On Fri, 01 Jun 2012 08:58:57 +1000, Jordan wrote:

On 6/1/2012 4:25 AM, Ed Huntress wrote:

Plus, the heat of friction introduced into the disk is distributed
*around* the entire disk, while the roughly equivalent heat of
friction in the work is concentrated at the spot you're cutting.



I've heard that, with aluminised corrugated sheets (I think that's what
we're talking about?), too much heat can damage the coating, to the
extent that its rust preventing action is compromised.
It's made me too nervous to use a friction cut, except for real
galvanised steel sheeting.

Not having done it, I don't know how much damage it does to the
coating. Keep in mind, though, that the zinc on galvanized steel melts
at a significantly lower temperature than aluminum -- several hundred
degrees F lower.

If you get steel hot enough to melt, any zinc on it is hot enough to
vaporize. That's not true with aluminum.

I suspect that any damage is confined to an area pretty close to the
cut. But that steel is now somewhat oxidized, and the coating is, too.
So any rust-proofing repair -- with zinc chromate paint, or
zinc-loaded epoxy -- isn't going to stick unless you clean it well.

--
Ed Huntress

Then, a steel circular saw blade mounted
backwards serves OK - something I learnt here.
Or as mentioned, friction cut an inch outside the finished line and trim
with hand snips.