November 2008


It has been a productive weekend. Having brought the ribs, or sides, to the right thickness, I rubbed on some orange shellac which really brought out the flaming in the Tasmanian blackwood.

The next task is to make the linings – these are backing pieces which help to attach the sides to the top and back, and also give a broader gluing area for the top and back. These important structural components need to be fairly robust, yet be flexible enough to be able to be bent into the shape of the mandolin. To achieve this, kerfs are sawn into the linings at regular intervals, so that the wood is cut, but not cut through.

This results in a flexible snake of blocks connected by a thin timber, which can then be steam bent into shape. They are much larger than those for a violin, as they help to provide extra rigidity to the instrument, and that is supposed to help the sustain. They also need to be large enough to provide gluing area for the sides – even after the sides have been cut away slightly to allow for the binding veneers.

I clamped a stop block to the scroll saw and was able to make the kerf cuts quickly and evenly, as shown in the photo.

You can read the rest of the story here:
Part 1 – making a start (selecting the timber)
Part 2 – preparing the top
Part 3 – cutting out the back
Part 4- starting the ribs
part 5 – sawing the ribs
part 6 – thinning the sides

making a travel mandolin – part 7 – kerfing the linings.

After sawing the ribs, there is then a fairly careful process of thinning the ribs to the right thickness of about 1.5mm. The sawing left rough faces which then needed to be smoothed out and the sides taken down to the right thickness. Initially I used double-sided tape to tape the sides down and took the worst of the sawing marks off with the plane. Then a more delicate process with the scraper, and finally, after selecting the best or face side I took to it with 380 grit then 600 grit sandpaper, and finally 1500 grit to get the surface really smooth.

I wondered about the colour mix, as the back padouk is very orange, and the sides, or ribs – blackwood – are very brown, and the top of birdseye maple is almost a pale honey colour. Would the brown and the orange clash? Actually, yes. But there is a solution, and that is to include a banding strip containing the colours of all the timbers. Here are the parts lined up to see the relationship between them.

mandolin sides

You can read the rest of the story here:
Part 1 – making a start (selecting the timber)
Part 2 – preparing the top
Part 3 – cutting out the back
Part 4- starting the ribs
part 5 – sawing the ribs

Some more progress, and a solution to a problem. Today I set about sawing the ribs – the sides of the mandolin. The ribs serve little real purpose other than to separate the top plate from the back and define the air cavity between the two. I settled on 50mm wide, 2mm thick and about 600mm long as a starting point. That would leave sufficient timber to scrape it down to remove machining marks and thin enough for steam bending to shape.

I ripped the boards to 50mm – no problem there on the Triton Mk3 saw bench, but the first attempt at resawing to cut thin strips failed with a very nasty and abrupt stop as the thin slat tore off and half disappeared between the saw bench and the blade, trapping the saw blade and bringing the whole process to a rapid stop.

The blade guard prevented kick back, so it was just a technical problem. I unplugged then freed up the saw, and reset it up straigth again as the force of the sudden stop had moved it out of alignment.

I pondered this for a bit and remembered the solution – make a zero clearance sacrificial false table. I had some 3mm MDF (medium density fibreboard) and found a piece about the right size – enough to cover about half the triton saw table. I set the blade to the height I wanted for the cut, then I removed the guard – note if you do that you need to be absolutely focused on your safety. I positioned the MDF above the blade, started the saw, and with one edge braced against the riving knife I lowered the MDF onto the blade, making sure that my hands were well clear of where the blade would cut. I then stopped the saw and there was the false tabletop with zero gap between the saw blade and the MDF. I cut a slot for the fence bolts, then clamped the MDF in position and set the desired gap between the fence and the saw blade.

At that point I replaced the blade guard and made a trial cut in a pine offcut before going back to the precious Tasmanian blackwood, ready to make the thin strips that will eventually become the sides, or ribs of the mandolin.

zero clearance saw table

You can read more on the progress so far as follows:
Part 1 – making a start (selecting the timber)
Part 2 – preparing the top
Part 3 – cutting out the back
Part 4- starting the ribs
part 5 – sawing the ribs

Cheers
Jerry

Some small progress this week – I selected some figured blackwood for the ribs and began preparation of the timber using my trusty old Russian plane freshly sharpened and reset. Once the surface is good on both sides I shall saw the board in half along its length and resaw it into thin slats ready for finally thinning and bending.

Cheers
Jerry

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