# Drill bit nomenclature... I just figured it out!



## Semper Vaporo (Jan 2, 2008)

For years and years I never understood why drill bits came in the standard fraction inch (1/8, 1/4, etc.) and metric sizes as well as the "numbered" and "lettered" sizes. I did not understand why the numbered and lettered sizes existed... I just figured they were a hold over from some earlier time before some Standards Bureau settled on the fractional sizes.

A few years ago, when I started to "PLAY" in metal working (bought a Lathe and Mill), I began to need to drill holes that I wanted to put (tap) screw (bolt) threads into and found I never had the correct size drill for the size of bolt I wanted to make a mating hole for. I purchased the best "small" set of drill bits I could afford and it did not contain the correct drill bits for drilling holes to be "tapped". I kind of figured out that I would need to purchase one of the 115 piece sets to finally get all the possible sizes, but, to get quality bits it would be too expensive to do so... so I just kind of muddle along picking the next larger size and hope there is enough material left in the hole to form threads when I am done. (It does most times make it easier to cut the threads to have an over sized hole, but it sometimes leaves me worried about the strength of the bolted joint!)

Sometimes I have to alter my design to use a different sized bolt so that I can drill a hole small enough to have decent threads in it for bolting something to the part with the hole.

I was just now reading the Harbor Freight flyer and noticed a drill bit set for sale that is the 60 "Numbered" bits and wondered what sizes those were. I grabbed my "Thomas J. Glover Pocket Ref." book and looked up the sizes (pgs 450-459). Then I turned to the table of thread sizes (page 598) and what drill bit to use and compared the numbered dimensions to the recommended "tap drill" to use and noticed that the Numbered drills are the correct sizes for drilling holes to be tapped.

WOW! Now I know!

When working with wood one normally does not drill holes that are to be tapped with threads, so one just uses drills that make clearance holes for bolts (yes, sometimes one needs to remove just enough material so a wood screw won't split the wood, but that in an in-exact selection process based on the piece of wood itself and so a drill bit size that is "close" is usually good enough). Thus most "Woodworkers" need only bits that make bold clearance holes and bolts come in standard sizes. All the Sets of drill bits I have ever purchased were designed for the Woodworker!

Now that I am into "Metal working" I need drill bit sets designed for the metal worker and in this realm one needs to drill both clearance holes and holes to be tapped.

In the past I have purchased drill bit sets that are inexpensive enough for me to afford and found that the drill bits sometimes cannot drill one hole in soft wood without being ruined by the act of using them. My personal opinion of the "TiN" (Titanium Nitride, I think) coated drill bits are a joke... they are the ones that have been the worst as far as longevity of use.

When I started working in metal I did purchase a good set of drill bits (www.WintersDrillBitCity.com), but now I realize they are the "wood worker set" (17 in the set... 1/16 to 1/2 inch). I paid a pretty penny for them and I love them, but there are no Numbered bits in the set. The 115 bit set from that same company is way outside of the realm of my wallet.

Does anyone know if this Harbor Freight set of 60 numbered drill bits are any good? i.e.: will they drill more than one hole in metal and still be usable? The advert says they are TiN coated and from past experience I have NO desire to repeat the loss of my hard earned cash!


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## coyote97 (Apr 5, 2009)

Hi to all,


just want to add some facts.
What u are talking about is not new and all in all there are two things to figure out:


1.) because the inch-system is hardly to get into even for educated workers, things are going to change to metric systems. Even in the US. 
In metric work, drillers for taping threads just have a simple decimal-number like dia 4,2 for a M5 thread. No more secrets to discover.


2.) cheap drillers do cheap work.
cheap drillers with a cheap coating gives expensive drillers, doing worse work.
Even though the TiN-Coat isnt much more "up-to-date", good drillers with a good TiN-Coat are very fine tools.
BUT:
having a set of 90 drillers from 1,0 to 10,0 means that a price of 90 dollars is one dollar per driller. for that it has to be roled, grinded, coated and provided in a Set. Only Chinese quality can be offered for that price.
A good TiN coated HSS-driller costs about a minimum of 3-4 dollars, what brings u to a price  of 300 dollars for a complete set.
To do hobby works, that should be ok nearly for life.


