MDF and rubber; spiral swarf from Forstner drill bits + LDF/MDF/HDF

Old-ish photo today, from a small project that entailed countersinking thin, flat fastener heads in fiberboard and in thick, fabric-reinforced synthetic rubber.

Before drilling the through-holes for the fasteners’ shafts, I used Forstner bits to wallow out shallow wells wide and deep enough to accommodate the fastener heads. The fiberboard is prone to chipping and crumbling around edges and holes, so I made wider and slightly deeper holes for a washer beneath each bolt head. Sometimes, the Forstner bits carved out vaguely rotini-shaped spirals of material, especially in the rubber. In the picture above, you can see one bit of corkscrew swarf from each sort of material.

The rubber is not EPDM. Instead, it’s a product I have seen described as neoprene, nitrile, and styrene butadiene rubber (SBR). My sense is that it’s primarily SBR with (maybe or maybe not) some neoprene and nitrile added for flame resistance (neoprene) and better behavior at higher temperatures and around oil and other stuff. It incorporated 3-ply polyester (or nylon, but I think polyester) reinforcement and the layers of fine mesh are visible in the image above as what resemble horizontal dashed lines.

For the the countersinking stage using the Forstner bits, I could stop before hitting the uppermost fabric layer. Then I swapped out the bits. With respect to the embedded fabric, making the through-holes was a bit like giving the polyester mesh a really vigorous noogie. Fibers in the drill path sheared off, wound themselves around the drill bit, and had to be pulled off between holes. The fluff that looks like tufts of crimped dog hair, sitting in a pile atop the hunk of rubber in the photo above, is a bit of that stuff.

Engineered wood products are an excellent example of a monetizing trash. Sawdust, shavings, chips, and scraps of wood, along with some stuff like wax, plus adhesives, go in and saleable products come out. Some of these materials will, because of the type of glue used, emit formaldehyde for years to come. But I digress.

Fiberboard comes in three hazily-defined flavors distinguishable in part by their density: low-density fiberboard (LDF), medium-density fiberboard (MDF, density sort of at or above 500 kg/m³), and high-density fiberboard (HDF, density sort of at or exceeding 800 kg/m³). Originally, long ago, I purchased several large, 8mm-thick sheets of the stuff with some metal shelving. I weighed and measured the scrap above and the density worked out to be a little under 700 kg/m³, so I suppose it’s MDF. OTOH, it bears a closer resemblance (color-wise) to Wikipedia’s image of HDF than it does to Wikipedia’s image of MDF.