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[QUOTE=ToddStock] Cumpiano is a great window into mid-1970's custom building techniques, but it's dated and does not reflect what a majority of custom builders are doing today. The go-bar/dish/outside mold system does require more tooling, but on balance, probably costs less than the clamps and jigs it replaces and results in repeatable shapes.[/QUOTE]

I agree totally, but the thing about this book is that you don't have to spend many $$$ on jigs and tools. Therefore it's a great book for beginners and "earthy" types of guitar builders.

I do not want to buy any of the flashy gizmos unless I was seriously considering guitar building for a living. There is nothing worse than having a shop full of tools that are appropiate for one job only; as it is, if I HAVE to buy something, I only pay up if it has a multi-use.

I wonder if Cumpiano uses the same techniques today?

It may well be that these techniques will come into vogue again; however, if you are properly tooled up according to the modern standard, it does make Cumpiano's ways outmoded.

I use his non-radius dish method, and I have a beautifully domed top. To glue the braces on, I acquired a load of thin sponge from the college I work at and fold it in half, to protect and to buffer the soundboard. I'll think I'll only go that far with the technique, as the other techniques I use to create a domed top will only have you crying "AMETUER!!!" at me, soooo.......



In conclusion I am saying that his methods DO have a place, but not the majority of professional builders choose to use them.

From my understanding, tops are arched for two reasons: movement due to humidity changes, and strength. I found the strength concept particularly interesting when explained to me at the Healdsburg a year and a half ago. When you take a piece of paper it flaps around length wise until you give it a U shape from end to end and it becomes stiffer. (I hope that makes sense)...Now thanks to this thread I thought about pre-stressing a top by gluing braces on a flat surface as potentially a way to increase responsiveness. Interesting. Now would that cause compression or the opposite at normal humidity? What really comes to mind for me is over the years how either method might affect potential cracks in the top. Probably not by much I bet.
    Personally, I built my own radius dishes and go bar deck blindly following what I read on the internet mostly. I made a dish using plywood, some scrap P-lam, and epoxy, finding that shimming up edges to a home made gauge's ends, gooping epoxy in the middle and tacking the p-lam piece to the center of my plywood circle, made a surprizingly accurate radius, after sort of screeding with the gauge. The laminate surface was perfect to glue on too because it cleaned up well.
    After building the first guitar though, I talked to a few local guys who don't even use go bar decks, which left me a bit confused. I still wonder if it really makes that much difference. I personally wouldn't trust how even my clamping pressure was if I used a rug. Braces that come loose can be a bummer. Hope I didn't ramble too much. Time for bed.

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"Preoccupation with an effect gives it power and enhances the error"
from "Your Owner's Manual" by Burt Hotchkiss.

I use a dish and a domed top, but just because everyone says that is the way to go. But there are some highly respected luthiers that still build with a flat top and put out spectacular instruments. I've also played guitars from two well known luthiers that have used the stressed top method and one of the two was the best sounding guitar I've ever played. Whether it is the stressed top or just the skill of that luthier, I don't know but I suspect the later. I seem to recall Roy Mcalister saying he does his vintage models with a flat top and I wonder if Greven is doing that also. And, frankly, my flat top Martin is pretty hard to beat for tone and I get a lot of people asking me about that guitar when they hear it. I'm seriously considering building a flat top again, but it's hard to buck the trend.

Kent    

[QUOTE=KentF]

I use a dish and a domed top, but just because everyone says that is the way to go. But there are some highly respected luthiers that still build with a flat top and put out spectacular instruments. I've also played guitars from two well known luthiers that have used the stressed top method and one of the two was the best sounding guitar I've ever played. Whether it is the stressed top or just the skill of that luthier, I don't know but I suspect the later. I seem to recall Roy Mcalister saying he does his vintage models with a flat top and I wonder if Greven is doing that also. And, frankly, my flat top Martin is pretty hard to beat for tone and I get a lot of people asking me about that guitar when they hear it. I'm seriously considering building a flat top again, but it's hard to buck the trend.

Kent    

[/QUOTE]

Tops need a bit of stress - otherwise they get too laid back

Kent - is the top of your Martin dead flat under string tension or does the top dome up a little?

_________________
Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

Actually I have two Martin flat tops, a D-28 and an OM-18. The tone of both is good but the 18 is exceptional. The tops of both are almost identical. They bulge slightly behind the bridge and sink slightly in front if the bridge, the sinking is almost unnoticable visually. I put a straight edge on my old Larrrivee C-05 and it is pretty much the same, though it doesn't sink quite as much in front of the bridge. But these are all good sounding guitars.

Beginning to question the value of the dish.

Kent

Actually the dish I made came out pretty funky, as I'm sure some of you experts may have guessed, now that I think about it. The laminate surface is not needed and causes my top to slide around a bit too easily I think. I just couldn't spend the money for every fancy jig yet. The challenge for me was penny pinching and improvisation on my first guitar. Doing more with less. Another issue I have with too many jigs is that they clutter up my tiny shop. I guess it takes years to solve that problem.

