How to drill a hole in a tricky-to-align place

[Robbie Rollie]

I need to drill a hole with a centre where the edge of another hole is. How could I hold the drill in the right place or otherwise make this hole without the bit slipping towards the other hole?

I need a 25mm hole with its centre at the back of the hole in the middle of the pictured triangle.

 

[Scarlet Pimpernel]

Centre punch, then small drill first.
It would be better done with a pillar drill, rather than a hand held drill.

 

[stuart45]

I think you would need to make a jig and bolt it to the plate so the drill bit won't move.

 

[Tigercubrider]

25mm is a big hole for a drill bit.
I'd sandwich the metal between a thick block of wood with a thinner bit of ply over the top.
Trace the shape onto the top ply before bolting or screwing the sandwich together using the three edge holes.
Use a hole saw centred on the target, the thin wood will stop the saw slipping

https://www.screwfix.com/p/starrett-csc25-multi-material-bi-metal-holesaw-25mm/768hy

 

[rsgaz]

Do you mean the centre of the new hole is literally on the edge of the existing hole, like this...

If so, no amount of clamping will prevent the centre drill trying to wander into the hole and pulling the holesaw off centre. File a groove to allow the centre drill somewhere to go(see below), then use a method already mentioned to guide the new hole on target.

OOI, how come we can't see through the centre hole?

 

[big-all]

if its a one off then consider a half inch drill centre punched in a triangular pattern then nibble and file to shape
but as said a template and holesaw if many need doing