Slotting Perspex for a Drop-Spine Box

July 2, 2011

Jeff’s post about slotting Plexiglas led me to the thought that board slotting may be a useful technique for creating clear-spined drop-spine boxes. A clear spine is advantageous in many ways. Libraries which function as museums might keep as much of the aesthetic of spines as possible while still completely enclosing the book in a hard box. Labeling is still possible if necessary but may be skipped entirely if the spine of the book is already labeled. The visibility of the spine acts against loss or theft, since one can see at a glance whether the box is full or not. Finally, the rest of the box still being constructed in cloth over board allows it both to breathe and absorb water (rather than the book absorbing water) should there be a leak or spill nearby.

The constructions I have seen involve making a thin card frame instead of the usual board spine piece, both on the inside and the outside, and covering it in cloth as part of the casemaking process. This frame needs to be minimally larger on the outside than the inside to avoid seeing the seams through the acrylic, and given that it is glued to either side of the acrylic, the raised edge is vulnerable to lifting either on its own or as people pull it from the shelf. It’s not an incredible problem, but it would be nicer to have something a little cleaner and faster to make.

Poly(methyl methacrylate) (PMMA–trade names Plexiglas, Perspex, etc.–because I don’t actually know what brand mine was, and to avoid the different UK/US standards, I’ll just refer to it as PMMA) comes in a sheet that is relatively easy to score and snap with a utility knife and a ruler. It can be manufactured with a UV coating, so in storage situations where light exposure is an issue, the longer wavelengths might be at least minimized while still maintaining a clear spine. And as Jeff mentioned, it does come with various degrees of resistance to abrasion, reflection, etc., so different budgets may be able to afford different grades of  PMMA, depending on the library’s priorities.

It wasn’t a huge thrill to slot; I found I had to go incredibly slow to avoid melting the PMMA with the warmth of the blade, and because everything is visible the slot needs to be perfectly even in order to not be visually distracting in the end. The blade needs to be exactly the thickness of the cloth to be inserted, because unlike board, the PMMA is inflexible (or at least not flexible enough to ease open the slot without serious risk of snapping the thin side right off, as I discovered…). And the dust inside, which is partially stuck to the slot from heat, needs to be cleared out thoroughly before the cloth can be inserted. But it does work! You’ll have to forgive the unusual cloth color for a box; it’s all I had around at the time.

A few notes:

Adhesives: EVA (ethylvinyl acetate) does hold up to a point, and I assume PVA (polyvinyl acetate) would do the same but didn’t try. Paraloid B72 is the best option: when subjected to tensometer testing, the cloth tore before the joint failed. I applied the adhesive using a syringe, and found no difference in strength when the Paraloid was laid down along the inside end of the slot but not completely covering the sides. (More on that later).

The samples above show the results of testing on the tensometer. Quantitative results didn’t seem terribly useful, although I have the figures if anyone is interested; really the test of the join needs to be that it doesn’t fail before the cloth, which is what would fail normally. If one wanted to be completely thorough there ought to be a fold test to see whether the hard edge of the PMMA causes earlier fail of the joint, but for now I just tested to make sure the adhesive would stand up to the stress of even a very heavy box. The EVA sample at top is representative of all the EVA samples; there would be some amount of distortion of the cloth before it pulled out of the slot relatively neatly. The two Paraloid samples show that occasionally the fabric would begin to pull out of the slot but this was almost simultaneous with the tearing of the cloth, so it didn’t cause very much concern.

Labeling: I stamped the PMMA with various gold foils on a PräGnant at 85 degrees F with relative ease. It wants relatively light pressure and no dwell. I haven’t tried letters larger than 14 point so I don’t know if it gets more difficult at larger sizes.

More images of the testing and prototype box are here. When I get some diagrams together I’ll post again with the procedure.

The one thing that has me stumped is that the cloth absorbs the Paraloid completely in some places and not as much in others, and the cloth is much darker where wetted with Paraloid. Introducing enough adhesive in the slot to completely cover the cloth leads to too much seepage once the cloth flange is inserted, which is even more unsightly. I tried sanding the PMMA from the outside just over the slot hoping to fog the material enough that the area would be opaque, but there just isn’t enough distance from the cloth in the slot to obscure it completely and it ends up looking messier. Any thoughts?

4 Responses to “Slotting Perspex for a Drop-Spine Box”

  1. Jeff Peachey Says:

    Looks great Abby. I wonder if slotting into the plexiglass parallel to the surface (rather than into the edge) might help hide the slot/ cloth join, at least when viewed on the shelf, which is the primary purpose of the clear spine. If the plexiglass is at least .250 inch thick, a .125 inch deep slot should hold, I imagine.

    Since you seem to have access to a tensometer, and if you are looking for more research projects (ha!), the relationship between the type of board (mill, pulp, binders, etc), the hinging material, dyes or paints on the hinging material, the type of adhesive to adhere the hinging material in the slot, the hinging material itself, and the starting point- thickness-depth-angle of the slot itself all need to be studied in greater detail, I think. Zimmern fold tested the material itself, but not the adhesion in the slot. I suspect even paste is a bit too strong for a “standard” slot (.150 inch deep, 13 degrees) and that if stressed, the board will fail in areas adjoining the slot, not in it which would be ideal. Of course, the slot is usually not stressed perpendicular to the hinge, but parallel to it when the book is opened. It seems most of us can take a guess at these complexities, and get close enough, but some data would be a useful guide.

    How about a clear spine, and built in plexiglass display/ reading wedge? Similar to this –
    Or is this just silly?

  2. auhteg Says:

    I suppose you could do that (integral cradle) although it increases the number of board thicknesses either side of the book—there are already two, one of which is visible, one of which gets hidden by the cloth flange—the way I did it, at least. I think you could do the flange in the way you suggested (maybe even there would be less stress on it, if it’s not permanently bent around that corner?) but maybe you’d want to sand the very edge of the PMMA so it doesn’t provide a cutting edge as the book is opened and closed. If I’m picturing your idea correctly… I’ll have a go at some point.

    With the integral cradle, I’ve done it the way you outline in that post, more or less, for a book at Columbia that because of its stab (re)sewing would always want a cradle in order to be read—we made it to fit around the book in the box so that the reader would have no excuse not to use a support. It hadn’t occurred to me to attach it to the box; mine was built to use in the box but was free from the book and box. But if you cut the slot extra wide in the PMMA on the box spine, say 4 cloth thickness’ worth, you could insert the flange from the outside board of the box *and* a flange from one side of the cradle. The rest of the cradle could be made of board, and in that way you could have the cradle and box attached still with the clear spine. Maybe?

    Lastly, the tensometer/fold tester: we have both, in addition to one that does shear tests and I think another similar machine that isn’t yet working. There’s an assignment for graduate students to test something on the tensometer in the first term; maybe someone will take the bait next year. I’ll pass along the testing wish list.

  3. auhteg Says:

    Good point about the angle of the slot, too. That might help, although I suspect even then the stuff just isn’t thick enough, or my sandpaper isn’t robust enough. There must be a way to do it, but perhaps not with the amount of control or easily-obtainable materials/equipment that would make it a feasible solution of people are to make boxes like this in their normal labs. My other thought was to tint Paraloid with pigment and try painting that on the surface. PMMA is soluble in acetone, which is the solvent in Paraloid, so it might react enough with the surface to fuse more than a normal paint would (thereby not chip off?)—but again, I haven’t had a chance to try that yet. It didn’t really seem like an ideal solution…

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