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Recently I have been restoring a 1948 Martin D-28. Brazilian back and sides, sitka top and bracing. Here is a couple pics of the top with a rule showing the top's radius.





My guess, this was a truly flat top when it was built. No radius dish involved... the back was in two pieces so I don't have any measure for it.

Anyone work at Martin back then and know for sure??

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Chris Oliver
Infinity Luthiers
...in the shop.

live every minute...

My 1955 D18 has a radius on the back. The top's pretty flat, with a slight belly behind the bridge. If it was radiused it was pretty flat. I suspect John Arnold, or John Hall (Bluescreek) could tell you exactly what was done back then.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

the tops had a large radii of about 42 feet on the bracing. the top was flat but was at a slight angle , it wasn't dead square. The lower belly is to be there. With this being a 55 don't try and change much , if you are retopping it you can re establish the geometry to a point.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Thanks Woody and John,

John, I won't have to replace the top on this '48, but some of the top bracing will have to be removed, cleaned up and re-glued. Because of the geometry of the top, should the neck angle be reset differently then current practices (about a half inch at the bridge location... as in your youtube video). I'm not sure how much these tops at this radius raise up with string tension.

thanks.

_________________
Chris Oliver
Infinity Luthiers
...in the shop.

live every minute...

It is normal to adjust the angle with a wedge under the fretboard extension. Trying to adjust that angle can cause you yo thin the top where you don't want to thin it. Ebony makes this a good clean fix.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Correct me if I am wrong here... but my understanding is that back in the day, Martin made the "Radius" in the top by springing the top onto braces with curved profiles (Like in the Cumpiano book.)

It wouldn't be too hard to replicate that method on the Restoration......

I think if it was me, I would reset the neck as a matter of course when replacing a bunch of bracing... especially if you are correcting a sunken top in like shown.

Thanks

John

The first thing you need is to get the bracing reglued. One nice thing is that you are dealing with HHG . Once the braces are done you need to address the reset. You do want to work the neck angle so you should be to that 1/2 inch line.
What is the condition of the bridge and the height of that. ? Call me if you need to

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Sorry John... this '48 is in need of a restore because of its participation in a flood. Someone had previously tried to work on this unit. The bridge and fretboard are missing. Everything else is mostly intact. Also, they decided to dump a pot of hide glue in the top bracing to stabilize them... I guess? Here is a photo of the top.



Nice...

I have alot of hide glue to remove, not to mention flood funk.

_________________
Chris Oliver
Infinity Luthiers
...in the shop.

live every minute...

you can do a good restore on this. It is a great guitar to get back into shape. You should get this in a mold.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

John, I agree... recently I removed the neck,





now I've got to clean up the inside, then get it in a mold.

_________________
Chris Oliver
Infinity Luthiers
...in the shop.

live every minute...