Sarah's Mandolin

[ScottR]

So I take measurements, and transfer them to both sides of the soundboard and draw out the F-holes using the little template I made.

The spruce top showed me a bit of figure that I didn't see coming.

Siminoff says to re-inforce the F-hole area with titebond impregnated gauze. I like that idea.

The gauze soaked up more glue than I expected. I'll clean that up after it cures.

SR

[ScottR]

While that is curing, I'll start shaping up the backboard. It is curly maple that has been roughly shaped on a pattern carver as the top was. And the surface is rough as the top was.

I sanded those marks out prior to doing any shaping. I thought I'd try a finger plane to carve with since thickness is critical, and it has a built in depth of cut stop.

SR

[ScottR]

This little dude was a challenge to acquire. I ordered it from StewMac along with other goodies for this project. The the package arrived, this was not inside. I contacted StewMac and the sent me one overnight. When that arrived, I discovered it had no blade. I contacted StewMac again and told them I was pretty sure it was supposed to come with a blade. They agreed and sent me one. This tiny little thing is about the size of my thumb from the first joint out, and is a right bastard to set up. You have to do it by eye and feel. Did I mention it is tiny?

Once I finally got it the way it needed to be, it worked like a champ.

I shaped and sanded to 100 grit....not finished but I wanted to stop and take a few pictures so Sarah, (and you) could see the figure of the curly maple.

And a couple wetted with mineral spirits.

SR

[Prostheta]

Beautiful! Is that a small bit of readout on the upper scroll?

[ScottR]

9 hours ago, Prostheta said:

Beautiful! Is that a small bit of readout on the upper scroll?

Ummmm, I dunno. What's readout?

SR

[Prostheta]

Readout is autocorrect on my tablet playing hell with my wording. "Tearout".

[ScottR]

Technically it is I suppose. It is just the rough cut from the pattern carver. Other than roughly locating the inside cut on the soundboard scroll, I won't be doing any shaping on them until after they are glued to the rim. They are cut a little oversize, so I need to get them flush to the sides to see what I have to work with.

SR

[Andyjr1515]

The figuring looks lovely, @ScottR  I've had one of those tiddly planes for a while - stunningly and surprisingly good once you get a feel of the setup.  This thread is reigniting my thoughts of trying a carved top arch top....                          Ref the thickness, are you doing it on a 'plane it and check it' basis or are you planning reference drill holes I've seen in one or two arch top vids.

[ScottR]

5 hours ago, Andyjr1515 said:

The figuring looks lovely, @ScottR  I've had one of those tiddly planes for a while - stunningly and surprisingly good once you get a feel of the setup.  This thread is reigniting my thoughts of trying a carved top arch top....                          Ref the thickness, are you doing it on a 'plane it and check it' basis or are you planning reference drill holes I've seen in one or two arch top vids.

I'm using the plane it and check it method more or less. I took initial measurements to see what I had to work with and then shaped the outside to my liking. I used the finger plane to remove wood in the areas that needed it most and then cleaned up the contours by sanding. My fingers have been pretty good at telling me that it's close to right. Then measure and sand to get the last few hundredths on an inch balanced out. It's hard to explain how much pleasure I get out of shaping wood by gently carving and sanding into shape letting my fingers tell when it's right.

With this kit the soundboard and backboard have been pattern carved to within a quarter inch of the target dimensions. Any future builds of these instruments will be done from scratch. I do believe then I would carve and shape the outer surfaces and using the drilling of reference holes to match up the inner surface properly, at least to the point that I could finish up like I'm doing here.

SR

[ScottR]

The gauze ended up being much thicker than I liked. What was the point of carefully contouring the top if I was going to change a big chunk of it like this?

So I sanded and re-contoured and filled voids with medium CA and shaped until I was happy.

And then moved on to cut the F-holes. I started by drilling out the round parts and then Scroll sawing the balance of the shape. These are much smaller than final size so they can be enlarged in the tuning of the sound box.

SR

[ScottR]

I made a template to locate the tone bars.

I used a nut on my pencil to mark the contour line needed to fit the tone bar.

 

After rough carving close to those lines I place sand paper in to the hollow and use short strokes to match the tone bar to the inside surface of the sound board. I think this is what Andy calls flossing....

