Official Luthiers Forum!

Am I correct-top in oven @200 degrees for 1 hr.?
What do you place the top upon in the oven?
Is it OK to bake if rosette installed?

I've baked tops at 200 degrees before and it worked fine, I use 180 degrees now, an hour seems fine, then just shut off the oven, crack the door open, and let the top cool down for a few hours...at least that is what I've done and it has worked nicely. I would not bake with the rosette installed as the top plates tend to move a bit as they go through this cycle which may lead to slight seperation between the top and the rosette. I've basically stickered my tops on each end(top & bottom) with a simple clamp system just to make it easy to put in and out of the oven and to keep the actual top off of the metal rack...they seem to be stable before and after the process, so I haven't seen a need to do much else.

Cheers,
Greg

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Gwaltney Guitars

uhhhh.... you bake them before you joint and join them.

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Brock Poling
Columbus, Ohio
http://www.polingguitars.com

I too bake them before jointing and joining them. I experimented with a pair of jointed top plates, after the baking session the jointed edges were no longer a perfect fit. So I joint and join them afterward and it works out nicely. I leave my top plates a tad thicker than Hesh, just to make sure I can sand off the pitch/sap? that comes to the surface. I joint and join after baking then run the plates through the sander, leaving it thick enough to work on the rosette and subsequent level sanding on it too.

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Gwaltney Guitars

Anyone tried basting their tops?

Thanks for the great info.

Martin, isnt that how you get a naturally burst top

I like my tops baked also.

I did have one mishap. I didn't preheat the oven and the top on the bottom shelve got to hot when the oven came on full to heat up. The top burned really bad. In another few minutes it would have started fire!!! And I was only heating it up to 190 degrees.

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Joe Beaver
Maker of Sawdust

Ya crazee yanks and your huge ovens. I can't actually fit tops into my oven fully. Not even half tops.

Mattia

I know what you mean... we are a little spoiled over here state side...

You should see them scream when gas hits $3 a galllon....

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Joe Beaver
Maker of Sawdust

[QUOTE=Mattia Valente] Ya crazee yanks and your huge ovens. I can't actually fit tops into my oven fully. Not even half tops.[/QUOTE]

You can blame Thanksgiving. You can't cook a huge bird in a tiny oven.

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Aoibeann

[QUOTE=Joe Beaver] Mattia

I know what you mean... we are a little spoiled over here state side...

You should see them scream when gas hits $3 a galllon.... [/QUOTE]

Actually cry. Its running about $100 to fill my truck up. I deal with a 5+ hour daily commute by bus so I don't have to drive. We will be moving once my son graduates from high school in a year. That is if we can find something that isn't a doublewide trailer or has 900 sq ft. for $250,000.

I miss Germany with its functioning, reliable, affordable and quick mass transit system.

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Aoibeann

[QUOTE=Aoibeann] [QUOTE=Joe Beaver] Mattia

I know what you mean... we are a little spoiled over here state side...

We will be moving once my son graduates from high school in a year. That is if we can find something that isn't a doublewide trailer or has 900 sq ft. for $250,000.

I miss Germany with its functioning, reliable, affordable and quick mass transit system.[/QUOTE]

I wish we could find anything for $250,000 over hear! My son and his wife are really lucky in that they have just bought a small semi-detached starter house near Canterbury for $320,000. And I have just sent off a cheque for the insurance on my house insuring for it's most recent valuation of $1.5m (that doesn't include the land!). No, we paid nothing like that 30 years ago, but house prices here are going up at 10% pa.

Yes I wish we had Germany's or even better Switzerland's transport system as well.

Colin

PS I can get tops in my Aga though

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

Ovens??? Here they fit all joined up in my 70's microwave oven!

Thats in interesting concept. Has anyone every microwaved their wood? If so, what were the results?

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Aoibeann

Maybe I missed something, but why do you bake your tops? Do you bake
the backs as well?

seems like ya oughta be be baking the braces too....nobody is mentioning that. Any thoughts on that?

[QUOTE=Aoibeann] Thats in interesting concept. Has anyone every microwaved their wood? If so, what were the results?[/QUOTE]

Lillian, someone might have done that before but not me, i was just being silly once more!

There are two different types of top baking. The one I believe is in
discussion here is the initial high temperature baking, sometimes referred
to a "setting the sap". This is where tops are baked for something in the
area of 200F for an hour on average, the idea being to lessen the
sensitivity to humidity changes in the future. I don't know if many folks
(or any, really) truly understand what is happening at a cellular level here,
but it does work. There are theories I've heard that range from
crystalizing the sap, to driving moisture out of the cell walls and in effect
hardening and stabilizing the structure somewhat. The latter sounds
more plausable to me, as I know that water can remain trapped within the
cell walls long after it escapes from within the cells and wood may be
considered dry.

The other type of baking is to dry the top immediately before bracing,
allowing the top to swell in to it's radius as it reacclimates. This has been
standard procedure with Steinway pianos for at least a century, and is
used to establish what they refer to as the crown of the top (the crown is
created for tonal reasons as much or more than structural). We did this at
Galloup guitars when I was there and it certainly brought a certain life to
a top that simply clamping in to the desired end radius would bring. It
took a great deal of trial and error to determine the things like the initial
radius to brace in to and the desired moisture content of of the top, but it
certainly did something. I know of classical builders who build a similar
stress in to thier tops by "spring loading" the braces, or clamping
radiused braces on to a top on a flat surface and letting the brace pull the
top in to a slightly compromised radius when unclamped.

If you've ever been in to a good piano shop you have probably run across
a display intended to emphasize the importance of humidity and top
crown on the piano's tone. They are generally a piece of spruce with a
tuning fork mounted to the center, and two ends glued to tall blocks with
an adjustable rod connecting them. As you tighten the rod it will arch the
spruce plate parallel to the grain and the tone of the struck tuning fork
changes dramatically, becoming much more powerful and clear. I once
tried making a demonstration board like this to keep on my counter, but
not thinking I set it up to bend perpendicular to the grain. Much to my
surprise the tone if anything became slightly choked as I flexed the top.
In afterthough this seemed an appropriate explanation as to why the tops
radiused by humidity control sounded so much more powerful than those
radiused by a dish. The humidity radiused tops would have naturally
curved much more parallel to the grain where all the change occurs with
humidity, and less so perpendicular to the grain. This of course would
end up not being the perfect semispherical radiused top that we think of,
but perhaps some form of parabola?

In any case, that's the second form of baking, although it probably
deserves a difference in terminology to seperate it. Perhaps it already
does and I just don't know about it. Sorry if I'm long winded, but I just
have a hard time abbreviating things.

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Eschew obfuscation, espouse elucidation.

Thank you David,

I like long winded explanations.

And, after reading your post, and the other posts, I would be interested in learning more about “Baking Tops”

For me, this is a fine example of how true the old saying is-

“Some study shows the need for more”

Robert

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Everything has beauty, But, not everyone see's it!

I corresponded with a fellow in Brazil who heat treated his BRW backs before building, and he said that he had a lot less subsequent cracking in finished instruments. He put the back plates between two hot metal plates that were heated with heating elements--rather like a side bender, but just flat on a table.

Hi Terry, yes, I bake my spruce braces too, seemed logical to me.

Greg

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Gwaltney Guitars

This "Baking Tops" idea, seems to me, is what I should be doing too!

However, it has me wondering -

what happens to the top after (at least in my case) it is subjected back to the average humidity level (50%-70%) of my area? Unfortunately, I do not have a work shop with a controlled environment.

Robert robertandsons39091.2658101852

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Everything has beauty, But, not everyone see's it!