CNC Manufacturing Guide
Wikihouse parts are transformed into 2D profiles and nested onto 2440mm x 1220mm sheets in CAD. Cutting files are supplied in .DXF or .DWG format, which can be converted by most CAM (Computer Aided Manufacturing) software to g-code for CNC production by the manufacturer.
A local CNC workshop will be able to offer expertise and guidance, but to help here is a quick guide:
Currently Wren parts can be 'unpacked' and prepared using desktop CAD software. Parts can be laid out onto cutting files manually using a variety of either proprietary software such as Sketchup (you will need sketchup pro to export a dxf file) or Rhino 3D, or freeware like FreeCAD or OpenCAD. Specialist Wikihouse tools to make this process far easier and accessible are currently in development on the Buildx platform.
Check the guide cutting file (.dxf) in one of the project repositories (ie. Microhouse), to for an example of the typical layer names etc. In fact you might want to use it as a template. The usual CAD layer format is:
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DONOTCUT: Information for instruction purposes only
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0_SHEET_SPRUCEPLY_2440X1220X18: Plywood material boundary for reference
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1_ANYTOOL_1MMDEEP_LABELS: Text labels, convert to curves and engrave at 1mm depth
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2_ANYTOOL_2MMCUTTHROUGH_SCREWHOLES: Markers for screws during construction. Drill through.
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3_ANYTOOL_CUTTHROUGH_INSIDE: Internal slots, cut through inside line
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4_ANYTOOL_CUTTHROUGH_OUTSIDE: External profile of parts, cut through outside line
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5_ANYTOOL_9MMDEEP_INSIDE: To 'Half-rout' engrave out area within lines, to 9mm depth
Parts need to be ‘offset’, to give the structure some tolerance. Without these tolerances, the frame will be almost impossible to assemble. While Wren parts are produced for 18.0mm structural plywood, the actual thickness of this material can vary from batch to batch between 17.1mm and 18.1mm, or sometimes more. The best method is to measure your material accurately first with calipers to check the variation in thickness. It's most likely you'll need to apply tolerances (offsets) to the individual parts to ensure the slots and connections are only slightly larger (between 0.25 and 0.5mm) than the material thickness.
If you material measures at 18mm a general rule is that the outer profile edges of parts should be offset inwards by 0.25mm (to make the parts smaller). Slots in parts should be offset outwards by 0.5mm (to make the slots larger). However, this does not apply to the ‘crush’ holes for spacers, which need to be tight. Tolerances can sometimes be adjusted by the CNC manufacturer on their CAM software, or initially by a designer using CAD tools.
Always cut a test piece first with the material and the machine you are going to use, and adjust the tolerances accordingly. It should be reasonably easy to assemble, but tight when assembled. You can download a tolerance test sheet with all major Wren joints at incremental tolerances for you to find the best fit for your material.
Generally the manufacture of the Wikihouse chassis components follow common CNC procedures. Whilst we have been involved in the manufacture of a number of projects, there is still many strategies and approaches depending on the CNC machine, router cutting bit, and speed of passes. The key is finding the right balance between running the CNC too slow, which will burn out cutters, or too fast which may leave splintered edge and risk breaking router bits.
WikiHouse parts can be cut on any 3-axis (or more) 4x8’ (2440mm x 1220mm) CNC machine, which range in price and performance from a Blackfoot , a Marchant Dice , a ShopBot through to more expensive industrial-grade CNC machines which can even auto-feed material to increase production speed. We strongly recommend you use a CNC with a vacuum-bed and a highly effective dust extract to keep the pace up. Always wear ear protection, goggles and dust masks.
Past projects have specified between 6mm and 10mm spiral upcut or spiral compression design bits (combo of up-cut and down-cut). Straight cutter bits can also be used, but tend to be slightly slower than spiral bits. Use a test piece to find which cutting bit works for you.
Previous CNC machining of Wikihouse parts have required 2-3 passes. However different machines will do the job at different speeds, and this matters, because this is the potential bottleneck. Assume you’ll need 5-7 sheets per m2 of floor area and approx 30 mins per sheet).