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You might be work hardening the steel, strange as it may seem, with mild steel.  If you begin drilling and (1) don't use enough pressure and (2) pause and restart drilling, that can lead to work hardening.

I had the same problem after annealing files to make patch knives.  Granted, files are not mild steel, but possibly the same thing is happening to you.  I tried drilling the holes and ruined two bits.  I posted a question about that here on IFI, and it appears that there is a stage of annealing called "sub-critical" annealing where you don't take the steel up in temperature to critical, but just below that.  Steve Sells posted the method, 



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B:  You did not state what kind of drill bits you are using.  I consider plain old twist drills suitable for wood and soft metal such as copper or bronze.  For steel I try to use tungsten or cobalt coated bits, they last a lot longer.  Also, I'd slow your drill down to as slow as possible.  I think the slowest belt combination on my drill press is around 400 rpm.  If you are not cutting properly I suggest stopping and annealing again. 

This is why many blacksmiths prefer to punch holes if they can.

"By hammer and hand all arts do stand."  

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Each size of drillbit has a "preferred" rpm for drilling steel.  Trying to match that helps as well as steady pressure.  Don't buy drillbits at bigbox stores or Wally world of HF if you need them to work well under tough conditions!  (I tend to get used industrial bits at fleamarkets and resharpen them.)

I once had to drill a hardened blade and bought a solid carbide drillbit for US$1 at the fleamarket, built a dam around it and used cutting fluid, used a large drill press and succeeded!

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You also did not say what kind of steel you are drilling. 

All the above plus Reanneal

To add to Thomas on harbour freight drill bits. Long ago I found a HF drill set that included numbers, letters, and fractionals. I couldn't say no because the cost for the whole set was less than a good comparable drill index by itself. I used each bit until they either broke or got dull and replaced them with quality bits. Now I've got great bits and a good index to put them in.  

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Drill bits are one of those areas where quality is worth every penny.  Skip the cheap chinese offerings. I had one set given to me that were so soft they unwound in use rather than breaking. If at all possible skip the home center bits as they are generally not much better, even if they have a good brand name.  Buy some quality bits from a machinists supply source--or online from similar.  USA made tend to be quite good--but there are some from offshore that are also great (Poland usually makes some good ones for example)  Once you use a top quality bit, it's darned clear why they are worth the money.

Down pressure is also key as already mentioned.  I don't know the bit size but you want enough pressure that you are generally continually producing curls (mild steel).  just for the sake of example, let's say you are running 600 rpm and want the chip load to be .0015 (small bit).  That'd mean you are drilling through 1.8" thick stock in one minute..and that chip load is small for most bits.  No hesitation.  Hard to get the proper down pressure on small diameter bits with a portable drill because one little twitch and you've busted the bit--which is why it's great you are using a drill press.  

Cobalt bits are better but plain should do the job you mention--if you've truly fully annealed the stock and it isn't full of carbide precipitation spots.  Fancy coatings rarely help on anything but commercial applications where the bits are pushed to the limits--the home center versions are mostly like fishing gear at the sporting goods store:  Designed to attract fishermen, not fish.

Anything over half inch should have a pilot hole first.  

Make sure the chuck runs true.  Some drill presses have chinese chucks which are waaay out.  Replace with a good brand like jacobs if using that style of chuck.  Sometimes the chuck taper in the spindle is bad and that's a hard fix--too complex to cover here.

Forgot to mention--never let the bit "rub" in the bottom of the hole, even for a second.  That quickly dulls any bit and even a great bit will magically become a crappy one on you.

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Welcome aboard Balistaplex, glad to have you. If you put your general location in the header you'll have a chance to hook up with members  close to you. I could show you how to drill holes in MAYBE 5 minutes, 10 if I included sharpening them on a grinder rather than a drill bit sharpener. I HIGHLY recommend a sharpener!

Quality bits are highly desirable but carbides are rarely a good choice, they tend to chatter and chip quickly. Carbides are a specialty bit so unless you're drilling metals requiring carbide tools use high speed or cobalt bits. 

If you have to er slow rotation speed is better. 

A tip I haven't seen mentioned is what to do if your bit jams in the hole, this is common when breaking through the far side of what you're drilling. WHEN you jam a bit do NOT lift the feed!! This invariable chips or rolls the edge of the bit! Turn the drill OFF and BACK THE BIT OUT BY TURNING THE CHUCK IN REVERSE, BY HAND. ;)

Preventing the bit jamming on break through is a matter of listening to the bit, with a little practice you'll hear the point begin to break through, ease up on the down pressure and baby it through. This takes practice as ALWAYS you do not want to let the bit rub. 

