blackleafforge

Good drill bits?

38 posts in this topic

I have been using a cheap set of drill bits that came with my drill for a while now and they are almost all broken or blunt. A fresh one only seems to last for about a minute of drilling through mild steel, is it worth investing in a very expensive set? I was looking at at 29 pice cobalt irwin set but it costs over £100. How much difference will I see? Does anyone else invest in expensive sets or is cheap and cheerful the way to go? 

Thanks 

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If you're drilling mild steel even cheapO HC drill bits should work just fine. I suspect you have the rotation speed way too high and you're applying too much feed pressure. I assume you center punch before drilling but do you clean the steel? A fine dusting of grit will dull bits especially if you've ground the surface. A grinder, wheel, belt, cut off blade, or whatever leaves abrasive grit embedded in the cut face. A few seconds with a file usually solves this bit of drill bit abuse.

How large are the increments you're using when you pilot holes? Do NOT use small increments! For instance if you need to drill a 3/4" hole, pilot it with a 3/8" bit and go straight to 3/4". Starting with say: 1/4" then 3/8", then 1/2", then 5/8", then 3/4" puts WAY too much stress on the outside tip of the cutting edge and they WILL blunt quickly. The rule of thumb is pilot no less than1/3 the final hole Dia.  and or increase the Dia. by 2x  per increment. Yeah, there are plenty of times you're drilling an "oversize" hole and just can't avoid more than one pilot step.

About your original question, oh YES I love my Bowman Cobalts I haven't had to sharpen one in the 30 years I've owned the set. I do however know the proper technique for drilling holes. Good tools can't shine if you don't know how to use them but you can attain knowledge and experience that's no problem.

Frosty The Lucky.

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Irwin is one of my favorite brands!  Just high speed steel is fine for most work though.  DEFINITELY a difference in quality will deliver in results!  Industrial quality will deliver for you!  Cobalt, titanium, etc. coatings are NOT indicative of quality!  Good U. S. made bits are hard to beat but Korean, Taiwan, Chinese bits can be very good too... and much cheaper!  Buy only from a supplier who can tell you the differences.  Good suppliers will have good bits.  They might have cheap ones too... but they know the difference!

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I like to have a decent wide set and follow up by buying top grade drill bits for the sizes I use most often.  (Actually I tend to buy up used good bits at the fleamarket and resharpen them!)

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I'm fully on the side of top-quality drill bits.  Not the home center offerings but the better versions you by from machinist supply houses--they're designed for maximum life and productivity, not whether they look appealing on a retail shelf.  Most of the time those colorful coatings on home center offerings are to catch your eye on the display shelf and have no significant benefit--not unlike fishing tackle which is designed to catch fishermen at the point of sale and not fish.  They tend to be of little benefit except at idealized feeds and speeds on production situations.  

Because you can narrow down the most-used bit sizes to about 5, it's not that expensive.  Get the cheap set to fill in the rarer sizes but get the good ones at whatever extra cost for the other 90% of drilling.  There is an order of magnitude difference between something like the home center oriented "irwin" and "Precision Twist Drill", "Hertel", or one of the many other machinist-oriented brands.

Frosty mentioned "...too much feed pressure":  There's a bit of a catch-22 with that.  With the larger sizes (3/8" and above roughly), the problem is usually too little feed pressure so the bit does too much rubbing and wears itself out.  You need to have the drill constantly cutting and ejecting chip(s).  That chip not only keeps the drill edge in proper cutting geometry but is also critical for removing heat from the cutting edge.  Feed pressure for a 1/2" bit is roughly on the order of 300 lbs to give the proper feed rate per revolution in mild steel (obviously that number will vary a LOT in practice).  If you use the "proper" calculated pressure on smaller bits in imperfect machines or by hand, they'll snap like glass at your first coffee-jitter.

Proper speeds are easy to look up on the internet for various materials but a lot of home drill presses don't have speed ranges which match "proper" well.  You sometimes have to do the best fudge you can on that.

Same for taps and dies BTW--HUGE difference between the home center stuff and the good stuff.  I'm happy to pay 5 times the price for a good tap because I get 10 times the results and 1/10th the aggravation.  

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I hadn't considered dust / grit build up being a problem, I had thought that using a cutting fluid might help but it seemed overkill for a hand held drill. I do put a bit too much pressure on sometimes, especially with a blunt drill I sometimes force it through with all my weight out of frustration! I also didn't consider cleaning the metal, I assume thats to stop grit and crap getting pushed in to the hole? Same with the speed, I usually just crank it all up to 11, I hadn't considered that may be another contributory factor. 

Are there any other machinist brands you would recommend? as a lot of the ones discussed seem to mainly be available in the US. 

Also are you sharpening your bits by hand or using a jig or other automatic contraption?

