Hi gents: Been unable to follow this forum on any regular basis since last fall; checked it once in a while, but I must have missed some good discussions. I’ve just noticed GI’s post and some discussion on fabricating scratch-built motor brackets. A key problem I’ve encountered whenever drilling 1.5 mm holes in chassis parts is placing the exact centre of a hole, and drilling it without the cutting bit wandering. (The wandering can be avoided with a pilot bit, but it’s often hard to use under these conditions without damaging the template, and without knowing the exact centre beforehand.)
When doing an architectural project, I find the centre of an existing large circle by the intersection of the perpendicular bisectors of any two chords. It’s impossible to use this method when replicating the exact positions of drill holes on a tiny piece of metal. But it is equally important to drill at those centres exactly, so that the components align perfectly. Is there a reliable way of doing this without any sophisticated equipment?
I devised, long ago, a method that seems to work, and does not require any expensive equipment. I’ve used it to drill 1.5 mm holes (for M2 threading) in chassis plates to align perfectly with the holes in the CNC fabricated bearing holders, where it’s critical to achieve perfect alignment. I’ve used it in reverse, to drill into scratch built bearing holders to perfectly align with existing holes in the chassis plate. I’ve used it to align holes between a suspension plate and base plate, as well as to drill holes in motor holders and motor stays aligned with holes in the motor housing and in the base plate.
The method is very simple and requires only two key components, besides other tools and materials that are already in most workshops. The first is a short piece of small diameter brass tube (K&S type) that fits precisely inside the original hole of the piece of metal you are replicating. The second is a very fine drill bit (usually between 0.5 mm and 2 mm) that fits smoothly inside and matches the inner diameter of the brass tube. I place the original master/ template piece in position onto the copy metal plate, and hold it in place with double-sided tape. Hold the appropriately sized brass tube tightly fitting into the hole of the template. Then carefully drill a hole in the copy metal using the drill bit that fits smoothly inside the guide tube. That hole can later be enlarged, or threaded if necessary, and it should end up precisely in correct position.
Photo: Aluminum bearing holder on motor plate, two brass tubes in position inside M2 threads, one drill bit inside guide tube. Spring-steel motor bracket from ‘Beardog chassis’ kit, taped down for copying, two brass tubes in position inside 2 mm holes, one drill bit inside guide tube. Other brass tubes of various diameters, other drill bits, M2 tap set.
I hope this method is of use to someone. Felix.
