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

luthier's bending iron

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.

luthier's bending iron
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.

luthier's bending iron

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!

luthier bending strap

Tomorrow is glue-up time!

Cheers
Jerry

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Armed with a bending iron and not afraid to use it, I set about shaping the linings to fit the top and back. I had prepared the timber (pine slats) by cutting kerfs and then cutting the linings in half along their length to make twice the length for half the effort.

I soaked them for about an hour in a large tub of rainwater, and then measured them up ready for bending.

I turned on the heat gun and waited a couple of minutes to ensure the pipe got really warm on the 600C setting, and set to work.

using a luthier's bending iron
I did the linings in sections so that complex curves were kept to a minimum, and left room for the end and neck blocks.

The linings were then clamped in place held by clothes pegs and allowed to dry so they wouldn’t spring back which would make gluing more difficult.

And here is the result.

mandolin linings

mandolin linings

Cheers
Jerry

A while ago, I used a piece of water pipe and a blow torch for bending the sides of my travel violin with some success, but I felt I needed something more reliable for the mandolin. I had read of the possibility of using a heat gun – the sort used to strip paint – to provide a steady heat source, but saw no plans for doing so.

It was time to think it through and find my own solution. And here it is.

luthier's bending iron

Please note that the air needs a place to escape so that the end of the heat gun doesn’t melt. But the solution is a durable one.

luthier's bending iron

The pipe structure comprises an internal plug with a square top – which is held in the vise. Attached is an T-junction connector, with one opening towards the heat gun, the other vertical. To the vertical end is attached a short piece of water pipe using a connector. And that’s it. The heat enters the wider aperture of the T-junction, finds the lower aperture plugged, and diverts up the vertical tube. The vertical tube is narrower than the T-junction, so the tube gets to be heated, while waste air is released out the top – away from the person doing the bending.

luthier's bending iron

On the hot setting (600C) the vertical tube is plenty hot enough to boil water on contact, but because the waste heat can escape, there is no heat buildup to melt the heat gun, and there is no hot blast of air against the body of the operator.

The proof is in this piece of binding which was used to test the bending iron.

luthier's bending iron

Cheers
Jerry