Whats the right Drill Bit?

I am looking for the right drill bit for drilling out 9/16" holes that have been laser cut out. I need to enlarge them to 5/8". There is so many different drill bits I don't feel like wasting my money on buying numerous ones since I don't know what is best. I'll probably need to drill about 20 holes with it.

I read somewhere carbide tipped drill bits might be best... ?

 

In steel I presume ? What about a step bit .

 

x2

 

Yea it's steel. Brackets are too thick for a step bit.

 

Absent a step bit - I never get a neat hole when overdrilling a hole like that.

The bit always wobbles eccentrically creating a chewed out looking hole rather than a neat one.

Could you use a step bit half way from both sides?

Drilling a deep hole in steel - use a cobalt bit.

 

Can't drill from both sides? Thicker than 1/4"?

 

If you fasten the steel onto a wood backing board, and put a small pilot hole in the wood in the exact center of the existing 9/16 hole, this bit might work well for you:

http://www.mcmaster.com/#8914a55/=vrqtby

 

5/16" ?

 

Conversely, if you just clamp the piece tightly in a drill press, with the existing hole centered on the drill bit, you might get a neat hole with just a drill press and some cutting oil.

What I said above about overdrilling was when I was handholding the drill...

In that case -
http://www.mcmaster.com/#8939a12/=vrqw65

 

that's the "screw size" it's designed for countersinking a hole, and you'll notice the large diameter is .625 which = 5/8"

 

Clamp the pieces in a drill press like Steve said , centre the hole by chucking a 9/16" bit in the drill and use that to make sure you are aligned with the existing hole , change the bit to 5/8 and drill

 

Oh , I see that now , interesting bit

 

McMaster Carr has every interesting tool in the world

 

Not all of them , for that I go to Lee Valley

 

I would NOT have thought of that - and would have spent *way* too much time centering on the tapered cutting edges of the bit.

 

Ahhhh wood working tools. I can smell the sawdust alread.

 

That's a good idea, I'll keep that in mind when drilling!

Also, the brackets are basically shock and link brackets and you can't drill from both sides since it's so close to the other hole. They are 1/4" thick, some thicker. I just know when they laser cut the holes out on the brackets it hardens the steel around the hole and wears out drill bits pretty quickly.

 

It really depends on the laser used to cut it. The HAZ is going to be .001 to .004 on most lasers on the market today. you should be fine with Cobalt bits i use Viking industrial bits made by Norseman drill as long as your drilling the hole .010 larger or more you shouldn't have a problem keeping the cutting edge of the bit of the HAZ. Just drill at the right speed and use lots of cutting oil.

 

OK cool. Thanks!