SR

 

[ScottR]

I kept working that till the fit was smooth. I went up to 220 grit mostly because it was thinner and therefor gave me a more exact fit to the inside of the soundboard.

When both were fitted, it was time for glue  up.

SR

[ScottR]

And whilst that glue up is curing, I go back to shaping the backboard.

First I shape the back exactly as I want it, and then I'll shape the inside to the required thicknesses and contours....

SR

[KnightroExpress]

Man, this is going to be a great little instrument. I love watching your builds come together!

[ScottR]

1 hour ago, KnightroExpress said:

Man, this is going to be a great little instrument. I love watching your builds come together!

I'm having a hard time believing how much fun this one is!

SR

[Andyjr1515]

Can't believe how neat that scroll sawing work is on the f holes. Love the shape of this top.

The flossing reference in my dreadnought thread (for the neck heel fit) is where the two parts remain static and the sandpaper itself is pulled through the lightly closed joint.  It's a term I picked up along the way and seems a reasonable descriptive term ref dental floss.  As a process for closing the joint on a variable plane it's quite effective, except I find it hard to prevent an 'exit curve' at the point of the sandpaper from the joint.  Long thin strip of cloth-backed has the best chance to be able to give a strong pull without it tearing.

[Prostheta]

Andy - my first thought on that would be to make the tone bars wider than required, floss them to fit and then shave them to the required width. That way the "exit curve" exists on the waste. Either that or use a small piece of service material either side of the paper ingress/egress points. What Scott is doing should avoid that entirely of course, as long as the paper doesn't bunch up during the work and the bar doesn't tilt.

Whichever - you guys both have eyes that see these details. In spite of these being established processes and methods, talking through them in terms of discussing difficulties and tricks helps show how they can be translated to other jobs. One being things like closing up set neck joints such as that which @Chris G did recently. Pull strips through the mating surfaces - perhaps with service material either side - helps allay that exit curve issue, especially on very visible things like that.

[Andyjr1515]

Yup....the oversize trick did occur to me.....after I'd done the job 

[Prostheta]

Most importantly, you'll remember to consider it before the next one!

[ScottR]

The challenge the tone bars presented was the inside edge needed to fit a constantly changing radius (compound curve) and the outside edge had to fit a different constantly changing radius. The 3M paper I used had a rubberish tacky back so movement wasn't a problem. I needed to be sure I was sanding the bars right over the target location for glue up. The strokes had to be really short, no more than 0.5" to start with and about a quarter inch for the final fitting. I went up to 220 grit, not so much to fine sand but because it was thinner paper and therefore closer to the desired final shape.

SR

[Muzz]

On 4/11/2016 at 6:51 PM, ScottR said:

 

UFO 

the tiny plane is so cool, and the mando top is looking amazing 

[ScottR]

I thought the little green men were coming for me.......but it was my wife they wanted.

I'd make the same choice.

Good to hear from you Muzz. You been out traveling?

SR

[Muzz]

Always great to chat to you Scott, really enjoying seeing your mandolin take shape. My buddies and I have been hard at work recording 6 original songs. Here is the Neve desk in the studio, I have been using a blend of real tube amp plus the pod modeling amp. Just about to have one of these strange beers. Look forward to seeing more sawdust

 

[ScottR]

Awesome. You'll have to post a link to some of your music when you get them ready. It's great to see the Cheery Bomb again looking like it's been getting work.

I've haven't pulled the trigger on one of those apple brews yet........

SR

[ScottR]

The tone bars came out of the glue up okay.

I did some preliminary shaping. The finger plane worked like a champ for that. I went on and sanded cuts smooth and then let them be. After gluing the top on I will attempt to tune them. Apparently the target tuning is A flat on the bass side and A sharp on the treble side. While I'm talking of tuning, I should mention that the F-holes  have been left smaller than their intended final size. They will be enlarged in order to tune the sound box further on down the line.

In preparation for gluing the top onto the rim I built a go-bar deck. I had to go back to the cardboard forms to keep from having to build a great big one to fit my plywood forms.

I cut up some jatoba into roughly 1"x14"x1/8" strips for go bars. Jatoba is extremely stiff. so flexing them ought to provide a fair amount of pressure.

SR