Joe's 1000x600x200 steel and aluminium router started

[devmonkey]

I'm looking for some recommendations on bed materials, machine will mainly be used for aluminium and composites, so preferably something that can take coolant. My last machine used epoxy soaked MDF which was far from ideal. The plate would need to be 800x1300.

I don't have a large enough piece of aluminium plate. So options I'm looking at are:

1. 20mm Tufnol, can't find this in sheets longer than 1200 so would have to alter the frame, this isn't really a problem. I'm not sure whether this is rigid enough to span the cross beams that are on 400mm centres??

2. Purchase a piece of 20mm aluminium plate large enough, quiet expensive.

3. Locate some aluminium extrusion T-slot bed profile 'planks', I can't find these either.

Thoughts?

A bit more research on different materials, Young's modulus (GPa):

MDF	4
SRBP (paxolin/tufnol)	6.5
Aluminium	69
Steel	200

The deflection of a rectangular section spanning two supports due to a downward force in the middle is inversely proportional to the Young's modulus * thickness^3.

So taking 16mm aluminium plate as a reference, thickness required for equivalent rigidity of those materials are:
MDF 41mm, SRBP 35mm.

Or another way, 25mm SRBP is equivalent to 12mm aluminium.

From this it is probably ok to conclude 25mm SRBP supported on 4 sides over rectangular bays in the machine frame that are 840x320mm is probably sufficient.

[devmonkey]

A bit more research on different materials, Young's modulus (GPa):

MDF	4
SRBP (paxolin/tufnol)	6.5
Aluminium	69
Steel	200

The deflection of a rectangular section spanning two supports due to a downward force in the middle is inversely proportional to the Young's modulus * thickness^3.

So taking 16mm aluminium plate as a reference, thickness required for equivalent rigidity of those materials are:
MDF 41mm, SRBP 35mm.

Or another way, 25mm SRBP is equivalent to 12mm aluminium.

From this it is probably ok to conclude 25mm SRBP supported on 4 sides over rectangular bays in the machine frame that are 840x320mm is probably sufficient.

I would probably use one large piece as the bed, then a second piece as the sacrificial board.

[JAZZCNC]

30mm HDPE makes a nice stable bed and you can cut a grid pattern to make it into a Vacuum bed. I bought a 10x5 sheet for £500 so if you get in touch with plastics supplier you might get a small piece or cutoff piece cheap enough.

[devmonkey]

30mm HDPE makes a nice stable bed and you can cut a grid pattern to make it into a Vacuum bed. I bought a 10x5 sheet for £500 so if you get in touch with plastics supplier you might get a small piece or cutoff piece cheap enough.

Ok thanks, that is interesting, YM of HDPE is only 0.8, how much support did you have under it, or what was the clear span? I guess we are only talking about supporting the mass of the part being machined and the downward force of the cutter, this is probably minimal, like to take a punt on what this force is?

Looks like an 8x4 sheet of 25mm SRBP is £380, this would give me enough for the base board and two spoil boards.