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Anyone out there using a cylindrical arch for their tops? What kind of radius are you using? I'm using 20', but thinking 15'. Also thinking about 12' domed back...

Haans: I think Howard Klepper builds in this fashion. Maybe he will drop in and shed some light on the subject.
Tom

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A person who has never made a mistake has never made anything!!!

Haans, Dave White uses cylindrical tops and backs, like maybe 15' on top and 10' on back, or maybe 12' and 8', something like that. Some pretty severe arching, and has some pretty good ideas about it's effect and why he likes it. He's very open and sharing also.

Joe

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Yo Hanns,

the two mandos me been building for eons have what I call "flexed curves" to them...Ya cylindrical...don't know the radius as me don't much use measuring gauges or rulers and stuff like
that...you know, just a wing and a prayer. Nor do I know what they sound like yet as one is in the
finishing stages and the other is still in the white.

Non the less, they certainly have the look and feel of a carved arch top which is what I was hoping to end up with.

Now here comes the hard part for you Haans....me put tone plates in them just like Lloyd Loar did with his F 5s. and me know you just love tone generators. So far I am very happy with the tap response and me be hearing things coming out of them sound boxes that my picker buddies don't...but then me always been hearing and seein things ... and ya the 60's were good to me.

Go here, see how me approached them.

http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=21036



blessings
the
Padma

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Audiences and dispensations on Thursdays ~ by appointment only.


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I did on this guitar, 5' arch for top and back.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

What did you think of the sound Laurent?

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Formerly JJH

I learn more from my mistakes than my successes

5' arch? That's steep Laurent!
Thank you all for the info, I've looked through the UMGF article Tony, but couldn't find any info on cylindrical arching, but might have missed something. Some info on Larsons, though...
"the" thanks for your cryptic support! Good luck with the "Tone reducers".

I think I'll re-rout my 20' cylindric sanding board to 15' and think about a 10' back.

Laurent, the pics sure don't look like 5'....I'm sure they are but just checking?

Also trying to wrap my head around the cylinder profile, can anyone post a pic of the sanding form/for my pea-brain to "get it"

Cheers,

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Gwaltney Guitars

Sure Greg, here are some photos of making the 20' arch. Basically, It arches only in the "across the bout" direction. It's flat longitudinally.





BTW, the, I am interested in your pulled down arch. I have been using a flat top and arching it when it's glued to the sides.

Umm Haans,

me understand routing or tooling up a dish cuz well its concaved . But why go through all the trouble to rout a trough when just a few culls with the arc removed will do the job for go-baring in some bracing. Routing produces so much sawdust.
Then maybe gluing down some door skin or 1/4 ply with a sandpaper surface for sanding the perimeter of the box.

Wood be much easier than routing in me brain.

Oh and thank you Haans for addressing me by my first name. Five years on these here forums and you are the first person to be so kind as to ever acknowledge me name.


Blessings
the
Padma

_________________
.

Audiences and dispensations on Thursdays ~ by appointment only.


.

OK...yeah I was visualizing it correctly, not sure why I was thinking it would be more radical than that. Just a tad taller at the neck and tail block, but flat along its length....I may have to try that soon.

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Gwaltney Guitars

Greg-
A 5' radius arc would have about ½ inch rise across a 16" bout. So the pic is hiding something from me as well- must be the angle.
http://liutaiomottola.com/formulae/sag.htm
Cheers
John

Well, you're right the, there's a lot of glue dust in routing these. I thought of your method, but elected to rout as:
1) I wanted a heavy board, so the paper digs in.
B) I wanted it to stay straight...notice the 1/2" baltic birch glued on the back.
3) I use it to bend the top on and clamp.
Just seemed to be worth the dust to me...
Naturally I would want to call you by your first name...wouldn't want you calling me Brentrup or some other name...

Hi Haans,
I made an arched top and back on the ABG I posted recently on TLC and, as someone mentioned, I used a spline curve, not a radius. If you support a piece of wood near to each end and press down in the middle, the wood doesn't form a radius, it forms a spline curve (or something close to it). The part outside the supports is going to stay straight so, between the supports and the middle it's going to change from straight to curved, and the biggest deformation is in the middle. As this is the way the wood wants to bend, it made sense to me to make my sanding sled the same way. Here it is. (Click for a bigger image).



The distance between the outside supports is 50cm (19"11/16) and the height of the support is 9.5mm (3/8") for the shallow curve and 21mm (7/8") for the tight one. The two pieces of MDF are simply screwed down along the centre line. The intermediate supports on the tight curve were just slid into place with some glue on them to make the sled less likely to flex in use. The middle of the sandwich is a piece of 1"1/4 particle board counter-top. Heavy and stiff! The equivalent radii would be about 5'-11" and 10'-10". The great thing about this method is it's quick and easy with no mess!! This is what the finished body looked like. It's also wedge shaped which makes it look a bit odd too.



One slight disadvantage of these shapes is that the linings aren't keen to follow the curves generated, especially if the body is also wedge-shaped. My developed sides looked like this!

That's a great idea Dave. I think Howard Klepper talks about spline curves too. Thanks for the photos too. A lot to think about. I assume you are bracing the top and back on the board sandwich, yes?

Howard Klepper's very lucid rationale is here, scroll down to "Top and back arching". Nice sanding sled Dave

Peace,
Sanaka

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...imagine there were no hypothetical situations...

Yes Haans, the top and back were braced on the sled. You can see a fairly detailed account of the building sequence here:

http://www.luthiercom.org/phpBB3/viewto ... =20&t=1487

NIce jigging Dave!! Lovely build.
Sanaka, I have read that page from Howard's site and have even used a modified form of Howard's "A" frame bracing (tone bars) on my 12 strings. Don't see that he mentions spline curves there though...
Larson Bros. used what they called "tensioned tops". Not sure if they bent the tops on curved ribs ala the's mandolins or just used radiused tops on radiused ribs. My new 6 string has a flat braced top glued onto a 20' cylindrically radiused rib, so we'll see what happens there. Sounds good so far. Of course there might be a point where it's too much like maybe flat top on a 15' rib, but maybe a 20' top on a 15' rib would be the way to go. Sounds like some good experimenting...but now I have to think about spline curves too.

It's at the end of the section on 'Top and Back Arching'

"Last, I use a spline curve for the arch because it is the curve that a thin panel such as a guitar top will naturally follow when flexed. This means that by using this curve the panel gains the most stiffness in proportion to the internal stress that the flexing induces. I use this arching system for both tops and backs."

If you send Howard a PM I'm sure he'll give you more details. I did, and he was very helpful. I've been looking for the reply he sent me but I'm b*****ed if I can find it. Perhaps it got accidentally erased.

Thanks Dave...I can't hear that well either!
I really hate to bother folks with questions in emails, especially when it involves something I think might be proprietary. I know the emails I get sometimes about specifics about my mandolins step way over the line...
However, I feel that forums like this one are about sharing and are voluntary.
I may just go with the spline curve. It's easy to make up and experiment with. Should be an interesting new year...

Y'all have a wonderful Christmas!