Official Luthiers Forum!

Dear OLF'ers. For giggles I was thinking of making myself a 335 style semi-hollow bodied guitar with a full center block. Because I happen to have and use a CNC machine, I was thinking of making the center block so that it already has the interior contour of the plates, rather than the essentially three piece system Gibson came up with. But thinking it through, I realized there might be unintended consequences in trying to be too cool for school.

For example, if I glued the rims to this nifty contoured center block it would be impossible for me to "drive the bus" and sand the rims flat. Any ideas on how I would get the rims flat with this bulge in the middle?

Secondly, not sure how I would glue this all up. In a vacuum bag? Would that crush the sides?

Third, it occured to me that I don't know the tolerance of Gibson's kerfed center block piece that is mated to the plates and the rim of the plates. If the spruce center block is proud, do you have a problem glueing the plate to the rims? If it is short, do you have problems mating it to the flat maple center block? How do you make sure that the spruce is EXACTLY even with the rim, and how critical is that measurement? How does Gibson do it in mass production?

Has anyone ever tried this (creating a center block that is already contoured to match the inside of the plate)? Anybody have any nifty tricks or ideas that would help putting this together?

I have built two 335 style guitars, one with a Gibson style maple center block and kerfed mahogany spacers and one with a partial block that I carved sort of like you are describing. In the latter case I was following the Australian plans that show a short block and I couldn't think of any other way to do it. I did a build thread at a different forum, looks like it is still active and the links work. The center block thing is pretty much the first two pages.

https://www.harmonycentral.com/forum/fo ... -an-es-335

It was a real hassle carving the block to fit (I don't have a cnc, just a couple of sharp planes). I used bass wood which is considerably easier to carve than maple - I might consider a block of spruce if I was ever going to do it again. I think the pictures show how I dealt with the rims and clamping.

Here is a build thread for the Gibson style 335 - there is some discussion of the kerfed blocks at the bottom of the first page.

https://www.harmonycentral.com/forum/fo ... nother-335

If I ever decide to build another I would certainly do it the Gibson way. Also I would ping forumite Ken McKay - Ken builds beautiful guitars in this style and was a big help to me when I built mine.

My second thought since you do have a cnc and will probably be using it to make molds for your top and back plate so you will have the shape of the inside of the top/back already programmed - it should be simple. I had to create a couple of templates from my top, rough carve and then basically chalk fit the block to the inside of the top. It should be exactly the same shape as your inside mold and so the same program.

I would also think that if you go thru all the trouble to create the molds for the plates you should make plates available for sale. I know several people who would like to build a 335 but don't want to go thru the hassle of making molds and all the laminating.

Thanks Freeman. So if you already had a one piece center block that was perfectly mated to the plate, you would still prefer a three piece arrangement?

You are right. Because I have the mold programmed (I will make both male and female molds) running the center block to match is trivial. That seems simpler than the three piece arrangement. But I’ve never seen that, and that makes me wonder if there is good reason no one seems to do it this way. I’m far from the only luthier to have a CNC machine.

My instinct is that prepping and getting all the gluing surfaces to line up perfectly is going to be a real challenge if it try to do it all as one. Or maybe I’m overthinking it. I guess I’m hoping for a sanity check before I go down that rabbit hole!

That is kind of a rhetorical question - I will never have a center block that fits perfectly - so I would have to make it. Its just like carving a neck or the top of a LP or anything else - I actually enjoy doing it and since I'll never own a cnc its a moot point. If I was trying for the minimum possible weight I might consider it. but it certainly does add complexity when jigging up the sides (notice the little blocks of wood under my mold?). The block with kerfed fillers is really kind of an elegant solution and was remarkably easy to do - all the router jigs where quick and dirty but they worked just fine.

The second instrument was going to get a Bigsby so it needed the full length block for the mounting screws, but of course you could make a full length carved block.

You actually could do the block differently - I've built a laminated top archtop sort of thing with bracing like an ES-175. My guitar had a dovetail neck joint, with a thin 335 style body you would need to do something like a longer M&T, but the "braces" could simply be a couple of spruce runners that support the pickups and bridge/stop bar (I used a floating bridge and tailpiece so that wasn't necessary). I don't have a good picture but this might give you some ideas



The spruce runners tie to the neck and tail block and were fitted to the inside of the top (by hand, of course). The legs of the bridge straddle the runners - you could position them for ToM studs for a 335. I like this guitar a lot, it is light weight and even has a half way decent acoustic sound.

(I'll add that I spent 40 years working in a metal fab shop with all kinds of fancy numerically controlled machines - mills, turning centers, laser cutters), as well as modeling software to drive them. I've made a bunch of jigs and fixtures with them but all my wood carving has been by hand. I have nothing against a cnc, I just like my little chisel)

Thanks again, Freeman. I guess I don't really understand your answer to my question. I wasn't really asking about whether you like CNC or chisels. At the end of your other post you said, "If I ever decide to build another I would certainly do it the Gibson way." My question was, why? Is it just the difficulty in fitting the center block to the top, or was there another reason?

There were really three parts to my response. First, you asked the hypothetical question "if you had a center block that was perfectly mated...." In my case that would never happen so I don't know.

The first guitar was built to a set of plans that aren't really correct. It showed a block that ended just below the stop bar and didn't show anything about kerfing. The fact that the block was only connected at the end of the sides meant that it was floppy in the mold and hard to deal with. I added a little blocks to my mold to try to hold it in place while I carved it, but it was a hassle. Obviously if you made a full length carved block that was also attached to the end it would be better.

The fact that the block stands proud of the rim by, what 3/8 or so, means that the rim in the mold doesn't sit flat on anything. I had to put a bunch of little blocks of wood under the rim to support it (in retrospect I would have made a 3/8 MDF piece the whole outline of the guitar for it to sit on). I don't remember how I sanded the rim - fortunately it was flat so I didn't have to fool around with a radius dish. Clamping was straight forward - I used a whole bunch of quick clamps set fairly lightly with a couple of deep clamps to the center block. The rim was out of the mold - I don't like that but it seemed to work OK.

I also wasn't happy with my choice of wood for the center block - all the hardware mounts to it and I would have preferred a harder wood - maple or mahogany or maybe spruce. I don't like bass wood but it was easy to carve.

The second guitar had the full length block that was level with the top/bottom of the rim. The kerfed pieces were fit to the plates then surfaced flat - it was totally simple to handle them and as I recall, I clamped the top plate in my go-bar with the rim in the mold. Used the quick clamps when it was time to put the back on. For both guitars I routed the neck and pickup pockets before I put the back on - the first guitar wouldn't sit still on my workbench because of the back of the block, the second guitar I could route or drill do whatever I wanted.

So, for someone like me who works in a corner of a garage with minimum of power tools building only one or two guitars I think the Gibson design was perfect and is actually kind of elegant. I'm sure there are lots of other ways.