Use layout dye, mark and center punch, drill 4 corner holes, use a saber
saw with a metal cutting blade and SLOW speed, clean up with a big file.
Should take about 30 minutes. It helps to file some squaring notches in
the holes with a 3 corener file to get the blade started square. Ugly
but it has been done a million times.

Ignoramus27829 wrote:

I have this compressor

http://igor.chudov.com/projects/CurtisCompressor/

and this hourmeter

http://igor.chudov.com/tmp/hourmeter.jpg


I would like to make a rectangular opening in the mounting base for
the motor and pump, so that the hour meter would be facing the same
direction as the pressure gauge, and look nicely, like it was mounted
by the manufacturer. I would prefer that to making some stupid
little enclosure for this meter or mounting it in odd places.

For this, I would need to make about 3/4" by 1/5" (that's a guess)
opening in the mouting base, which looks to be like it is 3/16" mild
steel.

The question is, can this be done sensibly with, say, a jigsaw and
bimetal blades.

Another question is, can such a meter take some vibration. It is not
bad, as such, and I suppose that these Stewart-Warner hourmeters are
made to withstand some vibration.

i

If you don't have a sabre saw, or the hole is small, awkward shaped
etc., you could try this. Mark out the cut-out using a scriber. Then
take a small twist drill (1/8" should be good) and use a drill press to
make a series of holes which almost touch. The outer edges of the
drilled holes should be a small distance (maybe 1/32") inside the
scribed cut-out. Now take a punch and hammer, grip the plate in a vice
and pound the cut-out until it drops out. If you did it right the
cut-out comes free without distorting the surrounding metal. Then just
use an appropriate shape and size of file to clean up. This approach is
hard work, but perhaps not quite as hard as you would imagine. With
care and patience it can give a neat result. The more careful and
patient you are the neater the hole you get. Make sure you don't make
the hole too big by filing carelessly and then trying to correct the
screwed up shape of the hole. I've used this approach several times and
it works well for me.

Best wishes,

Chris