The layers from the bottom up

 

 

 

Layer 1.

Your first layer is a piece of plywood. If you are serious use Baltic birch multi-layer for flatness. Normal everyday plywood works ok just make sure it is flat!

 

Layer 2.

Use some sticky tape window sealant foam rubber around the outer edge of the plywood. The tape will give a raised bump in the sandwich when complete it will raise the rubber up a bit for better contact with the glass. It is not necessary but will give you more depth in the frame itself for printing on very thick pieces of material though I don't know of anyone printing on 1/4 inch thick paper.

 

Layer 3.

Now lay down a piece of 1/4 to 3/8 (or thicker) foam. Do not use a stiff foam Styrofoam but most any foam rubber or flexible foam plastic will do.

 

Layer 4.

Lay Down a sheet of rubber. EDPM, Butyl, Neoprene or Buna-N will do. 3/32 to 1/8 inch works well. They pretty much all look and work the same. Natural rubber will decay under the UV in time.

 

Vacuum Port construction

Punch 2 holes (one if a small frame) in the Layer 4 sheet rubber. Take two 3 inch pieces of neoprene rubber hose (auto parts supply) and cut the ends even with a razor blade.  Using Super glue, glue the two short pieces of neoprene hose butted against the holes in the sheet  rubber to make the vacuum connections. Yes! Super glue works great. Two holes will be needed to be cut in the plywood and the foam to allow the ports access to the area below the frame. They will go through the plywood to the bottom of the frame where they will connect up to the vacuum line from the pump.

 

Layer 5

You now have a big sandwich. with the two (or one for smaller frames) vacuum ports dropping down through the plywood. If you were to lay a piece of glass on top now you would suck the area surrounding the ports to the glass and you would get no vacuum anywhere else. To prevent this from happening you need a vacuum buffer sheet. A lot of things can be used. I used stiffened felt I bought at Michaels. You can tape several smaller pieces together. Regular felt should work as well. You also might try using the material used in needlework that looks like a canvas stiff screen. You could probably use window screen or very coarse muslin. Almost any material you could blow smoke through would work.

 

This layer should cover all but the outer 1 to 2 inches of the rubber. The outer inch or so is the part that forms the seal with the glass.

 

Layer 6

Glass. The thickness depends on the size of the frame. Laminated safety glass comes in 3/32 and is excellent but costs @ $9.00 per sq. ft. The glass is taking very little stress as it being evenly compressed so fairly thin glass can be used. The glass should cover the complete area of the sheet rubber. For a serious project invest in the laminated safety glass. Watch for the trademark bug in the corner it could fall into the imaging area.

 

You will need a vacuum pump. It will need to be fairly substantial but don't go overboard. $150.00 is about the price you will need to pay for a new one.  C&H surplus in Pasadena Ca is a good source for used pumps.

 

This is the rough outline of how to make a foolproof vacuum frame. There are no standing seals to get damaged. How you hinge the glass and construct the details is up to you.

 

 

 

Note that the diagram shows the layers in different sizes for clarity. In actuality they are all the same size except for the vacuum buffer sheet.

 

 

 

Layer order from the top down:

 

Glass

Vacuum buffer (felt)

Sheet rubber

Foam compression layer

1/2 inch window seal foam rubber tape

Plywood

 

This is the basic design criteria. I'll leave the basic engineering, etc up to you.

 

 

 

--Dick Sullivan