I was using the laser to etch 40mm cubes with the letters of the alphabet and everything was fine. I bulk ordered some cubes and was surprised to find that the laser worked well but could not make any impression on the wood where the hard annular ring wood was. The mock-up image shows an example of the end grain that was causing the laser not to burn the wood. The darker wood is the hard compressed ring of the tree. This was disappointing because I did not want to have edge burn or smoke staining by holding the laser beam longer over the tougher wood. Besides which; it was a natural part of the grain and with every block being taken from a different part of the tree, or even a different tree, it would be a very difficult task to plan a laser etched letter or number for the six sides of each block.
Enter the CNC carver. I have some doubts about finding the best carving combination between workspeed, endmill and a softwood like spruce. I still may end up just painting them as coloured bricks and leave the carving or etching to a much more even surface of wood. I like maple but that is a bit expensive for kids toys. Anyway, the next issue was that I used a jig to hold my blocks for etching. You can see them elsewhere on this forum.
A similar jig for CNC carving would not be useful because it could not hold the block very steady when it was being carved. I see that my blocks have a tolerance from a nominal 40mm of ± 2 or 3 tenths of a millimetre. Clamping a block for carving while allowing access to the endmill and ensuring that the bit does not crash into the clamps appeared to be an insoluble issue. I discovered some flat cam clamps and these will do the job if I can extend the jig beyond the 130mm square table of SM1and that will provide room for the clamps. The pattern that I hope to build is illustrated by the following mocked up image.
The flat clamps exert a cam mediated compression effect when tightened and as long as I fit a pair of cam clamps, and the cube sits in a cube holding depression, I should be able to hold the cube workpiece still enough for CNC carving. The first problem to solve is that the steel pins which the clamps revolve about have to permit the clamps to revolve freely so that the workpiece can be clamped and unclamped at will. The clamps occupy a lot of space and if this wood block were to be held to the table by cap headed set screws, they would obstruct the movement of the clamps.
I am going to hold the wood to the table using countersunk hex set screws. This will allow the clamps to pass over the screw fixing without obstructing the clamps.
The steel pins shown also need a lot of room to be embedded into the wood correctly (20mm depth) so that the clamp does not sit proud of the wooden jig. My piece of wood is American walnut and its dimensions are L200 x W150 x D40mm. This is a fair bit larger than the 130mm square bed that was supplied as standard with SM1. It will not matter as to engrave the cubes, the bed movement will be limited to 40mm on the ‘Y’ axis rail and the ‘X’ axis movement will be the CNC head moving, not the workpiece.
The next image shows the underside of the wooden jig affixed to the SM1 table. With the table screwed to the ‘Y’ axis rail, the wooden block sits next to the ‘Z’ axis rail. There is about 1mm of clearance space between the two so when the table moves along the ‘Y’ axis, it will not crash into the ‘Z’ axis rail. The excess of wood extending beyond the SM1 table (at the bottom of the image) will face towards the door of the enclosure. Because of the excessive length of this wooden jig, the door will have to remain open during block carving so that the jig does not crash into a closed door.
The last picture to show you is the top face of the jig. It is a beautiful piece of American Walnut wood made from glued blocks of wood 40mm in depth. You may be able to identify the centre mark which will be the set origin point of the CNC end mill. Soon, I will start to carve a 40mm square with easing points at the corners so that oversized tight blocks will not bind or be difficult to remove. The set screws are 45mm in length and are made from A2 stainless steel with an M4 hex fitting. The countersinking was completed and the heads of the sets screws are fixed to the corners of the SM1 table. The holes were moved inwards a little to prevent the wood from splitting when it was drilled and countersunk. The excess of wood beyond the SM1 table boundary is the piece that will face towards the open enclosure door.
The arrangement of the clamps (shown in the mock-up illustration at the start of this post) will require me to drill two 20mm holes that extend to a depth of 20mm. I have to wait until the 15mm deep cube holding square has been CNC carved and then I will know where to place my cam clamp holding pins.
That’s all for now. I hope to have a bit more to show after the weekend. All comments are welcome.