Four Strings

Yesterday I made bent the bouts or sides into shape and clamped them in place so they would retain their shape ready for gluing.

I realised I would need more luthier clamps so I decided to make some more. They are easy and cheap to make. In my case, the ones I made for the violin project were too small for the mandolin which has a deeper body.

Making luthier clamps
I bought two lengths of 3/16-inch threaded rod and packs of washers, nyloc nuts and wing nuts for that size. I already had some 3/4-inch dowel.

I cut the threaded rod with a hacksaw into 12 equal lengths of 100mm (4 inches), cleaned up the cut ends with a file and threaded on a nyloc nut – just enough to bring the thread flush with the nut. The nylon inner coating will hold it in place as the fixed end.

Then I drilled a 3/16-inch hole in the end of the dowel to the full depth of the drill. It doesn’t have to be precisely centred but it helps to be reasonably vertical.

I then ‘salami’ sliced the dowel into half-inch or 1.5 cm lengths. I then re-drilled the next batch and so on until I had 24 dowels.

I then took the threaded rods and slipped on a washer, then dowel, then dowel then washer and finally wing nut to make the completed clamp. The dowels will not damage the instrument and will gently draw the top and back plates together against the bouts.

And here is the instrument glued up and clamped in all directions – a woodworker can never have too many clamps!

I also made a maker’s label and attached it where it would be visible through the sound hole.

What you won’t see is the hidden wish on the underside of the top plate – that will only ever be seen by a future repairer or someone with a dentist’s mirror 😉

Cheers
Jerry

And so to bending the sides. You will recall I made a luthier’s bending iron from a piece of water pipe and a heat gun, well here it is in action bending the sides, or bouts of the mandolin.

The first bend was the upper bout for the top quadrant to the right of the neck – this would be the least conspicuous if I made a mistake.

I ensured the bending iron was at the right heat – so water misted onto it boiled immediately

I had the bouts soaking in a tub of water for about 20 minutes. They had been thinned to just under 2mm with the wasp sander mounted on my drill stand. They probably needed to be a little thinner still – more like 1.0-1.5mm thick for easier bending.

Once the iron was hot enough I donned leather welding gloves – so my fingers wouldn’t get burnt if I made a mistake – and picked up the bout and the metal bending sheet that I had made earlier. The bending sheet provides support to the fibres of the timber and helps to hold the steam in the wood. I’ll explain in a moment how I made the backing strap.

I gently worked the timber, springing it slightly and pressing with a wrapping motion against the bending iron. You can feel it reach the right temperature and the point at which it wants to bend. Don’t rush this because – as I found – if you try to go too hard too quickly you will snap the timber and have to start over. It’s best to have a test piece or two so you can practice first on a non-critical component. Here is another view of the process.

Within about two hours I had all the bouts shaped and clamped to the body so they would dry and retain their shape. Blackwood is notorious for springing back to its original (flat) shape. I left it overnight to cool.

The bending iron worked well. I would get it really hot on the 600C setting then when it reaches operating temperature I dialed it back to 300C to maintain heat without stressing the heat gun too much.

Making the bending strap
The strap is quite simple to make. you need an empty steel food tin (washed carefully) with the top and base removed. I cut it open with tin snips/shears. Next I took two small size tent pegs and bent them in a vise into a triangle – these will form the handles so you are not dealing with a sharp tin amidst the heat! I folded the ends of the tin can around the tent peg on the side where the two ends meet, and hammered it so it made a good round shape around the tent peg, leaving about a centimetre (say half an inch) and drilled three holes and joined it with three pop-rivets. Complete the other end and voila – you have a luthier special tool bending iron backing strap!

Tomorrow is glue-up time!

Cheers
Jerry

Things are progressing well now. Having made the end block from maple out of a tree that burnt at home during the 2003 Canberra bushfires I glued the top and back to the end block and set the neck in place. The neck is a unit with the heel block and has slots cut in the sides for the upper bouts. These will be bent from Tasmanian Blackwood thinned to 2.0mm with the wasp sander.

So the state of play is illustrated here. The fingerboard is yet to be glued in place.

Having determined from classical guitar construction that the neck can be integral with the neck-block, I set about shaping the neck into its final form.

I began by chiseling the basic form of the heel, then taking the corners off the neck shaft and using a wood rasp and files to form the head junction and basic heel shapes. Then I used the luthiers mini thumb planes to shape the neck to its final form. The orange rubber mat is a cheap non-slip mat from a kitchenware store – it makes a great non-slip surface on which to work timber.

I drew around a 20c (Australian) coin to get the curves for the head decoration and cut that out on the hobby band-saw and smoothed it with the drill-mounted ‘Wasp’ belt sander.

Then I smoothed the heel curve with the same belt sander and hand finished sanding using 600 grit, then 1500 grit to get a smooth talc-like finish.

With one coat of orange shellac

The neck is now almost finished

Cheers
Jerry