So I bought this little trailer... http://forum.mopar1973man.com/threads/5385-Bought-a-trailer-Hope-this-wasn-t-a-mistake I'm determined to fix it so I won't have to fix it again. So I am going to run all the wiring in protective plastic tubing... Naturally, the holes through the angle iron frame are not big enough. MamaMia! This trailer is built of the toughest steel I've seen. I managed to enlarge the existing wire holes... one step at a time through my drill-dex, slow turning 1/2" drill and cutting oil. Now I'm trying to drill holes to tap to mount my cushioned clamps (tap drill for 1/4-20). If I could get a pilot hole, I could probably enlarge it. I've been using my old HHS drill-dex, and a new Home Store set... The angle iron is just dulling the drills in a single hole. What kind of drill bit do I need?

Here's a link for you that might help. I use drill bits that were tungsten carbide. LOL! That's why I have my Drill Doctor on my work truck and in the shop. http://www.wlfuller.com/html/drills_for_hardened_steel.html

Find a way to push harder. Get a good bit from fastenal or something. Go slow and push hard and use cutting oil. I mean 200RPM slow. The longer it takes the duller it is going to get so push harder but go slow as heat kills the bits too. Cutting oil helps. I think you know all this. I have drilled at least 20 holes in an I beam 3/8" thick with the same bit for tapping 1/4-20 and I did it all on the same bit and it was just like new at the end. I went really slow (maybe 200RPM) and used cutting oil and had the drill against my chest and arms wrapped around the I beam and pushed as hard as I could. You want to be going the right speed and have enough pressure to have it spiral out a constant chip on both flutes. This takes a ton of pressure when you do it with a cordless drill, I had purple bruises on my chest to prove it But my bit was still good hahaha. It was even a cheap piece of crap one so it's not like you have to have the best bit out there. I wouldn't think they would use something much harder than mild steel, I mean it's just a trailer. If it was stainless then I could understand the issue. Push harder!

We drill alot of holes in stainless building restaraunts. Most of it only 16 or 18 gauge. I watch guys burn up bits spinning them fast. Slow rpm, like ISX says, and alot of pressure and i can drill alot of holes with a bit and use it again later. I know you are not dealing with SS but it is worth a shot.

I was not impressed with Titanium coated drills in the past. So I checked around & the best deal locally was a 13 drill set (14 piece includes the case) Ridgid brand cobalt drills at Home Depot foe $25. If I can punch the first center hole, I can open it up.

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The hole I'd tried & failed to drill... tried 1/8" cobalt + cutting oil. I had to push a little but once it bit, it went right through. I think it might have work hardened from my previous attempts. The other holes, it sailed right through. Enlarging the holes, I actually had to hold the drill up because it tended to catch & slip breaking through. Very happy!

I've been drilling lots of holes & I'm in LOVE with cobalt drill bits. Today I drilled & tapped holes to secure lanyards for the hitch pins (coupler & tilt bed). Fussy? OCD... probably... but everyone who uses the other trailer which has a similar treatment likes what I did as everything falls naturally to hand.