The first item in building one of these boxes is to decide how big it needs to be.  This relates to press size, tray size, and the size of the largest plate anyone is expected to want to put in it.  Don't go overboard.  It takes up room, and a huge box costs more to build and makes a bigger mess during use.  It is good if any aquatint box can be contained in a separate room or enclosure, since rosin powder tends to float around.  Use a dust mask.

Once the size has been determined, shop around for the fan and electrical motor.  The best selection is usually available at a large electrical equipment supplier like Grainger (search www.Grainger.com for air conditioner motors - I'd recommend something like Grainger Item No. 4MB15 or 3M904 or 4ME13 - chop off the shaft you don't need) or McMaster Karr, but any company that supplies heating and cooling equipment is worth a try.  IT IS CRITICAL in building this type of aquatint box that it have an adequately large fan blade driven by adequate rpm and horsepower.  It's almost impossible to over-power it, but easy to under-power it.  I would recommend using at least a 1/2 horsepower motor with rpm at least in the 1600 range and a fan blade as big as will fit in the bottom of the box. (Probably nothing larger than a 1 horsepower motor.)  The blade should have a clearance of 1/2 in or more from the sides of the box and an inch or two from the underside of the plate support grid and the floor of the box.  Fan motors are usually designed to be cooled by the fan's airflow, which in this situation doesn't happen; however the fan is only run for a ten or fifteen second burst to stir up the dust, so they don't have time to heat up.  If they are run steadily and heat up, almost all have a "thermal overload protector" switch which turns off the motor, and a button has to be pushed to reset the switch.  As shown in the drawing, the motor has to have an extended shaft (6 or 7 inch lengths are common, and adequate) and end mounting bolts so it can be bolted directly to the floor of the box.  NOTE: make sure the fan blade and motor's direction of rotation will blow the air downward across the floor of the box and up the sides, not vice versa.  If your box doesn't seem to stir up the rosin adequately, you can try adding a vibrator to the underside of the floor of the box between the motor and the wall of the box and wire it to run simultaneously with the motor, though this probably won't be necessary.

Decide what the grid will be made of:  I have used extruded aluminum or steel stock, electrical conduit, and chain-link fence stretchers, cut to length to run from front to back of the box, spaced 2 to 4 inches apart.  You don't necessarily need to be able to take them out, though there may occasionally be some reason you might need to do so.  You definitely don't want them to come out and get in the fan blade while it's running, so situate them securely.  It is assumed that the door will occupy the widest dimension of the box, for ease in sliding plates in and out, so the bars of the grid will correspond in length to the shorter dimension of the inside of the box.

When the floor size of the box has been determined and the motor and fan procured, you can make a "cut list" to begin construction.  You'll need to figure out the precise dimensions for your box.  You have the floor size.  The top of the box will probably be the floor size plus the thicknesses of the walls.  Moving down from the top:  it's good to have at least 3 or 4 feet of vertical space inside the box above the plate support grid.  This dimension is flexible.  You have to have enough vertical space between the bottom of the grid and the top of the floor of the box for the fan blade, plus an inch or so of clearance above and below the fan blade.  Then there's the thickness of the floor of the box, which needs to be substantial enough to support the weight of the fan and motor, and then enough vertical space under the floor of the box to accomodate the motor.

The door is cut out of the front of the box.  Let the sides of the box lap the front of the box.  That way when the door is closed there will be an edge for the door's trim gasket of foam rubber to seal against.

Begin construction by joining the back, top, and sides of the box.  Locate the center of the floor by drawing diagonals from the opposing corners.  Drill a hole the same size as the diameter of the shaft where the diagonals intersect, and rub some grease in it to lubricate the shaft.  Put the shaft of the motor through the hole and mark where the mounting bolts contact the floor of the box.  Drill holes for the mounting bolts.  Remove the motor, and attach the floor to the back and sides of the box. Install the motor and fan.

Attach the bottom panel of the front (the front is cut into three sections; the bottom, the door, and the upper panel) to the floor and sides.  You may want to install electrical wiring and the on/off switch at this time.