Thanks

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BLFF,

I am a big fan of high sulfur cutting oil. I have been using it for many years and I highly recommend it. It lasts forever if you are not running a production shop.

I use a eye dropper or syringe to apply it to the bit.

It cools the drill bit, and washes out the cuttings and other crudd.

Muscling up on a drill bit and/or running it at top speed is ineffective, wasteful, often breaks drill bits and will dull them in quick time. It's a poor practice most of the time. (except in a pinch where you have one bit and no back up, & are in too much of a rush to go out & get one at that moment).

Just my two cents.

SLAG.

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I usually sharpen by hand unless I need top performance and accuracy.   As for cost of "cheap" tools far to few people factor in the time and travel expense.  Not living in town I try to buy *2* of what I need just in case!

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3 hours ago, blackleafforge said:

Snip...

I do put a bit too much pressure on sometimes, especially with a blunt drill I sometimes force it through with all my weight out of frustration!

snip...

Also are you sharpening your bits by hand or using a jig or other automatic contraption?

Thanks

The one skill I have managed to share with all the journeymen I have had through the forge that I know 100% will be useful to them is how to sharpen drills by hand.

It takes seconds to sharpen a drill and will save you hours of time and frustration. 

Why spend energy pushing on an overheating drill bit for a couple of minutes when with a few seconds of sharpening the hole will be done faster and easier with no risk to drill or workpiece...or peace of mind!

No brainer.

Alan

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Frustration, the great drill bit killer! I didn't even mention cutting oil. Wonder why? Drilling mild steel it isn't really that necessary a sharp bit at the right speed and down pressure will hog right through it. Why is hogging at the right rate a good thing? Well, the shaving separates from the parent stock and the heat generated is carried away with it. A properly sharpened drill bit has almost no contact with the parent stock after the edge has passed, all the bit's contact with the stock is where the shaving is bent up and slips along the bit's flutes.  Properly sharpened and hogged the shaving twists inside the flute so contact is minimal and the bit doesn't over heat.

Cutting oil lubricates the cut so minimal heat is generated and it aids the shaving being forced from the hole. This is how oil keeps things cool, not by acting as a coolant. I'm not talking about industrial drilling machines those often use a different strategy and require cooling along with lube. Be aware if your bits aren't parting out TWO clean shavings cutting oil may do more harm than good. If it's producing chips oil can cause them to stick in the flutes and when full jam, gall and there goes your bit. PingO!

If your bit is producing chips and this may not be because your bit is dull, some metals will NOT produce a clean shaving then use a light lube, water in a pinch can be better than oil even water soluble oil cutting oil. Now the fluid is flushing the cuttings out, cooling is happening but getting those cuttings OUT is a must.

Got side tracked there, we spent a LOT of time in metal shop sharpening tools, and keeping them sharp, especially drill bits. It's important to learn how to sharpen correctly but if you can't find someone who can show you how to sharpen drill bits and or don't want to spend the money on a fine grinding wheel buy a sharpener. I have 2 drill bit sharpening machines, one a gift one a garage sale buy and both do a splendid job.

After a while lets talk about correct bevel length and angle . . . for the metal being drilled, cut. :o See that one coming? I'll bet there are tool and die and machinists out there who know what I mean.

Frosty The Lucky.

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Error on the side of the best tool you can afford.  I Love a nice quality Cobalt bit. They stay sharp, and hold up so much better for me.  If you are drilling forged items, planish with the hammer at low heat and wire brush at the anvil as you finish your forging.  Then allow it to normalize, don't quench it, just let it cool naturally.  Once its cold, power wire brush the surfaces, to remove as much of the scale as you can, then center punch (which will likely remove the critical scale you would otherwise be trying to drill through) then drill your hole.  Don't forget to clean the backside of the piece as well, the drill bit has to cut there too...  I prefer to use a drill press so I can see how the bit is cutting better, and I have a better idea of feed pressure...  Be careful, on pieces that you burned slightly in the fire... Sometimes that increases the carbon in that area (or something???), because it gets supper hard, and its practically impossible to drill, and a pita to even grind...

I have some nice S-7 punches and I tend to hot punch, and counter sink my holes hot, saves on the drill bits;-)

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Invest in a set of either "presto" or "dormer" drill bits. - Presto are UK made, not sure about Dormer off the top of my head but either way you won't be disappointed. 

Slightly more expensive than your average brands but you can't beat them in my opinion. 

 

All the best

Andy  

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14 hours ago, Kozzy said:

 fishing tackle which is designed to catch fishermen at the point of sale and not fish.

:D:D:D

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21 hours ago, Frosty said:

 The rule of thumb is pilot no less than1/3 the final hole Dia.  and or increase the Dia. by 2x  per increment.

Did you intend to type "no more than 1/3"...?