Drilling holes in metal REQUIRES you to listen to your drill and bit, your tools talk to you all the time, it's up to YOU to learn what they're saying. 

When you need to drill in steps, the next larger bit needs to be 2/3 larger in diameter. doing it in small increments is a B A D thing! You want as much of the cutting edges of the bit cutting as your drill can power without stalling. 

The Ti coated bits seem to be mostly to prevent cuttings from sticking in the flutes rather than providing a better cutting edge. I think marketers claim harder for a couple reasons: they don't know diddly and OR they don't think non galling is as marketable as harder, stays sharp longer on the TV.

That's also how oil helps cool bits: first it lubricates the edges and flutes so cuttings don't jam and gall as easily. Cutting more easily ad helping the cuttings slide up the bit helps keep the bit cooler. 

A last tip and I'll leave it to you. When you're drilling salvaged steel, take a wire brush to it first, the dust and dirt trapped in the rust will dull even carbides, quickly. Also after you anneal wire brush the scale off it's not only hard, it's brittle and can chip the bit's edges. I drill normalized leaf spring with HS drill bits without dulling them unduly. I rarely break bits say drilling out a broken bolt or roll pin. Broken or stuck roll pins are a serious PITA!.

Low speed, steady pressure, oil and pay attention to what your drill and bit is telling you.

Frosty The Lucky.

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Another use for numbers and lettered drill bits is when you really need a snug fit between say a hinge pin and barrel. If my hinge pin is 1/4", i will slightly undersize the barrel when i roll it hot. i don't role it around a mandrel, I roll it over the edge of the anvil. I then drift it hot with a 1\4" drift. it cools a "bit" undersized because the hole shrinks. Then i drill it with a numbered drill bit just under 1/4. Then set the pin cold, apply a little cutting/drilling oil and work the two leafs. Remove the pin, clean out the swarf, and you have a poormans machine fit hingepin and barrel that will be tighter than the best store bought hinges you can get. what the numbered bit does is remove any forging scale and any high spots that just seem to naturally happen inside the barrel. undersizeing the hole and setting the pin cold create a very tight compression but it wont actually permantly open up the barrel, forge welded or rolled.This gives enough pressure to remove a bit of material and any slight irregularities between pin and barrel are worked out.

I use plane ole water for cooling on holes 1/2" or so and smaller, a good cutting oil for larger holes. 

To add to Frosty above, the end of a drill bit is flat. This flat increases with drill size. So the pilot drill is determined by the size of the flat area on your final bit. For max efficiency, you want your pilot to be just slightly larger than the flat. Here a letter or numbered bit usually is a "bit" closer. I rarely drill more than a pilot hole and the final hole size.

Altho you may feel this with a contemporary post drill, a feature of my old post drill and my camelback is the sensitivity i have feeling the cut. I do not use the self feed on either. It doesn't take long to be able to feel when you are drilling with the proper pressure. I can feel it ehen it is about to bind and I can feel it when its not biting and drilling. When you find this sweetspot, your breakage approaches zero and your bits stay sharper far longer.


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On 9/14/2020 at 2:55 PM, Frosty said:

When you need to drill in steps, the next larger bit needs to be 2/3 larger in diameter. doing it in small increments is a B A D thing!

 This explains the surprising mess I made night before last! 

I appreciate all the information and wisdom shared on this site!


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An item I have found handy to have in a hobby shop is a good Metal Shop Textbook that goes into details on things like feeds & speeds, step drilling steps, draw filing, etc.  As most shop programs have bit the dust I was able to find several for around US$1 at thrift stores.

For more advanced work keep an eye open for things like Machinerys Handbook, especially the older ones that had more on smithing in them.  (I have a copy of the 23rd edition but the smithing stuff was better pre 14th IIRC).

Like the ASM Handbooks I find that ones published in the 1960's tend to cover what I need to know and not be high priced as "antiques".

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Search on ASM Handbook,  (Used to be American Society for Metals IIRC; gone international now. They publish MASSIVE tomes on metals. I particularly like the one on heat treating.  Mine are generally decades out of date as I buy them on the used market when I find them CHEAP!)

From their website:

"ASM International's roots go back to 1913 when two blacksmith groups formed, one in Chicago and one in Detroit. At that time, the automotive industry was booming and the blacksmiths realized that they needed to compare notes if they were ever to meet the technical demands for heat treating and forging automotive components. As the group grew and flourished, they collaborated in organizing a trade show (in 1919), and combined to form the American Society for Steel Treating in 1920. In 1933, the name of the organization was changed to the American Society for Metals, recognizing that the need for metallurgical technology was broader than heat treating and forging.....and had developed many important reference books, such as the ASM Metals Handbook."

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