Setting up the slice of cypress in the CNC machine is relatively simple. I use ply wood strips screwed to the MDF base that I have fixed over the aluminium bed. The ply wood is flexible and acts as a spring holding the wood in position. I use 5 to 6 pieces to ensure the wood will not move. The slice is slightly thicker at one end so I use a wedge to level the wood ensuring an even cut for the CNC cutting bit.
The orientation has to match the pattern. The zero point is off centre and tricky to pin point.
Getting this zero point right is vital to ensure the engraving exactly matches the pattern I tested yesterday. I measure it carefully with a Vernier calliper. Double checking before aligning the cutting bit and setting X,Y and Z to zero on the CNC machine.
Next I just have to press START. I watch the machine and check that it starts cutting, by listening to it, at the Z=0 point. It does. The spindle speed is too slow causing the wood to vibrate slightly, so I increase it to 17,500 rpm, which is pretty much my default choice of speed. And I reduce the travel to speed to just 8%. So the cutter moves very slowly making a very neat, crisp cut.
It's going to take 2 hours for the numbers to be cut.
After 20 minutes I check the machine is cutting exactly where I want it to. I leave it to get on with its job.
100 minutes later the result is exactly as planned. After removing the piece from the machine I run it through the belt sander very gently and then rub the wood down by hand using a fine grade paper.
I then use a compressed air line to remove as much dust as possible. Next I use lint free cloths to wipe the surfaces to remove any remaining particles that may affect the quality of the varnish finish. It will take 5 to 6 coats to bring out the gloss finish I require.
I've experimented with various type of varnish but once again the cheapest is the best. I used well known brands but none were as good as Wickes' own brand gloss varnish. They have now stopped selling it so I bought all the stock remaining in the shop. The choice of brush was similar. I bought expensive ones, but ended up with the B&Q brand Diall. Does the job perfectly. Before I start varnishing I warm the room, and set up a dust cover which is nothing more sophisticated than a cardboard box.
The deep bark of the cypress will need several coats to protect it from the elements. I start with the varnish diluted with about 10% white spirit so that it soaks rapidly into the wood. After varnishing the bark, then the back, I finally varnish the front
so that it will then sit face up, and horizontal to avoid any runs. Any excess varnish, which is unlikely as it is being soaked up so quickly, will run to the back of the sign and I can sand this down later. We have probably 4 to 5 coats to go.
Keith Clarke
April 2022
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