What type of volume pot do I need to buy for my Eastman?

[voyage]

I'm going to put a CTS 250k volume pot in my Eastman archtop. I know it takes a straight shaft with a set screw in the knob. Does anybody know the diameter or length of the shaft or any other details I need to know to get the correct fitting pot? Thank you very much.

[sgosnell]

Probably metric. Most Asian pots are metric. But it's better to just measure the shaft. Without a caliper that can be difficult, but it's still possible.

[voyage]

I have a caliper so I can measure the width. What about the length of the shaft? I think there are long shafts and short shafts, I would expect a thin carved archtop to need a short shaft would you say? Thanks very much.

[nevershouldhavesoldit]

I have a caliper so I can measure the width. What about the length of the shaft? I think there are long shafts and short shafts, I would expect a thin carved archtop to need a short shaft would you say? Thanks very much.

AFAIK, the only guitars that use long shaft pots are thick top solid bodies. I've never seen an archtop that needed one.

[sgosnell]

Measure the thickness of the top at the f holes, add that to the height of the shaft above the top, and you'll have an approximate shaft length that is necessary. It won't be exact, because the thickness of the top varies across the top, but it should be close enough, because the length doesn't need to be exact. I would expect that a short shaft would be fine, but I haven't measured your guitar. Eastmans tend to have thinner tops than average, though.

[voyage]

Yes, it's a very thin top. Interesting you say Eastmans have thin tops.

[DRS]

Like others have said, the Eastman uses metric pots so the shaft is 6mm. USA 1/4" = 6.25mm. The difference is enough that the holes in the top probably are too small and the stock knobs almost certainly won't fit.

You can ream out the top holes easy enough (use a tapered reamer, not a 1/4" drill bit - the drill bit will catch and tear out the wood) but there is no practical solution for the knobs short of replacing them with 1/4" knobs.

[voyage]

Like others have said, the Eastman uses metric pots so the shaft is 6mm. USA 1/4" = 6.25mm. The difference is enough that the holes in the top probably are too small and the stock knobs almost certainly won't fit.

You can ream out the top holes easy enough (use a tapered reamer, not a 1/4" drill bit - the drill bit will catch and tear out the wood) but there is no practical solution for the knobs short of replacing them with 1/4" knobs.

Oh my god, you just gave me a mental picture that will haunt me in nightmares! Drill bit eating carved archtop.

I was sure I had solid post pots, but I just pulled the knob off last night and they are splined split shaft pots. Metric no doubt. Thank you.

[sgosnell]

I've used a drill bit to enlarge holes, but not a drill. I did it by hand (and small Vise-Grip pliers). Slow and careful, it's possible. But a reamer is certainly a better tool.

The shaft diameter only matters for the knob. The hole in the top has to accommodate the threaded outer portion, and that may require reaming. If so, it won't be much, and won't affect reinstalling metric pots later if desired.

[voyage]

Thanks. I pulled the knobs off. They're wooden knobs I bought on Etsy. They're not solid shaft pots after all, just a standard metric split shaft with splines so no need to change the holes in the top. I already have the correct 250k replacement pot. Thank you.

[nevershouldhavesoldit]

Yes, it's a very thin top. Interesting you say Eastmans have thin tops.

It's not just Eastman guitars. Remember that they started building carved archtops by following Bob Benedetto's book "Making An Archtop Guitar", and he's always made them in the style of the older archtops that we now revere (i.e. with thinner tops for a brighter acoustic sound and better projection). Tops got thicker and braces heavier to tame feedback when amplification came along. Heavier carved tops are part of the sound of classic Gibson archtops - the acoustic tone is darker. This is not a huge difference in thickness, but it's enough to see, feel, and hear.

Eastman carved archtops are beautiful instruments that sing with similar voice to others of the same style. I have a 16" and a 17", and I love them both.