Tuesday, November 22, 2011

Bush Installation Tip

I’m just on the finishing stages of Chris’s Hare. The bridge went on yesterday without a hitch- not that there ever is! It’s just so final, no room for error etc.

After 24 hours for the glue to dry thoroughly, the last few bits and bobs go on, the tuners, end and strap pins, truss-rod cover and pick-guard etc.

I just thought I’d pass on this tip for fitting push-fit tuner bushes like these Grover ones.

I’ve tried various ways of installing this type of bush- rubber mallet, g-clamp, brute force etc but you always run the risk of the bush going in cock-eyed and once in, they shouldn’t come out! StewMac do a fancy tool for this task costing £30. However my solution is much cheaper and extremely effect- I use a machine screw and a wing nut.

Use washers to protect the back of the head and the plating on the bush. Tighten up the wing-nut and Bob’s you uncle!

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Monday, November 14, 2011

Brendan’s Mandolin Part IV

The Rim

I tend to refer to the whole assembly of the sides, linings and end blocks as the rim of my instrument.

So the first job is to mark out the sides, looking at the grain and making sure that any grain that looks problematic is in area that doesn’t have to be bent too tightly. The sides for my twin-pointer have to be cut into 2 pieces where the point will be- a measurement that I check about 12 times before cutting!

The bending, as always, is done on my “iron”. This cocobolo was a real pain to bend just where the curve gets really tight at the points. Although the wood itself bends OK, the resin seems to boil and retain the heat, so that the wood keeps wanting to spring back. I had to call for reinforcements! I held the curve in place whilst Amanda sprayed water on it, to quench it!

Once bent, the sides are clamped to my mould to dry out.

Next, cedar blocks are shaped and glued into the points to hold them together. Then the two end blocks go in which gives us our final mandolin shape.

The linings are next; mine are solid, as this makes the rim of the instrument more rigid and less likely to absorb energy from the soundboard. As you can’t bend 5mm thick wood, two thinner strips have to be bent and glued together; which adds to the time taken.

With the general construction of the rim complete; the pretty bits go on. The end trim- here I’m using some sap wood and ebony.

Then ebony points-

Which after some careful shaping .......

Look like this

Before the soundboard and back can be glued on, small housing joints have to be cut into the linings to take the ends of the various braces- 13 of these!

The soundboard and back are glued on......

And finally the body!

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Friday, November 04, 2011

Brendan’s Mandolin Part III

The Back

Below you can see the beautiful cocobolo that I’ve got for the back of Brendan’s twin-pointer; he’s opted to go with the sapwood showing (good choice!). You won’t see better wood than this and as you can see there is enough here for two backs (the next one could be yours!).

The back is joined the same way as the soundboard, however to get the book matching just right, on such pronounced grain, you have to be really careful when you thickness it.

Next, is the joint’s reinforcement strip, I always have the grain running along the length of the back rather than at 90 degrees as many do. Why? Well- when the moisture content of wood changes, the wood will shrink or expand across the grain and not along its length. Also, the majority of moisture is lost from the end grain and cross banding is nearly all end grain! So, hopefully you can see that a back reinforcement strip with the grain running lengthways, should be much more stable and less likely to distort the back with changes of humidity. The strip is glued on in a curved jig.

Next is the X-bracing. I feel that the surface of the back should be part of the surface of a large sphere and as the mandolin’s shape is almost circular, an X-brace works incredibly well to the give the desired curve. I’ve always felt that the back should be a reflector of sound and by using braces to induce a curve, you put the back under tension so that it doesn’t flap or absorb sound energy. The rim of the mandolin will have to be shaped to fit the back.

The Soundboard

Before deciding on the final dimension for the soundboard, I decided to do a few experiments to gauge the stiffness of the red spruce. I find the easiest comparative test for me to carry out is to measure the deflection of the soundboard when a mass is placed on it.

I also did something similar for the bracing. Conclusion? The red spruce is stiff! Therefore I can make the bracing light.

One other concern is that I’ll have to drill a hole through the soundboard to take a wire for the pick-up. To reduce the chance of the ‘board ever splitting at that hole, it’s sensible to have a patch where the hole will be with its grain running at 90 degrees. How thick should the patch be? Thinner than you’d think! I glued some 0.6mm sycamore veneer to a piece of scrap red spruce and tried to break it. You can see the results below!

Well, with my experiments carried out I can confidently work on the soundboard and its bracing.......in private!

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Wednesday, November 02, 2011

Parlour guitar now sold

Wow! That was quick, less than a week- the parlour guitar is now sold, boxed-up and waiting to be shipped to its new home.

I’ve said it before and I’ll say it again- this is a great little guitar and I’m sure that its new owner is going to enjoy playing her.