To save money, there is a trick: 
only to buy the drillers needed. for G-scaling, there is no use of a M12 thread driller and taper. Single tools may be more expensive, but u can normally work with about 15-20 drillers. And using good industrial-quality means that they can be bought as single ones...one by one. and it means that u can buy 3 of a kind when u use a diameter very often.


We in our company do "deepholedrilling". Therefore, a single driller costs about 100-150 dollars. So we know a bit of quality-things like material, coating and costs.




greetings


Frank


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## Semper Vaporo (Jan 2, 2008)

Posted By coyote97 on 04/17/2009 3:53 AM
Hi to all,


just want to add some facts.
What u are talking about is not new and all in all there are two things to figure out:


1.) because the inch-system is hardly to get into even for educated workers, things are going to change to metric systems. Even in the US. 
In metric work, drillers for taping threads just have a simple decimal-number like dia 4,2 for a M5 thread. No more secrets to discover.


2.) cheap drillers do cheap work.
cheap drillers with a cheap coating gives expensive drillers, doing worse work.
Even though the TiN-Coat isnt much more "up-to-date", good drillers with a good TiN-Coat are very fine tools.
BUT:
having a set of 90 drillers from 1,0 to 10,0 means that a price of 90 dollars is one dollar per driller. for that it has to be roled, grinded, coated and provided in a Set. Only Chinese quality can be offered for that price.
A good TiN coated HSS-driller costs about a minimum of 3-4 dollars, what brings u to a price of 300 dollars for a complete set.
To do hobby works, that should be ok nearly for life.


To save money, there is a trick: 
only to buy the drillers needed. for G-scaling, there is no use of a M12 thread driller and taper. Single tools may be more expensive, but u can normally work with about 15-20 drillers. And using good industrial-quality means that they can be bought as single ones...one by one. and it means that u can buy 3 of a kind when u use a diameter very often.


We in our company do "deepholedrilling". Therefore, a single driller costs about 100-150 dollars. So we know a bit of quality-things like material, coating and costs.




greetings


Frank 






Thanks,...

Yes, I know my "revelation" ain't "new" but "I" just figured it out... after many years (too many!) of wondering about it.









1) As for whether the inch system is hard to figure out or not and Metric being "better"... I'd have to give a firm "NO" to that. Either system is just an arbitrary dimensional system where the base unit is just some arbitrary length. Yes, "Metric" is a bit easier to convert from one arbitrary length to some multiple of that unit (shifting the decimal point), but my Dad could add, subtract, multiply and divide in Feet and Inches IN HIS HEAD! without problems so I know that once the brain decides to memorize the multiplication tables in some mathematical base (base 10 or base 12 or base 2) then the conversion from inches to feet is no different than converting from centimeters to meters... one is in base 12 the other is base 10.

I doubt very much if the U.S. will ever "go Metric"... we have tried it several times, even by government mandate, and it has never taken hold and probably never will.

2) Without a doubt, cheap tools produce lousy results in the hands of the "duffer" "Do-It-Youselfer". Quality tools do make it much easier for the idiot like me to do a better job. I LOVE using good tools and abhor using bad ones. Quality tools are also much safer to use! Unfortunately, obtaining quality tools is difficult for two reasons: 

A) They are expensive! Few people can resist the temptation to purchase a whole set of drill bits at a price that makes them cheap per bit than to pay an exorbitant price for just one bit by itself... EVEN THOUGH, they will probably never use the majority of the bits in the set and will have spent more money "per used bit out of the set" than if they had just purchased the one or two that they end up using. OUCH!

B) Trying to find a single bit of QUALITY is often difficult. The stores do not stock the expensive stuff because we "duffers" don't buy it when there is the less expensive bit hanging on the display peg right next to it... so why stock the expensive stuff? To get good quality, too often one must special order it and wait for its delivery and that then delays the project an unacceptable length of time... "Hey I just discovered I need a #2 bit to complete a project I didn't even know I was gonna have to do today and to get that bit I can run to the hardware store and get one cheap bit or I can special order it, wait two weeks for it to get here and incurr the wrath of SWMBO for having yet one more DIY project half completed." No, I go buy the cheapie and muddle through with a junk tool and then curse the lousy tool... what is that adage? "It is a poor workman that blames the tool."

