Magnetic Base to Plastic Plates

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Removing the magnet top from my magnetic base

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Removing the adhesive under the magnet

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The converted base in my platen press chasse with a plastic photopolymer plate

 When I started letterpress printing, the only way to print with photopolymer was to make steel-backed plates and then use a magnetic base to mount the plate in the press. Over time I’ve acquired 4 bases in various sizes. One nagging problem with these bases is that the magnet is weak to begin with and degrades over time so that the plates don’t stay put. I resort to tape and spray adhesive to keep the plates in register.
I’ve been making due with my weakened magnet bases, but as I started work on my 2012 calendar I knew I was going to have to get the magnets replaced or go to a plastic plate system. This system, introduced half a dozen years ago, uses adhesive to attach transparent plastic plates to an aluminum base. I knew there were lots of advantages to the plastic plates (for instance they are easy to cut using scissors and because they are transparent, you can align for registration more easily using marks on the base), but I was loath to buy new bases and replace the steel-backed plates I use to print coasters and book covers.
Then John Sullivan at Logos Graphics, who makes my steel-baked plates, told me he converted his magnetic bases to use with plastic plates by removing the magnet top and replacing it with a gridded mat he got at an art supply store. He attached the mat with the same sheet adhesive used on the plastic plates (he sells it for $3 a foot plus postage).

I used a xacto knife and metal ink spatula to take off the magnet top, and cleaned off the underlying adhesive with goof-off. Then using the sheet adhesive I got from John, I applied the gridded mat.
Some final gory technical details: One mat won’t make the base high enough and John suggested red pressboard (available from NA Graphics) but I didn’t have enough, so I adhered a second mat to the bottom of the base. It helps to have a measuring caliper to get the right height. A Boxcar aluminum base is .854″ high, my magnet converted base was .860″ before and after conversion.

2 thoughts on “Magnetic Base to Plastic Plates”

  1. This is very interesting. I’m a beginner-just bought a kesley 5×8 and I want to mainly use photopolymer plates but I’m a little stuck on all the details. Everyone keeps telling be to contact boxcar press and start there! Something I was wondering about photopolymer is do they leave any kind of impression? I have used photopolymer to make stamps to use in clay for jewelry but I think they are soft and I wonder how they would make an impression. Curious!

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