Thickness of archtop top and back.

I am building an archtop uke based on the shape of a Hofner Senator guitar. The top, (spruce), and back, (maple) are both carved to shape on the outside. The insides are carved out to approximately 3mm thick.
My question is: how thin should I go?
As I understand it, the thinner they are, the more they will 'ring'. Am I right? I've looked at numerous YouTube vids but the more I look, the less I understand the Black Art of Tap Tuning!
Also, is the centre glue joint going to be compromised? If so, should I put a cross-grain strip over the joint?
Your thoughts on these questions will be appreciated.

Geoff Kewell.

Aloha Geoff, since I have been active again on UU, I have seen a few questions about arch top ukulele construction but have resisted joining in until now. In 2009 I started a thread on building arch top ukulele and had some plans available. Give me some time and I will add some pictures of those plans to google photos and post a link here. In the meantime, two excellent sources of information on arch top construction are Roger Siminoff’s book on Building a Bluegrass Mandolin and Bob Benedetto’s book on Building an Arch Top Guitar. The principles explained in those books also apply to ukulele. And a short answer to your question on thickness, the recurve area of the top should be about 1.8- 2.0 mm thick and about 3.5 to 4.0 mm in the center. The back should be carved about 10% thinner.
Bradford Donaldson

Here are the pics of the plans I drew up some years ago. Feel free to ask any questions you have.


https://photos.app.goo.gl/BUddG4RNGVWVSBSdA

Brad,

Thank you so much for coming out of the long grass to answer my query. The drawings and diamentions are really usefull and just what I was looking for.

A few further questions come to mind:

My top and back are already down to 3mm thick. do you think that a 1mm plate under the bridge area is called for?

Should I put a cross-grain strip along the back joint?

Should the back be braced like a conventional round hole Uke or is the curvature adding sufficient strength?

My design (a tenor), has 'F' holes and a cut-away. Should the tone bars stretch up into the upper bout?

What are your thoughts on cross bracing of tone bars? They would fit more neatly into the cut-away and would cross under the bridge area.

Your Dimentions Table lists 'solid linings'. I can't see where they would go, or am I missing something?

Questions...Questions!

Thanks in advance,

Geoff.

Having worked with archtop instruments some I'll share a few of my thoughts.

The top should not need a cross grain strip.

I think you should look to a F style mandolin to guide some of your decisions. A carved back does not need braces. Tops usually get "tone bars" or and "X", but that's it. Feel where the rigidity of your top is already, and compare with other Ukes you've done (if you have).

One big difference, though, is a mandolin and arch top guitar is designed for steel strings. A mandolin has 8 steel strings, so needs to be able to hold up to that string tension and down pressure on the bridge. I would think an archtop uke (thinking acoustic not electric) would have to be built lighter to be driven and respond properly to the lighter tension strings. Maybe tone bars aren't necessary, or very minimal. Maybe just one? Unless you are actually stringing it up with steel strings.

I'm interested to see how it goes.

For the record, my plans are designed for nylon strings. In my 37 years of building I have completed 407 fretted instruments. Of those, approximately 150 were carved top mandos, 9 were arch top guitars and six arch top ukulele. For further clarity, I assume that your design includes a floating bridge and a tailpiece. Please keep in mind that the acoustic behavior of these type of instruments are very different from flat top ones. The biggest difference with arch top construction is that the back contributes as much as the top in sound production. The primary mode of vibration of a carved top and back with a floating bridge is up and down as opposed to a flat top bridge which mainly rocks back and forth. I concur with Brett that there is no need for any glue joint reinforcement on the top and back. They are already much thicker than a flat top joint, if you can’t get them right you are in trouble lol. Also an X brace pattern is a possibility if you prefer. The linings I mention in my plans serve the purpose of reinforcing the glue joint at t the top and back, you may prefer to use kerffed ones on a cutaway, especially if you intend to bind the instrument. No bridge plate is necessary, the 3mm thickness should be sufficient for the center of the top and back, but you need to graduate the thickness down to about 1.8 mm near the edges.
Brad

Hi Brad and Brett,

Thank you both for your replies. Your information and suggestions are gratefully received. It just goes to show that no matter how much you know, you never stop learning!

