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Assembly with domed soundboard (Read 26938 times)
Matt Blacka
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Assembly with domed soundboard
Mar 27th, 2007 at 3:38pm
 
Hi, I know there has been other topics listed here about doming uke soundboards, how to do it, what radii are used, how to make dished workboards etc, but I haven't been able to find anything on how the doming affects the attachment of the neck and fretboard to the soundboard.

I have built one uke with a true flat top, as per Hana Lima 'Ia plans and manual, no problems. For my next few ukes I was going to try doming the soundboard, but am not sure how this will affect the attachment of the soundboard to the flat table at the end of the neck (spanish style). Should this area of the soundboard be kept flat or sanded flat? or is the dome radius so large that it doesn't affect the whole process? Should the neck be angled back slightly, so that it forms a flush plane (tangent) with the curve of the soundboard at the junction? Should the bottom of the fretboard be sanded to fit the dome for the area where it passes over the soundboard (from heel to soundhole).

Also, I'm interested to hear if people (particularly Mike and Asa) also use a dished assembly jig for gluing the sides to the soundboard (Session 6 Steps 2 onwards in Hana Lima Ia Manual), and if so, how this jig differs from the one shown in the manual (at the neck body junction section).

Thanks in adavance for your assistance
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Hana Lima Ia
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Re: Assembly with domed soundboard
Reply #1 - Apr 1st, 2007 at 2:30pm
 
Hi Matt,
Glad to hear you’re willing to dive deeper into the process.  This does open up a whole new can of worms for assembly.  Fortunately the size of the ‘ukulele makes it easier to deal with.  On the ‘ukulele, a 25’ radius is very slight so not much adjustment is needed.

If you angle the neck down just 2 degrees you will compensate for the dome (this will form the flush plane).  Create the neck angle by adjusting your heel slots.  Keep the attachment of the soundboard to the flat table at the end of the neck (spanish style) flat.

The radius is so slight you wont really have to sand the bottoms of the fretboard or bridge to fit.  It’s easier to see what I mean in a picture:
...

The 1’ box would be the length of the soundboard and the 8” box would be the width of the soundboard.  From heelblock to tailblock there is a difference of about 0.085” or just a little over a 1/16”.  For the width it is only 5 hundredths of an inch or so...just a little less than a 1/16”.
...


With the neck you add a little more length so the curve is more pronounced.  The 2-degree offset will take care of it.  Final adjustment can be done as usual with nut and saddle height.

We do have a dished assembly jig for gluing the sides to the soundboard.  That is one of the worms in the can…but once you’ve put in the setup time it’s all good!  I’ll have to post pictures, but that is another story.
-Asa
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« Last Edit: Apr 1st, 2007 at 7:23pm by Hana Lima Ia »  

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Matt Blacka
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Re: Assembly with domed soundboard
Reply #2 - Apr 1st, 2007 at 2:56pm
 
Thanks Asa,

that clears up a whole heap of questions, the drawings are great, a picture says a thousand words. Now I've gotta get to work making some domed boards and an assembly jig. I've got a few other jigs and tools in the making as well. As you say, its all in the setup time.

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Re: Assembly with domed soundboard
Reply #3 - Apr 11th, 2007 at 4:35am
 
On spanish foot type instruments usually only the lower bout is domed per Cumpiano.  If built this way, is it still necessary to change the neck angle?  Seems to me one could lower the bridge? ???
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Re: Assembly with domed soundboard
Reply #4 - Apr 11th, 2007 at 6:04pm
 
This is only if you were going to radius the soundboard.
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Matt Blacka
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Re: Assembly with domed soundboard
Reply #5 - Mar 2nd, 2008 at 3:09pm
 
Another quick question sort of related to this topic.....

I know that braces/bars are sanded on a domed workboard before being stuck down to the soundboard or back, so as to create the domed profile, but are the bridge patch and soundhole patches also sanded to the domed profile, or are they simply stuck down using the dished workboard?

I am thinking that if the patches are stuck down without being pre sanded, but the dished workboard is used during glue-up, that the domed profile will be held anyway due to the lamination between soundboard and patch being created using the dished form......if this makes sense?

Thanks,

Matt
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Re: Assembly with domed soundboard
Reply #6 - Mar 2nd, 2008 at 5:00pm
 
Yes, usually the upper bout is kept flat, but if you dome it you can sand the area where the fingerboard overlays the top flat.  If fact if you consult, OLF(luthiersforum.org) and check tutorials you will see a jig for sanding this area.  I would not dome the upper bout and make life simple for yourself.
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Re: Assembly with domed soundboard
Reply #7 - Mar 3rd, 2008 at 7:46pm
 
Matt,
I think that because the sound hole patch and bridge patch are so slim they can be glued down on the radius dish with a Go-Bar deck without any modification.

They will conform to the radius without a problem.

Lefty
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Matt Blacka
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Re: Assembly with domed soundboard
Reply #8 - Mar 4th, 2008 at 10:53am
 
Thanks for your responses.

I glued down a bridge patch last night, which I pre-sanded to the domed profile. It worked fine, and is holding the dome shape in that area of the soundboard, even without the tone bars being placed yet.

I am making three fan braced ukes at the moment, but I don't think I wiill worry about pre-sanding the rest of the patches for the others.

Matt
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Re: Assembly with domed soundboard
Reply #9 - Mar 4th, 2008 at 11:33am
 
Matt,
Glad I could help.  I have not built a uke with a domed soundboard, however, the one steel string guitar I built I did not radius the patch.

