Introduction to CNC Routing using 2D .DXF Drawings

As all of you have been inducted know, our CNC can process .DXF files and .STL files. .DXF files are for 2D profiling and .STL files are for 3D reliefs.

This 3rd year group wanted to make a simple site base where the roads are removed to a depth of 2mm and the road names are engraved within that. The first job was to source the material they wanted to cut, they chose 18mm MDF 12200 x 900mm brought from Taskers in Wavertree.

When processing a .DXF file for the CNC we advise that you use AutoCAD and follow the procedure from the ‘Introduction to the CNC Router’ hand-out given to you when you were inducted into the Creative Workshop.

Applying that procedure to this job;

  • Open the site map in AutoCAD (in this case from a Digimap download)
  • Check the units are in millimetres, type UNITS > Enter and select ‘Millimetres’, (often Digimap files are ‘Unit-less’)
  • Check what scale the drawing is to, measure a distance you know in the real world, if you know a road is 6500mm check that distance on the drawing is also 6500mm, and therefore the drawing is at 1:1. (confusingly Digimap figures are in Meters, so when you select UNITS > Millimetres you are now working at 1:1000, but by testing a real distance against a distance on the drawing you can work out the scale)
  • Scale the drawing for your model, this model is at 1:100. (so the road that was 6500mm at 1:1 is now 65mm and 1:100)
  • Start breaking the drawing down into layers, the CNC uses layers so each different cut type needs to be on a layer that is named and coloured properly. (There are a few quick ways to do this from Digimap, its worth coming to find me for some tips and tricks)
    • Outside cuts are on a layer named ‘OUTSIDE CUT’ and are coloured RED
    • Inside cuts are on a layer named ‘INSIDE CUT’ and are coloured GREEN
    • Area Clearances are on a layer that includes the depth in its title so for example are named ‘2MM AREA CLEARANCE’ and are coloured YELLOW
    • Etch lines are on a layer named ‘ETCH’ and are coloured BLUE
  • So this job has 4 layers illustrated on the print screen, they are;
    • OUTSIDE CUT – to cut the final shape out
    • 2MM AREA CLEARANCE – to remove the roads to leave a 2mm curb for the building plots
    • ETCH – to etch on the top surface
    • ETCH WITHIN CLEARANCE – to etch the road names on the roads which have been removed 2mm deep.
  • It’s vital that AREA CLEARANCES are perfectly closed loops that do not have any double or open lines anywhere on the layer
  • To Clean up the file;
    • first make sure that only layers you wish to cut are in the drawing, all layers you don’t need are turned off, to delete these type PURGE > Enter and press ‘Purge all’
    • then select all and type EXPLODE > Enter
    • then type OVERKILL > Enter to delete double lines (make sure all the boxes in the top half of this dialogue box are DESELECTED)
  • Then save the file as a 2004 .DXF and bring it to the photography studio for it to be checked, just as you would for a laser cutter file. If they approve it you will then be able to book a session on the CNC.
  • On the print screens you can see why Layers are important when setting up tool paths as they are used to speed up the inputting time, files that don’t use layers will not be cut.
  • This job used an 8mm slot drill and a 2mm slot drill for the area clearance (the roads) and an engraver bit for the etching.

 

This file is fairly simple and took 1 hour to machine.

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