Making hole bigger

[howy1]

Have any of you got a way of enlarging a 20mm hole in eight sheet metal up to a 28mm , as the hole is already there you cant centre the drill of the hole saw , dont really want to file .
Thanks Howy .

 

[Burnerman]

Consider chain drilling 3mm holes up to the diameter needed, and then finish with a half round file.
John

 

[Nozzle]

It's tool abuse, but what I found recently was you can thread a spade bit through the hole, connect it to your drill then pull the spade bit through the hole and enlarge it using the should of the drill. It's not very good at self-centring and I think it might have even worked better with the drill in reverse. It worked okay on wood, steel might not be so good... Like I say it's tool abuse but you only need the job doing once..

or a press (but centring it is also not going to happen)

Or a step drill, but one that size is £££

Nozzle

 

[Tigercubrider]

Can you clamp a fresh bit of wood or metal to the inside and cut through both?

 

[howy1]

Thanks all , i rather like the idea of clamping and cutting through both , someone i chatterd to somehow modified a holesaw so that you had two saws one for exsisting hole to line up and the larger for new hole , i have yet to figure that though . Howy

 

[SammyInnit]

http://www.screwfix.com/p/erbauer-spiral-flute-step-drill-bit-6-30mm/7877d

They also do 6-36mm which I have. They last really well.

You can get some dirt cheap but I don't think they go as big as these do.

 

[howy1]

Sammy , never seen one of those looks just the job cheers Howy .

 

[SammyInnit]

Sammy , never seen one of those looks just the job cheers Howy .

They're a bit pricy I'd have said but they last really well and come in for all sorts.

 

[bernardgreen]

A Q-Max hole punch such as this

https://www.rapidonline.com/q-max-qma275m-q-max-sheet-metal-hole-punch-27-5mm-86-5316

which is 27.5mm diameter. Rapid are out of stock but there will be many other stockists

 

[Burnerman]

Do these things actually go through 4mm material? I thought they were for much lighter stuff?
John

 

[bernardgreen]

Circular sheet metal punch, 27.5mm point size, round shank type, punching holes in sheet metal up to 16 gauge mild steel, punching operation is performed by simply assembling the punch into a pilot hole and tightening with an Allen key, no electrical or compressed air supply is required,

16 gauge is approx 1.6 mm, I can recall cutting 3 mm thick aluminium ( or alloy ) with ease.

Probably would struggle with 4 mm material

 

[rsgaz]

i have yet to figure that though

Gaz

 

[howy1]

Gaz , what can i say the ultimate of what i am looking for , just got to source it .
Howy .

 

[rsgaz]

Check your existing holesaw set first. With the 28mm holesaw threaded on fully to the small arbor, is there just about enough thread poking out on the inside to be able to thread the 20mm holesaw on with it?

Gaz

 

[lostinthelight]

If you have a hole saw of the correct size, first bore a hole through a piece of chipboard , then remove the centre pilot drill.
Position the hole in the board centrally over the hole to be enlarged and hold in place by whatever means is suitable , enter the holesaw through the chipboard and cut the sheet underneath.
The side of the hole the chipboar stops the saw wandering.
litl