Newbie- So Many Possibilities???

[Plecc]

Hi all,
I have been thinking about building my own cnc mill for a few years now, but kept being put off by the cost of some of the components.
Recently i found a local ebay supplier of linear bearings and precision rails that appear more than adequate for a small A3 size mill.
But in the spec for the bearings it mentions that they use a plastic cage.

http://cgi.ebay.co.uk/x2pcs-SC20VUU-...item335c276b72

Has anyone ever tried similar bearings? if so are they a waste of time?

For my lead screws i have found some 16mm acme twin thread which looks the part, but I'm struggling to find any anti-backlash nuts that are any good.
Does anyone know of a supplier or a way i could make some?

For the frame i would like to use steel or ali both have pros and cons, if i use steel box the frame could warp slightly while welding. Unfortunately I'm no tig pro so if i use ali i will probably go for the extruded profile stuff that bolts together, my main concern with this stuff is that it could flex at the joints when being moved around, and the fixings coming loose over time, are these common problems?

Finally i cant decide what axis layout to go for, i would love to be able to work ali, perspex and nylon on an A3-A2 sized table.
do i go for:-
Moving gantry (probably with twin lead's on the gantry axis)
Fixed gantry (Probably a single lead under the table)
X-Y table with a fixed mount for the z axis/

Sry so much at once!

Plecc.

[ahren]

For the extrusion approach, most extrusion (at least 8020's) comes with a built in 2 degree "spring" in the extrusion that fllattens out and serves as a locking feature when you bolt to it. I've had tons of customers build machines from extrusion, and it can make for very nice machines that are adjustable and square-able with a minimum of fuss.

You can also bolt steel to the extrusion in critical sections to stiffen things. If you use cold rolled steel, you can use this as a rail for a linear bearing system in addition to being a stiffener. Check out some of the build log links from my site if you'd like to see some examples.

Best regards,

Ahren
www.cncrouterparts.com