[VAC] Re: water heater done

["Dr. Gerald N. Johnson, electrical engineer" <geraldj@xxxxxxxx>]

To make a hole drilling jig, get a piece of pegboard. Screw on a strip
of wood or metal a suitable distance from a row of holes to act as a
stop for the sheet being drilled. Then make a bushing that is the
diameter of the pegboard hole with a hole in its center the size of the
drill. Drop bushing in pegboard hole, drill through the bushing. Move
bushing to the next hole. Pegboard material comes in at least a couple
sizes of holes and spacings.

Me, I'd reach for my milling machine and turn the table crank ten turns
between holes..

Using a jig will make cleaner hole alignment than marking and drilling.
One can get decent spacing along a line with a good set of dividers.
DON'T scribe a line though, it will always show and makes a stress
concentration for the aluminum sheet to break on the line. If I don't
need quite such perfect alignment, I'd mark and center punch the hole
locations and punch the holes with my Whitney Jr. No 5 hand punch, which
did come with a spacing shoe that I've not used in the past 35 year. The
punches have a point so they will fit into good center punch marks. The
beauties of the hole punch are that there's no burrs around the hole
(which are a standard problem with drilling except in 2024 and 6061
alloys) and no wandering away from the punch mark. With a lot of
practice I can often set that point on penciled cross hairs. I can also
move a hole over 1/3 diameter when I messed up.

A counter sink turned slowly is one effective method of removing the
burrs from drilling, also a larger drill bit. I often use something like
a 1/2" or 3/4" drill turning it by hand to remove burrs. There are also
special deburring tools that work well too.

I agree that a film of Vulkem on the back to the patch would be a good
idea. Not so much that it holds the sheets apart, not so little that it
doesn't squeeze out as you push the sheets together and the pop rivets
complete that pull.

Gerald J.