is it possible I've heat-treated this angle iron?

[Tyler Davis]

I'm making up a mobile base with 1 1/4" angle iron. I use an angle grinder with metal cutoff wheel to buzz them down the length. Then I drilled the first set of holes in the corners. Now I'm trying to drill the second set of holes for the wheels, and I can't get through the metal. I'm using a benchtop drill press and leaning on it pretty good. I've tried a couple different drill bits (none of them particularly high quality, but the same ones I used to drill the first set of hole)

Is it possible that I've hardened the angle iron? It didn't get very hot - warm to the touch, but I could still hold it...

[Jamie Baalmann]

I doubt you heat treated it. I think that involves dunking in water in between the heatings. I'm pretty sure your bit is just dull. Angle iron has a way of destroying cheap bits pretty fast.

[Tom Veatch]

...Is it possible that I've hardened the angle iron? It didn't get very hot - warm to the touch, but I could still hold it...

Then, you didn't change the material hardness. It would've had to get much hotter than that (unless you've got asbestos hands;)).

I vote with Jamie, dull bits. Been there, done that, sharpen the bit (or use a new one) and it goes right through.

[Alan See]

One of my coworkers does a lot of metal work on his days off. He told me last year (after some angle iron I was cutting had RUINED a $200 steel cutoff blade) that angle stock made from scrap steel can vary wildly in hardness from point to point in the same piece. His theory is that its hardness depends on what type of scrap it was made from. If old car hoods and ball bearings all go in the same melting pot,The ball bearing steel will leave "hard spots" scattered through the steel. He says he always specifies an alloy when he orders steel just to protect his blades from these hard spots on recycled material. Of course, he could be wrong. Just passing on what I've heard from an "expert".

[Marcus Ward]

I think I'll call shenanigans on the 'different stuff in the same melting pot' theory. If it's hot enough to melt and roll, it's hot enough to destroy any temper and mix the ingredients well enough that you'd have consistent hardness. It's not like a pressboard sandwich.

[Chuck Saunders]

You certainly won't retain any temper and the ball bearings will melt and the mixture will become fairly homogeneous. However there are often hard spots in hot rolled steel, due to carbon or trash concentrations. Alot of it is in the surface. Good bits tend to cut much better than the increase in cost.

[Rick Hutcheson]

The one thing I have found is that old bed frame angle iron is very hard. Not sure why but what you are describing as ruining drill bits, my guess is you are useing old bed frames. A sharp bit and just plan on destroying the bit to get it drilled.

[Dave Anderson NH]

If you are using run of the mill inexpensive drill bits, you have been heat treating the steel, unfortunately it has been the steel of the drill bits. If you overheated the bits, you drew the temper out of them and they are now soft steel. When drilling in steel you should be using a relatively slow speed and light machine oil as a lubricant/coolant. Additionally, back the drill bit out fairly often to clear the chips which enhances cooling, and makes the bit work less hard. It's a cutting tool, don't force it. All that does is increase friction and hence heat things up faster. Let the bit do the work.

[Mike Parzych]

My first thought is that you may be running at too high a speed on the drill bit, and have work hardened the spot you're trying to drill. Best way to drill steel is low speed with a lubricant, and not a lot of pressure. It is possible to raise the hardness of steel in a small spot by drilling it too fast and dry.

If it's angle iron you bought at a BORG for instance, it was made to fall within certain composition parameters - the allowable range for each element that are in the steel (manganese, carbon, etc.) So it's pretty predictable in how it will react to machining.

"Trash" angle iron, or metals with no specific element parameters (like rebar) can vary widely. Too much of one element makes it act weird. Too much manganese for instance makes it get harder and harder the more you work it.

Now that I've rambled....just try a lower speed and lubricate it with oil - even motor oil will do.

[Tyler Davis]

OK, I will slow down the RPM's and use some bar and chain oil to lubricate.

I will also pick up a new drill bit - what brand / qualities should I be looking for in a "good" bit?

[Gary Click]

Interesting comment about Bed Rail Angles.

My "day job" is an engineer in the railroad trackwork industry (making switches). We sell new rail shorts and used rail to the rerolling industry that heats (without melting) and rerolls the rails into other shapes, one of which is bed rails.

Due to the high carbon content (.8%) of the rail steel the result is a very strong and somewhat hard piece of "angle iron". The hardness may vary but it is likely in the 32 to 38 Rockwell C range. Consider that the average cheap drill bit has .6% Carbon, is heat treated to Rc 55 and begins to temper or soften at 400F and you can see it is an unfair contest which the bed angle wins. Also due to the high carbon content welding a bed angle is very difficult and prone to crack. Another common material rerolled from rail is steel fence posts.

If you are like most Americans and laid down on a bed that used angles iron made from ASTM A36, the default minimum standard, you would find the center of the bed heading for the floor.

[Michael Weber]

What the others said. Also, it may help to predrill with a smaller diameter bit first rather than trying to hog it out at once.

[Chuck Saunders]

Thanks Gary, I learned something interesting today.

[Rob Luter]

It's very doubtful that you hardened the steel. Angle Iron is basically 1018 hot rolled steel. Hardness will be about 65 on a Rockwell "B" scale. Being hot rolled, the black scale on the exterior is a little harder, but not by much.

Like others that have commented, I think the issue has more to do with the speed of the drill. The larger the drill, the slower you need to go. Here's a drill speed chart you might find useful.

http://www.ibiblio.org/twa/info/drillSpeedChart.pdf

You need to go slow and make sure you use liberal amounts of lube. Home center drill bits are marginal for wood use and generally unsuitable for metal. The steel is pretty bad and you can burn the edge off the drill point in a heartbeat. I would bet they won't work in wood very well now either. Pick up some good bits at an industrial supply store and you'll be amazed at the difference. They're not real cheap but they work.

Bar and Chain oil should work pretty well, but it doesn't really need to be that heavy. Light machine oil will work just fine.

My $0.02 worth ($.01 after taxes and fees)

[David G Baker]

Tyler,
If the drilled hole is near a welded joint the metal could have been tempered during the welding process. Did you use cutting oil on the first cut? Cutting oil will speed up the drilling, help keep the metal cool and reduce the amount of force needed to drill the hole. Any chance that the metal is stainless? Stainless hardens very fast with very little heat.

[Tyler Davis]

update: I picked up a cobalt drill bit from Ace and used the cutting oil. It chewed right through the steel with no problems

I found it very difficult to sort through the misinformation about drill bits. There are a zillion different kinds at every store and most aren't labeled with their alloy type or hardness rating. Is there something I should be looking for to avoid buying more cheap ones? The individual cobalt bit was $9, so a set would be pretty expensive

thanks for the help

[Dave Anderson NH]

You're right Tyler, drill bits can be confusing when you add in all of the specialty types for working with metal. In spite of this, a medium priced set from one of the industrial supply houses like MSC, McMaster-Carr, Grainger, etc would offer a number of choices. Bits from cobalt steel, HSS (high speed steel), and any steel wtih a high molybdenum content wil wear well. Many places sell bits with a titanium nitride coating to increase wear resistance and it's normally a light yellowish color. In my experience, they are generally not worth the money. Expect to pay anywhere from $40-80 for a set ranging from 1/64" to 1/2" by 64ths. While this is not the best quality for this price range, it is more than adequate for almost any non-industrial use.