HPL, Revisited

[Alan Peterson]

A few months back, I posted a question on what it takes to bend HPL (plastic laminate; i.e., Formica) sides. I want to kick the stakes up a bit higher: creating an ersatz arched top out of plain old Home Depot HPL, using a heat process roughly similar to vacu-forming plastic.

Here's what I'd like to try: mark an outline to define the top on a short rectangular sheet; clamp the sheet down inside a frame and expose both sides to a radiant heat source; pour a quantity of sand onto the heated sheet so it "dishes" slightly inside the frame under the weight of the sand; allow to cool, then cut along the outline.

Absent is the actual vacuum portion of the process - I'd allow the weight of the sand to define the shape of the top's Z-axis.

The product support people at Wilson Art told me, while its possible to bend a sheet of their material (as in a guitar side), a compound curve is out of the question. I'm thinking that its such a gradual arch along such a large sheet of material - AND that it's a thermoplastic material to begin with - that I should expect some deflection I can work with.

Except for the obvious question of, "Why the hell would you want a Formica archtop?", is this worth trying out, or should I just go to the movies instead this weekend?

[Clay Schaeffer]

Hi Alan,
I think HPL is a thermosetting plastic rather than a thermoplastic material. Although it does deform better when heated it doesn't become thermoplastic like corian does. You might still be successful as I have seen the material warp 3 dimensionally. You might also do something similar to what Graham McDonald does to form his "Press top" mandolins, making a form and clamp and heating it in an oven.
Why not an HPL archtop? I just finished making 14 HPL back and sided stick dulcimers. They are fun little instruments that players find hard to put down.

[John Sonksen]

As a cabinet maker I can say I have used hpl hundreds of times. The number one thing you learn not to do is try to bend it along both axes simultaneously. Basically HPL is paper layers embedded with resin. It creates a durable surface that is fairly impact resistant with sufficient substrates. However it is very thin and offers zero structural support. As part of the manufacturing process the glue side is ground leaving very fine linear striations along the length of a sheet. Because of these if you rotate it torsionally, these will act as weak spots where tearing can begin. Once it starts it will tear like paper and will be razor sharp(trust me I lopped off the tip of my ring finger with it once).

I would say even if you were successful in bending it it still could, over time easily crack down the road. It would be a lot of work for something that I would guarantee would fail. Well it may not fail if you keep it in a display box and never touch it again.