My technique for drilling bolt holes and installing T-nuts entails:
- Position the driver in the desired location on the baffle.
- Hand-drill the first 2-3mm of the holes with a drill bit of the same size as the fastener (6mm in this case), taking care not to shift the driver's location.
- Remove the driver and finish drilling the holes with a drill-press to ensure perpendicularity.
- Flip the baffle and use a stepped bit to increase the size of the hole so it is just wide and deep enough to accommodate the T-nut on the reverse side.
- Thread the M6 fastener with a flat washer into the hole and T-nut, and tighten thereby pulling the T-nut into the back of the baffle.
- Before it is fully seated, apply some adhesive to the T-nut - making sure to avoid the threaded area - so it is secured to the baffle and straight to avoid cross-threading or popping it out.
A similar technique could be used for threaded inserts. The key is getting them perfectly aligned thread wise.