I have broken off 6 drill bits trying to drill out a bolt that broke off. I have managed to drill 1/8 of a inch in to the bolt. What type of drill bit is the best to drill a bolt out? I have also broken off 3 of those reverse thread drill bits trying to get it out. Help

Where have you been buying your bits? Also, where is the bolt you're trying to drill out? Is it some place on the car you could use a propane touch to heat cycle it? That can help break it loose.

As for the best type of bit, I prefer the left-handed (reverse) bits myself. Remember to drill slowly and don't apply too much pressure. If you aren't using a variable speed drill buy/borrow one.

For smallish bits. You want high speed and low feed. You also want coolant, and a steady, steady hand. Dive the bit back out a little, every 5 seconds or so, to help get out the chips. Keep the pressure on the bit perfectly centered. It's also essential that the bit be sharp. If it's not sharp, all you do is make heat.

Edited December 17, 201113 yr by cygnusx1

Don't use WD-40 as cutting fluid/coolant. Bacon grease works GREAT if you don't want to buy actual cutting fluid. Sharp bits are a very good suggestion. I've had shockingly good luck with Harbor Freight's Cobalt bits. Their other bits are crap IMO, but the cobalt ones are pretty amazingly good, and the price is so low that you don't have to freak out about losing or breaking one.

Yeah use cutting oil or similar for sure and take your time. Try to drill from vertical if possible and do not put any side forces on the bit when drilling.

When the frustration level exceeds the maximum allowable for your mind-set, consider welding it out.....

Try MSC industrial supply co.ATL. Ga.800-645-7270.You might try

either end mill bits or all carbide bits.Not cheap,but the good stuff.

I used them to drill out the bolt and broken easy out.Good luck.

For smallish bits. You want high speed and low feed. You also want coolant, and a steady, steady hand. Dive the bit back out a little, every 5 seconds or so, to help get out the chips. Keep the pressure on the bit perfectly centered. It's also essential that the bit be sharp. If it's not sharp, all you do is make heat.

My experience is different. I drill 9/64 pilot holes- stepping up to 17/64 and/or 21-23/64 holes- all day long in stainless steel pipe and steel I-beams. We have great success with pressure and low RPM. We never use any lubricants and a single bit will drill dozens of holes.

Maybe we're just lucky. We teach our helpers- "if it's curling, it's cutting" and is proof that material is being cleared fron the hole. In my opinion, high speeds overheat the bit and it loses it's temper. The relatively low volume of cutting/cooling fluid that you can apply by hand doesn't provide sufficient cooling to be of any use. There are "feed and speed" charts for various drilling applications, I'm just relating my experience, which I have used on automotive bolts, etc. with the same success.

I will add that Blue is correct regarding keeping the drill/ bit straight without exherting any side load. Using too much pressure and cocking the angle will snap bits all day long, regardless of speed or lubricant.

General chart not mentioning feed rate.

http://www.ollivier.nl/html/drillspeedchart.htm

Here is some good info:

http://store.curiousinventor.com/guides/drill_speed/

Edited December 20, 201113 yr by cygnusx1

i spent last weekend drilling out a few broken bolts on my z and found that a torch was my best friend

Recommended for all the Canucks:

$11

http://www.canadiantire.ca/AST/browse/6/Tools/PowerToolAccessories/DrillBitsSetsAccessories/PRD~0543650P/Mastercraft+100-piece+HSS+Drill+Bit+Set.jsp?locale=en