MIMF

I made some wooden knobs for a custom electric guitar I am building with a 1-1/2" hole saw. Center hole is 1/4". Pot shafts are about 7/32". Any good tips on making them fit tight? Thanks!

You can coat the inside of the holes with glue and let it dry, I'd use HHG or Titebond 1. Repeat if necessary.
That's some big knobs, I've used a 3/4" hole saw for knobs.

It may depend on the pot you are using. Bushings like this might work with a 1/4" drill and 6mm pots.

Sku: BSH
Split Shaft to Solid Shaft Adapter Bushings
on these pots
Bourns Pro Audio 500K Sealed Guitar Pot-Long Shaft
MfgId: 95A1D-Z28-EA0503LGTR
from
http://www.guitarelectronics.com/

You probably can't change the bit on your hole saw, but a #1 bit will drill just under a quarter inch and fits a 6mm split shaft very tight. I think a 7/32 bit is too small for a 6mm shaft. I use it on a lathe, but you may be able to drill the center hole with everything locked down on a drill press, and the then cut the outside without a drill bit. I've never tried it.

Thanks for the tips. I was thinking of a DIY solution like using tape. The knobs are made of cherry, closer to 1-1/4" in diameter. They have a top recess for a US quarter. Used a 15/16" bit to make the recess, then used the hole saw to cut out the knob. I checked my pots- the shafts are 6MM.

For holes that are only a few thousandths too large I usually find a nice curled up wood shaving on the floor and CA it in the hole.

Greg - those bushings Dave suggested should do the trick dimension-wise, but I think you'd need to install a set-screw to secure them to the knobs. Most of the good hardware stores in my area carry set-screws, and with those large knobs you can drill & tap and use a fairly long set-screw, so they should hold just fine, especially if you drill across the grain rather than into the end grain. You have at least 0.014" to take up, not allowing for the knurling, and while I think masking or duct tape would work, it doesn't feel like a permanent solution to me.

IF you can drill accurately into the center of those knobs, another and possibly "cleaner" solution would be to plug the hole with a 1/4" dowel, and drill out to 5mm, or 7/32 which is 5.533 mm. I don't know how much interference you need on that split-shaft. 5mm might be too tight, but the 7/32 might be good. You'd have to do a little test-fitting to see what size works best.

Edit: You should be able to secure those bushings with a dab of epoxy rather then the set-screws. I'd do the set-screws, but that's just me...

The 6mm is closest to 15/64" drill size for future reference.

David King wrote:The 6mm is closest to 15/64" drill size for future reference.

If a conformable material (e.g. plastic or wood) is drilled to 15/64 for a 6mm split-shaft, does that provide enough interference to firmly grab the knurling?

Good question Steve, 15/64 is .234" and 6mm is .236" so it looks promising. Unfortunately I've never measured a pot shaft that was actually .236" and rarely seen a hole drilled in wood that wasn't a bit larger than the drill size. I think that if you were to soak the hole in water to swell the grain, let that dry thoroughly and then soak that wood in thin CA you would end up with a decent interference fit.

A Number 1 drill is .228.
This worked the best of all the ones I tried. Very tight fit.

How about plugging those holes, cutting the plug flush and re-drilling? I can't see the back-side of the knobs in these photos, however, this approach may be an option.