Kit's Machine

[Kitwn]

The original steel gantry was a bolted design and a complete disaster so something new was required. The quote for two lengths of aluminium profile, including delivery to the wilds of Western Australia had me reaching for the smelling salts, so it had to be steel again. I bought a cheap stick welder for about 1/3 the cost of the two pieces of profile and went for it. Fortunately I still had enough material left in stock.

This was my first attempt at welding and uses a technique I have described as ‘Bird Poo’. An angle grinder, plenty of car body filler, some sanding and a coat of paint hides a multitudinous multitude of sins.

To keep things simple I decided to put both rails on the front face and use epoxy to provide a guaranteed, perfect level surface… Ha, ha. Unfortunately this was before I’d heard of the recommended West Systems 105 resin/209 hardener combination so I bought some cheap stuff off eBay. The advert includes two options, Low Viscosity (LV) which they claim is self-levelling and High Viscosity (HV). All I can say is that if the LV is low viscosity, how are you supposed to get the HV stuff out of the tin?
To be fair this product is aimed at filling cracks in concrete so should not be criticised for its poor performance on a CNC machine.

I also chose to drill the holes for the rails before applying the epoxy (can’t remember why now) so there were greased screws in the way to prevent the gloop from flowing. The end result is probably less flat than the bare metal was but is glass-hard so I have shimmed the rails rather than chip off the epoxy.

By a stroke of luck, my choice of 16mm supported rails and a 1610 ballscrew with matching mounting blocks meant that with the ballcrew mounted directly on the same epoxy plane as the rails there's a sub-1mm gap between the ballnut and the Z axis backplate. A can of ice cold Guinness was consumed to provide a suitable shim.