Gridfinity Holder for Hardness File Set

These files are super handy for spot checking mechanical parts prior to assembly, to verify that they are manufactured to the correct hardness.  I bought them several years ago while rebuilding the transmission of my MGA, to verify proper heat treatment of the layshaft (countershaft in US mechanical English).  For several years, there were a lot of bad layshafts in the parts system, which were not made to the correct hardness.  A bad shaft would typically cause a transmission that should last for 80K-100K miles, to only last for a small fraction of that mileage.  Due to the low mileage accumulated by most classic cars these days, it took a long time for the parts suppliers to first realize there was a problem, second to admit it, and then to get a handle on it.

Since removing the transmission and disassembling it a second time due to a bad layshaft is a real PITA, I needed a way to make sure the part I was installing was one of the good ones (it was).  There are of course other ways to test hardness that are more accurate, but they tend to carry a large price tag, and are out of reach of most mechanics and DIYers.  These are accurate enough for a spot check, and a lot cheaper than a calibrated Rockwell tester or something like ultrasonic or eddy current test equipment.

Like my other Gridfinity models, the base is altered to accept 6x3 magnets as a press fit, with the upper surface of the magnet holes modified to make the slicer bridge across correctly for a clean result.  Due to the size of this model, I have included sacrificial “mouse ears” in the CAD to give the ends more surface area to help prevent them warping off the bed.  These will need to be removed after printing.

The unit pictured was printed out of Overture PLA on my Bear upgraded Mk3S+, using a 0.6mm nozzle, at 0.3mm layer height.