Right now, I cannot guess which one or two bits I will need in the next year, so ordering just those one or two now is not possible. To be ready for the next DIY project I need to purchase the whole set, but that is too expensive to do if I get quality ones... caught between a rock and a hard place. Buy the cheap set and get lousy quality which makes for lousy project or don't buy any now and then can't do the next project in a timely manner.


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## SteveC (Jan 2, 2008)

Posted By Semper Vaporo on 04/16/2009 11:21 PM
{snip...}[/i] I kind of figured out that I would need to purchase one of the 115 piece sets to finally get all the possible sizes, but, to get quality bits it would be too expensive to do so... _so I just kind of muddle along picking the next larger size and hope there is enough material left in the hole to form threads when I am done.[/b]_ (It does most times make it easier to cut the threads to have an over sized hole, but it sometimes leaves me worried about the strength of the bolted joint!) _{snip...}_

_{snip...} _When I started working in metal I did purchase a good set of drill bits (http://www.wintersdrillbitcity.com/), but now I realize they are the "wood worker set" (17 in the set... 1/16 to 1/2 inch). I paid a pretty penny for them and I love them, but there are no Numbered bits in the set. _The 115 bit set from that same company is way outside of the realm of my wallet.[/b]_

_Does anyone know if this Harbor Freight set of 60 numbered drill bits are any good?[/b]_ i.e.: will they drill more than one hole in metal and still be usable? The advert says they are TiN coated and from past experience I have NO desire to repeat the loss of my hard earned cash!

C.T.

While there's no argument that buying the highest quality tool for any given task, results in two things; better quality work, and the best long-term investment of your money in your tools.

However, if you look back at the first of your statements that I've highlighted (i.e. blue), while you've got quality tools, the resulting output isn't. Which is the direct result of your second statement that I've highlighted (i.e. blue).

For the following I'm sure to get a bunch of flack, but in answer to your third statement that I highlighted (i.e. red). Again there's really no argument that the twist drills from Harbor freight to which your refer are in no way quality tools (i.e. $49.99 / 115 = $0.44/bit, or the non-coated set $39.99 / 115 = $0.35/bit, and that doesn't take in to account subtracting the included cost of the drill-index). I would say that either set would be an equitable investment for you, and provide a step up in the quality of your output. Over the last 10~15 years I've purchased two of the non-coated 115-piece sets and have been satisfied with the service they've provided. As for why I decided against the TiN coated version, the first time you sharpen (yes, that's correct, all cutting tools need to be sharpened) any of the bits the coating is gone.

In my personal experience, the longevity of twist drills (for that matter any tool), especially in metal working, depend much more on the manner in which the individual puts them to use. I've destroyed , and have observed others destroy, more good quality twist drills than I'd like to admit to, by simply trying to make the bit do more than it was designed to do (e.g. too high a speed, feed rate, drilling a big hole in one step, lack of lubrication etc. etc.).


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## coyote97 (Apr 5, 2009)

Posted By SteveC on 04/17/2009 11:14 AM
In my personal experience, the longevity of twist drills (for that matter any tool), especially in metal working, depend much more on the manner in which the individual puts them to use. I've destroyed , and have observed others destroy, more good quality twist drills than I'd like to admit to, by simply trying to make the bit do more than it was designed to do (e.g. too high a speed, feed rate, drilling a big hole in one step, lack of lubrication etc. etc.).


No question, our grandfathers had to work with very bad tools and they made big, heavy steamengines out of this situation! So it can not only be the tool-question. It is -too- the way we work with it.


Whats well known is the coating question: bad coating goes of an rips down your tool like sandpaper. better NO coating than a bad one. a price of 10 dollars more for a whole set of drillers CAN not be good coating.


What has to be told is that sometimes the coated drillers grip or bend in the hole...especially in stainless steel. Most people think its because stainless is hard to cut. But drillers break because they got stuck. most stainless materials are even very good to cut..as long as we talk about drilling.