Install the flashing , to round out the corners where the floor joins the walls.  It is probably preferable to cover the entire floor with metal, since rosin is less likely to adhere to it, but wooden floors seem to work OK. I have attached the flashing (usually about 6 inch wide aluminum) by cutting (with tin snips) two lengths to go along opposing sides of the floor, drilling approx. 1/8 in holes about a foot apart along the center of it, and pressing it into the corner so that it is bent into a curve; then putting long (3 or 4 in.) drywall screws through the holes and into the corner to hold it in place.  That's the easy part.  The hard part is the other two opposing sides.  What's hard is cutting the ends of the strips of flashing into a complex curve that will meet the other curved corner nicely.  Measure the dimension at the top edge and at the bottom edge of the side you're going to cover, that way you at least know where your curved cut has to start and end.  Make a curved cut that you think leaves a bit too much metal on. (You may want to do this with a short piece of scrap, just to get the curve.) Bend it and put it up to the curved corner already installed. Trim it until you get a satisfactory joining of the two ends.  Once you have the curve, you can use it as a template to mark and cut the remaining ends.

Install the grid.  The top of the grid should be flush with the top of the lower front panel, and with the bottom of the door.

Install the upper front panel.

Install the door, including trim moulding with gasket, handle, hinges, and latches.  The door should open easily, close easily and snugly.  Make sure all cracks are filled with caulk or putty, since rosin will blow out of any cracks or gaps in joints.
 

This is a detail drawing of the trim that goes around the outside of the door on the two sides and across the top.  The bottom of the door should have a gap provided to hold a strip of foam rubber that will seal it when the door is closed.  If it's too tight, the door will be hard to close. The door should be operable with one hand, since the other one needs to hold the plate that's going in or out. Consider spring-loaded hinges, and magnetic latches.

Please feel free to email me at elgon@etchings.org, as I am sure these plans will benefit from further refinements.

USING THE BOX

Procedures for using this aquatint box are much like any other type of aquatint box.  You put powdered rosin in the bottom of the box.  A box built to accomodate a 24 X 36 in.  max. plate size would probably have about a 30 X 40 in. box-floor size, and would probably be 5 or 6 feet high, overall, and would require maybe two lbs of powdered rosin initially, since a lot of the rosin in a new box initially ends up stuck to the inside of the box or in corners and crevices.  I have never used anything but Graphic Chemical powdered rosin (the brown stuff) in these boxes, but assume ground lump-rosin or bitumen would work as well.  With some rosin in the box, close the door and turn on the fan for about a 10 second burst.  The fan should get up to full speed for most of that time.  Turn off the fan, wait about 5 to 10 seconds, open the door and slide the plate in. I usually give the front of the box a couple of good thumps with my fist just before sliding the plate in to dislodge any clumps of rosin or debris that might otherwise fall on the plate as it is being slid into the box. The longer you wait after turning the fan off before you slide your plate in, the sparser and finer will be the particles of rosin you get on your plate.  If the accumulation of particles is too light, you can turn the fan on, off, and slide the plate in for some more accumulation.  You can also do this after you have cooked the first layer of rosin particles. In fact, you get a less grainy aquatint if you first collect and cook a very fine dusting of particles then add more rosin to it and cook it again.  The trick, of course, is not to get too much rosin on the plate and block out too much of the plate.  The plate should be lying face up on some kind of a tray.  A piece of corrugated cardboard will do, or thin plywood.  The backing tray should project a couple of inches or more beyond the edge of the plate.  This makes for a more even coating of rosin particles on the plate.  When you remove the plate from the tray, brush the excess rosin dust back into the box.

After you have run the fan 10 seconds and turned it off and waited 5 or 10 seconds, open the door and slide the plate on its tray into the box. Close the door and wait 2 or 3 minutes for rosin to accumulate on the plate before taking it out and cooking it.  These timings will vary from one individual to the next, depending on how coarse or fine, or heavy or light the aquatints are they habitually like to use. They will also vary with how much rosin powder is in the box at any given time.  When the rosin accumulation coming out of the box starts getting too light too often, throw 2 or 3 tablespoons of rosin powder into the box.

If you find that you're getting hairs, dust, splinters, or other debris on your plate, you can remove the larger particles and junk from the bottom of the box by putting a large tray in the center of the grid, and running the fan for a few seconds with the tray laying on the grid.  Large particles blow from the floor up around the sides of the tray and are deposited on the tray.  You can then take the tray out and dump the junk. If that doesn't fix it, you may have to vacuum out the bottom of the box, with or without the grid in place.