

You could fine tune the sound of each pickup by putting a loading cap where each pickup connects to the blend.
That's especially helpful if one pickup sounds OK and the other is too bright, or if you want each to have a different tonality.

Less control but simpler is a whole-circuit treble bleed, which can either go where the blend "feeds" the volume pot at the output jack.

You're correct that higher values will make the signal darker - 680pF is a good middle of the road value, but I've used as small as 400pF and as high as 1200pF depending on the pickup. The effect is like using a longer cable with a passive bass.

The easiest (also quick and 100% reversible) way is to try it out using a pair of alligator clips.

Connect a clip to the hot wire, and another clip to ground.
The other ends of the alligator clips go to either side of the capacitor:

I just hooked the black alligator clip to the pot for clarity.
That's probably where you'd want to solder your loading cap, but there are easier spots (ground wire, output jack, etc) to make a test connection.

Also, ignore the pot and capacitor values - that's just what I had handy.

Hope it works for you!