Drawing Brickwork in CAD For Laser Cutting

[John_B]

I'm drawing my first building for laser cutting in FreeCAD, although I'm led to believe that most CAD software works in similar ways, and am trying to work out how to draw brickwork. If I was 3D printing I could draw rectangles, either the shape of the bricks to extrude, or the shape of the mortar to pocket, that would appear on the CAD model and export in an STL. But for laser cutting I think I just need a single line for the mortar courses, that I could sketch but won't affect the CAD model so I can see what it looks like, although I think I could export it as an SVG. If that makes any sense! I've skimmed through the Design For Laser Cutting topic, that's got loads of pictures of laser cut brickwork, but doesn't provide a clue to how to draw it! I could draw the walls in Inkscape, but I'm trying to use FreeCAD as much as possible because I need the practice.

How do other people draw brickwork? If I at least knew how it was done in other CAD software, I might be able to work out how to do it in FreeCAD.

And No, the answer isn't to use Fusion 360 like everyone else, because there's not a Linux version!

 

[simond]

John,

used TurboCAD for all my laser designs, including my loco shed.

I draw horizontal lines at the appropriate spacing on one layer, and then lock it. On a different layer, I then draw a vertical line one half brick in from the end of the panel, and on the row above, one whole brick from the end. Highlight these two lines, and then “pattern” them along the courses. This should give you two courses of bricks. Then highlight the verticals and pattern them up the wall for as many courses as you need. You can, of course, draw other brickwork, as required, but try to make something that your computer can copy by pattern.

then save this as a plain brick wall. And back it up.

then take your saved file, save it under a new name, and on another layer, draw the outline of your brickwork, and any window, vent, or door apertures. This will obviously be a “cut” line in due course.

the other lines will be ”etch” lines when you program the laser.

you might be able to cut several pieces from one plain brick wall drawing. In any case, you will save time by erasing any etch lines on the scrap that you don’t need.

ensure that your etches and cuts are the right way round (I use blue for etch and red for cut) and see what the laser makes of it.

good luck and post pictures!

Simon

 

[adrian]

If I at least knew how it was done in other CAD software, I might be able to work out how to do it in FreeCAD.

To be honest I prefer sticking with 2D CAD (QCAD) for drawing out stuff for the laser cutter. My FreeCAD ( stable version 1.0.0 just been released) efforts are solely for 3D printing.

 

[SARSn3.5]

G’day John,

I’m in South Australia, modelling the local narrow gauge prototype (3’ 6” gauge) in S scale. Colonial buildings here were built typically with brick quoins infilled with local stone set in lime mortar.

I use AutoCAD LT for all my 2D drawings. My workflow uses “part drawings” of corner quoins, and quoined window and door surrounds. Each brick face is drawn to include the bedding mortar course and the perp end: so, the lines on my cut file drawing represent the centre-line of the mortar courses and define the centre-line of the laser’s path either as a vector etch (a partial thickness cut) or as a full thickness vector cut.

The line, as drawn, has no thickness. Not so the laser cut path – on the laser that I have access to, the kerf is more or less 0.20mm wide. So, mortar courses and perp-ends scale as follows: 1:43 – 3/8”; 1:64 – 1/2”; 1:76 – 5/8” and 1/152 – 1¼”!! In the larger scales this all looks OK – mortar courses here are 3/8” to 1/2" wide, and I’ll assume British bricklayers use about the same thickness. Allowing for kerf width in the drafting allows a gain when the file is run – brick faces look well-proportioned against the mortar lines.

If the corners of the model building are to be joined with finger joints more considerations arise. If the projection representing the interlocking bricks are drafted to the same width as the gaps, that is, are drawn as extensions of the lines representing the middle of the mortar lines described above, when the cut file is run, the kerf will “disappear” – the fingers will lose half the kerf width each side, and the spaces will gain half the kerf width each side. The interlocking that looks so elegant in the drawing will, in reality, be very sloppy. The solution is to offset each of the mortar line projections involved in the finger joint into the gaps by half the kerf allowance. The drawing shows the fingers fattened by the kerf allowance and the gaps shrunk by the kerf allowance. When the file is run, the allowance is again “disappeared”, and the fingers interlock with a sliding fit.

The other requirement with finger joints is that the material thickness needs to match the scale width the model bricks. I’m using up 1.8mm scrap card put away for a rainy day many years ago. I haven’t seen anything similar in any of the local stationary or art shops. 1.8mm equals 4½” in S scale, a good match for the width of standard bricks here. Its OK for the moment, but future problems await.

In summary, I’ve found I needed to work backwards from understanding what the laser I have access to is actually doing with the files I am using on it and with the materials I expect it to handle. Sorting out speeds and power on an unfamiliar machine for every new material is obviously important for satisfactory results, but to achieve the detail and fit of parts expected in model making I needed to understand kerf allowance, and how and when to apply it.

Gavin

 

[Oz7mm]

For some time now I have used the engrave rather than the cut function of my laser cutter (an HPC 6840). This gives a preferred look to my eye at least.

For the engrave function to work with the software (Lasercut 5.3) you need to draw enclosed areas so this requires a series of rectangles to represent the horizontal and mortar lines. Arches present another challenge and I wouldn't pretend that either the drawing or engraving times are short but I do prefer the result.

This picture has been on WT before. It's the old country end bridge from the first iteration of Love Lane before painting. The lighting suggests the appearance of the bricks is convex, rather like embossed plastic, but it is solely a trick of the light.

John