Manual Drilling - Breaking Bits

MaverickNH

MaverickNH

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I was drilling the 2nd of five 2.5mm holes in in 7x16 LMS lathe bed to mount the rack, and broke off the bit as it punched through. I was using a piece of 1/4” square stock set on the ways shoulder to keep me from going too far, with the drill bit all the way into the battery-powered drill, but when it punched through, I must have lost true and - snap.

Any suggestions on how to do it better with a manual drill? No drill press handy… Ten new bits will arrive from Amazon tomorrow. Fortunately, I could push out the broken bit in the hole as I had flooded with Tap Magic while drilling.

BRET
 
MaverickNH said:
I was drilling the 2nd of five 2.5mm holes in in 7x16 LMS lathe bed to mount the rack, and broke off the bit as it punched through. I was using a piece of 1/4” square stock set on the ways shoulder to keep me from going too far, with the drill bit all the way into the battery-powered drill, but when it punched through, I must have lost true and - snap.

Any suggestions on how to do it better with a manual drill? No drill press handy… Ten new bits will arrive from Amazon tomorrow. Fortunately, I could push out the broken bit in the hole as I had flooded with Tap Magic while drilling.

BRET
Click to expand...
1. Invest in good bits and learn how to sharpen them.

2. Practice.

We’ve all broken drill bits, taps, etc. it’s one of the reasons pro shops have EDM machines at the ready. These things are called expendables for a reason. Don’t heft discouraged, just know it’s part of the process. You’ll do it less as you learn.

Oh, and get a drill press. Usually available cheap on Craigslist.

John
 
With experience, you will learn to recognize the sound/feel as the drill is about to break through. Reduce pressure when you do and baby it the last little bit. If not, the drill will punch through without removing the last bits of attached material and screw itself through instead of cutting out those bits. With larger bits the drill will just stall, on small ones the bit may break.
 
2.5mm is very small. you need high speed to cut with a smaller bit.
As Mr Whoopee says, ease off as you are poking through.
If you don't know when that is, mark your bit with painters tape or a sharpie so that you see when it's approaching.
Keep withdrawing your drill bit to clear chips, it will help prevent packing, and should it break, will lessen the chance that it is so packed you can't get it out.
 
I’ll get more practice tomorrow with new bits. As long as I don’t break a bit off before it holes through, I’ll be OK. The holes get tapped thereafter.

The holes are pretty close to the junction between the side of the bed and bottom of the ways, so not much room for a drill guide and the drill has to stick out a little more than an inch to clear the chuck. Clamping it up in a drill press would work nicely.

Maybe there’s a Black Friday drill press waiting for me!
 
MaverickNH said:
I’ll get more practice tomorrow with new bits. As long as I don’t break a bit off before it holes through, I’ll be OK. The holes get tapped thereafter.

The holes are pretty close to the junction between the side of the bed and bottom of the ways, so not much room for a drill guide and the drill has to stick out a little more than an inch to clear the chuck. Clamping it up in a drill press would work nicely.

Maybe there’s a Black Friday drill press waiting for me!
Click to expand...
pics would help
 
A 2.5mm drill is just shy of 1/16" inch which is as small as most people go. They are susceptible to bending and breaking, especially when drilling metal with a hand drill. Drilling metal requires more drill pressure which leads to breakage. Drilling cast iron castings can be especially tricky as there are often hard spots or voids within the casting.

When drilling with a small drill, watch the drill bit to avoid bending the drill. The nature of a hand drill puts the force off center which will naturally cause a bending moment. This can be reduced by using your other hand to apply force directly in line with the drill while the hand on the trigger is mostly controlling the motor.

Hand drills, especially the battery operated kind, are lacking in rpm which makes it difficult for drilling with small drills. The drill will tend to take a bigger chip which is more likely to cause a jam and breakage. One has to go easy and let the drill do its cutting-at its own pace.
 
Three mm is a small tap. You can expect to break a few of those, too. If you are going to use taps, you are going to break a few....
 
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