The metric/inch question is nothing we should argue about. what i wanted to tell is that in the last few years even drawings from the US dont use 1 1/4 inch or 3/128 inch. most drawings have decimal numbers based on inch, but mostly doubled and one number changed in metric dimensions. 
inches in decimal leads to the use of very many "0": ±0,05mm is about ± 0,002 (inchbased). even finer tolerances makes even more "0" and there are more faults in production because of this.
The modern inch-system has (refering to threading) really "workable" norms.
The old system often used the same thread-number per inch for different (often not normed) diameters. Its a mess! And only done to use not too many different tools.
We had that here in Germany, too, before there was a big machinery-norm called the DIN.


We are working on a 1:1 scale steam-loco that was built in 1922 while the "königlich Württembergische Staatseisenbahn" changed to the "Reichsbahn" and Systems changed from inches to millimeters. THAT is even more a mess.
For the interested ones: www.zhl.de


Greetings


Frank


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## RimfireJim (Mar 25, 2009)

S.V.:
One approach you might consider is determining the proper drill sizes for the threads you want to tap, then buy only those sizes of drill bits in high quality, PLUS an inexpensive complete set of number drills and maybe letter drills (if your hole diameter requirements go that big). That way you'll have good bits for the tapped holes and a bit for any other size hole you may need to drill on occasion. If you find that certain sizes from the inexpensive set get used frequently and get dull, replace them individually with high quality bits.


One thing to consider: the type of finish on the bit is optimally suited for the type of material you are drilling and if cutting fluid is being used. Doesn't mean they won't work for other combinations, but you want to have the best match for the bulk of your work. Check out the info on this page for a brief overview of drill bit composition and surface treatments: http://www.mcmaster.com/#metalworking-and-multi-purpose-drill-bits-and-rods/=1hlrqx


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## 3lphill (Feb 22, 2008)

Good Afternoon,
I just checked the drill vendor we use, www.fastenal.com, has 2 branches in Cedar Rapids. I am fond of the Norseman brand that they carry, but they have a wide selection of brands to choose from.
Phillip


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## SteveC (Jan 2, 2008)

Posted By coyote97 on 04/17/2009 3:53 AM
{snip...}[/i] 1.) because the inch-system is hardly to get into even for educated workers, things are going to change to metric systems. Even in the US. {snip...}[/i]

Frank

There's no argument the metric system is more scientific, precise and easier to convert from one measurement to another while working within the metric system.

While it may make economical sense to use one common system in the commercial environment world-wide, for a multitude of reasons. Many individuals (myself included) have no great difficulty in using either of the systems of measurement to which you refer. As far as I can see the non-metric system of measurement will suffer a very long and lingering death, if it doesn't stick around forever.

It has been my observation, the biggest resistance to changing over to the metric system on a personal level, and I don't mean the initial frustration that individuals feel when having to learn something new and unfamiliar or the natural resistance to change. I'm speaking of the innate feeling of unease that most human beings have when dealing with things they can't visualize.

It's funny, but many of the characteristics of the metric system that give it, its desirability also create the innate resistance that humans exhibit toward it. For instance, take the definition of the foundational element of the metric system the 'metre/meter' using either the original or current SI definition. I would venture to say that there isn't one individual in one hundred thousand (if that many) that can visualize either of those definitions. They just accept it and learn how to correctly make use of the system, regardless of that feeling of unease they conceal.

If you examine the other older systems of measurement, for the most part they were all based on things that human beings could see, hold in their hands, even taste. Additionally, in many cases though not accurate to any great degree many of the natural body parts of the human body can be used to perform a generalized comparison measurement. Even many of the terms used related directly the parts of the human anatomy. Because those are the exact same elements that were the foundation on which the systems of measurement they're use to were built on in the first place. That is why I believe the abstract and impersonal nature of the metric system will cause the older systems of measurement to stay around on a personal level for a very long time, if not forever.


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## SteveC (Jan 2, 2008)

Hey C.T.

