Archtop Rebuild Measuring the Top and Back?

[Eric Knapp]

Hello,

It dawned on me that I have an old archtop that's all apart and thickness calipers that are pretty accurate. When I made it I didn't know how accurate it should be so I got a Starrett that is to the 0.01mm. (I was young!)

Should I map the thickness of the top and back? Is this something that people are interested in? What kind of granularity would be best? I was thinking every centimeter but that seems like a lot of data points. Is there a database of measured old guitars out there in the intertubes?

Thanks,

-Eric

[Brian Evans]

I would be interested to know the thickness of the top and back. Basically the middle of the arch, the edge and the recurve area, and see how it graduates top to bottom and side to side. To be honest, I've seen that done for mandolins before but never for a vintage guitar. I Can't recall where someone has taken a 1930's guitar apart and measured it, although it's probably been done.

Brian

[Jason Rodgers]

If you were willing to measure every centimeter, then I think a 2 inch grid would be sufficient.

[Eric Knapp]

I would be interested to know the thickness of the top and back. Basically the middle of the arch, the edge and the recurve area, and see how it graduates top to bottom and side to side. To be honest, I've seen that done for mandolins before but never for a vintage guitar. I Can't recall where someone has taken a 1930's guitar apart and measured it, although it's probably been done.

Brian

Thanks for the feedback. I will be measuring the top and back and I'll post it here for the curious. I also want to see the contours so I'll be making some sort of graphic showing them. So far there are no surprises, the back is 6 to 7 mm in the center and the recurve is 3 to 4 mm.

-Eric

[Eric Knapp]

If you were willing to measure every centimeter, then I think a 2 inch grid would be sufficient.

Thanks, I'll probably go a little finer than that but maybe not go so nuts with every cm.

-Eric

[Brian Evans]

How come a good Wisconsonian like you is using metric? Every measurement I have to multiply by 2.54 to understand it... Even though Canada is officially metric, all of my tools, mills, lathes, micrometers, etc are in inches. I can't estimate in metric to save my life. Except I know that 10 cm of snow is nothing but 70 cm of snow is all day and part of tomorrow...

[Eric Knapp]

How come a good Wisconsonian like you is using metric? Every measurement I have to multiply by 2.54 to understand it... Even though Canada is officially metric, all of my tools, mills, lathes, micrometers, etc are in inches. I can't estimate in metric to save my life. Except I know that 10 cm of snow is nothing but 70 cm of snow is all day and part of tomorrow...

Ha! Well, my dial indicator is metric and only metric. I'll post the data both ways when I'm done.

-Eric

[Beate Ritzert]

[So far there are no surprises, the back is 6 to 7 mm in the center and the recurve is 3 to 4 mm.

To me this is a surprise: i thought (and built my archtop accordingly) that the top and the back should be of the same mass, similar to violins.

[Mike Conner]

Eric,
The thinkess data will really be interesting! No problem with metric for me - I convert every day in my day job as an engineer, though I "think" in inches. Most of my measuring building archtops is in decimal inches (rather than fractional). Plus, decimal dimensions are easier to type

6 - 7 mm (about 0.250") for the back seems really thick for a solid plate. I target the more common 0.175" at the center, and perhaps 0.095" or so at the recurve (maple or walnut). A top plate would be 0.220" at center and down to about 0.125" at recurve (Englemann spruce).

Given that this was a factory produced guitar from the 1930's, back when woman were strong and men were good looking, all the children were above average, and the strings tended to be heavier, perhaps the heavier plates shouldn't be a surprise.

Oh, and how about the side thicknesses while your at it!
Thanks for making this effort!

[Brian Evans]

I agree the measurements seem on the thick side. Center of back .24" to .28", call it just under 1/4" to just over 1/4" when I aim for 3/16" (.19" to .2" in actuality). I aim for 1/8" or a little less on the recurve. I carve the recurve when the box is closed, I tap the front and feel the back and work until I feel uniform vibrations around the outside third of the back (from the edge of the recurve in towards the middle).

Beate, I'm not sure of the equivalency of mass top to back, but with only back measurements to look at so far we don't know what the top looks like. I try to carve my tops with a center thickness of around 1/4" tapering to 3/16" at the edge with a recurve of 1/8" around the perimiter of the top about 2" in, smoothly blending into the top so you almost can't see it but have to feel it. Backs I do the same, but maximum thickness of 3/16" more or less. The back wood is usually heavier than the top wood but gets carved thinner - my new goal is to have a definite difference in tap tone pitch between the top and the back. My first archtop had them fairly close, and I have a bit of dead note as a result (my current theory, anyway)