There are some good videos on youtube about all over printing. Some good suggestions can be found there. I've always used a large pallet but could easily see a table being just as easy if the volume was low.
Many of our colleagues used what is called the long table system. Some are actually a series of platens but others are literally tables with registration guides. Think of a series of 4ft x 8ft tabletops lined series to each other. Many all over prints are printed this way but the cutted fabrics have yet to be sewn.
For sewn shirts, I've seen people use 1/4 plywood as platens. I did not see the platens close up though, only the printing in progress. I believe the corners of the plywood are used to to register the platen on the table. However, long tables usually have angular bars where registration screws on the frame rests against.
I've seen metal platens for all over prints on you tube. Why don't you also give it a search.
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