DIY mill...

[irving2008]

Been doing some structural analysis of my proposed gantry frame, planned to be constructed from 50 x 25 x 3mm aluminium rectangular tube.

I found this structural analysis program called 'Framework' downloadable for free from: http://home.wanadoo.nl/wolsink/

It produces load, stress and importantly, displacement analysis for any arbitrary 2D and 3D frameworks.

Here is a screenshot of the calculated displacement for a gantry frame as described with a 10mm thick aluminium spindle support on 16mm round rails - the max displacement under 100N cutting load at the tip of the cutter is 1.01mm in this example (which is clearly too much - and they are exaggerated in the diagram) and most of the displacement is due to bending of the spindle support. I have yet to experiment with making it a U channel instead.

I suspect in reality 100N is far too big a load for a mill doing light cuts on PCBs and Aluminium. Calculations using the torque/HP of the spindle motor and a 4mm 2 flute cutter at 300mm/min feed suggest 20N is more likely giving a 0.2mm displacement which should be easily resolved with a thinner U channel for the spindle support. More work to come tho...