Mounting large plates

I’ve got a poster project coming up. The plates will be approx 18”x24” for six colors (i.e. six plates). I need to find a better way of mounting these plates. I’ve used MDF and plywood before and have always had the same problem. There are low and high points, and the boards don’t sit perfectly horizontal, so one print might ink perfectly but the next might miss spots, or over ink. I’m also shimming them up with chipboard to get to type high. The boards usually come in 3/4” thickness. Printing on an SP-20. Any suggestions?


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MDF is notoriously unstable with humidity changes, and plywood is not a lot better. One solution could be to obtain some thick sheets of acrylic plastic, like window glazing, 1/2, 1/4, and 1/8 would put you just over type high depending on the plate material thickness. They should be flat and dimensionally stable. A plastics supplier should be able to furnish what you need if you choose this route. Colors shouldn’t matter for your purpose, and depending on the dealer they may have cut pieces that would suit for less than full cost, though 18x24 is pretty big for scrap.


Boxcar bases will cost you a lot, but if you are likely to do posters for many jobs, then its likely to be worth the cost to be able to print without having to worry about the base. You can focus on getting to the job and printing rather than spending time (which means lot revenue) trying to “cheap charlie” a basic piece of equipment.

If you are going to print a number of posters - this job and
more jobs in the future - amortize the cost of the plates into the cost of the posters.


Talk to A plastics supplier about fiber board. It’s that thin brown board that electrical parts are mounted to, you can get it in very thick widths.

You can get dimensionaly stable plywood milled flat to any specific height that might be less expensive then the alternatives mentioned above. I don’t know where you are located or if there is someone near you that could make it but I do have the number for a company in Wisconsin that makes this product if you need it.

Hey Jonsel, you haven’t said so, but I am assuming you’re using photopolymer?

This is JIG PLATE- it is flat, 6061 Aluminum.

If you look at what 7/8” is, and try to find out what the thickness of standard plastic backed polymer plate material is, you might find they add up to about type high.

Then it is a matter of pricing out a 19x25 inch sheet of Jig Plate.

Read about Jig plate as to what it is, give the company a call. At 167.96, even if you have to shim it a little, you’re looking at a better plate than 6 or 7 MDF boards. If you do 6 projects on MDF, at the size you stated (18x24), you have just spend more money than the jig plate. Even if it isn’t perfect.

The real way to do this is to buy a 1” Jig plate, and have it ground down (Blanchard ground) to 7/8”, but that would cost more.

“Cast Aluminum Plate
Aluminum Cast Tool & Jig plate is continuously cast, aged, stress-relieved, machined plate providing sound dimensional stability with minimal or no distortion even after extensive machining operations. Cast Aluminum Plates have a precision machined surface for superior flatness and thickness tolerance and are protected with PVC plastic on both sides. Cast Aluminum Plate typically has a surface finish of 25 RMS or better.”

Thanks, Haven. I’m going to get in touch with them today and see what they can do. It has to be cheaper than the $1,000+ Boxcar Press wants for their largest base.

I may go for the cast aluminum plate instead of the jig b/c they offer a .875” height. Using .75” means I have to shim up with several layers of chip board and I figure that is causing some of my problems.