Making your own laser cut models

Arthur Moore

The almost finished building from the parcel office end. Given the sunny weather all the doors and many of the windows are open, but station staff and passengers have still to make their appearance.

I wanted to create a model based on Lyme Regis station building in the LSWR period, but there was one big problem. The awning valence is rather ornate and nothing with this design exists commercially. I had a drawing of the station through the SW Circle and I also had Vic Mitchell and Keith Smith’s excellent book, Branch Line to Lyme Regis.

The photographs in this book were able to confirm and, in a couple of minor details, amend the source drawings before I started to create my own detailed CAD drawings. I decided it would be totally impossible to cut the valance out by hand, so laser cutting was the only option. I then decided I might as well try to create the whole station using laser cut parts.

Fortunately I still have Autocad software from before I retired, so I was able to create the drawings in that. Mnay engineering and archictural practices still use Autocad so, assuming that most people do not own this very expensive software, they may be able to access it through a friend, or through someone in their club.

Some of the laser cutting agencies will work from a paper drawing but with the added cost of them converting this to a CAD file. Free software such as DoubleCAD is also available and this has built in file conversion facilities and will output in .dxf format, which most agencies can use. Check which version of the file the agency wants, as the format varies from year to year and many agencies will not want the latest version.

The laser cutter uses software such as CorelDraw and this also has the ability to convert from a wide range of other file types. However, you always want to check with your chosen agency before you start work, so as not to waste a lot of your time creating a drawing in an unusable format.

What are the advantages of using a software package and a laser to cut the parts?
On the design side, the big plus is that you draw something once and then use a ‘Copy’ or ‘Array’ command to make multiple copies of your first drawing. The valence pattern repeats around 200 times on my model, but I only had to draw it once. Similarly with any repeated element, such as doors and windows. Draw them once and then copy to as many positions as you need. The laser accurately follows your drawing, so you know that you will get what you have drawn, accurate to a few thousandths.

You also have a wide choice of material which can be cut with a laser. Typically this might include 1mm, 2mm or 3mm MDF or ply, 0.8mm engraving plastic or Rowmark, clear plastic for glazing, card and paper. Typically a laser will cut a line 0.2mm to 0.3mm wide, depending on the thickness of the material, so if dimensions are critical you may want to offset the cut line by half that amount.

In addition to cut lines, the laser can do engraving, for planking or brick effect, but usually only to one depth. This might be around 20% of the depth of the material, but the exact depth will not be guaranteed. Typically the company will do a short test run to make sure it looks right and then go ahead with the depth set by eye. Too deep a cut tends to make the material warp. Lines which are to be cut, and those which are to be engraved, need to be drawn in different colours on the drawing and you need to agree the colours beforehand with the laser company. Some companies can also do cut very light scratchmarks, which may be useful if you want a line against which to align another piece of the model. The awning as it is today at Alresford

Scared to get started? If you have never done any CAD drawing you may be frightened, but I am entirely self taught and I think that a typical 2D drawing package is easier to learn than some of the track planning software. You need to learn quite a limited number of commands. Line, circle, cut, trim, extend, offset, delete, undo, copy, move, array, fillet, layer (or colour command), so that cut and engraving lines can be drawn in different colours. With these you will be able to get started on a drawing. Commands are logically grouped together, if you need arc instead of circle you will quickly find out how to add this to the commands you have already learnt. All the drawing packages have extensive built in help and you can find free tutorials on-line.

You see on screen what you are drawing, so it is easy to see if you are creating what you want. The only thing which is not obvious is if you have the same line drawn twice in the same place. If you do, the laser will go over that line twice and, if it is an engraving line, this will be cut to twice the depth of the others. This is especially an issue when you create an array such as my valance. You need to think carefully to make sure that a line from one edge of the pattern you are copying, will not be overlaid on one from the other end of the pattern. Part of the drawing for the valance. Green is for the cut lines and red lines are engraved to show the planking. I only had to draw the detail on two of the planks and I then used the ‘Array’ command to repeat the drawing hundreds of times.
Design tips Engraved lines are made before the piece is cut out, and need to be differentiated from cut lines. So in my case these are drawn in red. Cut lines may also be in two different colours. For example, if you want a window frame, you should draw the inside of the frame in one colour (in my case magenta), then draw the outer frame in a different colour (green). That way the laser cuts out the waste material, before cutting the frame away from the main sheet of material.

Part of the drawing for door and window overlays. Note how the parts are butted up, to reduce the number of cut lines and therefore the time and cost of doing the job. These are typical of the lines where you need to make sure that you do not draw over the same line twice

It is not essential, but you can if you wish leave a small gap (3mm) in the cutting line for the outer edge of the window frame and insert a short line in the engraving colour (red) to fill the gap. If you do that, these pieces will be held to the main sheet by a tab and I think this is worth doing where you have lots of small pieces.

