Sunday 1 March 2020

Laser Cutting Learnings Part 1

  I have had the opportunity to have access to a laser cutter not far from home. Ray a friend of mine has been mentoring me. The cutter is an Epilog Zing 16 that has a 16"x12" work area so it is a high quality cutter. Epilog  The comments I make here are based on building HO Scale things. I will cover drawings, materials, scale limitations, operation and conclusion.

  I have been drawing in 2D Cad for years and use it to design and print my projects see How I Build my Scratch Projects. I currently draw with a program called LibreCad and the files are saved as .dxf  and this format is more compatible to programs than the .dwg format. Drawing for the laser is different in a few ways, when I drew in the past I could make changes to the drawings on the fly as construction moved along and now  I must  have the drawing complete before starting to cut. When making my E Class Station it was the first time I had drawn windows and doors as opposed to buying commercial parts. When drawing on paper if there happened to be two lines one on top of the other it didn't matter now  with the laser you do not want this because it will pass over the line a 2nd time but not really cut anything. Now if the laser was at my place I could fix things on the fly but not when I have to travel to Ray's.  If  I had a laser here it would read right from my drawing program and read the dxf file direct. The other thing you have to keep in mind is having tabs on small parts so they do not blow around once they are cut. You also have to consider the order you want things cut in and how it is laid out on the page so there is a minimal amount of waste.

 The laser has the capability to cut a lot of different materials. The only ones that are of interest to me at this time are styrene, card stock, laser board, paper and wood.

I normally build in styrene and would like to keep on doing that but it does have some limitations when cutting. I like styrene because I find it easy to glue and paint because it is stable and has different types of scribing available and is easier for me to buy. The problem with styrene is that if you have cuts that are close together (<.03") it will/may cause the styrene to warp due to the heat from the laser. If you are cutting .01" it is almost too thin and .06" is almost too thick and requires more heat to cut. So you really can't place lines closer than scale 3" even then you may run into trouble. However cuts like building walls are amazing and everything fits just like it would in the drawing. If I was going to add holes for grabs on a freight car they would all be perfectly sized and aligned.

Card stock cuts nice but is a little harder to glue and paint. It may have stability issues over time due to changes in temperature and humidity. I know lots of people still use it. When we cut the E Class Station we did it in card stock first because I can get it for almost nothing and I wanted to see what mistakes there might be that I had not anticipated. I also wanted to see how the roofs would fit. I glued it together surprisingly fast and did find a couple of things that needed to be changed.  I now cut all new projects in card stock first so I can test fit.

Laser board is like a thin laminate, almost like arborite or a thin veneer, I do not know how else to describe it. It is very stable and you can cut it as thin as .01" and it has good structural strength with small pieces like the diamond harrows below. It has to be ordered and has a cost to it.

Paper is easy enough to cut, so on the next 2 E Class Stations we will cut out the sandpaper that will be used for the stucco finish. It will be glued to the styrene walls. This requires drawing two sets of walls. One for the styrene and one for the sandpaper which is easy to do. You can also cut out stencils for signs with 60# paper and use an airbrush to paint it on. For this I use a program called Inkscape which is a free graphic illustration program.

Wood is something that can also be cut and you see lots of wooden laser cut kits. I just have not had a chance to play with it much yet.

Scale limitations are still something that you have to adjust to and this really applies to doing drawings for 3D printing. I can draw anything to the exact dimensions but they do become unusable in some cases because they don't have any stability left. You can only go so small and so thin. In the drawing below of the station  I had to make some adjustments. The window parts and the front dormer walls had to be cut to minimum of scale 3 " depending how close other cuts were done because of heat. That is getting really thin. If you have a scale 8' 1x4 it will bend in the middle if you hold it at the end, which does not happen with a real 1x4. I had to increase the size of  some of the parts so that the cut lines were not as close together for the reasons that I had mentioned above. We could use card stock or laser board but would have had to laminate pieces together to get the right thickness which I really do not want to do but it can be done because each part will be exactly the same. The window parts for the stations had to be adjusted slightly larger for the above reasons. The good thing is that most of the time no one will ever notice. To help you understand this, Ray would hold up his caliper set at .01" or .02" saying can you really see the difference. In fact you really need back light to see the space of .01".   This theory applies to things you may even be building by hand. I have had comments that a wall on a structure looks too thin in .04" styrene which scales out to ~3.5" where the real wall would be 4.5" with 1/2" sheeting on each side which comes out to ~.05". You see the point if you hold up the caliper set for .01".  No one can see .01" at any distance without using a caliper. Why do I use .04" -  because I can't buy .05" and .06" would be too thick and is harder to cut by hand and keep your accuracy and it requires more heat from the laser. So in some cases like with my 16" cultivator shovels it is just easier to cut by hand out of .005" styrene! Also while we are talking about scale we have been conditioned to see things that are out of scale but have become so accustomed to it that they look correct.

Operation of this laser is not difficult but we are using a top of the line machine. What it has taught me is that I doubt I would be happy with a $500 machine. You may need an air supply, possibly water depending on the machine and exhaust system to the outside. The laser setup is really like setting up a printer and some of the commands look the same, as if you were printing. There are 2 types of line types you use Raster and Vector. Vector are the lines that you are going to cut and Raster are the lines you are going to engrave in  the material. You have to keep these 2 types of lines on different layers in your drawing. So with Raster you can take a plain sheet of styrene and Raster lines for boards on each side making the floor of a flatcar much easier to build for only a fraction of the price. You can not buy  this type of product from Evergreen. Now Raster works best if the lines go horizontally across the drawing. If you draw something like this | | | | | | |  the laser will go from left to right and only does a dot at a time on each line, each pass. If you were paying for the cutting this would cost a lot. Your printer would print the lines in the same way and also take far longer then say printing one long line across the page. When it is cutting it cuts vertically and horizontally. This laser is interesting to watch as it cuts because it jumps all over the place and you think it has missed a bunch of lines but what it is really doing is reducing the amount of heat to any one area, very smart. There is a given amount of waste and can be limited by how you lay out the drawing for cutting. When I am  cutting by hand there is very little waste just something else to consider. Lots of things to learn and I have found it very interesting.

In conclusion I am just trying to point out some of the issues with using a laser and these issues really come to life if you are going to send out something across the country to get cut. Now having said that, its capabilities are amazing and it simply speeds up construction and accuracy.  I really appreciate the time that Ray has spent with me. Ray is an NMRA MMR and has done lots of fantastic models and has produced his own runs (250) of construction models in his own shop. Thanks Ray for all the help.
I will do a 2nd post with more examples in the future.
Here is a picture of a diamond harrow that we cut out. I have to add the teeth on the holes and add chains to hook it up to the drawbar. That is just a regular wood pencil beside it

This station is all cut on a laser

3 Wood grain bin parts floor, roof and walls
Here is a picture of car sides cut with the holes for grabs, widow and  door