8020 Sandwich?

[mdierolf]

What do you guys think about using 8020 sandwiched between two 3/8" pieces of steel to build an XY table which linear rails could be bolted?

I haven't drawn it out in cad, but here's a rough example:

----------------
XX            XX
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The X's are double-width 8020 (not sure on the dimensions yet), and the -- is steel plate.

It seems like the resulting structure would be fairly strong, and resistant to bending or twisting in all directions. It seems like the extrusion should be as wide as possible, and as short as possible to improve the strength of the structure.

This is for a metalworking machine, which will be used for milling 6061 aluminum. I'm looking at a 20x40" travel if I can make it work.

My current thought is that the failure of this design would likely have to do with vibration dampening, and that the mass of the table would not be sufficient vs the power of the head (a belt driven x2 spindle to start with, perhaps more later.

I'm guessing the answer to vibration dampening could be to fill the aluminum/steel sandwich with epoxy granite, or to use steel square tube instead of 8020.

Any Thoughts?
Mark

[YZF]

I agree that it looks quite stiff... Is the reason for the 8020 to be able to bolt the linear rails to the T-slots?

[mdierolf]

The ease of mounting is one benefit - the other is that it would be quicker to assemble, and I could mount accessories on the edge of the bed such as limit switches, toolpost for vertical milling, toolchanger, dial indicator, etc. since I would have an extra off-table t-slot.

After much thought, i'm thinking my best option would be to built it with the extrusion, and if it doesn't work that way, I could easily remove it and install steel tube, which would either be welded or screwed in place. If I need to remove it, the piece would still be usable and I wouldn't have wasted much time/money (all the work is in drilling the mounting holes on the top/bottom plate), and all the pieces would still be usable if I upgraded to steel.

I think my focus should be to get to this point, see what happens, and go from there.

Mark

Originally Posted by YZF I agree that it looks quite stiff... Is the reason for the 8020 to be able to bolt the linear rails to the T-slots?