12-string weissenborn

[dea]

I'm a relatively new builder, currently working on S/N 05, but have only built conventional steel strings. My son has requested that I build him a 12-string Weissenborn. I bought a plan for a 6-string Weissenborn from Terry Buddell and am now trying to decide what modifications are needed to react the additional string tension on a 12-string. Terry's plan is for a very deep guitar having a body thickness of 5", 4" at the neck. I think this will help react the string moment a lot but am still thinking that I may need to reinforce the X-brace and some of the sound hole braces with some 0.06" thick carbon fiber sheet. Was thinking about reinforcing the neck side walls with cf also. I saw comments from Bob Geelong on this forum reference using cf on a conventional Weissenborns so I think I may be on the right track. I know that many people build 12-string Weissenborns but haven't been able to find anything on the net referencing construction details. Can anyone be of help?

[Bob Connor]

G'day Dea

And welcome to the forum.

I built a weissy with two sets of six strings on it. So the total strain on the top will be quite a bit more than a 12 string given the second course on 12 is quite light.

I put extra bracing under the end of the fingerboard in the form of an "A" brace. I have put carbon fibre on top of the A frame braces in other Weissys.

The top was Sitka at a little under 3mm, had a Christmas Tree bridge plate.

The bracing is fairly hefty as you can see in the pic below. I had to put "F" holes in this to accommodate the two sets of strings but if it has a traditional soundhole I'd be putting a soundhole patch in ie doubling the thickness of the top around the soundhole. I also had to modify the bracing a bit to fit in around the cats eye "F" holes.

Jay Hoad (SA muso) currently has the instrument and has been touring with it for the last 18 months. I haven't heard from him for a while so I assume it's still in one piece.

Hope this helps.

Here's a pic

[dea]

Hello Bob,

Many thanks for the quick and helpful response to my questions. I will try to use an A brace and sound hole patch as you suggest. Can you tell me the purpose for the Christmas Tree bridge patch as shown in the photo you attached to your post?
Thanks again,

Dea (Dave) from Indianapolis IN

[Bob Connor]

The Christmas Tree bridge plate was a late addition by Herman Weissenborn to strengthen up that area behind the bridge to stop excessive bellying in the lower bout.

Add this with the sound hole patch and the A brace you have a fairly comprehensive solution to stop the dip in front of the bridge and bellying behind the bridge that is evident in the earlier (pre 1926) Weissy's. (and other cheap copies I've seen)

I guess it doesn't matter playing-wise on a lap slide if you get that sort of deformation but as always it's a balancing act between soundng good and having your instrument implode/explode.

Cheers

[dea]

Bob,

Can you give me an idea of the dimensions you used for bracing on this Weissenborn? The plan I have from Terry Buddell is a little confusing. One note calls for 3/8" X 1/2" high but another note calls them out as 3/8" X 3/4" high. From the photo you posted, it looks like some of the braces on the lower bout are contoured but I can't really tell from your picture if the X-braces and A-frame braces are left with a square or rectangular cross section vs. being somewhat bullet shaped in cross section. Thanks.

dea (Dave from Indy)

[Bob Connor]

The X-braces be 13mm high by 8mm wide Dave.

The two upper transverse braces are 12mm x 12mm

Regards