Thread: Howto drill large hole?

Hi All;
I have to drill a few 5/8" holes in 1/8" steel.

There is something I'm missing in drilling large holes because the drill frequently chatters and makes the hole "triangle" shape.

I'm using a cheap Ryobi bench drill press. I start with a pilot hole 1/8", enlarge the pilot hole to 1/4", then drill 5/8".

I'm using oil to lubricate while drilling. Drill speed is on the slow side to get torque - 900 to 1250RMP. New 5/8" drill...

Any hints? I sure don't like making a mess of things...

Thanks, Norm

Norm,
is it clamped down hard on the table? Clamping down well should result in a round hole. If you still can't get it right then a step drill bit may be the answer.

Mick

PS just had a thought, if there is play in the quill then this might be contributing to the problem.

Hi Norm,

Try this, tear some heavy cotten rag into 1" wide strip x 4" long, fold in half and then in half again, you should now have a 1" square piece of material. Place over centre of 1/4" hole and drill through wad with 5/8" drill. Drop speed right down say 200 rpm

Best regards

Dennis

Dennis,
sounds interesting, what's the reason for this? I assume it's to stop the chattering which is generally responsible for the non-round holes.

Mick

Drill 1/8" pilot only, don't bother with 1/4". Make sure the 5/8 bit is sharpened correctly, with both cutting edges of even length and angle. Slow the drill down as slow as it goes. Might take a little longer to cut but at least the bit's not bouncing around all over the joint.

My first thought when you said triangle holes is that the bit is sharpened unevenly, but speed may be an issue as well.

Your pilot hole only needs to be slightly larger than the small flat in the centre of the tip of the 5/8 bit. Any bigger and you risk the bit biting.

As Mick says, clamp it down.

Dan

Mick,

Fill's in behind clearance angles on drill point and stops drill walking around and stabilizes the drill even more when the lands of drill reach material and start sizing hole.

Dennis

What cub3 says
The cutting edge needs to be in constant contact the full lenght of the cutting edge, but cause you are drilling 1/8 thick plate the tip is protruding thru the bottom before the full round is cut on the top causing the drill to cut quicker and start to wander because you have now lost your pilot hole for the drill to follow. By putting the cloth down first it slows the cutting action and cushions the bit to stop chattering and hopefully wandering.
Also helps to only put light but constant pressure on the bit as well. The plate must be clamped as secure as you can get it.

Hi Fly,
You could re-sharpen your 5/8" drill bit to cut sheetmetal. This is a bit awkward to explain, but basically you grind away about 95% of the cutting edge of the drill, this becomes clearance. You leave a point on the drill to act as a pilot much like a centre drill. As you grind away the cutting edge leave a little point at each extremity of the cutting edge. In effect you have a 3 pointed drill bit, the centre point slightly more proud than the 2 cutting tips. Clamp your workpeice to the drill table with a peice of timber for the drill to run into.Drill on slow speed and use a cutting oil or coolant such as soluble oil.If you find that you don't get through the 1/8" plate on the one side, then turn your plate over,use the location that the centre point has drilled and work back from the other side. Good Luck.
Regards,
Gary.

Thanks All, I'll try some of these suggestions but I think the main clue it that I was running my drill too fast. The lowest I can get is 600 RPM on the Ryobi. Hmmmm...

As with all suggestions, one has to apply them within the context of one's shop. I'm not sure, at this point, which will work but the cloth suggestion sure has my curiosity aroused...

Thanks, Norm

As Mick says a step drill is the go. They make them in imperial and metric but seeing you want to drill 5/8 it is exactly the same as 16mm.

Here is a link to a previous post that I made on drilling holes in thin metal.

http://www.woodworkforums.ubeaut.com...88&postcount=7

Slow is the go, 600 may be a bit too quick, , Drill the pilot hole then to the largest size you can under 5/8 then finish with the 5/8" drill, clamp the job well and feed it into the job SLOWLY,
Give yourself enough clearence so that you can change the smallest drill for the largest without moving the drill press table

Rgds

Go and buy or grind you own sheet metal drill they look the same as dowling bits for timber they have three points on them

Norm

If you make a practice of drilling holes larger than 1/2", particularly in relatively thin steel, you might to consider the superdrill. See below

http://www.practool.com/100101.php

Works very well, but the larger you go the slower you should be drilling. My press goes down to 190rpm from memory and that is more than fast enough for anything over 25mm. I have also used their drill to drill 2 1/2" holes in the end grain of white box.

You must clamp the work firmly but there is no chattering problem with this fly cutter syle.

I have no association with this company (for the cynical).

Regards
Paul

try using a hole saw run it slow and use cuuting compound

Originally Posted by bob the builder

try using a hole saw run it slow and use cuuting compound

I would think by now the job would be complete:confused:. If so fly1835, how did you get to do the task?. As it was mentioned that 600 rpm was the ssslllooowweesttt speed on his ped drill, that would be too fast for a hole saw to be correctly used, especially if several holes were to be drilled. Alternatively, you could use a cordless or electric drill that would give you the slower speeds but would be a pain if several holes were required.

As mentioned previously, a step drill would be the way to go.

Regards
David