Using Carbide Concrete Drill Bit on Metal

[alvinamorey]

Last evening I dug out an old gate that came with my rural property from my scrap pile. I planned to take this thing to the recycler several times but never did. Last evening I had a pony break his fence, and it was too late to buy anything. It turned out this old gate was made to fit the situation. The only problem is that one end did not have a hole drilled into it to run a wire thru it so I could wire it to the post. This homemade gate is made out of some sort of extremely hard angle iron. I'm thinking it might be old bed frame iron. I had to drill that 1/4" hole, and ran my battery powered drill battery dead and barely left an indent in the 1/8 inch thick steel. I got my plug in drill and I must have run it for 15 minutes and had only penetrated the steel about 1/32 of an inch. The bit looked sharp when I started, but was dull by that time. I got another used bit (of unknown quality). That one turned bright orange and the end of it melted. Frustrated, and not having another bit that size, I grabbed a

5/16 carbide tipped bit intended to drill concrete. In less than a minute I went thru the steel with little effort. I never thought that concrete bits worked on metals (steel / iron), but it worked great and did not show any dullness after drilling thru this extremely hard steel. Has anyone else used these bits on steel?

By the way, the gate worked great. Its only a temporary fix, but I'll keep this gate now. Now I know why farmers keep everything. One never knows when a piece of junk will come in handy.

Alvin

[DerbyDad03]

-- re: Its only a temporary fix

You left off the other half of that common home repair statement:

It's only temporary...unless it works.

[beecrofter]

Masonry bits are pretty damn good substitutions in the field provided that aren't rounded over from using them on actual masonry:) As for some of the real hard angle iron out there, much of it was re- rolled from slit up sections of railroad rail and the top and bottom being seperated from the web and rolled into angles. I used a piece to make a timber framers bruzz that takes a nice edge and holds it.

[Toller]

I have heard it doesn't work, but your experience obviously shows it does.

From your description you were drilling the steel dry? That isn't going to work.

[Chris Lewis]

According to Toller :

Carbide drills once they're used, have fairly rounded tips - they "cut" largely by bashing their way thru masonry. Which is why hammer drills make masonry drilling so much easier, but does almost nothing for wood or metal.

Mild steel drilling is with sharp-edged tools - ordinary twist drills with proper edges and relief angles. In a drill press with a good bit, you see these nice continuous swirls of metal swarf coming off the drill bit. A carbide tripped drill ain't sharp.

_However_, particularly with hardened steel (which can't really be "cut" at all with edged tools), you can cut with a fairly dull bit - by melting your way through. Problem being that the drill bit tip has to stay hard while the stuff you're drilling gets soft. With an ordinary drill bit, the tip just deforms and you don't get anywhere, and you feel like you're trying to push cooked spaghetti thru a cinder block.

Carbide has a considerably higher melting/softening point than steel. So, in some cases a carbide drill bit would work fine. If you use a lubricant or coolant, this won't work at all, because the work simply won't get hot enough.

There are special drill bits specifically designed to get hot and melt their way through hardened steel. Had a shop instructor demonstrate one once - piece of hardened steel could not be scratched by a file or a normal cutting tool. With the special bit in a hand drill, he got through it in seconds. Threw droplets of molten steel, sparks, and the hole glowed for a few minutes... Eye protection _definately_ advised.

[John McGaw]

minute I went thru the steel with little effort. I never thought that

snip...

Way back when, I had a company that serviced video games, pinball machines, and the like. Breaking into these when someone at the game room lost the keys was pretty easy and a standard drill bit would punch the locks on any of them in 15 seconds flat. The only real problem came when I had to break into a change machine somewhere and this invariably happened a couple of times a year with one customer or another. These machines had serious locks on them, usually made my Medeco IIRC, and these were made with hardened steel bars trough the bodies at odd angles and depths for the purpose of jamming and breaking drill bits. I found that it was wise to keep a half-dozen fresh masonry bits in the toolbox to open these. In the event that one did catch and snap the money involved was trivial. Even with the carbide bits it would still take

5-10 minutes to get the machine open but at least it was doable.