Good luck with your ukes, How about some photos.
Lefty
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Re: Assembly with domed soundboard
Reply #10 - Mar 4th, 2008 at 1:19pm
 
On a fan braced ukulele (or a classical guitar) the only braces that run parallel to or close to parallel to the centerline are the tone bars which start below the sound hole and are notched to fit over the bridge plate.  Since the bridge plate is glued in place before the tone bars (and is placed in a cross grain direction) there should be no problem with gluing the plate in flat and then adding some curve with the tone bars.  Most of the dome effect will have to be provided from the shaping of the sides.

By the same token, the two enharmonic braces can only provide side to side doming, and any doming shape above the enharmonic bars must be accomplished by shaping the sides.

On a steel string guitar (which is commonly domed) the main support is a X brace that when shaped forms the doming for the top.  While the sides and linings must also be shaped to match the doming, the top bracing supports the doming before the being glued to the sides.

While classical guitar makers frequently dome the backs, most seem to use flat tops, particularly if they are using a spanish heel.

If you are going to use a domed top, think of using a tenon joint with matching mortise in the body heel joint.  By robbing 1/8 inch from each side of the Hana Lima neck cuts ( 3/4" instead of 7/8"), you can get up to a 1/2 inch tenon which is wide enough to use two 8-32 X 2" hanger bolts to bolt the neck to the body, or glue the neck joint if you prefer.

On my steel string guitar I missed the angle slightly and had one devil of a time getting things to work out because I had used a tapered sliding dovetail joint for the neck/body attachment.  A tenon joint will allow you to fine adjust the heel to match the body and get the neck set angle to fit perfectly.  The tenon joint (and seperate neck) also makes banding the body a lot easier with both a domed top and domed back.  It can be done with a spanish heel, but is easier with two piece construction.

Good luck in your adventure.  Keep us posted on how it goes and what you decide and learn as you go along.

Don
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Re: Assembly with domed soundboard
Reply #11 - Mar 5th, 2008 at 6:51pm
 

Don,
  Well put.  Thanks for the info.

Lefty
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Re: Assembly with domed soundboard
Reply #12 - Sep 7th, 2008 at 10:29am
 
Hi Matt,

Just want to revive this thread as there hasn't been much talk of domed fronts or backs lately.

I'm assuming that you've completed this uke by now. I'm in the same place now that you were then. I've cut a 12 foot radius work board for my back and am thinking about making a 22 foot radius for the sound board. My intention is to stick with the Spanish heel and angle the cuts 2 degrees (+/-) like Asa suggested.

Which route did you end up taking? Was hoping to get feed back on the building process form you or anyone else that wants to give me any hints.

Also have seen a little info on using a solera ( a term used for something similar to the Assembly Jig on pg. 71 of the Hanalima book) with a dish cut into it to create a dome in the area below the sound hole and the lower bout. Pete Howlett did a video on ukulelecosmos.com about it, but not much info about shaping tone bars or the bridge was included. Does anyone have any info on this technique as well?

Thanks,

Mark Schrier
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Thanks, Mike and Asa!
 
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Matt Blacka
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Re: Assembly with domed soundboard
Reply #13 - Sep 8th, 2008 at 10:56pm
 
Hi Mark,

I haven't finished this series of ukes yet. I have one that has pretty much been boxed up, and another three that are waiting for their sides to be bent (soundboard, backs, and necks completed though). You can check out the pictures on my website. They are all designed to have a Spanish Heel style of construction.

I redrew the concepts that Asa had posted before, with the angled heel slots, and worked out that the angle I needed was a fraction over 1 degree, to get the soundboard and fretboard to be on the same plane/angle at the neck/body joint. All four necks had their heel slots angled back by as close to this angle as possible.

When I made my domed workboards, I made two for the back dome and three for the soundboard dome. I have since cut one of the domed soundboard workboards down to the same shape of my assembly jig, and modified my original flat-top assembly jig to take the domed board as its surface. I also added an adjustable neck support to the assembly jig, so that I can accomodate the slightly set-back neck angle. For the one uke I have assembled, this modified jig worked very well.

The domed workboards worked fine for sanding and gluing braces using a go-bar deck.

One thing that may be of interest, is that I worked out a modified shape that the sides have to be cut to before being bent, to get the correctly domed soundboard and back profiles. Solving this problem required a combination of maths and CAD to investigate the height that the sides should be at all points around the side, where they join to the back and soundboard. This is a strange three dimenional problem, where the height of the sides at any point depends on the distance of that point from the apex of the dome. This is very different to a side shape for a uke with an arched back and flat top. I can write some more about these calcs if you would like.

Anyway, thats my current position on the domed soundboard/back thing.

Matt
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Re: Assembly with domed soundboard
Reply #14 - Sep 9th, 2008 at 3:30pm
 
Hey Matt,

Thanks for the reply.

It's interesting that you can develop a shape for the pre-bent sides. I figured that I would have to put the bent sides in a mold and shape them in a dished jig. Are you trying to keep your front and back as parallel to each other as possible. I hope that makes sense or at least it would if both pieces were flat. I am envisiong the top (soundboard) edge of the sides being as straight as the radius will allow, but the back edge being a little sloped so that the body is a little thinner at the neck end. Can you describe what you've achieved in your design?

So it seems that the main concern when setting the neck angle is to make the fretboard fit as flat as possible on the sound board. Does it seem like the relationship between the fretboard and the bridge works itself out? In my mind, I see the bridge needing to be a little taller than on a flat sound board.

I checked out your blog. The woods you are using are pretty neat stuff. Hope your builds continue to go well.

Best Regards,

Mark
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Thanks, Mike and Asa!
 
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