Just my two shillings, try to pickup some old 3/8 & 1/2" pawn-shop bits & practice regrinding & drilling mild steel.  When you can refurbish them reliably, get some split-point cobalts, run them slow & watch how they cut in different materials.  Cutter grinding is a useful skill in itself.

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No, as the discussion was about making the steps large enough not to chip the edges of the drill bits.

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Great discussion. I grind drills every day, and I even get to drill holes sometimes :(!

SO, if anyone wishes to review a thread from 2014, here it is:

The bonus content is a bonified chart on the composition of twist drill steels AND a link to a very good site.

To emphasize what others have said, the #1 drill killer is

Too much speed, too little feed.

Robert Taylor

 

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I'll just mention carbide tipped masonary bits..............

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21 hours ago, Smoggy said:

I'll just mention carbide tipped masonary bits..............

Carbide masonry bits are great . . . for masonry. They aren't shaped correctly for cutting metals they're intended to break their way through stony material, not cut it. If you don't have a carbide grinding wheel, green or blue wheels you can't regrind carbides for metal.

Why not use one anyway? You have NOT lived till you TRY digging embedded bits of carbide out of the bottom of the hole you were ATTEMPTING to drill. IF you manage to get the carbides to bite into the steel the edge of the super hard tungsten carbide formulated for impact rather than any kind of bridging strength snaps off. Think flaking flint or obsidian. Now you have a sharp edge that will bit into darned near anything but it's very thin and very VERY brittle so it bites a little and snaps off and sticks INTO the stock you're trying to drill. :(

The problem with that action is every chip leaves a nice fresh edge on the remaining carbide which bites in and snaps off till the entire bottom of the hole looks more like sand paper than steel. A fresh carbide bit will only add to the blockage. Got a diamond bit and all the equipment to get diamond to go through steel without popping all the grit out of the matrix? :unsure:

Believe me Carbide bits that are designed to cut metal are pretty low on my to use list even though they do the job well. the downside being the amount of knowledge and skill necessary to use one without making the hole impenetrable. The only efficient minimum hassle way I know of to finish a hole blocked by carbide chips is to drill from the other side till that bit encounters the chips and is blunted then use a punch.

Just saying.  Frosty The Lucky.

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I like Sutton drill bits especially the Cobalt one. Drill Stainless without too much anxiety.

I use coolant and low speed all the time for everything. 1:10 mix of cutting oil and water. Essential for the annular cutter, cheap and saves your drills from even getting warm. 

I have sharpened drill bits for 50 years by hand ... until I got myself a Drill Doctor, the top of the line model. Love it.  

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An annular cutter is a saw rather than a twist drill bit and oh baby YES it needs a lubricant, more a flushing agent. Getting onne jammed in the hole is a seriously REAL PITA!.

Drill Doctor! That's the sharpener I couldn't think of. Ceramic stone that runs flat and wet. Mine is the cheap model and it's a far better sharpener than I am.

Frosty The Lucky.

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We use Chicago Latrobe and drills from Pan American Tool at work both HSS and Cobalt. In the wrong hands you can dull any drill bit. The wax type drill lubes are nice as they dont make as much of a mess. For large holes 5/8 and up I really like the holesaws made for metals. They have a material thickness limit but I don't tend to work with steel much thicker than 3/4 usually.

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17 minutes ago, Frozenforge said:

snip... For large holes 5/8 and up I really like the holesaws made for metals. They have a material thickness limit but I don't tend to work with steel much thicker than 3/4 usually.

Are you talking actual hole saws or Rotabroach cutters?

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Alan

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Your Rotabroach is what we call an Annular cutter or drill bit but not what I was thinking of when I used the term. I wasn't thinkig of a hole saw either though I use the heck out of them.

Frosty The Lucky.

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Yes ... terminology even in the same language tends to get confusing, nothing like a picture.

Core drill is another term. Those things are gold for drilling large holes. No need for pilot hole and you can even cut at an angle if you have the right machine. Go slow, plenty of coolant and a 2" hole in a 3/4" plate can be cut in minutes. Try doing that with a twist drill ! May be if you use a mill do drive the bit. 

Holesaws are a hateful contraption. A necessary evil. Built flimsy by nature, needs a pilot hole, only good for sheet metal, plagued by poor quality, costs a bomb if barely adequate. Well you get the idea ... I dislike them ha ha

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Can't get good hole saws down under? If it took a whole minute to drill a 2" hole in 3/4 steel with mine I'd replace it. They need to be flushed either with a light fluid or compressed air though you can drill dry if you're careful. 

I've only ever used core drills on mineral, stone, concrete, etc. Running into a piece of rebar in concrete takes serious care or it'll ruin the bit. So you know we were drilling stone or concrete and our bits weren't intended for anything else, heck we had special bits if we planned on drilling much or far into concrete. 

Frosty The Lucky.

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