Jill of all trades, but mistress of few !

[HiltonSteve]

1. I originally suggested wood / MDF construction, but having seen the construction methods others have used and investigated various suppliers of extruded aluminium profiles, that seems a much better way to go. I have so far come across a number of such suppliers, having downloaded the Valuframe catalogue and checked out the Rhonmac (same system as Valuframe?) and Marchant Dice websites. I've also seen references to Bosch. Is there anything significant to choose between these, or other, systems / suppliers?

I have not had any experience with many aluminium extrusion suppliers, I used Hepco for my 80x40 and when I ordered it I told them that the 3 lengths needed to be within 0.5mm and cut 90 degrees, when they arrived they were spot on, just tapped the holes and bolted them in.

2. I've read through all the posts concerning HiltonSteve's very impressive build. If I've understood it correctly, Steve, you've used just one guide rail each side on the x-axis (but 2 for y- and z-axes). Your gantry appears to have additional rigidity through the Al plate that connects each side beneath the bed. At the sort of size table I'm considering (around 8' x 4') I'm expecting to need to use at least 3 legs per side (I envisage it being free-standing, not bench mounted) and, very possibly, at least one under the centre. These additional (non-corner) legs would preclude an under-bed connection between the gantry sides. I'm presuming I would need 2 guide rails per side for the x-axis and 2 for each of y- and z-.

You are correct, I used 1 20mm rail each side for the X axis. For the Y axis I used a rail top and bottom of the gantry crossmember which is why I made the crossmember out of 20mm (same size as the rail), made it easier to mount and align. The Z axis has 2 rails running down the front face. So each axis has 2 rails and 4 bearings which make it very solid, no play anywhere at all.

3. Again with reference to Steve's build, the entire gantry / y-axis structure seems very solid with 15 / 20 mm Al plate throughout. Does it really need this for sufficient rigidity? I imagine I will have a greater need for care here with a 4ft + y-axis, but was hoping that the use of extruded profile with, perhaps, rather thinner Al sheet skinning would suffice. Am I kidding myself?

I used 20mm plate for the gantry sides and the crossmember, the rest is 15mm. I went for these sizes as that is what suited it best when doing the design, bolting 20mm rail to the edge of 20mm thick plate is quite easy! Then thought if the crossmember is 20mm then the side plates need to be so it looks right, then used 15mm for the rest because....well, I did!

Yes it may be over the top and I may have got away with 10 and 15mm plate but it would have made my design more difficult to put together. The cost difference of using thicker material outweighed any potential build problems I may have encountered and also guaranteed a good solid machine. Also I thought about how I could manufacture the parts and what machinery I had available to use, John S did the side plate profiling for me on his beaver CNC then I machined all the rectangular plates one Saturday morning on my mate's bridgeport, then drilled and tapped everything in the afternoon at home, so most of the main structure was made in a day!

The way I did it made sense to me because it was quick and easy to build because of what machinery I had available to make the parts, not everyone has these resources available so you have to do things differently. If I had a CNC mill to play with for a day to make my bits then I would have done things a lot differently!