Spotting drill or centre drill

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I would usually drill through both clamped plates with the tapping drill, then use a clearance drill on 1 plate.

Emgee

I too drill through both plates with the tapping drill, then clearance drill. For starting the tapping drill I first use a spotting drill (using the dials on the milling table handwheels to place the spotting drill), then the tapping drill.

Thor

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I would spot it with a drill the same size as the existing hole, only needs a light touch to give a point for the spot or centre drill to use.

Emgee

Spotting drill.

I use the same size drill as the existing hole, so its a nice tight fit when I drill the start of the hole in the other plate, gets the new hole nice and central. Just sink the drill in to the edges of the tip, then change to the tapping size drill or pilot drill if you are going to use one. I don't bother with a centre drill or spotting drill in this instance as the larger drill has already provided the starting divot in the bottom plate.

Exactly what I do ! Saves time and you end up with an accurately drilled hole.

If you by chance have a set of transfer punches use them

I'd do them separately using the DRO to set out the holes. Spot and clearance size in one plate. Spot and tapping size in the other and while it's on the mill use that to also guide the tap perfectly perpendicular

Missed the edit, if I did not know the hole ctrs then use a spotting drill if I have one that fits existing hole if not use a drill bit of the same size to transfer onto the undrilled material.

Edited By JasonB on 11/02/2022 12:58:09

Hi Br

I thought you made it perfectly clear.

Must be missing something ?