Enlarging 54 mm holes to 100mm - Nowhere for pilot bit!

[David P]

I installed decking lights a while ago, and they are crap! I can get a refund ok so thats fine. However, new ones I have seen are 100mm and I want them in the same places as the crap 54mm ones.

Drilling the deck was hard as its some sort of hardwood. Drilling the original holes was OK, but the core drill sometimes jammed in the holes.

The new lights are completely recessed, i.e. they sit inside the hole, no collar to hide a ragged jigsaw cut.

How can I get an accurate 100mm hole wtith a core bit not the holes have no-where to put the pilot hole accuratly?

[Grunff]

You blank each hole with a piece of ply from behind (assuming you have access to the underside).

[Christian McArdle]

Either put some solid material for the pilot to go through, such as a bit of spare MDF, or just hold the drill nice and steady, until it develops a rut to hold itself!

Christian.

P.S. The second technique might require some practice... (and should also have a safety clutch/torque control in the drill)

P.S.2 You should be using a hole cutter designed for wood, not a core bit, which is designed for masonry.

[David P]

I wasnt sure if the term was hole-saw or core bit. I think I used the right one.

As I do have access to the underside, of course it makes sense just to fix something in place there. Thanks for that.

Any recomendations on an affordable elctric drill with torque/clutch?

[Christian McArdle]

Only the cheapest twist drills don't have torque control. Just remember to set it about a third of the way round to protect your wrists if the bit snags.

Christian.

[David P]

I wasnt sure if it was a hole saw or a core bit!

Of course it makes sense to attach something underneath (have to lift the boards for the wires anyway).

And yes, a cluthch/torque drill would be good too. Any recommendations for a sensible priced one?

[fred]

In article , David P writes

No need to attach it to the bottom, a metal plate fixed to the top with a couple of screws and a hole in the middle to guide will do the job. Alternatively the hole saw might be deep enough for you to do it with thin ply on top. Needless to say, the plate will need to be smaller than the new hole saw ;-).

My last one with this was a 750 watt Bosch (sorry no part no. but one of the green ones) and it did the job for me, cost about 60quid. Current one doesn't have it & I miss it. The torque control was a yellow knob on top.

[Jon Telfer]

A router plus circle jig + guide bush would do that to a very neat finish. May be overkill if you didn't have plans to use the kit for other jobs though.

Jon

[David P]

I do have a basic Bosch router. TBH, never really used it as there were no instructions.

I need a 100mm hole, and hole saws seem to be 101 (not good enough).

So how would I make or sort out a circle jig ( I know that sounds dumb!)

[Rob Morley]

screw the router to a bit of thin ply plunge the bit through the ply unscrew router measure your radius to the edge of the hole thus made drill a hole at the required distance screw to workpiece reattach router cut a perfect circle

You'd need to screw a bit of wood under the existing hole in your decking to give you something to screw the pivot to. It's also a good idea, once you've determined the pivot point, to enlarge the hole for the router bit so it doesn't get clogged.