"Ryan" wrote in message news:
Short of using a jig saw (which I am not
convinced would work too well)
I have done stuff like that with a drill and file, a pain.
a jigsaw is fine on metal, though even on alluminium i use proper
hacksaw blades, the things they sell for metal are overpriced and the
few I have been given were crap - still Sandvik don't know how to make
a hacksaw blade anyway;-).
Yes i modified the jigsaw so i don't have to grind a bayonet on the
blades.

I chop out bit's for motor bikes with a jigsaw and 1/2"
plate is no problem, i cut blanks like your on about and get circles
within a
64th without any problem.
The way I cut a hole like that is.
Scribe the circle and drill some holes -equally spaced about the
inside of the scrap bit- big enough to get the saw blade through, four
or five holes will be enough.
Criss cross the waste with the saw till some big bits fall out.
Then cut almost to the circumferance[scribed line], cutting at an
angle to the radius and keep making cuts like this all the way around
the inside of the circle, cutting at an angle to the radius.
The plate should look like a cross between a negative of a circular
saw blade and an odd comb at this stage.
Then repeat the above bit, cutting at the opposite angle to the
radius, so the bits fall out and your left with a round hole with
little bit's to file or bore out.
It's very simple and with a jig saw you can get very close to a
circle, or any other shape you want. the number of cut's you make 'at
an angle' will determine how long it takes, go around the circle once
making say eight cut's, this will get the big pieces out and then
repeat with the cuts closer to get closer to a round hole.

The only thing to watch out for is the foot of the jigsaw marring the
surface,
it isn't to bad if you make sure you don't get swarf under the foot.
They cut much better at slowish speeds, don't push to hard the hss
blade will chop through the cheapo rear blade support. cut dry, wet
lubricant will just make a mess.

When you want to make a straight cut try a woodworkers circular saw
if you haven't used one on alli you will be suprized how good they
are...

--
richard