You might find the following interesting,

*Sizes.com
Materials - Wire*

*Machinery's Handbook*
*For*
*Machine Shop & Drafting Room*
*Pub. 1915*
*(re: Wire Gage)*


*Machinery's Handbook*
*For*
*Machine Shop & Drafting Room*
*Pub. 1915*
*(re: Twist Drills & Counterborers)*


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## Semper Vaporo (Jan 2, 2008)

SteveC:

I purchased a clone of "Machinery's Handbook" (it was cheaper!) and although I have used some of the tables in it, when I really begin to study the prose in it, my eyes tend to glaze over and I lose conciousness.... just like when I read about my medical insurance!

The story of the origins of the "Standards" is pretty much what I had assumed to be the case. As is the cause of the overabundance of them.

----

As to whether it would be easier if it were all metric... there are the same number of drill bits required to create all the holes necessary to work with the number of metic sizes available for the purposes required. You still need bits to create loose, normal and close clearance holes and different sizes of bits to drill the hole to be threaded based on the size of the thread and the type of material... BUT, by having both inch and metric standards (amongst the other ones) then there is the need for twice the number of drill bits so one can drill holes for either inch or metric bolts.

As a bonafide woodbutcher (aka: ne'er-do-well DIY woodworker) I am used to needing a saw and a hammer to construct a project from the raw material; "wood". The same saw can cut either Fir or Pine or Hemlock or Maple or Oak... though I do know that it would be better to have both a cross cut and a rip saw for the difference in cutting across or with the grain, a plain ol' "saw" will do 90 percent of the time for either.

If I cut a board and I have missed the mark sightly, it is seldom noticed because wood will shrink and swell with changes in humidity and paint covers a multitude of mistakes and extra nail heads. If I have missed the mark grossly, patching in another piece is sometimes a course of action and when that won't work then more stock is readily available locally at relatively low cost.

BUT, when working with metal, a "slight" error in measurement can mean the need to obtain a totally new piece of stock (that the local stores do not stock, so order it and wait for mail delivery!) and a complete repeat of all the steps that have been done to it up to the point of the revealing of my ineptitude. Sometimes that leads to the wallet saying that this project is not ever to be completed because I could just barely afford the original cylinder casting that I just destroyed by drilling in the wrong place with the wrong sized drill bit or broke off the tap in the hole because I used the next smaller tap-bit than I should have because I was afraid if I used the next larger one there would not be enough material left to hold a thread.

Yes, there are those that would say all I need to do is melt the hunk of bronze down and re-cast it, but that entails the purchase of a smelting furnace and that was outside of my wallet contents in the first place.


Anyway, I started this thread only because I was so pleased with myself for having discovered the reason for the numbered drill bits and that I better understood the reasons for such huge number of bits sets that are sold. I am sure there are those reading this that are thinking; "Whoa, you just now figured that out!?!?" but I bet there are at least one or two others that are thinking; "So that's why!"


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## Havoc (Jan 2, 2008)

I just bought a set of cheap metric drills 1mm-10mm is 0.1 steps. After some time you find that some of them get used much an need replacing: then you buy a 10 pack of industrial drills. The others go a long time for the odd hole you need once in a while. Don't think that expensive brand drills are better than chinese. The worst I ever had were very expensive Dormer drills. Break easier than toothpicks. 

The US is metric, they only don't know it yet. Most soft drinks bottles are metric, the complete car and semiconductor industry and even their definition of inch is metric, not the other way round. Won't take long before everything is made in china and everything there is metric.


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## coyote97 (Apr 5, 2009)

Dear Vaporo,


 its the destiny of us tinkers to find out things that are clear to others. or even to event things that have been invented decades before....








But jokes away--i know the feeling of having found out some facts.
Especially when there are some experts arround that cannot tell about a thing they should know. With our german standards, we have to fight now for 40 years to bring standard-notion to the branch, but there are always some old people to tell the truths from about 50 years ago.
And even worse! What is told from former days somtimes itself is 50 Years old. 
And for more, younger employees hear this things, carrying them over decades......
...so: yes, standards are some kind of difficult issues. Not just to bring them on a sheet, but also to bring them in the heads.




So--it really is ok and as i think a kind of a perception to find out things by your own.


