Laser Engraving Wood

Laser Engraving Wood

It may seem trivial to talk about laser engraving wood but considering that it is one of the products that most of us do a lot than we should spend some time talking about it. We can talk about raster engraving and vector engraving as two separate processes when it comes to wood.

Raster Engraving Wood

When a laser is raster engraving (Figure 1 shows us some samples of raster engraved images) the laser marks with a back and forth motion. This motion is similar to what you would see with a laser printer or an inkjet printer. The laser slowly moves its way down the table. The amount of the movement is dictated by the dpi that has been chosen in the driver. When we are engraving a message in wood we use the raster movement of the laser to create the message.

When we are raster engraving wood most of us have our preferences as to how deep we need to engrave into the wood. The deeper that we need to engrave into the wood requires that we use more power (or slower speed). The higher the power or the slower the speed will cause the laser to penetrate farther into the wood. So when you are laser engraving wood it is the power and or the speed of the laser that will determine the depth that you go into wood. If you want a deep cut the laser will typically need to run slower which means the job will take longer to engrave than if we required a shallower engraving or cut.

Figure 1

Vector Cutting Wood

Vector engraving (Figure 2) in wood is when the machine runs like a plotter or a rotary engraving machine. Output from CorelDraw is vector lines not bitmaps or raster images. Typically to cut out material such as wood you require high power and a slow speed. When you are cutting out the wood because of the high power sometimes you create excess flaming. Most laser machines come with an air assist system so that you can blow out any excessive flaming that may occur. It is not cooling that we are doing here as cooling would defeat the purpose of supplying power to cut out an object.

Figure 2

One thing that should be talked about now is how air assist works when you are vector cutting. The first rule is that you should really only use air assist when you are vector cutting. Using air assist when you are raster engraving tends to cool down the engraving area and thus defeats the heat of the laser to effectively vaporize the wood. Secondly for the most part only use air assist if after testing the material with and without it that there is a noticeable difference. Figure 3 is a piece of birch plywood that had not had air assist used on it. Figure 4 is the same material with air assist. In my opinion there is no noticeable difference. This is not to say that air does not work it just means that you need to test before you use it.

Figure 3

Figure 4

DPI and Speed

One of the characteristics of wood is that it tends to be rather porous. Because of this porosity and because of the grain of the wood typically wood plaques do not need the same quality of engraving that is needed on other products such as metal or plastic. For this reason you may find that you can run at lower resolutions (check out figures 5 and 6) than you would need on other products. This causes two things to happen. The first is that the lower the resolution the faster the job engraves (the quality of an image can suffer if you lower the resolution to much). Since most of us base our pricing on time than the faster that we can go means we can save money on producing an image if we use a lower resolution. Secondly because we are laying down less dots (600 dpi has twice as many dots as 300 dpi) than we need to adjust the power or speed so that we are supplying more power to the engraved area (figure 6 is different resolutions same power and speed. You can see that as the resolution goes down so does the depth of engraving). So there is a trade off. A lower resolution can decrease our engraving time but we may need to supply more power to the engraving machine to make up for the lack of dots that are there. For this reason just because you lower your resolution from 600 to 300 does not mean that you are decreasing your lasering time in half. You may need to supply more power so if you need to slow down to supply more power than your speeds may decrease.

Figure 5

Figure 6

Cleaning the Engraved Area

When the laser burns away the area it tends to leave a small amount of residue. If the wood item has a sealer finish on it than all you need to do is to take damp rag or shammy and wipe off the excess residue. If the wood is raw than the residue left by the burning process can cause a permanent stain. Thus you will need to either mask off the wood so that there is no stain or sand down the wood after you have lasered it. The sanding process will get rid of any residue that stains the wood.

If you get an actual burn on the edge of your engraving you can decrease the power or even your air flow. Sometimes a powerful exhaust can cause the exhausted air to flow very close to the top of the plaque which will drag the frame on top of the plaque.

Painting MDF (Laminate plaques)

One of the problems when you laser engrave MDF is that the engraved area tends to come out rather white or light. For certain plaque colours this is fine and we prefer to leave it as is. However there are times where this is not acceptable and has to be changed. There are also times where we are trying to match up colours that may be in a logo. Because of either of these two reasons we need to paint the laser engraved area.

One of the most common misconceptions when you talk to people about painting MDF plaques is that they think that you need to go deep into the MDF. Actually if you go to deep you actually make it harder to paint. Also because MDF is wood fibers held together by a lot of glue than you need to provide a lot of power to achieve this depth. Figure 7 shows a plaque that has been laser engraved and has not been paint filled.

Figure 7

Painting MDF is actually quite easy. Typically when I am painting the wood I will use a water based acrylic. You can either place the paint on by spray or by sponge brush. Once the paint is placed on the plaque allow it to almost completely dry and than wipe of the access paint with a damp paper towel. Figure 8 shows paint that I typically use to gold paint fill my plaques. It is available in my area at hobby or craft stores.

