I ran into a mysterious drilling problem and am trying to find an
My wife got a greenhouse kit from Harbor Freight. Good kit but not too
sturdy; the doors and some panels blew off in the first windstorm. One of
the things I tried to do to strengthen it was to attach a 6-foot angle iron
to the light aluminum door header, which had been torn by the storm.
I bought a 1/8 inch thick angle iron at Home Depot, 3/4 inch deep on each
side. The first thing I had to do was to drill four 1/2 inch holes about
evenly spaced over the bar so that the iron would fit over the four nuts
protruding from the existing frame. This was done easily, not binding or
overheating of the metal in the drilling process. I used my hand drill for
Next I drilled six 5/16 inch holes in the thin aluminum header; again no
problem. I then marked the corresponding spots on the angle iron, for where
the bolts would go through. These holes would be on the same face of the
angle iron where the 1/2 inch holes were drilled earlier. The first hole, at
the right end, was easy. The second one, at the left end, just wouldn't go
through. No problem, I got another 5/16 drill bit, same type of titanium
coated bit with pilot hole maker; that one wouldn't go either.
That evening, I went to Home Depot and got two 5/16 inch cobalt drill bits.
This morning, I tried one in the hand drill and it wouldn't go through the
iron. Just made a dimple in the iron and stopped cutting. I took the angle
iron into the shop and put it on the drill press with the second cobalt
drill bit. It wouldn't drill through either, just made a slight depression
and started overheating, turning the metal red it the drilling area. I tried
drilling all along the bar but got the same results everywhere I tried. So
I gave up on that angle iron and will get another or try an aluminum bar or
The thing I don't understand is why this iron suddenly became too tough to
drill. When I drilled the original five holes, there was no overheating
which might have tempered or crystallized the bar, especially not the entire
6 foot length of it. The original five were spaced out over the entire
length, so it wouldn't be a case of localized hardening of the steel. And
since I tried four drill bits of two different types, I can't blame a dull
bit. Any ideas on what just happened?