Me again - I f----d up... (Pot heights)

[CC1]

Hello, me again.

 

The SG inspired bass is coming along really well. I have Fender Vintage PBass pickups, A Hipshot Kickass Bridge, Gotoh GB707 machine heads. All alignment and routing etc has been done well, and after my first pass with the neck pocket routing was 1mm too wide (0.5mm each side of the neck), which is surprisingly a LOT of give, the second pass was perfect and I can shim the sides/ sawdust-glue the gap. Should be good.

 

However, I have a pot problem.

 

This is a back-through build, no pickguard plate. Because short/normal pots would mean leaving very little wood at the surface, I opted for long shaft (19mm threaded part). Turns out, that's WAY too long. With fairly substantial knobs on, the knobs are sitting 4.6 and 5.9mm proud of the surface.

 

It puts me in a weird situation where 19mm pots are ~5mm too long, but the next size down is 9mm - but the thickness of the wood from the cavity to where the knobs would be is 9mm already. So if I lost 10mm of thread, I end up somehow going through the guitar.

 

I can't get a second nut and suspend the pot in the cavity - because then the bottom of the pot hits/crosses the plane of the cavity cover (the whole thing is slightly thinner than I had anticipated: ~31mm rising to 35mm through the neck part)

 

I would really appreciate some tips that don't involve "well next time don't suck" and "what you should have done is..." because I already know what I should have done, I'm wanting to salvage this as I've poured months of my life into this - and it's a gift for someone so I'm trying to keep standards.

 

My initial thoughts are:

- Custom Pots : Previously stopped by ebay (as only found one place on the internet that sells them, in Canada), a guy sells essentially "blanks" for 6mm shafts - set that blank in something, and you've got a custom knob (be it wood/ epoxy). I can then make extra tall knobs with the right amount of rebate to account for the protruding thread (and be precise for each pot, +4mm on one and +5mm on the other)

 

- Bulk out the gap: Fill the 4-5mm gap between body and knob with a series of cascading felt/metal washers

 

- Bulk out the gap 2: Make some wide flat cones in epoxy to do the same job as above

 

- Bulk out short shafts : Do buy 9mm threaded pots, don't route the cavity any deeper, and then find a way to make an extension bit for the split shaft

 

 

What are your thoughts on any of the above, or something else to try?

 

Many Thanks lads and lasses

 

CC1

[Bizman62]

The top looks pretty thick at the holes so could it be possible to use a forstner bit to make the top about 6 mm thick around the pots or even all of the cavity? That would leave 3 mm for the nut and washer on a 9 mm shaft which should be plenty enough. 5 or 6 mm should also be strong enough unless that wood is very soft in which case some reinforcement is needed. If you route the bottom of the cavity flat you can glue a piece of cross grained 0.5 mm veneer on the bottom. If you just make the pot holes deeper gluing a large washer with epoxy to the bottom of the cup is also an option as well as using larger washers on the top.

Or you can drill the top thinner for the 9 mm shafts on the outside and partially sink the knobs!

 

Yet another option is to make higher knobs with a cup wide enough to hide the shaft.

[CC1]

Thanks Biz

 

It's a solid block of Ash, and whilst I would hope that's strong enough, my fear would be any bangs/drops that impact the knob would be like a well placed holepunch and would just plough the knob and pot through into the cavity. I suppose that's his problem if he does that (but then, if I don't put the strap locks on right and it causes him to drop it, stain on me...)

Add to that, attached is the body profile. 29.6mm at the point of the Vol pot, 33.2mm at the point of the tone pot. Also notice the variation in angle. To sit square in the face, I've (crudely) chiseled out a bevel (camber?) in the pot hole. So any 'forstenering' will be done at an angle and I worry about ploughing straight through also. I don't have a drill press. My forstener bits have stop gauges, but that's not going to work well drilling on an angle.

 

My preferred option, which I think gives me the most room for error, is to do the 'tall pots' as custom (I think I could style it out/visually make it less garish by making the knobs themselves tapered and wider)

 

I have though also stumbled on the fact that pot-shaft extension bits, are in fact a thing. I have ordered some standard 9mm pots (a necessity anyway, since I originally bought two log pots by mistake), and am looking at appropriate extension shafts and couplings. Because if the shaft is too long - well I can just dremel the tips off. But you can't chop down the threaded part, which is where it's too long.

