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A site about the lives of Andy "Guido" Kimble and Erica (Fry) Kimble.  We hope you enjoy it.

After ordering the kit, the first task was to build a huge torsion box table, that will be the base surface for the CNC machine.  The table is a gigantic 126"x52".



This table required the following to build:

  • 49"x97"x3/4" MDF: 3 x  $28.22 = $84.66 (MDF sheets come one inch larger than typical material sheets.)
  • 49"x97"x1/2" MDF: 3 x $21.34 = $64.02
  • TiteBond II Weatherproof Wood Glue 16oz.: 2 x $5.48 = $10.96  (I suggest you buy a 3rd bottle.)
  • + $12.81 Tax = $172.45 Total


{yoogallery src=[/images/stories/BlackFoot40/CNC-BlackFoot-TorsionBox/]}

The construction is pretty straight forward.  Typically, you would want to do more to level the table surface (which is on the floor here, because I built it upside down).  The problem is that this thing is so incredibly huge.  I glued down ONE end cap, and left the other end cap free until after the entire grid was in place.  The design of the torsion box is intentionally set up to minimize the stress due to the separation in the table face panels, and long rails.  Lots of glue, and lots of nailgun brads later, it was finished.  Here are rough instructions...

  1. Have the sheets of MDF cut, for the top and bottom of the torsion box, at the store.  The three sheets of 3/4" MDF should be cut 52" long.  Two of the 1/2" sheets should be cut 63" long.  Have the last sheet of 1/2" MDF ripped (lengthwise) to about 30" wide (this will just make it easier to handle).  Take all this home.
  2. Use your table saw (or a circular saw if you are clever) to cut the 3/4" MDF 49"x52" panels to 42"x52".  You'll probably need a helper.
  3. If you want, cut the two 1/2" MDF 49"x63" pieces down to 48"x63".  This is totally optional, and has only an aesthetic effect on the finished table.  I didn't do it.
  4. Take the wider long 1/2" MDF 19"x97" board, and cut 3 panels about 19"x32" out of it.  They don't need to be exactly 32" long, but must be longer than 30.5".  You'll be dealing with the exact measurement later.
  5. Set the fence on your table saw for a 4" cut, and don't touch it until the following steps are complete.  You want them to all be the exact same 4" width.
    1. Rip the 1/2" MDF 30"x97" board into 7 long strips 4" wide (4"x97").
    2. Take 2 of the [smaller] 3/4" MDF 45"x49" boards, and crosscut (cut along the 49" axis) them into as many 4"x49" boards as you can make.  This is actually a little overkill, and you'll have a few extras.  This will probably make 20-22, and you need at least 16.
    3. Take the remaining 3/4" MDF 45"x49" panel, and cut 2 boards off it 4"x49"
    4. Take 2 of the 1/2" MDF 19"x32" panels, and rip them into at least 7 boards 4"x32".
  6. Use a chop/miter saw to cut the 7 long 1/2" MDF 4"x97" boards to a 4"x94".
  7. Use a chop/miter saw to cut the 3/4" MDF 4"x49" boards into at least 93 separate 4"x7.5" pieces.  It's handy if you have a few more extras.
  8. Take 3 of the 4"x7.5" pieces of 3/4" MDF you just made, and cut 2 of the corners off, on one of the long sides.  Cutting the corner off just keeps glue from getting on it, so it doesn't have to be measured.  I cut mine about 3/4" back from the corners.  You'll be using these as spacers, to get the grid spacing correct as you build along.
  9. Use a chop/miter saw to cut the 2 pieces of 3/4" MDF 4"x49", down to 48" long (4"x48").
  10. Lay out the 3 panels of the top, each 3/4" MDF 49"x52".  You can try to do as Wood Whisperer did, and set them up on saw horses.  The size, and panel divisions will make that incredibly difficult.  I chose instead to lay them out on the garage floor.  I did my best to shim them to be as straight and level as possible.  Make sure they are butted up as closely as possible to one another, as this will end up being the top table surface (we're building it upside down).
  11. Center one of the 3/4" MDF 4"x48" table ends on one end of the 3-panel table, and glue it down.  You'll probably want to leave this a little while, so that the glue sets well.
