Drilling on a curve?

[Pete Zahut]

I've got a couple of wall lights for use in the bedroom. They're actually meant to be permanently wired but I need to add flex to them so that I can plug them into a standard 13A socket. There's a picture here

and, although these are not the actual fittings I've got, this illustrates the problem very well.

The bottom of the fitting is curved and I need to drill a hole to take a rubber grommet that will then allow an entry for some black 3-core 0.5mm flex. I've never tried to drill on a curve before - any particular techniques to it?

TIA

[Toby]

Not really in my experience - Assuming the material is metal, like the one you linked to, to avoid the drill bit wandering, you would be best off using a centre punch to mark where you want the hole first.

[Peter Scott]

Make sure the fitting is well held, ideally with something solid behind the thin metal. Make a decent centre punch dent and start with a small drill that is good and sharp. Then use larger drills. Better still use a tapered reamer to open up the starter hole.

won't leave ragged edges.

Can you drill from the inside? If you wander at first it won't show.

Peter Scott

[John Rumm]

You would need to place the metal over something to use as an anvil, and then centre punch where you want to start drilling. Failing that, a U shaped notch would probably do as well - couple of snips with string side cutters, wiggle the tab created until it fatigues and falls off, then file to final shape.

The other option would be to make up a decorative wood "platform" for the lamp to sit on, and have the cable exit throug that.

[Peter Scott]

lamp to sit on, and have the cable exit throug that.

I was going to suggest a slot, but in my experience wiggling to fatigue the tab is likely to distort the metal that its attached to.

Peter Scott

[ARWadsworth]

Angle Grinder.

[Peter Scott]

Thermit???

[John Rumm]

For once the canonical uk.d-i-y answer is actually pretty good ;-) Clamp firmly, and take little nibbles to avoid overheating the metal.

[Pete Zahut]

Thanks for all the quick answers guys, that's brilliant :-)

[PeterC]

After marking with a punch, I've always started on a curve with a wheel-brace (if it's possible to secure the part being drilled) and 'rocked' the wheel. The bit won't wander as it does only about ½ - 1 turn.

[Dave]

For once I agree, but mark where you want the hole to be and very gently use the angle grinder to make a small light cross on the curve. This will act as a scribed mark for the drill to bite. Start off with the smallest twist drill you have, to avoid wandering of the tip.

Good luck.

Dave

[Tinkerer]

I did very similar once. I found it easier to drill from the inside out. It meant the drill going into the hole at a slight angle but I placed a bit of scrap metal between the drill tip and inner face to prevent it moving forward and started with a small drill. Once the hole was started this piece of scrap was removed. The curve had no effect because the drill would have had to climb up. Any imperfections in the shape of the hole were hidden by the grommet. Of course you might have to remove the switch temporarily to make space to work.