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I was reflecting on what is it that I like about CNC assisted maching. I have been able to machine many different kinds of material using a number of processes that need a lot of thought and care, especially when one is a relative newbie to CNC machining. I spent a fair bit of my time learning how to machine slate, glass and ceramics. These materials all need different things from the machining standpoint but there are a few similarities that can assist a person to build up a library of different skills and techniques. The materials mentioned in this post are ceramic tiles and 4mm thick float glass and the techniques used are laser engraving and drag engraving.
Picture one shows a 6 x 6" ceramic tile from B&Q. I bought a box of 44 of these tiles for £5.98 so each tile cost 13.59p, which makes them more than cheap enough to experiment with. I used a technique to engrave the tile known as the Norton method. It is a process where the tile is coated with white paint and then the design is engraved. The white paint contains a titanium dioxide whitening agent and this is what gets burnt to the ceramic tile and makes a permanent non removable finish.
The technique is to clean the tile to remove grease marks and other dirt that may create unwanted voids in the engraving. I use acetone which is easy to come by and relatively cheap to buy, as well as being low in toxicity. I would recommend wearing nitrile gloves if you cannot stand the cold feel of the acetone on your skin. Any P3 rated respiratory mask will keep you from smelling the chemical and you will be safe from any untoward effects from inhaling the vapours.
After the tile is clean and dry, I spray the tile with a matt white paint (Rustoleum) and it is dry enough to work with in 30 minutes. I have created an MDF jig which just accepts the 6 x 6" tile and holds it at the depth of the tile. This becomes important because I always focus my laser beam at 3mm (1/8") so that I can ensure that the sharpness of the detail is visible. I then burn the image using LightBurn software and then wash off the remaining paint from the tile using acetone. That's it!
My laser is a rated at 4.2 watts of output power. It is a class 4, blue diode laser and it operates at a frequency of 445 nanometres. I purchased some safety goggles and ensured that the lenses were of sufficient optical density (OD) to protect my eyes fully. It is possible to determine the correct OD from one of the many sites on the internet. I cheated and contacted a company which provides laser safety goggles to UK industry.
After answering a few technical questions about beam strength, beam size, exposure time and materials, I was provided with a suitable pair of safety goggles and the lenses were marked thus: "190 ~ 470 & 800 ~ 1700nm OD5+ CE" It is worth noting that some lasers supplied by companies in Shenzen may not be supplied with adequate safety goggles. I know of two cases where the supplied googles were supposedly produced with an optical density of 2. The picture of the safety goggles is for completeness but it is difficult to make the text very easily visible.
The image on the tile is named 'vanishing point' and it is typical of the view along a deserted railroad in an empty landscape. The clouds were accentuated by use of a red filter for this monochrome image. The detail of the cinders and the wire suspended by a pole on the left of the foreground are a fair representation of the detail one canachieve and expect from a modestly powered blue diode laser.
The dark green 'specs' image shows the safety goggles and the next two images show the detail that must be engraved on every lens pair when the goggles are for laser safety puproses.
The next image to discuss is the laser engraving of a piece of very hard 4mm thick glass. While the white paint method can be used and does sometimes work to some extent, it often leaves thick glass untouched, especially with a low powered laser like mine. Some of the newer stacked diode lasers will have an output power of 30 or 40 watts and that will be sufficient to mark glass. What stops glass from taking a good clear laser engraving is the reflection of the laser beam, which will prevent it from creating the microfractured structure that leaves an image engraved into the glass.
I had heard of a technique using just black paper behind the glass. I decided to use the technique and setting my laser head at 3mm above the glass, I lowered it by 2mm so that the burn would appear within the glass. I used black card behind the glass and a full power burn gave me an image. The image is the one below named 'coffee cup' and you can see how the black paper which was burnt has somehow transferred the image between the layers of glass. Before leaving laser and glass, the final images are of an eagle engraved directly onto the glass over about 14 hours at maximum power very slowly, and using the white paint method in about 45 minutes. In this case the white paint method produced a much better result.
The last technique to talk about is drag engraving. This is carried out by means of a 90 degree diamond bit which isd placed in the spindle and brought to the workpiece. The spindle is not switched on and the diamond is dragged along the workpiece. I have used this method to engrave slate and glass. I use a little cutting oil (CT90 or similar) to keep the diamond moving with as little friction as possible. The tool is sping loaded and the diamond is kept compressed into the tool barrel by a couple of millimetres. In this way, it is always in contact with the workpiece. The last image shown is a cat engraved onto 4mm thick hard glass. It required about 4 minutes to complete the work because it only has to have the tool follow the pattern. The technique works well with simple outlines. These are some of the reasons I find the CNC machine to be a source of great amusement.
any and all comments most welcome.
