i need tips on drilling mild steel

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I have been using titanium drill bits to drill mild steel. Sometimes it goes like butter. sometimes my bit just melts down and i get nowhere. My recent project involves making a tubing bender jig for bending 3/4 inch square tube. I used 3/16 plate to start. I got a 2 inch trailer / ball dealio from menards. My plan is to use the trailer dealio to fix the plate to my trailer hitch / car for stability. I drilled three 3/8 inch holes in the trailer dealio and attached the plate. I found that drilling the holes in a 1/2 inch piece of trailer delio was no prob. two of the holes in the plate were fine, then the next one was not. So im trying to figure out if the 3/16 plate might be harder by the edge where it was sheared? What gives? Why do some holes drill fine and others cause the bit to melt/ degrade to an un-usable mess? What is the best way to have my bits perform perfectly all the time? Does the metal im drilling harden somehow in certain situations that makes it more difficult? I am a little baffled by this. Why can some holes go like butter and some just ruin the bit? Thanks for any tips you might offer up!
Reply:Several things affect drilling.  First off make sure that your bit is high speed steel.  Many are coated with titanium oxides to help keep them sharp but it is really not that important.  They should however be marked HSS.   A sharp HSS bit can go dull if your drill bit is turning too fast.  The chips should not turn blue from heat.  If they do the drill bit will quickly go dull.  If you are just drilling with a hand held electric drill keep firm pressure and occasionally dip it in a can of water beside you.  Soluble cutting fluid is ideal but sometimes people do not have.  The chips coming off should not be any hotter than when they turn brown from the heat of drilling.  Drill bits often go dull and people continue to use them.  At that point the end will just rub and produce more heat until it melts and is ruined.  Some plates are softer than others.  The main thing is to keep firm pressure when you are drilling by hand.  You should see little chips curling off the end and coming out the hole.  If the end of the drill rubs it wears out faster than when it is cutting.   Generally the smaller the drill bit the faster it has to turn.  a very crude formula is 4 X CS /diameter = rpm    For mild steel the Cutting Speed is 100 feet per minute  and in the formula you use the diameter in inches.  4 X 100 divided by 3/8 =  400/.375 = 1066 rpm   This is the Maximum speed allowed.
Reply:Thanks lotech!
Reply:Originally Posted by [email protected] have been using titanium drill bits to drill mild steel. Sometimes it goes like butter. sometimes my bit just melts down and i get nowhere. !
Reply:Difficulty drilling close to a edge usually happens due to work hardening caused by heat from a abrasive saw or torch. Try using a cobalt bit they take heat a little better though they dont take binding in a hole. If your bit gets dulled ie you punch through and hit the floor and you try to drill the bit spinng and no cutting will harden the steel once this happens drilling become difficult even with a drill pressMillermatic 252millermatic 175miller 300 Thunderboltlincoln ranger 250smith torcheslots of bfh'sIf it dont fit get a bigger hammer
Reply:I will say, my practice at sharpening TIG tungstens gave me enough confidence to easily sharpen 1/8" drill bits by hand.  You will have to have a drill bit gauge, but not a big deal.  Pay attention to drill speed.  If you are using a drill press, ensure the work is carefully clamped.  --zip
Reply:Um, no, speed on a 1/4" bit should be ~1100 rpm or so