Is there an easy solution to converting a cabinet from leaxan to flex face? Would using something like 1/2"x2" flat aluminum bars fastened to the inside of the frame be a stupid tension system?
Most cabinets are not strong enough
One problem with a retrofit is that most cabinets are not strong enough to support a flexible face. The returns will tend to "concave inward," on the long dimensions especially. If the cabinet is made with angle iron and a metal skin, the odds are better this won't happen. But most people these days build lightweight cabinets made out of aluminum extrusions. So...fastening flat aluminum to the inside of the cabinet to anchor the face may not work well, since it would be relying on the strength of extruded returns to tension the fabric.
The best way to retrofit is with the retrofit kits available from extrusion makers. The support for the flexible face is provided by the frame rather than the cabinet, and the assembly can then be attached by a top hinge to the top face flange of the cabinet. This allows for a flex face that is easy to service safely by one person and does not rely on the cabinet for strength. Of course, these kits are not cheap.
Regarding wrinkles, this is generally not the fault of the frame system. Rather, it's a fabricator issue. Duck-billed pliers, both the locking kind and the kind that do not lock, are essential, in my opinion. I have even used homemade stretchers successfully. These were bar clamps with a locking duckbill welded to one end of the bar. The duckbill clamped the fabric while the stationary clamping leg hooked over the edge of the sign cabinet. The trigger leg, in the middle, pulls the fabric when actuated. Turning the trigger leg around, so that it faces away from the permanent leg, allows for better pulling power. (I wish I had a picture.) They aren't pretty, and they're a little hard to weld up, but they work. I used them in addition to handheld duckbills.
Homemade frames
Using one-inch aluminum tube to make a homemade retrofit frame actually does work. Yes, it's cheap. It's a pain in the butt and requires at least two workers for any future service work. And you need to lower the whole face to service the sign. But, it's cheap, it works, and can be done without wrinkles. The trick is to add center braces so the perimeter frame members do not bend inward too much. The braces need to be installed parallel to the florescent lamps so they do not create shadows. To do this, you position the braces a few inches
behind the frame, attached with diagonal pieces of tube welded to the perimeter frame. (Again, I wish I could show a picture.) The braces then lie protruded into the spaces between the lamps, floating beside them without obstructing light. The small diagonals need to be welded to the frame in a way that the frame can still lie flat against the front of the cabinet.
Careful tensioning of the fabric using truss-head screws an inch or inch-and-a-half on center can be done with no wrinkles. The finished unit will cup somewhat on the dimension not braced, but attachment to the cabinet flattens it out. A hassle? Of course. But so is installing and servicing a large polycarbonate face when there is no hanging bar to help do it safely. Two or three people and two trucks either way, right? And the polycarbonate will turn yellow; the flex face will not. Also, you can strip and re-letter a flex face in situ. I have even done eradication while the face was in place.
Homemade frames like this don't allow for extreme tensioning, but they work, they're cheap, and most people won't notice that the sign is jerry-rigged. Make sure the customer understands that the cost of service calls will eat up any savings from the initial conversion. An engineered retrofit kit is
always superior and safer for servicing.
Brad in Kansas City