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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Finishing wood using Danish Oil

There are many choices for wood to use in CNC projects, and just as many ways to add a surface finish. But, whichever choices you make on materials and finishes the important thing is that we’re trying to bring out the beauty of the wood colour and grain structure. It’s perhaps one of the big joys of working with wood that it can start off looking really quite plain, even dull, but change completely with a little bit of loving care finishing it off. So, I thought I’d write a post about Danish Oil as I find it a very easy and effective way to bring out the traditional look of hardwoods.

A definition of Danish Oil is hard to pin down, as there’s no set recipe, but it’s usually around a third varnish and two thirds oil (click here to read more on Wikipedia). That means it needs to be mixed-well before use and dries hard, so can be used with or without a later clear-coat. It can also be bought with lighter and darker stains mixed in, to help give a variety of finish effects, so is very versatile. Personally I like to use the natural version, which has very little stain in it, to retain the natural beauty of individual bits of wood.

As an example, below is a photo of my routed Mahogany fish before and after finishing. After a light sanding (very important to open up the surface for a good oil finish) it had two coats of Danish Oil applied simply using a bit of cloth to rub it in. Once dry I added some gold enamel paint to the routed grooves to add detail and then the fish was very lightly sanded to remove over-paint and give a smooth finish. That’s all the finishing it had and hopefully you’ll agree that it looks a lot nicer than it did before.

A routed fish with and without finishing

Another example I can give is the photo below of my Walnut Darth Vader head routing project. The image on the left is before finishing and, even though the Walnut already looks good, it was rather plain. To get to the look shown in the right-hand image it had two coats of Danish Oil, and a light sanding when dry, to bring out the grain and the beautiful colours. The gold enamel paint was then added to the grooves, as doing it before the oil can make the gold look duller because of the small amount of stain in the oil (which sometimes can be a nice effect, but not for this project). I then gave it three coats of Plasti-Kote spray on clear-coat as I wanted a shiny finish. Then, a couple of red Swarovski crystals added a bit of sparkly bling to the eyes.

A Darth Vader project with and without finish

Hopefully you’ll have enjoyed seeing the hardwood projects above come to life using simple finishing techniques. If so, perhaps you’ll think Danish Oil something worth trying out on one of your projects too 🙂

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Routing a fish with 1.5mm Mahogany sheet

Mahogany is a wonderful wood with fine, beautiful looking, grain. It’s ideal for any CNC routing project where you want to give your work a professional, and high-quality, look. So I thought it a good idea to write a short article about my experience of working with it on my cheap Chinese 1610 CNC machine. I decided I’d use a small (c. 50mm or 2″ long) fish design because it includes some shallow work for inlay, as well as a full-depth cut around the outside. The sheet was cut from a 1.5mm thick sustainably sourced plank and, according to my meter, had a water content around 9%. Below is a photo of the wood on the CNC during cutting.

A mahogany fish being cut on a CNC router

As this was a small piece I chose to use a 1mm end-milling bit, so that the shallow details would look tidy. Bits/tools of that size are easily broken through overly deep or fast cutting. For that reason I cut in two passes for the shallow details and three for the outside cut-through, which equates to between 0.5mm and 0.6mm depth per pass. Also, I kept the feed rate down at 50 mm/min which, although a little slow to watch, usually keeps my small diameter bits in one piece. The spindle speed was the maximum of 1000 rpm which, together with the low feed rate, provides a nice clean cut in my experience.

As you can see in the photo below, after just a light sanding, including using a folded piece of sandpaper to run along the shallow grooves, the fish looked quite nice. The only issue I’ve found, if it can be called an ‘issue’, is that the cutting tolerance around the bit is a little more than I’d like: with a 1mm diameter bit I ended up with 1.5mm wide grooves. That’s a 50% overcut which, given the simplicity of the spindle system, and the amount of vibration, is probably technically not bad for a small tool, although it does cause some difficulties cutting thin grooves for things like hammered wire inlaying. Overall though, my experience is that Mahogany can give inspiring and impressive results.

The completed Mahogany fish with the 1mm cutting bit

If you want to have a go at routing your own fish too, below is the SVG file for you to download and use in your favourite software. If you need a DXF file for your CNC router software don’t forget Inkscake will let you save one from the SVG file. And, click here if you’d like to see how this project turned out after some Danish Oil finishing.

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Cutting 1.5mm Mahogany with a 5W diode-LASER

Sometimes it’s nice to push the boat out and work with a nice (but obviously sustainably produced) hardwood on a special project. Once the staple of work and school desks, and plenty of furniture, Mahogany is an obvious choice for that, having a lovely dense feel and beautiful grain. So I decided that I should test some 1.5mm thick Mahogany to see just how easy it would be to cut it with a 5W diode-LASER. You can see the results in the photo above.

As the photo shows, the LASER has no real chance of cutting through in one pass, but at a feed rate of 100 mm/min, at approaching 100% power, two passes did the job. According to my meter that was with a water content of 12%. However, it does leave quite a bit of charring to clean away, although, as the photo below shows, it wasn’t so bad that it could be considered a game-stopper.

The back of the Mahogany after the laser cutting test

So, as with many other materials, cutting a mirrored version, so that the back becomes the finished front face, could be a good option. But, to give a good idea of how well you can cut quite detailed items out of Mahogany sheet, here’s a photo of a 30mm high Santa figure I cut at 100% power, 100 mm/min feed rate and two passes. Personally I was quite happy with the results.

A small Santa figureblaser cut from Mahogany sheet

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