I use disc cutters all the time.
I don’t know exactly what you are using. I have three sets, which I
got through Contenti: a “small” set that has seven punches from 1/8
to 1/2 inches in diameter, a “larger” set with five punches from 1/2
to 1 inch in diameter, and a set of “large diameter” with two
punches - 1 and 1/2 and 1 and 5/8. The first two sets are good to 18
gauge and the large diameter set is good to 12 gauge, but they say
needs to be used with a press. I use it successfully with a vise on
thinner metals, 22 gauge and thinner. Might work in a vise with
somewhat thicker sheet, but have not tried that yet.
Here’s my experience with what I am using (and if it is not what you
are using may not be relevant): Work on a sturdy surface. Put the
metal between the two halves (upper and lower) of the thingy (some
high tech jargon there) with the holes. Close upper half down
firmly. Place punch widest end (cutting end) down into desired hole.
Use a big enough hammer to give your strike some weight (of course
take into consideration the size of the punch). Strike top of punch
firmly several times, or until the punch drops down through the hole
with the disc beneath it. Sometimes I get it on the first strike,
especially with small punches and thinner sheet, but thicker/bigger
and it takes me two or three, being a relative weakling.
It’s hard to envision what you are doing incorrectly from your post.
Perhaps you could explain more fully. It should be easy. I love
mine. They save me a lot of sawing and with my physical limitations
I am always looking for ways to save myself from unnecessary
repetitive movements. Or rather, save myself for those I really need