 

I do like the idea of the recessed knobs anyway and it had crossed my mind. I could perhaps combine the strategies: 9mm pots, extension bits (then custom cut to length to suit), AND lower the knob height with a 2mm recess into the face - still leaving me about 7.8mm face thickness.

 

Thanks for the advice. I'll post back with how I get on. 

1 hour ago, Bizman62 said:

The top looks pretty thick at the holes so could it be possible to use a forstner bit to make the top about 6 mm thick around the pots or even all of the cavity? That would leave 3 mm for the nut and washer on a 9 mm shaft which should be plenty enough. 5 or 6 mm should also be strong enough unless that wood is very soft in which case some reinforcement is needed. If you route the bottom of the cavity flat you can glue a piece of cross grained 0.5 mm veneer on the bottom. If you just make the pot holes deeper gluing a large washer with epoxy to the bottom of the cup is also an option as well as using larger washers on the top.

Or you can drill the top thinner for the 9 mm shafts on the outside and partially sink the knobs!

 

Yet another option is to make higher knobs with a cup wide enough to hide the shaft.

 

[Bizman62]

53 minutes ago, CC1 said:

pot-shaft extension bits, are in fact a thing.

I've heard about them, too. But even with those you'll have to have the threaded part come through the top for about 3 mm.

My current build has a radiused top and the control cavity is lined along the flat bottom so the top is of unequal thickness. I'm planning to partially recess the knobs, there's a pillar drill or three in the workshop. You're right about forstner bits, they'd most likely slip and slide on a slope! A handheld router with a cove bit might work with the bearing stuck into the pot hole, especially if you attach a rail on the lower side to keep the router horizontal.

[CC1]

5 hours ago, Bizman62 said:

I've heard about them, too. But even with those you'll have to have the threaded part come through the top for about 3 mm.

My current build has a radiused top and the control cavity is lined along the flat bottom so the top is of unequal thickness. I'm planning to partially recess the knobs, there's a pillar drill or three in the workshop. You're right about forstner bits, they'd most likely slip and slide on a slope! A handheld router with a cove bit might work with the bearing stuck into the pot hole, especially if you attach a rail on the lower side to keep the router horizontal.

You're totally right, that makes much more sense to basically level it off (loving the ms Paint work btw)

 

Not sure why 3mm would be a problem, if the hole is basically 10mm currently, and the thread is 9mm. I suppose if I route from the top by say, 2mm, and lose 2mm from the cavity side (to re-level it), I get 6mm thickness (acceptable), with 3mm of thread proud for the washer and nut. The knobs I have are slightly recessed, so should sit over 3mm quite nicely I would have thought.

 

Thanks for the advice

[Workingman]

Why not cut the pot shaft to the length you want it?

[Bizman62]

5 hours ago, Workingman said:

Why not cut the pot shaft to the length you want it?

It's about the threaded part, not the shaft.

9 hours ago, CC1 said:

Not sure why 3mm would be a problem, if the hole is basically 10mm currently, and the thread is 9mm. I suppose if I route from the top by say, 2mm, and lose 2mm from the cavity side (to re-level it), I get 6mm thickness (acceptable), with 3mm of thread proud for the washer and nut.

That's what I've been trying to tell. 6 mm thickness is usually enough, I went down to 4 mm on my T-type. Then again, the Tele control cavity is much narrower which adds to stiffness across the grain. On my Semi-Hollow Neck Thru build the Ovangkol top is about 6 mm and the pots are near the f-hole. The inner curve of the f-hole doesn't give in.

[Prostheta]

9mm thickness between the front and the cavity is rather a lot. If the plane of the cavity can't completely support thinning it out here for 9mm threaded sections, I'd agree with the partial dishing and partial thinning approach. Just ensure that whatever is cutting isn't "grabby" and is cutting correctly. A Forstner bit that isn't being guided 100% by its rim can bite and gouge. If that becomes part of the "thinning" approach, consider temporarily glueing a dowel into the pot hole so the spur can centre before the outer cutters settle into a groove.

[Prostheta]

The ideal tool would be a spot facer run in reverse through the pot hole spaced to the correct size, but that's not a cheap tool at those sizes.