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"Preoccupation with an effect gives it power and enhances the error"
from "Your Owner's Manual" by Burt Hotchkiss.

I use dishes as well, but this thread has me wondering something. What if you use a "dish" that is arched only in one direction, such as along the long axis of the guitar? It would look like a portion of a cylinder. You get the strength of an arch, but it would be essentially flat in the other dimension. It would actually make the darn things (dishes and guitars) easier to build.You might get an advantage of the dome top's structural integrity with the responsiveness of a true flat top. Does anybody do this? It might make for an interesting experiment. Wadya think?

[QUOTE=Doug O]

[QUOTE=Hesh1956]Good points Doug and even Cumpiano pitched the building board in favor of a mold.

I bought Cumpiano and Natelson's book when I started too but decided that I needed a system to follow at least in the beginning. More builders seemed o use dishes and molds so I went that direction.

Are you using a go-bar deck? It is a much better way to glue braces onto the top and back and the top and back to the rim IMHO.[/QUOTE]

I used a go-bar deck when gluing all the braces to the plates.  For attaching the plates to the rims I used a thinned plywood caul that screws to the mold per Kinkead's book.  It worked well, but plan to go-bar the plates to the rims next time.

Doug

[/QUOTE]

Does anyone have any pictures of gluing the top or back plates to the rim using a go-bar or otherwise?

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Time is a great teacher, but unfortunately it kills all its pupils - Louis Hector Berlioz

Chansen / C hansen / C. Hansen / Christian Hansen - not a handle.

Christian

[QUOTE=ToddStock]results in repeatable shapes.[/QUOTE]

 

That is the point, Cumpiano has stated his reluctance to use of molds as being partly because he wants freedom and uniqueness to his instruments. 

Jon,
   I would recommend that if you're not clamping in a radius dish clamp
the braces on using clamps, but with no backing board. This will allow
the top plate to be flexed to the radius of the braces rather than clamping
them flat and depending on the braces to pull the top to its default or
final radius.

   If you do use this free method, do the brace gluing in stages with the
"X" braces being first and then going to the top bar and popsicle style
braces above the soundhole and finishing up with the bridge plate, tone
bars and finger braces off of the lower legs of the "X" braces. This is just a
suggested sequence and can be modified, but I would stick with the "X"
braces being the first installed in any case.

   Once a glue joint is secure with the braces being pulled flat and glued
to the top, it's unikely that the assembly will be able to settle into the
amount of radius desired or intended. It will achieve a radius to a degree,
but the tension between the components will limit it.

    I hope that makes a little bit of sense.

     Bot this is sure a great discussion. It brings back alot of memories of my early days of building and discovery.
    The first point I will bring up is from Kent F

Actually I have two Martin flat tops, a D-28 and an OM-18. The tone of both is good but the 18 is exceptional. The tops of both are almost identical. They bulge slightly behind the bridge and sink slightly in front if the bridge, the sinking is almost unnoticable visually. I put a straight edge on my old Larrrivee C-05 and it is pretty much the same, though it doesn't sink quite as much in front of the bridge. But these are all good sounding guitars.

This isn't from the radius of the build but a result from the stressed on the top over time.

    I used to use all above mentioned methods . The gobar is indeed the more efficient of the ones mentions.
A radius on the braces , then glued to the top or back on a flat board will not give you the true radius. But that radius will change anyway over time. We radius more for the clean lines of the joint.
    If you don't have the sides set to match your raius you will develop tell areas on teh guitar over time.

   I now use a vacuum clamp as it allows me faster set up on the glues . Cupiano's book is a great resource but as stated is very dated and alot of the techniques even he moved away from but we still owe the man a big dept in education .
   I to shape bracing on the belt sander and glue in shaped. I can do small tweaking once I have the guitar together
john hall

I am planning on using the radius dish for sure. I spent enough time rigging up my drill press table to double as a dish making table, so I am darn sure going to make good use of that time.

I was asking, because I learned everything about making the dishes here. I am using Cumpiano's book as a guide. After I started trying to route some dishes I stopped and read the book and saw that they are not used. After this discussion, I see their value.

Now for one more question, If I am going to throw together a go bar deck that is 24 inches from bottom to the top, how long should the go bar sticks be to get enough bend/tension in them to be effective (the dish is made out of 3/4 playwood). I planned on getting some thin wooden dowels as I do not want to wait 2 weeks for fiber/plastic go bars. I just want to make sure I cut them to the correct length.

    The gobar at 24 inch is this between the tops or outside .
   A 3/16" fiberglass rod will produce about 8 lbs. You have a good range for that force. I use same length . You need about 1/2" inch deflection minimum
john hall