It pays to pack the pieces together. If you wanted to cut four 50mm squares, you might draw them as four separate items, but if you draw one 100mm square in green (which the laser cuts second) and then divide into four with magenta lines (which are cut first), then the laser has less work to do and so will be quicker and, therefore cheaper.

The laser is a focussed beam and I think there is a slight taper in 2mm or thicker material. However this is certainly not noticeable in the finished model. On thinner material any taper is imperceptible.

On my design, the interior and end walls fixed into slots in the side walls and similarly slots in the roof dropped onto pegs in the end walls for accurate location. This worked well and I would use this construction method again. The inner wall is 1mm shorter than the outer wall to allow for the floor thickness. The two walls accurately align on their top edge. Interior view of the side wall (upper picture) with its slots and below shows the tabs on the interior dividing walls. The outer lamination of the side wall hides the slots from view as they are only on the inner wall.

Choosing an agency to do the cutting I approached several companies that I found on the web and through the Guild. As it was quite a large building, several individuals said they did not want to undertake the job, or were too busy. One well known company quoted, but was very expensive for a one-off, so I went to Rob Burge at Lasercraft Devon. His price was reasonable, around the same cost as purchasing a laser cut kit of a similar sized building and his quality and delivery were both excellent. I had also forgotten to duplicate one part on my drawing and Bob kindly cut the extra parts free of charge. The package arrives from LaserCraft Devon. Now assembly can begin.
On the sides and ends, interior and exterior walls have been laminated together. I painted all the parts before assembly and also put non-opening windows into the sides. The opening windows (bottom left) will be fitted later. On the interior wall (second from right at the bottom) you can see the lugs that locate this wall into slots in the sides. On the end wall (bottom right) you can see the lugs at the top of the wall, which locate the roof..
Trial assembly held together with rubber bands for the moment. Again you can see the roof locating lugs on each end wall. The lower level wall at the left hand end is the gents’ toilet.
Now it is time to glue the walls together ensuring that everything is square.

Would I do it again? Too put it simply, this building would not have been done without laser cutting. There is no way that I could have accurately made the 2000 cuts in the valance perfectly equal and even. I could have used laser cutting only to make the valances and cut the rest of the model by hand, but I am very happy with the completed building and I am sure that it is more accurate than if I had attempted to cut the rest with knife and fretsaw.

Next time, I would not use card for the thinnest parts, such as window frames. The laser cutting was entirely accurate, but I think these parts would have been better with thin plastic, to give more rigidity to the overlays. I certainly made some mistakes on my drawings. Unless you are creating drawings commercially and can do a prototype and then a production version of your drawings there is almost certainly going to be something you get wrong.

In the main these were minor tolerance errors and I just needed to ease parts together with a file, but I had made a couple of mistakes which fortunately were correctable and are not visible in the finished model. If you really mess up a part, you can just correct that part of your drawing and have that piece re-made.

Limitations of laser cutting The laser cutter can only engrave on one side of the plastic or wood so, if you need both sides engraved, you have to laminate two pieces together, remembering to mirror the drawing for the second side, so that the laser engraves on the correct face of both pieces.

Finishing the model Apart from the laser cut parts, I need Plastruct for the roll bars on the roof and for the drainpipes, Scalelink drainpipe parts, wire for door handles and paint. There were two parts I could not buy - the stovepipe chimneys with conical caps and 90° drainpipe bends. Both of these I drew and had made using a 3D printer and this will be the subject of a separate article in another Gazette. The partly built roof assembly, which includes the ceiling to the rooms below and the underside of the awnings. Pictures of the original building are unclear, but I have assumed that the building had a lead roof and I used half round Plastruct for the roll bars.
Again just scraps of card and a plastic knitting needle, but it works fine as one of the four stoves.

Painting If you look at the photo of the building circa 1907, there is peeling paint in what appears to be dark brown and the building is in clear need of re-decoration, but I have not come across any pictures between 1907 and 1914 showing the building after painting. I therefore decided to follow the HMRS livery register No. 3 which says ‘A wooden building might be painted overall in pinkish buff. The local paint foreman mixed the colours himself and there were no centrally imposed colour standards, provided the finish looked earthy.’ I hope that my model reflects that sentiment. Here is a close up of the valance on the model, which started this whole process.The building from the gents toilet end. There are skylights over the ladies and toilets. I have still not decided whether to also fit the glazing over the exterior part of the gents’ toilet, but I think it will probably look more complete with it. The model also needs poster boards and posters with which the original was liberally covered. Finally the roof needs some weathering.

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