Base advice

[Graham S]

Here is a SKETCH of my router to be. I have almost all the parts. The uprights on each side are some seriously chunky extruded t-slot ali section. The X rails are THK beauties, the Y axis is a Thomson superslide with ballscrew on it's back. The z- axis is a Aerotech ballscrew stage.

The length of the x and y axis is about 25", travel obviuosly less.

I intend to drive the x axis with two lead screws from one motor with belt connections.

Sounds OK so but I need to make the base.

The machine will only be weilding a 900W Kress router (to start with). Mostly routing of wood and ALI but also some small mould making stuff. I want the machine to be nice and stiff. A little over built perhaps.

Suggestions for the base please. I was thinking a structure from extruded ali with ali plates top and bottom torsion box style but what about this resin concrete I hear about? After all I don't have to move it around when cutting.

Also ideas for a t-slotted top? Mill your own, build it up, use extrusion?

Cheers,

Graham

[ynneb]

From my understanding. Steel has great tensile strenth than aliminium. If you are going to the effort of making a solid base then you might as well use steel all round.
Besides steel is far cheaper too. Consider that most professional machine are made of steel and not Ali. If you go for concrete fill, you can always add glass fibres to it to give it far greater strength and stability.

Personally, if you are just cutting timber, then all these measuers might be a bit of overkill.

[Graham S]

Most professional machines are not this size. I don't have a problem with the two ali uprights as they are the good stuff with plenty of webbing. What I want is a base that won't warp or flex and will keep the uprights in the same relation to each other.

I assumed that the concrete used for such things was not off the shelf concrete with glass added but rather a special concrete.

No not just timber, the moulds will be aluminium.

Graham

[High Seas]

Graham
You've seen Clyde's approach to a torsion box right?
http://cnczone.com/forums/showthread...ht=torsion+box

You could build it to support the HMS Ark Royal if needed! Or use it as a vacuum platform as well as a base for the machine. It could be Ali and rivetted or otherwise mechanically fastened - or built of composites and glued up. Another member used recycled tyres (well here thery were -ires) to add some dampening. I suppose that could add some dampening and still allow you to pull a vacuum thru the base and elminate the need for building a T-slot base at the same time.
Mass is always good - till ya gotta move it! Its worrying the mechanical stability, resonance, cost, availability, and fabrication that gets added to the seemingly simple choices -- eh?
Cheers - Jim

[Graham S]

I did indeed see it and very nice it is too. However, I don't want to make an MDF base. I could of course make the same sort of thing from ali in a number of ways.

I had been thinking a structural ali outer frame (4 pieces of say 40X80 section form a square) and then in the middle some stiffeners in one direction and so many in the other direction. All bolted where they meet. Not quite as nice as Cliff's interlocking but easy to do. Or I could do it like Cliff in thinnish Ali plate. Maybe get it welded up somewhere so I can have more webbing but keep it quite thin and hence lighter. Could even go for diagonal webbing.

Or I .....

I think I am looking for more accuracy than most. On my mill I have generally not been that bothered about a bit of backlash here and there but for this one I want it to be right, at least as good as I can get it.

Vacuum is also nice and cool you can build it in but for some stuff such as CNC milling operations and 4 axis stuff I want to be able to bolt things (vices and axes) down. Lots of threaded holes are an option.

Graham