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I Forge Iron

Those fat drill bits

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Hi. I just bought a large hand drill off craigslist. It is 10 amps, with a 3/4" chuck, and the data on it says that it can drill a 3/4" hole in steel. I also bought a whole tray of fat S&D drill bits. I just tried the drill out, and it really required some hard pushing. I tried to make a rivet bolster out of a junk end of a steering rod. Not mild steel, but not really hard either. Spark tested intermediate, and could be cut easily with a Starrett bi-metal hacksaw blade. I needed to sit on the drill to make the 1/4" hole. There was no way any chips were going to come out for a 3/8" hole. So, I rigged up a "blacksmith's drill" according to the Blueprints and went to work. That big drill just flew through the steel, kicking out a bunch of cutting oil smoke and brown chips.

By the way, the rivet bolster performed well at the forge, but it requires careful measurement of the rivet before setting, else the heads will come out asymmetric.

So, I looked around for a feed pressure chart, and surprisingly, it was pretty hard. One thing that I noticed was that magnetic drill spec's listing 3/4" hole capacity have about 1000 pounds of feed pressure rating. Then, I found this:


Wow. So what do I do with those 1" plus S&D bits? Drill magnesium? :D

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Sure wish you would have put a picture of the drill up to look at.

Hand drilling iron is not easy any way you look at it. You don't start with a big bit, you drill a small hole and then keep drilling a bigger one, hand drill is not a drill press you know. Sounds to me like your 1/4 inch bit was real dull.

In a Hand drill you also need to be careful or you will bend the 1/2 inch Shank on the silver and deming bits.

Rough figuring that a 1/4 inch hole is 1/4 or a square inch, 100 lbs of pressure (you leaning on the drill) will exert over 400 lbs per square inch on the drill, and that is not taking into account you are only putting pressure on the two thin cutting edges.

Moral of the story don't expect a portable drill to perform like a drill press.

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Thanks. It is this one:

DeWALT 3/4" 375rpm Drill/Power Unit (DeWalt-DW138) - PriceGrabber.com

The funny thing is that 1/4" bit drilled very well on some mild steel angle iron with a smaller 1/4" hand drill. The 3/8" bit was new. The psi figure for the drill point is useful for calculating forces. Maybe these D-handled drills are more oriented towards drilling wood.

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Not sure what kinda deal you got on the whole set up but have a little patience and remember that drill was meant for the big stuff. Consider drill speed and proper drill practices. I don't know what you plan on drilling but With good bits and some experience that rig should drill anything you'll ever need. I've got a bad case of tool envy about now.


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take a look at your large drill from the point end and take a small drill and look at the point end, notice how big the chisel is on the big drill compared to
small drill, you can thin these chisel edges on the large drill by thinning the web and grinding more heal clearance behind the cutting edge,
i have drilled 1/2 inch holes in steel with a cordless drill by properly addressing the cutting tool ,
i thin all the webs on my drills , stay away from split point drills however
they cut great at first but are delicate and chip out real fast expesially in handoperated tools
thanks chuck

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  • 3 weeks later...
  • 7 months later...

spend the money on good quality, titanium nitride coated drill bits, they fall through most materials.

With a good quality bit and a very poor drill you can do alot more work.

If you have got lots of 20mm + holes to drill a "roto broach" magnetic 'slugger' is the best. these are like a little hollow milling cutter. They leave a little 'plug' of steel that falls through the plate. you can drill a hole in seconds.

Johns Top tip of the day...... if you are drilling a large ish hole with a hand held drill do not 'lock' the power on with the little side toggle, just lightly hold the main switch right at the end. if the drill grabs, which WILL happen sooner or later it stops (well massivly reduces the chances) of it spraining / breaking you wrist.

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Hey John N.
What's your opinion on cobalt bits. I've used them before but didn't really notice any difference between them and TiN. Then again I was only drilling 1/4" holes in 1/4" HR stock IIRC and was using a press, not a hand drill. Any advice.

I've had decent success with the TiN coated HSS bits from harbor freight. I try to avoid the split points, as our drill doctor is a little older and doesn't quite sharpen them properly. Other than my brother breaking a couple of the smaller bits when he was trying to drill a Grade 5 bolt for a castle nut (mechanic does NOT equal machinist in any way, shape, or form), I really have no qualms with the HF bits, at least on a hobbyist level.
-Aaron @ the SCF

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To be honest ive never used a colbalt drill bit, for that matter ive never seen one used!(and ive worked in heavy engineering for a bit) , we sometimes used to use colbalt or stellite when turning pot hard material, but never used them for drill, course its all C.B.N and ceramics now,

I buy sets of the TiNi coated HSS bits (not sure of the brand) for approx

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There's a big difference, in my opinion, between the TiNi bits and cobalt bits, especially when it comes to harder metals. A friend of mine called me a few weeks ago needing help with a bolt snapped off in his engine block, and a chromium vanadium bolt extractor snapped off rather neatly, and conveniently might I add, in the middle of it. After an hour of nothing with the TiNi coated bits, which he swears by, I got fed up with it and got my cobalt bits. After about 30 minutes, most of the extractor was eaten away with only a bit of dulling to the tip.

At $2 a bit from Northern, it's a bit pricey, but I'd be more than willing to spend it. Since I've been using them, I've noticed that the work's been going a lot faster.

That's just me though.

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  • 1 month later...
RW: are there any US dealers? There are not any listed on their site.

They seem to be some useful tools, especially for the unusual things farmers get into most of the time.

Doesn't appear to be any listed on the web site. A phone call with a credit
card handy would probably get you the required items. I have purchased
books and other items from the US in using this method.
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