Top thickness around controls cavity
This is my first post in the LC, although I've been lurking here for a bit reading just about every thread that I can. I'm very new to building (still haven't finished my first from-lumber bass) but already have a few builds at various stages of planning and design, including sourcing the wood.
Recently I've been looking a lot more at figured tops and a question has popped into my mind that I didn't immediately remember reading an answer to from one build thread or another:
Is there some rule of thumb about how thin a top should be, especially relating to strength around the control cavity? Obviously it must be thin enough that the pots can extend through. But how thin is too thin? Are there some commonly used ways to reinforce the top in this area (something like a veneer layer under the top)?
It seems that bookmatched tops are typically sold in a thickness of about 0.25" (or thinner). Should I avoid buying tops that are thinner than this?
I imagine the answer would change based on the specific wood in question, I am just curious what a good thickness to shoot for would be.
I think, if I remember right, it's a little bit less than 1/4" that you want where the holes are. If the top is thinner or it's not very strong, you can always just leave some of the body wood there (drill/route the cavity from the back without going all the way through the body wood) and use a large bit to drill to the depth you want just around where the pots will be on the inside of the cavity.
Hopefully someone can tell you an exact depth, but if you already have the pots and knobs, you can just measure the area between the bottom of the knob and the end of the shaft part of the pot.
The thickness of the top is not a huge issue because when it is glued to a solid body instrument, the (usually) harder body wood would reinforce the top wood. It's not like an acoustic instrument where the top is bearing all the stresses from the strings and forearm and such. So even if your top is less than 0.25", there is still the body wood underneath it to add any support needed to the control cavity.
I used a 0.25" top for one of my builds made out of some pretty weak/fragile wood. I was worried that having the pots mounted to that wood alone wouldn't be a good idea, so I started cutting a brass backing plate to sit between the pot and the wood to reinforce it. In the end, I just got some long-shaft pots and cut the cavity to leave a bit over 0.25" thickness. That left a layer hard body wood on top of the fragile top wood and that seemed to work just fine.
It depends a lot on the lengths of your pot shafts and any switches that are to be installed. I'd go for the thickest dimension your electronics will allow.
On my most recent build, I was using particularly brittle redwood and decided to reinforce the inside of the cavity with an essentially break-proof polycarbonate laminate glued to the inside floor for strength.
I've used a spade bit to thin the top wood to accomodate the size of the pot's washer, but no bigger. Once the pot is installed, the wood there is under the compression of the pot's nut. It's plenty strong.
Thanks for the responses!
It seems like the quick consensus is that 1/4" is probably fine, but thicker is better if possible.
I really like the idea of thinning it just enough for the pot, while leaving the rest of the cavity a bit shallower. I'll keep that one in mind.
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