But the discussion shows, how fuzzy the different standards can be. What makes it even more difficult to find a way through! 


To have an important part of a work broken is always annoying, and there is no reason for me to think "he should have done this or that".
Its bad to hear that such things happened and i really hope that you will find solutions to go further.
Working with metal i know that basically every work should have a very stable clamping, regardless if the tools are cheap or expensive or if the parts are big or small.
At home, i have no opportunity for safe works and so i did a lot of damage in my hobby, too.




And one last sentence to the quality-question:
perhaps in some years, chinese will be able to perform 100%, but not now. so, chinese products can be "good enough" and they are affordable. So a chinese driller CAN be "good enough", too.
There is nor reason why an expensive tool must be good. It SHOULD be good.
So, bad tolls may be expensive, too.
But one thingis for sure:
really good tolls CANNOT be cheap. The most thing they can reach is "worth a price", but not cheap.


Therefore an Example:


for a production in Turkey we needed to have a bunch of machine-tools like drillers and taps and so on.
Money was short so we bought a "basket full" for 3500 DM, that is about 2000 dollars. Polish or Russian production. For German tools, we feared the price.
The same thing in "good" would have cost about..mmmhmm....9000-10000 dollars.


With the cheap tools we were not able to bring in ONE thread! Not one! We had to find out that a M6 Screw doesnt match a M6 hole.
So after some tests, we through away the rubbish tolls and bought just the needed things for some hundred dollars, and it worked for months!


There are things that are to expensive, regardless how cheap they are.






Frank


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## Semper Vaporo (Jan 2, 2008)

Yes, the soft drink industry was at one time a big proponent of metric liquid volume measurements... but my Coke (tm) and Sprite (tm) bottles today are English liquid measurements; listed as "12 Fl Oz" and under that in parenthisis is "(355 mL)", so to me, it seems they have thrown in the towel too. 


The local hardware store does now stock many metric nuts and bolts and it is becomming a much larger area of stock than it ever used to be and it may well be that North America will one day be Metric if we keep importing goods from countries that use it exclusively... Just another manisfestation of the loss of home manufacturing... but I doubt if I or my kids or grandkids will ever see the inch/foot/mile system go away or never need to use the drill bits from 115 bit set if they get into metal working.


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## xo18thfa (Jan 2, 2008)

C.T. Stay away from the cheap Chinese drill bit sets. I have tried a couple of sets. As the bits get smaller they send a few of the same size, so you don't get all the sizes you are supposed to. Measure with a caliper and you will get odd sizes. They are fine for drilling framing lumber, and drywall.

Invest in a quality set of HHS with bright finish and you won't be sorry. 

Same thing with taps and dies. That Chinese stuff is only good for fishing weights.


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## Jack - Freshwater Models (Feb 17, 2008)

Semper, 

The history of manufacturing technology is interesting. Much of machining history is well documented and interesting. Much of our hole and thread dimensions can be traced to Maudsley and Whitworth in the UK and Wm. Sellers in the US. If such things interest you it is worth researching on the web and in books. 

Cheap drills aren't all that bad if you take the time to sharpen them properly but then learning to sharpen drills is a skill that takes some knowledge and practice. I mostly use "bright" drills in fractional/number/letter sizes. I have some extra drills resharpened with 0deg rake that I use for brass/bronze since that cutting geometry cuts better in brass/bronze. Where you want to place the hole precisely you need to use a center drill or spotting drill before you use the twist drill. I also use reamers when accurate holses are desired. Drills aren't really suited to super accurate holes. Drill the hole about .010-.015" under and open it out to size with a reamer. A fair substitute for a reamer is a twist drill that hs had the "corners" eased or rounded so it follows the first hole easily. Another thing to consider is that for modeling purposes, we really don't need super precise holes in most cases. 

Metric is being used in US industry and is here to stay and will probably become our standard over time. I am in the process of completing a CNC router today and many of the parts are metric not because I wanted metric but because metric parts were the only choice. I prefer imperial units but am forced to go metric sometimes. 

