Cutting hole in steel sheet

[JohnD]

I need to cut a 105mm round hole in the back of a cooker hood.

(This is because the maker, who use to provide a top hole and a back hole to suit the whim of the householder, has discontinued the back hole in the one I want, and the duct in the kitchen wall means I would have to mount the hood too low if I used an elbow out of the top).

I have in mind something like the hole saw I use for cutting pipe-holes in kitchen cabinets, but it is rather a large hole, and in thin steel sheet, which I am not used to.

I have got a Dremel-like tool I could use to smooth the edges.

Any suggs? Tin opener? Hacksaw?

 

[Burnerman]

Personally I'd try chain drilling, I think, after first scribing the hole with spring dividers......maybe using a 3mm jobber drill or similar. You could then finish off with a file or your Dremel.
John

 

[rsgaz]

Could you clamp/screw/bolt a piece of wood either side of it? If so then just use a jigsaw. If the material is as thin as you make it sound, then a jigsaw will be no good at all alone. Similar problem with a holesaw for very thin stuff, it'll just rattle, vibrate, not cut properly, snag and annoy the heck out of you.

A hand nibbler perhaps?

Gaz

 

[JohnD]

I've known hand-held HSS drills polish the surface of metal without cutting into it. Would punching it first fix that?

I have got a small drill press but I don't think I could clamp the hood under it.

 

[Burnerman]

As the tip of an HSS drill is actually flat, a centre punch mark makes starting the hole much easier.
Stainless can be a bit tougher than mild steel, but a good drill will go through without any bother.
Best if you can support the material with timber as you drill, of course and a spray of WD 40 helps too.
John

 

[joe-90]

Make sure the thing still works if you cut a back hole. Most I've fitted lately don't.