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plywood – CNC Maker Zone

Choosing a wood finish to enhance colour and grain

After all the love and care we put into our CNC projects their success often hinges on how well we finish the exposed wood surfaces. Sometimes we may just want to leave them plain, even unsanded, but usually we’ll be wanting to bring out the colour and grain structure to show off the beauty of the wood we’ve chosen. So what is the best way to do that? Should we just cheat and use clear-coat, or should we use traditional techniques like Danish Oil or Shellac sanding sealer? How much work is involved varies a lot depending on which we choose, so is the best way the one that involves the most perspiration, or can simple ways provide more inspiration?

To try to answer some of those questions I decided to do some tests with six of my favourite woods: Basswood, Oak, Cherry, Walnut, Mahogany and Birch plywood, as shown in the photo below. I then decided on four finishes: plain unsanded wood (A), Plasti-Kote aerosol clear-coat (B), Danish Oil (C) and Shellac sanding sealer (D). The last three were all done in two coats and after light sanding with 400 and 1000 grit sanding paper/pads. I think one of the most interesting things the photo shows is that all three surface finishes, even the simple spray-on clear-coat, enhanced colour and grain significantly.

Comparison images of the six woods before and after applying surface finishes

The unsanded woods (A) were obviously a little plain and dull, but still nice for many uses. The simple clear-coat (B), however, was much more interesting as it’s a very simple finishing process yet brought out the colour and grain structure very well. The main comment in comparison to the other finishes is that it gave a slightly darker look to the wood, although not in an unpleasant way. In comparison, I think the Danish Oil (C) gave a slightly nicer look to the grain, as well as bringing out the colour of the wood beautifully. Probably that’s due to it being mostly oil (see my post here) and so likely soaked deeper into the wood surface before hardening.

The sanding sealer (D) also gave a nice finish, although it was slightly duller. That’s not surprising though as its’ purpose is mostly to provide a sealed surface that can be lightly sanded smooth before applying other coatings. In the past I’ve used it with a finish of wax polish for a traditional look, and I think that would work well with the results here. The only other thing to note is, for me anyway, that the finishes improved the plain colours and grains of the Basswood and Birch plywood, even giving them some of the look of pine which could be useful for many projects. However, for a more exciting look they may benefit from a little wood stain/dye: in the case of the Danish Oil that can include darker oils that are commonly available.

Overall, I think the main conclusion from my tests is that simply applying a synthetic clear-coat to a carefully sanded wood surface is just as effective as more traditional techniques. Certainly it enhanced the colour and grain of all of the woods as well as giving an extra level of darkness if that’s what you want. Of course, using the other, more traditional, techniques gives subtly different effects so they still have a role to play and can be used with a final clear-coat too for some nice effects. Really it’s all down to our judgement, but without any need to feel guilty that using a cheap and simple clear-coat is cheating: in fact it’s a useful technique that compliments traditional finishes very nicely.

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Cutting 3mm plywood with a 5W diode-LASER

If you’ve searched the internet about laserable materials you might have decided that plywood is the most popular sheet material out there. And, you might be right which is no surprise given that it’s a very versatile material due to its strength and the solid-wood look of its surface. However, the glue used to bond the layers (i.e. the plys) together can give off noxious and toxic fumes when burned, and is also difficult for a laser to cut. Also, the glue and its thickness can vary around the sheet, making cutting potentially inconsistent.

That’s why using a LASER mounted on a CNC machine means we really need to make sure the plywood we use is LASER-safe. LASER-safe plywood has a special glue that reduces the fume problems and is easier and more consistent to cut. So, to see how useful it can be with my 5W diode-LASER I tested cutting a piece of 3mm thick LASER-safe Birch plywood. The results are shown in the photo above. I found that two passes, at 100 mm/min, around 100% power was successful at cutting right through.

However, probably due to variations in glue thickness, and some curving of the sheet (and maybe water content variations: my meter said 8% although it’s hard to be sure with plywood) for some cutting I find I really need three passes. Below is a photo of the back of the test sheet, which showed that cleaning up the burn marks isn’t a small job, but nonetheless isn’t so bad that it’s not worthwhile.

The back of the plywood laser cutting test

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