Gauge to rethread self printed screws and bolts

prusaprinters

When bolts are printed on an FDM printer, they should be orientated horizontally to achieve better stability against bending and torsional forces. This requires supports and leaves a burr on the thread when the support is removed. Due to this burr and the limited resolution of FDM prints it is necessary to rethread the bolts using a thread cutter. It is essential that the bolt is strictly perpendicular to the thread cutter when starting to rethread. This gauge fixes the bolt in a perpendicular orientation for the first turns, until it is safe to continue rethreading without fixing.The gauge consists of a holder-plate where a 25 mm thread cutter is inserted and fixed with two M4x16 mm screws. The holder-plate is mounted to a base plate either by two M3x5 ..10 mm countersunk bolts or by glue, and so can be clamped to the tabletop. The M3 and M4 threads need to be recut with a tap. All parts can be printed without support. To achieve an optimal stability against bending forces on the base plate when it's clamped vertically, print the base plate in vertical orientation (120 mm length on Z-axis, 45 mm width on Y-axis), using a brim of sufficient width.There are fixings for M3 ... M10 bolts which can be placed into the holder-plate. Dependent on the length of the bolt you can use the upper position on the holder-plate and the fixing with the brim oriented up or down or the lower position.To rethread a bolt, the gauge should be clamped horizontally to the tabletop. After some turns it is safe to remove the fixing and continue without, probably with the help of an electric drill screwdriver. For screws that would exceed the bottom of the thread cutter the gauge can be clamped vertically.When you do not have a thread cutter, a metal nut may be used as an expedient. There are adapter plates for M3 ... M10 nuts. Although the nut may fit tightly into the plate, it should be fixed with a drop of glue. However, especially for M3 and M4 the results may be unsatisfying.