What is the function of the kerfing in the spruce block on an ES-335?

[Dave Locher]

I have read many times that there is a kerfed spruce between the arched top and the maple center block on a Gibson ES-335/345/355, but until recently I had no idea what that actually looked like. I always assumed they meant there were strips of spruce, shaped to match the top and running from strap button to neck. I owned a 335 years ago but never investigated its construction closely.

I recently saw this photograph which seems to clearly show a solid block of spruce, carved to fit the contour of the top, with groves cut into the INSIDE surface, where it mates with the maple center block. What is the purpose of these grooves? I believe decades ago I read a McCarty interview where he said that the kerfing really made a big difference, but I don't understand luthiery (or physics?) enough to figure out what those grooves might do to the sound of the guitar?

It is a little hard to tell, but in this photo you are looking at the body of a 335 that has been cut in half vertically to view the construction. Photo borrowed from ES-335.net (http://es-335.net/laminations.html, http://es-335.net/interior.html)

[Dave Locher]

Here is a better photo:

[Dan Smith]

Dave, That is really weird.
Maybe someone thought it had acoustical properties?
I belive the top and back are glued to a Maple block so I don't consider the Es-335 an acoustic guitar.
They do make an acoustic sound when unamplified though.
This is very interesting and I look forward to reading responses.
Dan

[Barry Daniels]

You guys should know that Gibson never did anything for acoustical benefits, right? Just kidding, sort of. Gretsch does something similar and the stated reason is ease of construction. The kerfs allow the wood to conform to the arch of the top so a solid block does not have to be carved to fit. Gibson's reason is likely similar.

[Dan Smith]

Yep, i just thought about why kerfs are used. To bend wood.

[Barry Daniels]

Either that or tiny passages to let the musical fairies pass through.

[Dave Locher]

That makes sense - they have to get to the f-holes somehow.

[Randolph Rhett]

I believe the reason it is both carved and kerfed is because it is carved only lengthwise, and kerfed to fit across the body. That way you can do the length wise carve mechanically (on a shaper or similar machine) and then quickly fit it to the body. No complex curves to try to deal with, and you can carve any width piece of spruce. At least that is what it looks like they are doing. There is a video on YouTube of the ES-335 being assembled at the Memphis factory, but I can't find the link now. I have no actual inside knowledge, of course.

[John Mueller]

See 34:00 for info on spruce block. https://www.youtube.com/watch?v=7CfQGXuPlMg

[Dan Smith]

I thought Gibson was much more automated than what is shown in the video.
At least, they were in the 1970's.
Thanks for posting the video.

[Dave Locher]

So it really is just a manufacturing thing? I guess I can see how they would consider that a breakthrough idea at the time, but I always thought they meant a breakthrough in sound, not ease of manufacture!

[John Mueller]

Ease of manufacture equals money saved. Sound is nothing when compared to that!