EDIT: countless spelling errors
Picture one shows a 6 x 6" ceramic tile from B&Q. I bought a box of 44 of these tiles for £5.98 so each tile cost 13.59p, which makes them more than cheap enough to experiment with. I used a technique to engrave the tile known as the Norton method. It is a process where the tile is coated with white paint and then the design is engraved. The white paint contains a titanium dioxide whitening agent and this is what gets burnt to the ceramic tile and makes a permanent non removable finish.
The technique is to clean the tile to remove grease marks and other dirt that may create unwanted voids in the engraving. I use acetone which is easy to come by and relatively cheap to buy, as well as being low in toxicity. I would recommend wearing nitrile gloves if you cannot stand the cold feel of the acetone on your skin. Any P3 rated respiratory mask will keep you from smelling the chemical and you will be safe from any untoward effects from inhaling the vapours.
After the tile is clean and dry, I spray the tile with a matt white paint (Rustoleum) and it is dry enough to work with in 30 minutes. I have created an MDF jig which just accepts the 6 x 6" tile and holds it at the depth of the tile. This becomes important because I always focus my laser beam at 3mm (1/8") so that I can ensure that the sharpness of the detail is visible. I then burn the image using LightBurn software and then wash off the remaining paint from the tile using acetone. That's it!
My laser is a rated at 4.2 watts of output power. It is a class 4, blue diode laser and it operates at a frequency of 445 nanometres. I purchased some safety goggles and ensured that the lenses were of sufficient optical density (OD) to protect my eyes fully. It is possible to determine the correct OD from one of the many sites on the internet. I cheated and contacted a company which provides laser safety goggles to UK industry.
After answering a few technical questions about beam strength, beam size, exposure time and materials, I was provided with a suitable pair of safety goggles and the lenses were marked thus: "190 ~ 470 & 800 ~ 1700nm OD5+ CE" It is worth noting that some lasers supplied by companies in Shenzen may not be supplied with adequate safety goggles. I know of two cases where the supplied googles were supposedly produced with an optical density of 2. The picture of the safety goggles is for completeness but it is difficult to make the text very easily visible.
The image on the tile is named 'vanishing point' and it is typical of the view along a deserted railroad in an empty landscape. The clouds were accentuated by use of a red filter for this monochrome image. The detail of the cinders and the wire suspended by a pole on the left of the foreground are a fair representation of the detail one canachieve and expect from a modestly powered blue diode laser.
The dark green 'specs' image shows the safety goggles and the next two images show the detail that must be engraved on every lens pair when the goggles are for laser safety puproses.
The next image to discuss is the laser engraving of a piece of very hard 4mm thick glass. While the white paint method can be used and does sometimes work to some extent, it often leaves thick glass untouched, especially with a low powered laser like mine. Some of the newer stacked diode lasers will have an output power of 30 or 40 watts and that will be sufficient to mark glass. What stops glass from taking a good clear laser engraving is the reflection of the laser beam, which will prevent it from creating the microfractured structure that leaves an image engraved into the glass.
I had heard of a technique using just black paper behind the glass. I decided to use the technique and setting my laser head at 3mm above the glass, I lowered it by 2mm so that the burn would appear within the glass. I used black card behind the glass and a full power burn gave me an image. The image is the one below named 'coffee cup' and you can see how the black paper which was burnt has somehow transferred the image between the layers of glass. Before leaving laser and glass, the final images are of an eagle engraved directly onto the glass over about 14 hours at maximum power very slowly, and using the white paint method in about 45 minutes. In this case the white paint method produced a much better result.
The last technique to talk about is drag engraving. This is carried out by means of a 90 degree diamond bit which isd placed in the spindle and brought to the workpiece. The spindle is not switched on and the diamond is dragged along the workpiece. I have used this method to engrave slate and glass. I use a little cutting oil (CT90 or similar) to keep the diamond moving with as little friction as possible. The tool is sping loaded and the diamond is kept compressed into the tool barrel by a couple of millimetres. In this way, it is always in contact with the workpiece. The last image shown is a cat engraved onto 4mm thick hard glass. It required about 4 minutes to complete the work because it only has to have the tool follow the pattern. The technique works well with simple outlines. These are some of the reasons I find the CNC machine to be a source of great amusement.
any and all comments most welcome.
EDIT: countless spelling errors
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