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January 6, 2019 – CNC Maker Zone

Measuring water content in wood

The water content of wood we use in CNC work is obviously important for many reasons. One is that the quality of router cuts, and the depth of LASER cuts, will be adversely affected if the wood is wet. Also, and maybe more important, is that wood will change length as the water content changes, and as different woods shrink and expand at different rates that can lead to a nicely finished project coming apart over time (or even a lovely finish cracking). And it can have some bad effects on some finishes causing slow drying or cloudy clear-coats. For those reasons I decided to invest in a moisture-content meter so I can get an idea of how dry my wood is before using it, as well as to let me monitor changes as the wood acclimatises to indoor life before I cut it.

The one I got was only a few pounds on eBay so I’m not expecting really accurate readings, but testing some thin wood sheets at home I’ve been getting sensible readings between around 7% and 12% so hopefully it’ll be useful. Using it is very easy once set to the wood mode: the two metal pins are pushed into a non-vital area (end-grain is a good place too) like in the photo below and, after a moment, the reading appears on the small LCD display. Personally I’m quite happy with it and with a little luck it’ll provide me with a good idea whether my wood is too damp to want to use and let me monitor it to make sure I know when it’s ready for a project.

Measuring water content in wood with a moisture meter

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Cutting white paper with a 1500mW diode-LASER

1500mW LASER diode modules are a very inexpensive accessory for cheap CNC machines, and are ideal for things like burning images and text onto wood. However, with a little care they can also be used for cutting thin materials. One of those materials that is likely to be widely used, especially when crafting or carding, is white paper. So I decided to see if I could cut some white paper, which was around 80 gsm (grams per square-meter) and came from a notebook.

Being white and fairly smooth it’s actually quite difficult to cut as it reflects a lot of the LASER energy. But with some care focussing the laser dot to be as small as possible, and adjusting the height of the LASER (as they often have short focal lengths so shouldn’t be too high), I was able to do quite a nice cut as shown in the picture above (100% power and 100 mm/min). Fortunately, the dot on the 1500mW LASER is quite small so I thought it could be fun to see how small I could cut out my dragon and the result is in the photo below: at less than 20mm wide the cut quality was still quite good.

A 20mm wide LASER cut white paper dragon

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Improving lead-screw binding with a flexible coupler

CNC machines have plenty of moving parts and if we want our routing and LASER cutting to be as good as possible the movements need to be as smooth and unrestricted as possible. When I built my cheap Chinese CNC it came with rigid shaft couplers for connecting the threaded lead screws to the stepper motors. That meant that the motor spindle and lead screw couldn’t be adjusted to be perfectly in-line, just because of tolerances in parts and mountings. So, for part of a full rotation the lead-screw was binding (i.e. becoming hard to turn) and the rest of the turn was fine.

If you find you get the same problem, you could just do what I did: change the rigid couplers for slightly flexible ones. In the photo below I’ve shown the difference between the two. The bottom one is the original rigid one and changing to the new one involved no more than loosening the grub-screws, moving the lead-screw to the side, then inserting the new coupler, pushing in the end of the lead-screw, and tightening the grub-screws. For just a few minutes work it made X and Y axis motions so much smoother. And, for only a few pounds/dollars per coupler it was a cheap job too.

A flexible and rigid coupler

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