I sketched a rough design using a conventional fixed table, bridge and z-axis on the bridge.
In my design I look at the machine from the front so that the table depth gives the y-axis and the bridge provides the x-axis.
Plan A: My idea for the y-axis was to use two diameters of aluminium tubing that fitted tightly but didn't bind. The narrower tube was approx 1m long and the outer tube approx. 15cm. BUT... The inner tube was too weak and flexed while the outer tube was too loose and wobbled while being very likely to fill up with dust and lock up.
Plan B: find some cheap v-bearings.
Unfortunately evenings searching the web found nothing :(
V-bearings seem difficult to find and those that do exist are expensive.
Plan C: Eureca!
I discovered that in-line skates have really nice bearings however they do have some lateral wobble. Skate designers have solved this for me by combining two bearings in a single wheel and this means that general wobble is reduced significantly.... so... can I use skate wheels as complete units?
The downside is that skate wheels are silly prices when you just try to buy the wheels on-line BUT.... if you look on the second hand market, you can pick up a pair of kids skates for as little as 6Euro with 8 really good wheels.
12 Euro later and I has 14 nice wheels.
I used the 8 best wheels to support the x bridge. 2 wheels each side bolt onto the vertical parts of the bridge and take the weight of the bridge. "C" shaped brackets then hold 4 more wheels rolling down the sides of the table. The horizontal wheels are spaced a few mm closer than the width of the table so that it clamps tightly and avoids wobble.
The wood is 18mm ply.
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