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Tops and Backs, and reasons for arching, radiusing, doming, etc. Just some finer points..... actually, all the dirt on what, how, and why-for this is done, please. Muchly appreciated!

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DES - Shepherd, MI

Strength. A dome will distributes loads more efficiently, therefore can carry greater loads with less section modulus than a flat top. Same principle as and arched door way

Plus, it gives us a reason to buy cool radiused dishes!

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http://www.presnallguitars.com

How is quite simple, you shape the attaching end of your braces with the appropriate radius. Most use some sort of shaping jig to achieve this accurately and repeatable, but it can be done by hand on a belt sander. Glue them up in a bowl profiled with the proper radius. This imparts the arc into the top or back. Sand the rim with linings using a radiused bowl with 60 or 80 grit sandpaper attached, It is a good Idea to have one set of bowls with sandpaper and one with out for glue-up, Bowl sanding adds the radius contour to the rim and lining. That is the process in a nut shell. Each of us have little tricks for the upper bout on the top to accommodate the fretboard extension. I do it by ending the radius prior to the upper bout by making the upper transverse braces and grafts flat bottomed and gluing them on last using a slab of polished granite as a backing plate in my go bar deck.

The most common radii is 25 foot for tops and 15 foot for backs. However I use 28' for SJ and OM tops

Let me recommend Luthiers Suppliers for the purchase of gluing and sanding bowls. I use to make mine but due to time restriction I am buying mine now. It is not a hard job to do. I have great jig in the library of plans for this job. If you decide to make your own be aware that it is a very dusty job and should be done out doors and with a respirator and safety glasses.
MichaelP38702.4967592593

Michael, I gather you're referring to "doming", right? What about arching?   I recall a posting of someone doing this in only one direction. Thanks, BTW!

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DES - Shepherd, MI

Arching does much the same thing. I think Howard Klepper builds with only a side to side arch/curve of some kind. It's not very common.

There was good post on this some time back over at the Luthiers Corner at Acoustic Guitar Magazine. Check out this link.Don A38703.1734722222

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Don Atwood
Arlington, VA

I agree with Michael, just buy them from me and save yourself some hassle I'm sure you will be happy. Just for reference, the most common radius we sell is 15' & 25', then 15' & 28, then 15' & 30' in that order. Good luck!
Tracy

Another very good reason for doming tops and backs (THE reason, according to some) is to allow for wood movement (with changes in moisture content resulting from changes in humidity). As the plate shrinks, it will flatten rather then split. Todd Rose38705.5168402778

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Todd Rose
Ithaca, NY

https://www.dreamingrosesecobnb.com/todds-art-music

https://www.facebook.com/ToddRoseGuitars/

[QUOTE=Darin Spayd] Michael, I gather you're referring to "doming", right? What about arching?   I recall a posting of someone doing this in only one direction. Thanks, BTW! [/QUOTE]

Hmm?? I guess I missed that one. I am not sure which dirrection would be of benafit that domeing does not provide. In my thinking domeing is the better structrual shape. If you arched across grain only you would need to vary i.e. multi compound radius the the the x-beace and tone bars as you decended or accended the centerline to achive this with out naturaly causing a dome affect on a top anyway.This would be near imossible I would think. I could see how this could be achived easer on a back with conventional ladder bracing, but with the profile height decreasing butt to neck, you end up with a dome affect again. I must be be missing something here.MichaelP38705.5359259259

Just to add a bit to what Todd wrote... If you build a top or back with flat braces (zero arch) it can easily collapse & form a reverse arch if the assembly was not done under controlled humidity conditions.Daniel M38705.5371064815