  12. Take one of the long 1/2" MDF 4"x94" boards and glue it in place, perpendicular to the table end board.  It's going to cross the 2 gaps between the table face panels.  Use weights to hold it down flat.
  13. Take one of the short 1/2" MDF 4"x32" boards, and use the chop/miter saw to cut it to the perfect length so that when butted to the long strip, and with the opposite table end set in place (not secured/glued) the table end board is flush to the end of the table top.  You're going to cut each of these 7 shorter portions of the long runs custom each time, to ensure the end boards fit perfectly flush.
  14. Glue the custom-cut 1/2" MDF 4"x30.5" board in place, butted to the long strip (glue the butt-joint too).  The long strip, with extension, should be 2" inset from the edge of the table "top".  Take a small scrap of MDF, maybe 3"x3", and glue it across the butt-joint to strengthen it, and clamp it.
  15. Set one of your spacer boards (with the corners nipped off) about 3-4" away from the long strip, with its end up against the table end board.  The nipped corners should be down, against the table "top".
  16. Glue down one of the short 3/4" MDF 4"x7.5" grid boards, perpendicular to the long strip, using the spacer board to ensure it's 7.5" away, in parallel, to the table end.  DON'T FORGET to glue not only the board to the table "top", but also to the long strip.  If you have a nailgun, put some brads through the long strip, into the short board, to help hold it.
  17. Leave the first space board in place, and set a second spacer against the first short gird board you glued down, and then repeat gluing down and nailing a second grid board.
  18. Keep working your way down the first row of the grid, using the spacer boards.  Using 3-4 spacer boards was good for me.  By the time I was laying the 4th grid board, the first one was set well enough to carefully remove its spacer board and leap-frog it down.  Just keep leap-frogging the spacers down until the whole row is done.
  19. Without gluing them down, custom-cut the next 4"x32" board, so that it will set the table ends flush, using the next long board you intend to use.
  20. Once you have the board custom-cut, glue down the short custom-cut board BEFORE the long strip, against the first (glued down) table end.  You want to intentionally alternate where the joint is, to give the table more strength.  Nail through into the grid.
  21. Glue the long strip down, butted to the custom-cut short board.  Nail through into the grid.
  22. Keep building rows.  Build the grid, using the spacers.  Then custom-cut the next 4"x32" board and glue it down with its long counterpart, alternating the joint (and gluing a scrap across it).  Use weights and heavy objects to "clamp" the pieces down.
  23. Put pencil marks on the perimeters of the torsion box, marking where the internal grid is.
  24. Put glue on all the edges of the grid, and place the two "bottom" 1/2" MDF 48"x63" panels in place.
  25. Use a panel square to draw lines across the "bottom" where the grid is, then nailgun the panels in place.  You should also put lots of heavy weights and objects on it, to help clamp it down.

A couple of things to note is the weight, and the paint required.  There is a picture of one end of the table on the bathroom scale, and that one end weighs 175lb!  That means this table probably weighs about 400lb total (or at least 350lb).  This torsion box that is 126”x52”, 5.5” thick, and weighs roughly 350lb. made from MDF. A 49”x97” sheet of ¾” thick MDF weighs 96lb. To make a solid MDF table that was 5.5” thick would weigh 970lb!  It will also take about 16 cans of spray paint to paint it.  The MDF just soaks up paint, which is good, because it means it won't be soaking up moisture.

[contentheading]Downloadable Plans[/contentheading]

Download this file (BlackFoot v4.0 4x8 Torsion Box Design (Guido Kimble).pdf)BlackFoot v4.0 4x8 Torsion Box Design (Guido Kimble).pdf[Torsion box plans.]440 kB