Cutting holes in galvanised steel

[teddysnips]

We've had all our plastic guttering and downpipes (rainwater goods, if you like) replaced with Lindab galvanised steel. Jolly nice it looks too, and apparently maintenance-free for a good long time.

However, there was a problem with the gutters overflowing so a representative from Lindab came to take a look, to make sure that the correct type had been fitted. Apparently the problem was because the builder had made the hole in the gutter above the "hopper" too small. Because the builder's now off-site I think I'll have a go.

The Lindab rep said that there are two ways of doing it - drilling a succession of small holes and then joining them up, or using tin snips to cut the hole.

Maybe the Incredible Hulk could cut through this stuff with tin snips, but I can't. I managed to drill round and then cut the joins between the holes with the tin snips but it was a long and painful job. The main pain is because the drill bit skitters about when starting the hole.

I don't really want to drill piddling little pilot holes, so do I have any other options that I haven't considered?

Sorry to go on at length.

Edward

[George]

Why did'nt you just wait till the people who fitted it came back? you paid for them to do a job and a satisfactory one.

anyway do have a dremmel drill or clone?

[keith_765]

Jig saw with a metal cutting blade ?

[meow2222]

Aviation tinsnips are geared, so easier to use than traditional british pattern ones.

To stop the bit sliding about, hold a nail where you want to drill and give it a tap with a hammer. The slight indentation stops the bit wandering.

However, if you cut galv you expose bare steel, and rusting will begin as soon as it rains.

NT

[John]

Now that you have cut it, it will rust as the galvanised coating has been damaged.

[Harry Bloomfield]

[e-mail] explained :

I understand the galv to some extent migrates to cover the cut edges [1], besides which the rusting will make very slow progress.

The effect is suggested to be better if the edge has been cut with a shearing action (tin snips) rather than the tearing action of a drill.

[The Natural Philosopher]

nibbler.

[Cicero]

=================================== If this is a case of enlarging an existing hole then a large round file would do the job. If you don't like manual work you could use a file bit (can't remember correct name) in your electric drill.

Cic.

[Peter Parry]

Not if you cut holes in it it won't - it will rust. Wonder if this is the system someone locally had fitted a few years ago which was eye wateringly shiny for a bit before producing lots of rust streaks down the walls?

[cerberus]

----- Original Message ----- From: "The Natural Philosopher" Newsgroups: uk.d-i-y Sent: Monday, August 20, 2007 1:02 PM Subject: Re: Cutting holes in galvanised steel

Use an off-cut of 'bendy plywood/hardboard' within the gutter (obviously covering the offending orifice)...& then drill through again! ???

[cerberus]

----- Original Message ----- From: "The Natural Philosopher" Newsgroups: uk.d-i-y Sent: Monday, August 20, 2007 1:02 PM Subject: Re: Cutting holes in galvanised steel

Use an off-cut of 'bendy plywood/hardboard' within the gutter (obviously covering the offending orifice)...& then drill through again using a 'hole saw'! ???

[teddysnips]

I can't afford aviation tinsnips just for this job (there are 24 holes to cut) The nail idea will do me very well. I spoke to Lindab about the gavl/rust - their website says "To provide long time rust proofing the steel is coated with 275g zinc per m2. The galvanised coating is naturally self-healing, any scratch or cut being automatically sealed by zinc ions which migrate to re-coat the uncovered steel". I can attest that the current holes - too small - which were cut some six weeks ago are all entirely rust free, and we've had a fair bit of rain up here in Gloucestershire.

Edward

[Cicero]

================================== Their brochure includes a 'touch-up' paint. It might be worth asking if that is for the kind of job you're contemplating. It might be for cosmetic purposes only.

Try a cheap pair of aviation tinsnips:

they don't work you won't have lost much.

Seriously, if the builder cut 24 holes too small I would be inclined to ask him to do the remedial work.

Cic.

[meow2222]

Most file bits I've seen have the serrations running the wrong way, and are thus so slow as to not be worth using. Do you know a supplier with serrations running along the bit rather than almost across?

NT

[meow2222]

=A31 from poundland

NT

[Cicero]

=================================== You might be right. The only one (for metal) I can see immediately in my box has spiral grooves. It might be a 'Wolfcraft' but *they* seem to be all for wood use if current stock in Machinemart is any guide.

In any case my original suggestion wouldn't be much use to the OP (too tedious) as he needs to expand 24 holes. I doubt if he will do much better with snips unless he is either a contortionist or removes the gutters to get good access.

If there's any access from below I think it would be easier to make a few short cuts in the perimeter of the existing holes and use a pair of pliers to create a funnel effect without cutting out any metal. It might be possible to do this from above (which is open) by using a suitable hammer to tap the perimeter downwards.

Cic.

[Pete C]

Hi,

If you have a fairly powerful 'Dremel' type rotary tool, you could try some PCB router bits (try Ebay).

These are used for routing glass fibre PCBs so should be able to handle thin steel sheet OK. Don't breath any zinc dust coming off, best wear a suitable mask.

If you want to help the zinc re-heal itself try coating the cut area with a little zinc rich primer or 'cold galvanizing spray'.

cheers, Pete.

[Pete C]

If the galvanizing is a decent thickness (ie hot dip not electoplate) it will plate over the adjacent bare steel in the presence of any water.

cheers, Pete.

[Chris Hodges]

My B+D ones aren't too bad, but for significant enlargement of holes in steel I wouldn't bother.

I'd centre punch (using a nail if I didn't have a centre punch), chain drill and finish off with a hacksaw blade - wrap one end in a lot of gaffa tape if you don't want to buy a proper handle.

I reckon in this situation it is quicker overall if you drill pilot holes: once round with e.g. 4mm on ~10mm centres, then once round with

10mm and there's only a little bit of finishing off to do with the saw. C

[Chris Hodges]

Or a cutoff wheel to fill in the gaps if you start by chain drilling.