A variation on a frame for my Metal Maslow CNN w/ Makita Router:
For about $100 in material (with a $20 off coupon that I have), I can build a modified version of the Bolt Together Frame. Let me describe my variations / why, and see if the collective experience here can look for any issues I should consider.
RAIL: 12’ long, using the metal rail from the Metal Maslow CNC.
EXTRA A-FRAME: Adding a third A frame to the center (or just off center to one side or another if this location is a problem.
A-FRAME SPACING: Moving the A Frame locations to 8’ apart, reducing the overhang at the ends to 2’ at each end.
RAISED RAIL: The 12’ rail is raised 1’ higher than the default / basic a frame design
WASTE BOARD: Replacing the 3/4" plywood with 1/4" thick Hardie Backer Fiber Cement Backer Board, counter sunk screws, and a layer of 1/2" MDF on top of that to act as an easily replaced fairly cheap waste board. The overall thickness should be about the same, so the Z geometry doesn’t change. This backer board is not the same as “standard” fiber cement backer board. It is stronger.
MATERIAL: I’ll be using 12’ 2x4’s for this design, so the 2 10’ 2x4’s can become one 12’ one since only ~64 inches is used from each one.
Add cross members between the outer A-frames and the center A-frame to provide more support in the Z direction and rigidity between the framing.
I may add a cross member from the overhang of the rail down to the A-frame as well, but will gauge that after it is built as that will be easy to add.
The top surface of the cross member where the wood that sits in the workarea rests, I plan on routing the top of that cross member lightly and setting aluminum angle material there to create a long lasting work surface. It will be inset just so far as to be flush with the original uncut side of the 2x4.
The backer board will be heavier than plywood, but an extra ~50lbs give or take on the frame doesn’t bother me. I plan on adding offset lift wheels to be able to move the frame around and then set the frame down for the added stability. The lift wheels are not factored into the cost at this point and would be added later (probably the week after I build the thing).
I like that the cement fiber backer board doesn’t burn. I will watch the CNC machine when it is running, but making the backer board out of something that doesn’t catch fire is preferable to me. I am not sure how flexible that 1/4" backer board is, so the extra A frame and extra cross member should help keep it nice and flat. If when I go to buy it, if it is not stiff enough, I’ll pickup a 1/4" piece of very smooth plywood instead of the fiber cement backer board.
Another option would be to use their 0.4" thick backer board. If I went that route, I would cut into the 2x4’s just enough so that only 0.25" of the board stuck out in the z direction, so that when you add the 1/2" MDF waste board to the top, it would still only be 3/4" like in the original plans, not changing the geometry.
I’m very interesting in your thoughts on this and concerns.