This is only my second instrument build, not counting the plywood guitar I made some 60yrs ago when I was 14yrs old. What a dog that was, but I did get strong fingers from the awful action.

My first uke build was from a kit and was built using mainly blind logic. It works well to my untutored ear and I play it regularly in public. However, I can see how I could have improved it.

Some say that I'm mad to take on an archtop build, but nothing ventured...but then, some people say that I'm mad to build them at-all!

My archtop might turn out to be a real Turkey but I'm determined to give it my best shot!

Thanks again,

Geoff.

Geoff Kewell said:

Hi Brad and Brett,

Thank you both for your replies. Your information and suggestions are gratefully received. It just goes to show that no matter how much you know, you never stop learning!

This is only my second instrument build, not counting the plywood guitar I made some 60yrs ago when I was 14yrs old. What a dog that was, but I did get strong fingers from the awful action.

My first uke build was from a kit and was built using mainly blind logic. It works well to my untutored ear and I play it regularly in public. However, I can see how I could have improved it.

Some say that I'm mad to take on an archtop build, but nothing ventured...but then, some people say that I'm mad to build them at-all!

My archtop might turn out to be a real Turkey but I'm determined to give it my best shot!

Thanks again,

Geoff.

Click to expand...

My very first instrument was an archtop. It was crazy and it really didn't turn out that great. It doesn't have strings on it even anymore. But my second one was pretty nice.

I've thought an arch top uke is a really cool idea, but have also wondered how one would pull it off and get good sound out of them, too. Or do they have their own unique sound not to be compared exactly to a conventional ukulele. That's why I mentioned mandolin, or maybe even looking to violin family instruments for guidance.

I'll probably give an arch top uke a try one day, too.

Brett,

If you havn't actually tried to make an archtop instrument then I urge you to have a go. I have to admit that there is something extremely satisfying, (dare I say, sensual), running your hand over the curvature of the plate after sanding it smooth! I can't wait 'till I have a good few coats of Tru-Oil on it.

Moving on...Today I had the great pleasure of handling a beautiful violin owned by a friend. It was built in London in around 1790 and is still being played to a very high standard on a daily basis. Would it be too much to ask that an instrument built by one of us would still be around and played in the year 2248? Discuss!

Geoff

Geoff Kewell said:

Brett,

If you havn't actually tried to make an archtop instrument then I urge you to have a go. I have to admit that there is something extremely satisfying, (dare I say, sensual), running your hand over the curvature of the plate after sanding it smooth! I can't wait 'till I have a good few coats of Tru-Oil on it.

Moving on...Today I had the great pleasure of handling a beautiful violin owned by a friend. It was built in London in around 1790 and is still being played to a very high standard on a daily basis. Would it be too much to ask that an instrument built by one of us would still be around and played in the year 2248? Discuss!

Geoff

Click to expand...

As I said my first instrument was an archtop. And my second.

Brett S. said:

As I said my first instrument was an archtop. And my second.

Click to expand...

Sorry Brett. I should have read that more carefully.

My intention is to help beginning arch top builders avoid the many pitfalls inherent in this kind of construction. My first arch top guitar, I used an X brace to arch the back into shape rather than carve it, it did not work too well. Had I done some research, I would have discovered that Martin had done the same thing many years ago and also found it did not work.
As long there appears to be some interest in this discussion, I will continue to contribute what insight I have. Some history may be useful in understanding the concept. The arch top guitar replaced the banjo in the big bands back in the 1920’s. They were loud enough to be heard through the horn section of a band. The hallmark of a good arch top instrument is that it is loud, but has less sustain than flat tops. That is why arch top guitars are popular with jazz musicians. The same music played on a flat top guitar can sound muddy because the notes continue to ring. A good arch top ukulele should have the same properties, loud initially but with less sustain than a flat top ukulele.
Brad