Drill Bits

[luvrbus]

Isn't the channel on a H series Prevost T1 or M4 steel ? drill bits come in all different angles so you may need to experiment a little with different bits you get the right angle on the bit for the type steel you are drilling a bit will last a long time
Fwiw most of the cheaper bits sharping doesn't do much good as the harden part is lost if they get hot 

good luck

[belfert]

I actually had real good luck using cordless drills to drill my holes.  I used a corded Dewalt drill some of the time, but it didn't work as well.

I was drilling into regular steel and found that high speeds worked the best.  I thought steel should be drilled at low speed, but it took forever.  I experimented with higher speeds and it drilled a lot faster and didn't seem to hurt the bits.

[Jerry32]

You are right about   high speed as that seems to work better. I have a Milwaukee hole shooter that turns fast and had to drill some 1/2" holes under the bus and they went through very well .  Jerry

[bevans6]

Mild steel wants around 100 feet per second tool speed, using an plain HSS tool.  For a 1/2" that is around 750 rpm.  For a 3/8" hole, around 1,000 rpm.  That assumes correct feed as well, and appropriate coolant.  Half that is probably fine for a hand held drill.  You need more pressure than a hand held drill can provide for the correct feed.

If I was drilling those holes, and I wanted clean round holes so I could plug them after, I would drill pilot holes with a 1/4" or a 3/16 drill, and use a Unibit step drill to bring it to size.  I've got a couple of Unibits that I've had for 20 years and they still drill well in mild steel sheet.  Only good up to around 16 gauge though, but they drill a round, smooth hole.  A two flute drill tends to drill triangular three lobe holes in sheet steel.

Brian