Jack


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## Totalwrecker (Feb 26, 2009)

I've had the same set of high quality decimal drill for 30 years. I use oil or wax when drilling and I resharpen them as needed. Ya gotta let the tool do the work, a sharp edge in quality metal will cut like butter, force it and the heat burns off your lube.... 

I have trouble believing that metric is any more accurate than a thousandth of an inch. 

A tenth of an inch is how much metal is removed to make your wedding band one size smaller....


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## carlferg (Mar 18, 2009)

You can buy quality jobber grade drills of all sizes online from McMaster/Carr supply. I'm a tool&die/moldmaker and we have excellent results with these on tool steel machining. However as others have cautioned here proper RPM, feed rate and lubrication are crutial to success and tool longevity. Carl


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## Les (Feb 11, 2008)

Posted By Semper Vaporo on 04/16/2009 11:21 PM
For years and years I never understood why drill bits came in the standard fraction inch (1/8, 1/4, etc.) and metric sizes as well as the "numbered" and "lettered" sizes. I did not understand why the numbered and lettered sizes existed... I just figured they were a hold over from some earlier time before some Standards Bureau settled on the fractional sizes.


/// There are several standards at play. It's a tad overstating to dismiss them as 'holdovers'. I suggest you go buy a used copy of the Machinist's Handbook, or Machinery Handbook. You'll be amazed at what you learn. For only one instance, you'll note there is a small screw called a #4-40. That means it is a #4 diameter with a 40 pitch--or 40 threads to the inch. There is another #4 screw, called a #4-48. It has, guess what, 48 TPI. This is done to increase the holding power of the screw/nut combination and are much favored by gun enthusiasts, where momentary shocks are part of life. I'd have to go look, but I believe each requires a different 'tap drill size'. To find out why is why you need either of those two books. These high TPI-count taps and drill sets are nowadays ususally called 'gunmaker's tap and drill sets. But they have use in industry as well.

A few years ago, when I started to "PLAY" in metal working (bought a Lathe and Mill), I began to need to drill holes that I wanted to put (tap) screw (bolt) threads into and found I never had the correct size drill for the size of bolt I wanted to make a mating hole for. I purchased the best "small" set of drill bits I could afford and it did not contain the correct drill bits for drilling holes to be "tapped". I kind of figured out that I would need to purchase one of the 115 piece sets to finally get all the possible sizes, but, to get quality bits it would be too expensive to do so... so I just kind of muddle along picking the next larger size and hope there is enough material left in the hole to form threads when I am done. (It does most times make it easier to cut the threads to have an over sized hole, but it sometimes leaves me worried about the strength of the bolted joint!)

////IMNSHO, Don't even _think_ of buying the HF drills. You're wasting your money. Instead, do as someone else has suggested and buy the taps and dies and drills you need. For each size screw, you'll need two drill bits, a clearance drill, and a tap drill. The latter drills a smaller hole to leave the CORRECT amount of material to be tapped, to ensure the maximum practicable holding power. i.e. no stripped threads from overload. Also, someone noted that if you do that, you find you have no proper drill or tap when you want one. You get around that by buying three of all sizes of everything. When you get down to your last one (or two, if you are prone to worry) you send off an order for three more. All in all, you'll be saving money over purchasing a massive set of drill bits.


I was just now reading the Harbor Freight flyer and noticed a drill bit set for sale that is the 60 "Numbered" bits and wondered what sizes those were. I grabbed my "Thomas J. Glover Pocket Ref." book and looked up the sizes (pgs 450-459). Then I turned to the table of thread sizes (page 598) and what drill bit to use and compared the numbered dimensions to the recommended "tap drill" to use and noticed that the Numbered drills are the correct sizes for drilling holes to be tapped.

WOW! Now I know!


/// Yup. There's a reason those 'odd' number-drill sets are still around.



Now that I am into "Metal working" I need drill bit sets designed for the metal worker and in this realm one needs to drill both clearance holes and holes to be tapped.


/// See my comment above.

In the past I have purchased drill bit sets that are inexpensive enough for me to afford and found that the drill bits sometimes cannot drill one hole in soft wood without being ruined by the act of using them. My personal opinion of the "TiN" (Titanium Nitride, I think) coated drill bits are a joke... they are the ones that have been the worst as far as longevity of use.

