I stuck pencils through the pick-up holes to make them easier to see.
Experiment with the pick-up hole sizes. It may be that the holes closest to the vacuum connection need to be smaller than those farther away.
Drill the pick-up tube in the first compartment for 1/4" pick-up holes - 1/4" holes will probably be too small to allow much draft, but it's a starting point and 1/4" won't likely be too big. Don't drill the other compartments yet.
Screw the peg board on temporarily, attach a vacuum, and get the box drafting.
Lay some scrap balsa on the peg board over the first compartment and make some balsa dust. If the dust settles immediately onto the peg board you're done with the first compartment.
If the dust doesn't settle immediately and tries to float away, the pick-up holes are too small. Re-drill the pick-up holes to 5/16" and test again. The key here is _draft_, not >hurricane<. All you want is for the dust to settle immediately onto the peg board, not float away.
You may have to re-drill a few times to get the draft about right - use 1/16" increments. Once the first compartment has a suitable draft, do not drill it any farther.
Drill and test the second compartment, and then the third compartment.
When the third compartment tests ok, re-check the first two compartments. You may find that the second compartment needs larger holes than the first compartment and the third compartment needs larger holes than the second compartment.
All the holes in the pick-up tube in my draft box are 1/2", and I use a 4.5 horsepower 12-gallon Rigid vacuum to drive the vacuum system.
One last word - the joints in the box do not need to be closely fitted - they just have to seal. If your joints are less than wonderful, seal them with silicone adhesive.
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