Destroying Drill Bits

I have a bread box full of what I call random bits that are all hand sharpened. I generally use them
first for general work and save my good sets for posterity. To err on the slow side when drilling holes
is advantageous as less heat is generated. Watching the chips coming out is helpful too since one can
get helpful information as to what is going on inside the hole. I'm not beyond stopping the drill and
taking a close look at the geometry of the cutting edges and resharpening it for better results. Using
a speed chart to drill holes can actually work against a person as one is relying on it rather than paying
close attention to the drilling process.
 
Calandrod said:
Very helpful. Thanks. Should I always be able to touch the drill bit without getting burned? I read that somewhere but don’t know if it’s true.
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Being able to touch the bit after drilling is hard to say. In a perfect setup where you have constant coolant or oil flooding the area, then yes. If you are just putting a dab on as needed, then probably not. In my mind I don’t want the bit or workpiece getting hotter than 200-300 degrees. But the cooler you can keep it, the better results you will have.

I have tend to read the smoke coming out of the hole as a reference to when to add more cutting oil. As long as I see smoke/ steam I know that I have the minimum amount of coolant needed. If the smoke stops, then I know it’s too dry and needs to add more.

I know that if I use oil, then there is less chance of “welding “ the bit and workpiece together. Since I am also a welder, I realize how much an oily and dirty metal makes for a poor weld.

Touch the workpiece from time to time to get a feel for how hot the piece is getting. Be sure to raise the drill and there are no chips spinning before bringing your hand close to the bit though. If hot enough to be uncomfortable a 1/2” away from hole, let it cool back down before continuing.

As you gain experience, you will learn to know when you can push on, or need to stop.

I encourage you to try your hand at resharpening your used drills. If it’s dull and not cutting, you have nothing to loose except a bit of time at that point anyways. The drill is junk in that condition.

Get a new drill bit ( a bigger one is easier to see) and really look close at the tip to see the geometry of the cutting lips. Try to grind the dull bit in the same way. A bench grinder, or sander will probably be the easiest, but a hand held grinder, or even a dremel tool would work.

One trick I have just learned is sometimes hard to get a smooth grinding edge. I find that if I turn the grinder off, and wait for the wheel to slow down, I can get a nicer finish when the wheel is slowing down. I’m tempted to put a foot switch on the grinder so I can feather the power to achieve a slower speed. Or come up with a variable speed grinder.

I attribute the better finish due to the wheel imperfections in the surface. When it is running full speed, there are going to be slight highs and lows in the surface, and when you touch the part against the wheel, the high spot will hit your part away, but your hand pushing it back to the wheel will then hit the low spot harder, and this is how your wheel gets rough and unbalanced.

Use a very light touch, especially on the wheels you use to sharpen tools. Don’t push tool hard, and let the grinding wheel do the work.

Sorry for the long winded post. I guess the older I get, the more I like to talk to a captive audience.

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Slow rates, but cutting! Rubbing, but not cutting is a sure path to wear. Heat is the enemy. A hot bit edge will dull fast. You use a coolant to cool. You use a lubricant to try to prevent friction/heating. When you see two equal spirals from a two fluted bit you have the right cutting rate and a bit which has been well sharpened (hard to come by on small bits) so the two edges are matched. When you only see one spiral from two flutes, it is indicative of a poorly sharpened bit and maybe a poor feed rate.

Dave
 
Photos look dry.

Whatever oil is handy will work, fancy stuff better.

We get atf and other stuff from yard and estate sales, and we get decent results.

The bigger the drill, the slower the speed.

If speed is right, the chips will be hot, and drill not so much.

Peck. The hole, squirt oil, push bit to get cutting, the metel coming out brings out the oil, so you need to repeat often.

The oil helps control heat, the heat is in the chip, and if it is slipping past the cutter, the cuter stays a bit cooler.

This is Hobby, so take your time. Your tools will thank you.

We have used a hole saw in lathe to cut 3.5 inch diameter through 1.25 plate, 40 rpm, and the saw stayed cool.


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I recently had a case where I blew multiple different drill bits on a single workpiece. I tried altering the rpm, pressure etc. and discovered that it was my cutting fluid that just wasn’t up to the task.

Switched to Rocol RTD and ended up making multiple holes to the same workpiece without destroying any more bits.
 
cathead said:
Using
a speed chart to drill holes can actually work against a person as one is relying on it rather than paying
close attention to the drilling process.
Click to expand...
I think this is a really succinct and to the point remark about any work we do in the shop. Charts and tables are all great, and useful, for establishing a baseline but we still need to pay attention to what’s happening as it plays through. Is it cutting, is it drilling, does it look square, does the angle look right…. I think these are all so important and key to learning and understanding how and why the tools and machines do what they do.
 
Your bits are probably poor quality, and/or dull.
Use oil and slow spindle speed on steel, but feed the drill quickly so you get nice, long (razor sharp) chips.
Speed charts are often too fast. They are mainly for shops that need to pump out parts as fast as possible, replacing/sharpening the cutting tools frequently
 
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