/// I have used standard high-speed steel drill bits (not 'drillers') in industry for years. I find no reason to change. I think the coated bits came out wtih the CNC machining, where things happen fast, quick and for a long period. That isn't the case in manually-controlled machines, and the cheap 'plated' drill bits are sucker bait, so far as I'm concerned. Do you use any form of cutting oil, lubricant, anything, when drilling holes in metal? No? Start doing so and soon you will feel so pleased at how much longer your bits will last before resharpening--which you can't do with the smaller sized ones, anyway.

When I started working in metal I did purchase a good set of drill bits (http://www.wintersdrillbitcity.com/), but now I realize they are the "wood worker set" (17 in the set... 1/16 to 1/2 inch). I paid a pretty penny for them and I love them, but there are no Numbered bits in the set. The 115 bit set from that same company is way outside of the realm of my wallet.


/// Buy your bits/taps/dies etc from a reputable house, like McMaster-Carr, or the like. You can ask on minimum quantities.

Does anyone know if this Harbor Freight set of 60 numbered drill bits are any good? i.e.: will they drill more than one hole in metal and still be usable? The advert says they are TiN coated and from past experience I have NO desire to repeat the loss of my hard earned cash!

/// The only drill bits I use from HF--and I am an HF afficianado--are the spade wood bits, because they're easily resharpen-able on a grinder, and cheap. For the kind of work I do, they're good enough. My metal bits are expensive ones. I just bought the HF tool bit grinder ($150) because I've wanted one for years for putting correct angles on cutting bits, a difficult thing to do with a common wheel grinder. Don't buy their cheap drill bit sharpener. It's a genuine POS.

///One thing that wasn't discussed was 'purpose'. Do you want clean, crisp holes where you intend for them to be, or can you be satisfied with triangular-shaped holes, mushed out top and bottom and wandering off center from where you started? Many jobs can afford this sloppiness. Some, like precision modelling, cannot. This leads into the tooling itself: the common wisdom is, "Buy the best tool you can afford." I don't necessarily agree with that. Sometimes it's very valid to start out wtih a cheap tool, like a HF job, and use it until you figure out what its limits are. Very often, an newbie can't hold the tolerance the machine is able to give until he gets some practice, and by then he might be skillful enough that he doesn't particularly need the expensive stuff. I routinely used Harding lathes that gave 0.0001 tolerance. That's one-ten thousandths. Not many commonplace machinists can hold that tolerance, even if the machine is able to give it. So why spend the extra money? If that sounds like an extreme example, think of this: I own a 1/2" Walker Turner drill press. I use it rarely. What I mostly use is a HF 1/2" cheapie. Why? Because it's as accurate as I need it to be. That's the definition of 'purpose'. Why have two, then? If I need to put a hole 'spot on', I know which machine I'll use. I rarely am faced with that need.

When you move into lathes and mills, the argument gets a little dicier, but the theory's still the same. I've always thought the real reason amateurs are urged to 'buy the best you can afford' is the secret hope that the machine will make up for the lack of skill of the operator. It won't.

Les


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## Semper Vaporo (Jan 2, 2008)

Ed: Thanks for the comments. I appreciate it... may I point you to a story of mine that I posted some time ago?

http://www.mylargescale.com/Community/Forums/tabid/56/forumid/24/tpage/1/view/topic/postid/3350/Default.aspx#3662

I think it is an example of what you just said.


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## SE18 (Feb 21, 2008)

I bought a template to figure out the sizes of all my bits, which were thrown together in a pile. The bits come in handy as rulers. For example, if you have a router or table drill and want to verify the distance between the cutter and the work, you can insert, say, a 3/32 bit between the pieces, or metric distances.


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## imrnjr (Jan 2, 2008)

I bought one of the titanium coated sets from HF....it is truly CCS (Cheap China S#$*)...I get about 3 holes in the mid sized bits, and maybe 2 in the larger sizes. The small numbers (less than 3/32's) are so soft they will flex with the least bit of pressure. Save up and get agood set to start with. 

Mark


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