How to

How to make giant protractors

How to make giant protractors

A customer from distillery cooperage contacted me. They needed to replace their giant protractor that they use for barrel making. Their old protractor had had a hard life and was getting very damaged as you can see below. It was becoming inaccurate and unreliable, so it was time for some new ones.

old distillery protractor
Old distillery protractor

Maximum protractor diameter

Two protractors were required at 1000mm diameter. My laser is bed is 1200 x 800mm which meant that the maximum diameter of protractor I could make was 800mm. The cooperage was was happy for me to make them at that size.

Robust materials

The coopers wanted something not too thick and heavy, but robust and shatterproof. It was also important that the degree markings and numbers should be easy to read.

My main suggestions for materials were plywood, mdf and perspex. Plywood is heavier at the same thickness of the other two materials. It’s more expensive and can shatter if dropped. Engravings on perspex are always white in colour and not as clear as engravings on ply and mdf. So we ruled perspex out for those reasons.

Next, I made sample engravings on ply and mdf and sent them for evaluation. As birch ply is lighter in colour than mdf board, it was the option of choice as the engravings were clearer on the blond wood.

To make the protractors as robust as possible whilst keeping them light and easy to use, the coopers asked for 4mm ply rather than 3mm.

Making the engravings stand out more

Artwork for the protractors was right first time. All the cut lines and the degree lines and numbers were a single line thick, and the laser vector engraved all of these, giving thin but clear marks. But the coopers asked if I could make the lines bolder.

I have a cunning way to do this. When the machine is properly focused on the surface of the material, the beam is as small as possible to give a clean cut or accurate engrave.

If the beam is defocused, the beam becomes wider and therefore engraves a wider vector engraved line. I made another sample to demonstrate this and the coopers gave the go ahead to make the protractors using that fix.

Laser cutting and engraving the giant protractors

I did this in two steps. First, I defocused the laser and engraved all the degree markings and numbers. Then I refocused the machine and performed the cutting as shown in the video above.  I did it that way round to ensure the plywood stayed as flat as possible throughout production. It’s easier to do this if the material stays as one integral sheet.

The ply for the second protractor that you see being cut in the video above was more inclined to warp, so I had to hold it flat by weighing it down with slates.

My customers were really pleased with their new protractors. I think they’re rather beautiful!

 

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