Holesaws and arbours

Can you get something like a piece of wood in the box section, if so line it up with the hole mark the centre and simply use your 30mm saw with its matching arbour with its centre drill.

Richard

Not got much room, I might be able to get a bit of broom handle, reduce it to 20mm (if only I had a lathe) and insert it into one side's existing hole, while drilling from the other side ... not straightforward might have to enlist the neighbour to hold the broom handle.

Annoyingly I know have a 2nd 20mm holesaw, that's a different thread, maybe it fits a different arbour that does have the flats, but it's gone off and hid somewhere in the last hour ...

Found it, but nope.

Is this the magic bullet I need?

How about using a stepped drill

I can only find my narrow one, prices in shops for a wide one seemed expensive, did consider an amazon cheapie, but have ordered that Starret adapter.

Any chance of using one of these?

Attach a piece of wood to the far side, use the 20mm saw and pilot to drill the centre in the wood, swap to the 30mm saw.

It would work, but I'm reluctant to spend £40 which will then guarantee that I find my old one straight away ...

What's wrong with this simple, cheap solution?:

Pin some scrap wood to the side you want the 30mm hole.

From the other side use the 20mm hole saw so the arbour makes a pilot hole through the scrap wood.

Use that pilot hole to guide your 30mm hole saw (from the side you want to drill from).

Less than 1cm clearance that side ...

How do you propose to drill from that side? "I have a 20mm hole through some box section, I need to enlarge the hole to ~30mm on one side." It's hard to understand what you have in mind.

That starret reduction arbour does work, although it's not as universal as the description implied, out of about 6-7 arbours I have, it only suited one of them in combination with the 20mm and 32mm holesaws.

Thank you. Didn't know such an arbor existed. Thinking about it, this will only work with certain sizes. The smaller arbor will only take a holesaw up to 20mm thus if you already have a hole larger than 20mm the trick won't work.