CNC mill conversion update

So the mill has been working nicely since last week, until the ‘temporary’ bodged z-axis coupler gave in. I ordered proper Oldham couplings for all axis last week, but forgot to take them to the lab this evening (doh). However, I took the free time to take apart the machine and gave it a clean and calibration.

The machine was suffering from 0.5mm slop in the table that was very dissatisfying. Gandolf and I had tried to remove this slop the first time around, but found there was no way of getting rid of the slop and keeping the full travel of the table, particularly on the Y axis. This time, I came to the same conclusion.

When the Y axis travels forward, the center of gravity moves from being supported between the base footprint of the machine, to being over unsupported air. This means the table would fall off if it were not for the rails holding it down. So the linear rails change from applying a force upwards (to counter downward gravity/weight), to downwards, as the Y axis travels. This shift in polarity of force totally changes the edges the table is sliding upon, hence requiring different calibration parameters on the machine screws that are there for fiddling.

On Stephen Giles’ sage advice, I did the best job of calibrating one portion of the rail movement. So we have lost 5cm of Y travel, in exchange for near 0 slop. Which is a good deal in my opinion.
I have not reassembled the machine fully yet, as I still have the couplings to attach. So its out of order but when its reassembled it will be even better!

Tom Larkworthy

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