Figure 8

Figure 9 shows that I have spread the paint on the plaque so that all the engraved areas are filled with paint. Next we need to take a damp paper towel and wipe of the paint. Typically I do not allow the paint to totally dry. This makes it easier to remove the excess paint.

Figure 9

Now just keep wiping off the paint until all the excess paint is removed. Be careful on the areas where there is a large lasered area as you may wipe out the paint. Figure 10 shows the plaque cleaned and finished.

Figure 10

Shoe Polish

One of the problems with lasering some woods is that the engraved areas are not dark enough. A quick way of darkening an engraved area is by using a black shoe polish. Just rub it on and than rub it off. Note: you may need to be careful not to get to much shoe polish in the surrounding area as the polish can become trapped in the pores of the wood. The nice thing about shows polish is that it has an applicator built into the top of the bottle. For this reason make sure that the shoe polish is the one in the bottle not the round can.

Painting Walnut

Although I have seen dealers use the same painting techniques to colour solid wood items typically the results are not as good as what you get on MDF. Figure 11 shows you what happens when you paint wood. This is because the paint tends to get trapped in grain of the wood. This is especially true when it comes to wood such as oak where there are a lot of grain. Figure 11 shows that I have small patches of silver painted trapped in the grain of the wood. This paint is still prevalent even after persistent cleaning.

Figure 11

What I suggest to people is to use a mask and burn through the mask. Once the mask is burned you can paint the wood. Once the paint is dry you can peel off the mask.

Note: The best mask that I have used is vinyl transfer tape see Figure 12. Products such as masking tape are not good as they tend to be to porous are the edges. This porous edge allows paint to seep out past the border of the engraved area.

Figure 12

Foil on Plaque

One of the classier effects that can be used on wood is placing a gold or silver foil to highlight a logo or text. The biggest problem with foils is getting them. Typically some manufacturers require that you purchase a sizable roll. Company’s such as LaserBits carry stock on the foil. This stock includes a number of colours.

Figure 13 shows a finished plaque that has had a gold foil applied to it.

Using this foil is quite easy and requires some practice. The first step is to make sure that the wood item is totally clean and free of any dust or other particles.

Figure 13

Once you have cleaned the wood item take you foil and LIGHTLY place it on the item. Make sure that it is completely down. Do not apply to much pressure to the foil as we will be weeding off the access foil. Create your artwork in CorelDraw. The artwork can be either raster based or vector based.

If the artwork is raster based than any of the artwork that is black (which will be laser) will burn away the foil. Any area that is white will retain the foil. Note: depending on the image you may need to have a border around the outside of the image so that you can weed out the foil. The nice thing about a raster image is that you will not have to weed to much of the foil as most of it will be lasered away.

If the artwork is vector than you laser will cut away the image that you want. Once the image is created you will need to weed away the access foil to finish off the image. Using a vector image usually means that you can process the image quicker than with raster.

Common types of wood used

Although we could spend a lot of time talking about different woods some of the more common woods that are available in today’s award market include walnut, maple, oak, ash and alder wood. Typically I like to stay away from oak as it tends to have much grain and does not look very good when it is laser engraved. Maple tends to be a good wood as it is light. The problem with maple is that sometimes it does not show up the engraving as well as the engraved area tends to stay light. One of the most popular woods is Walnut. It can be found in most component catalogues. It is a good wood to engrave with its only know being that the plaque is dark and so is the engraved area. One of the woods that I like is alder wood. This wood is nice as it light like maple. However unlike maple the engraved area tends to darken up and thus is more legible than maple.

A couple of nice woods for vector cutting include birch plywood and cherry. Cherry is nicest however you can get birch stained in a number of finishes. A lot of the nice cut samples done by the manufacturers are on cherry. Air assist can greatly enhance the edge quality of some thicker woods.

Manufactured Wood Products

Plywood standard building grade plywood is a material that usually does not produce an acceptable result when engraved. It is also a very difficult material to cut. Since the grain of the wood chips in the plywood when run in different directions, it is difficult to obtain a consistent depth when engraving. Air bubbles within the plywood cause problems because they severely disrupt the laser beam when cutting. Because of the air bubbles it is virtually impossible to cut cleanly through standard plywood. There are specialty plywood products (such birch) that can be found in hobby shops or specialty wood stores that will engrave and cut much nicer than the standard plywood products purchased through your local home renovation store.

Figure 14 Figure 14 – Photos look great on Alder wood where there is little grain and a nice brown is created. Sample from Epilog Laser Systems.

Figure 15 Figure 15 This picture frame is a combination of raster engraving (text and picture) while the vector portion of the file has taken care of the gold text and the frame cutout. Sample from Epilog Laser Systems.

Figure 16 shows some birch plywood vector cut out.