Drilling 1/2" holes in 1/4" HRS plate

[ACHiPo]

Feeling like I'm making this harder than it needs to be, but it's taken me 2 hours to drill 4 1/2" holes and 8 3/8" holes in 1/4" plate (actually 24"-long angle).

I center-punched the locations, pilot-drilled using Bosch TiN coated drills (3/16" until it broke, then 7/32). The 3/8" holes weren't too bad using my 18V cordless drill, but I needed to pull out my Bosch 1/2" corded drill for the 1/2" holes. The first one went fine, the second one grabbed the bit when it broke through and took me for a bit of a ride (now icing--externally and internally )

After deciding that I wanted to keep my thumb, wrist, and shoulder attached, I decided to move to the drill press. The Bosch 1/2" bit is dinged up a bit from the last break throught. Chucking it into the drill press I can see that it's running about 0.020" TIR, so I swapped in an old HSS 1/2" bit. With the angle firmly clamped, I was able to punch through a couple holes using oil and mineral spirits as lubricant, but the last two holes I drilled were more dramatic than I'd like--the drill seized several times, lots of smoke, etc.

I still have a few more of these to drill. What am I doing wrong?

TIA!

 

[jlsmithseven]

Maybe the drill bit is getting dull, did you try sharpening it after cutting a few holes? If you're pushing really hard, it's probably due to a dull drill bit. Try letting the drill bit cool down between holes as well, it's probably pretty hot...not sure if that would make a difference or not, just trying to give my experience and process.

Also, for the 1/2" holes, try drilling with a 3/8" drill bit first and then go in with the 1/2". It might just be that it's too much material at one time for ya! Good luck!

 

[Terrywerm]

It sounds like your bit might not be as sharp as it should be. A sharp bit consumes less power and will cut through a 1/4" plate like it's made of butter - with or without lubricant.

Your pilot holes are properly sized, so they should not be a problem. jlsmithseven mentioned that you could step up to a 3/8" hole before drilling the 1/2" hole. It's not a bad idea, but this puts more pressure on the outer ends of the cutting edges on the bit, making it more likely to chip the cutting edges if you apply too much pressure.

As you are drilling in the drill press, start easing up on the pressure as the bit starts to break through the bottom of the work. Keep a little bit of pressure on the bit as you start to drill through the bottom, but not too much. Too much pressure allows the bit to take too big of a bite as it breaks through, resulting in the problems you experienced. You might also want to place a piece of scrap material under your work piece when drilling so that the drill is still cutting into something other than a shrinking cross section of your work piece. This would also help to reduce the problem of jamming up as you break through.

 

[mikey]

I still have a few more of these to drill. What am I doing wrong?

I agree with Justin - a pilot hole will make this go much easier. You only need a drill the size of the web of your 1/2" drill and drill through. For both drills, I suggest slowing your speed to the slowest your drill press will go and use a high enough feed pressure to produce a continuous chip. Use coolant or cutting oil. When doing holes like this, I can usually do so with very little heat produced. The fact that your drills are hot is a tip off that your speed is too high.

I do agree with you that clamping the work down when drilling holes is the safest approach. Hope your hand gets better soon!

 

[RJSakowski]

It takes a bit of pressure to push a 1/2" drill bit through steel. The drill press is the way to go. You don't realize how much of a mechanical advantage the rack and pinon create but it can create a lot pf pressure. Use a sharp drill and keep the pressure up to the point of breaking through. As you feel it cutting faster, lighten up on the pressure to avoid the break-through grab.

If you go too slowly, the drill will skate over the work and quickly go dull.

 

[darkzero]

Just a thought to add. HR mill scale can be tough on HSS. It could be dulling your drills if the sacle hasn't been removed. Maybe try spot drilling with carbide to break through the scale & follow with the HSS drills.

 

[ACHiPo]

Wow once again amazed at the helpful folks here! Thank you! I have a nearly new set of cobalt drills and will try one tomorrow to finish the rest of the holes. Will definitely use the drill press, as that Bosch hand drill has more torque than is comfortable!

Will post updates tomorrow.

 

[wawoodman]

And clamp it to the drill press table.

DAMHIKT

 

[Chipper5783]

Forcing a dull drill will break down the land. When you sharpen the drill, you have to ensure the land is the full diameter of the bit, or else the bit will bind, heat up, require a lot of torque and generally give poor results.

Maybe you need to cut the bit back a good amount and repoint it?

 

[Glenn Brooks]

+1 for clamping, proper speeds and feeds, and a very sharp bit. Also drilling into scrap underneath your work will mitigate getting hung up on the bottom surface of the piece. After a sharp bit, maybe the scrap underneath is the best thing you can do to punch through your plates. Most home use drill presses don't have a large enuf motor to drill 1/2" holes in steel plate. So you will have to watch your feed and speeds closely at the end. Doesn't take much for the edge to grab the bit and stall it out with 1/2 HP or less...

If all else fails, I've found step drilling with several bit sizes helps immensely when drilling 1/2" and larger holes with my Delta 16 DP.

Glenn