Making the CNC machine has been an ongoing side project for a long time. It’s a machine that is able to flatten slabs too wide for the thicknesser, cut out intricate shapes in sheet materials, like plywood, engrave letters and pictures, shape 3D objects, mill flat accurate surfaces into aluminum and steel, use a drag-knife to cut out materials like card, cotton, leather, vinyl, etc.) and even draw big line art pictures with a pen. You can see the CNC beast being made (and tested!) in this video.

The machine’s frame is made from old I-beams, that we got from e-bay, partially filled with glass & steel-reinforced concrete. This both adds vibration damping and some rigidity to the I-beam – which is otherwise not very good at resisting twisting forces (although the endplates and midsection bracing also help with this).

One couldn’t just use regular garden-variety concrete for a precision machine tool like this because it would shrink and move way too much. We spent a l o n g time researching concrete mix design to get suitably stable and strong ‘machine tool grade’ concrete. It also added about three months onto the build while we waited for the mix to cure enough, and then dry enough to be sealed with paint.

Of course, it’s not like we were really ‘waiting’ as we had loads of other projects on the go, including making the rather unusual gantry! Because the gantry is whizzing back and forth along the length of the frame, it has very different properties from the frame. Instead of being very stiff and vibration damped at all costs, something the frame achieves with steel and concrete (lots of mass!), the gantry is all about stiffness to weight ratio. Therefore we use aluminum extrusion (from a retired old stair-lift), which has good strength to weight, and strategic epoxy granite (unparalleled vibration damping), as well as our own DIY aluminum castings, to form the gantry.

For more, here’s a video all about how the gantry goes together.

The gantry is driven by a twin servo, ‘rotating ballnut’ design. This took some tweaking (see these videos), but has the big advantage of helping to prevent whip (a problem where the ballscrews violently wiggle about, causing excessive wear to the bearings) at higher speeds, and much reducing the rotating mass, and therefore the inertia of the system. All ultimately lead to faster and more efficient movement.

The z axis (the one that moves the spindle up and down) is made from old alloy wheel we melted in the furnace and cast to shape. We refined our casting process a lot by doing these relatively large castings. Indeed if you are interested in home shop casting there are a lot of tips in this video – which also shows the z axis spindle plate being cast:

There is a great deal more to say about the CNC machine, in fact, we are in the process of writing a book/guide to help would-be DIY CNC builders… In the meantime, we’d love to hear your thoughts or questions, either here or in the comments on youtube. If you would like to play with the 3D CAD model of the CNC we build you can find that here: https://ko-fi.com/floweringelbow/shop

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Posted: 05|10|22 at 3:09 pm. Categorically squeezed into: Invent.

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