Drill Bit Selection Guide: Types, Uses, and Maintenance

One of the most important tools in any metalworker's arsenal is the drill bit. Drill bits are cylindrical cutting tools that are used to create holes in various materials such as metal, plastic, wood, ceramic tile, and concrete. But not all drill bits are made the same, and choosing the wrong one can lead to disastrous results.

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Using the wrong bit can result in damage to the material, decreased efficiency, and even injury to the user. Therefore, it's essential to understand the various types of drill bits available and their unique features, including materials, coatings, point angles, and lengths.

Whether you're a seasoned metalworker or just starting, this guide will equip you with the knowledge you need to make informed decisions and achieve the best results.

Drill Bit Materials

Here are the three most common types of drill bit materials:

High-Speed Steel (HSS)

High-speed steel (HSS) is a type of tool steel that is highly resistant to heat and wear. It contains tungsten, molybdenum, chromium, and vanadium, which provide increased strength and durability. HSS drill bits are suitable for drilling into soft metals, such as aluminum and brass, as well as wood and plastic.

• Advantages: HSS drill bits are relatively affordable, easy to sharpen, and have a long lifespan when used correctly.
• Disadvantages: HSS drill bits are not suitable for drilling hard metals, such as stainless steel, and can lose their sharpness quickly when used on tough materials.

Cobalt (HSCO)

Cobalt (HSCO) drill bits are made from high-speed steel with added cobalt, which enhances their strength and heat resistance. They can withstand higher temperatures and are less prone to dulling. Cobalt drill bits are ideal for drilling through hard metals, such as stainless steel, cast iron, and titanium.

• Advantages: Cobalt drill bits are highly durable, resist wear and tear, and maintain their sharpness for longer than HSS drill bits.
• Disadvantages: Cobalt drill bits are more expensive than HSS drill bits and require specialized equipment for sharpening.

Carbide (Carb)

Carbide (Carb) drill bits are made from tungsten carbide, which is a dense and durable material that can resist high temperatures and wear. They are ideal for drilling through hard materials, including ceramics, glass, and masonry, as well as hard metals like stainless steel and cast iron.

• Advantages: This type is incredibly durable, can maintain its sharpness for longer than other drill bit materials, and can handle high-speed drilling.
• Disadvantages: They are the most expensive of the three materials, and they can be brittle, which can cause them to break if they're not used correctly.

Design Features of Drill Bits

To choose the best drill bits for metal and other materials, you should consider the design features that affect their performance. These are the three key design features of drill bits:

Drill Point Angle

The drill point angle refers to the angle at which the cutting edge of the drill bit is ground. It is measured in degrees and can range from 90 to 150. A 118-degree angle is the most common, but other angles, such as 135 degrees and 90 degrees, may be more suitable for specific materials or applications.

Common Drill Point Angles

• 118°: Most commonly used angle for general-purpose drilling in metal, wood, and plastic. It is ideal for drilling softer metals, such as aluminum and copper. It also offers a balance between sharpness and durability. However, it may not perform well on harder materials.
• 135°: Better suited for drilling harder materials and alloys such as stainless steel, cast iron, and titanium. While it can handle harder materials, it may not be as effective on softer ones.
• 90°: It is used for creating countersink holes, deburring, and chamfering, but not suitable for drilling.

Drill Point Lengths

The drill point length refers to the distance from the tip of the drill bit to the beginning of the flute. There are three types of drill point lengths: standard, jobber, and long.

• Standard: Offers the most rigidity and is best suited for shallow holes in softer materials. Since it is rigid, it may not be suitable for deeper holes.
• Jobber: A versatile length that can drill holes of various depths and range of materials and is suitable for general-purpose drilling. While versatile, it may not be the best choice for drilling in hard-to-reach areas or extremely deep holes.
• Long: Offers the most flexibility and is ideal for drilling deep holes or in hard-to-reach places, but may be more prone to breaking or bending.

Flutes

Flutes are the grooves that run spirally along the length of a drill bit. They serve to remove chips and debris from the hole as the bit cuts into the material. They are also typically wider and deeper on larger diameter bits. Flute design can greatly affect the performance and efficiency of a drill bit.

Types of Flute Designs

• Standard flutes: Standard flutes are straight and are found on most drill bits. They are versatile and suitable for most materials and drilling applications, but may not be the most efficient option for harder materials.
• Parabolic flutes: Parabolic flutes have a deeper flute design and are more efficient at chip removal, making them suitable for softer materials, such as wood or plastic. They may not be as effective for harder materials or larger diameter bits.
• Helical flutes: Helical flutes twist along the length of the bit, creating a longer cutting edge and improving chip evacuation. They are suitable for harder materials, such as metal or concrete, that require extra cutting power. On the other hand, they may be more difficult to control and require more force to start drilling
• Double flutes: Double flutes have two sets of flutes that run parallel to each other, providing extra stability and control for drilling straight or accurate holes in wood or metal. They provide extra stability and control, but may produce more heat and friction during drilling.

Drill Bit Coatings

Drill bits have different coatings, each with its features, advantages, and disadvantages.

Black Oxide

Black oxide is a coating made by blackening the surface of the drill bit to enhance rust resistance and reduce friction. It is made from iron oxide and magnetite. They are best used for drilling soft metals such as aluminum, copper, brass, and mild steel.

• Advantages: Provides wear resistance and corrosion resistance. It also reduces friction, increasing the lifespan of the drill bit.
• Disadvantages: Not suitable for use on hard metals. It can also be easily scratched, which could affect the quality of the workpiece.

Bright

A bare metal finish with no coating. It is the most common type of drill bit. They are best used for drilling plastic, wood, and soft metals.

• Advantages: Easy to sharpen and provides good accuracy in drilling.
• Disadvantages: No rust resistance, and has a high friction level, causing heat buildup and reduced lifespan.

Titanium Nitride (TiN)

A gold-colored coating that provides heat resistance and hardness. It is made by depositing titanium nitride on the surface of the drill bit.
They are best used for drilling hard materials such as stainless steel, cast iron, and titanium.

• Advantages: Provides high heat resistance and hardness, which extends the lifespan of the drill bit. It also reduces friction and prevents galling and welding of the drill bit to the workpiece.
• Disadvantages: It is a relatively expensive coating.

Titanium Carbonitride (TiCN)

A gray-colored coating that is harder than TiN. It is made by depositing a layer of titanium carbonitride on the surface of the drill bit. They are best used for drilling abrasive materials like high-silicon aluminum, fiberglass, and carbon composites.

• Advantages: Provides a harder and more wear-resistant coating than TiN. It also has high lubricity, reducing the heat buildup and friction between the drill bit and workpiece.
• Disadvantages: It is more expensive than TiN.

Other Common Coatings Used in Drill Bits

• TiALN: A dark gray-colored coating that provides extreme hardness and heat resistance. It is best used for drilling hardened steels and stainless steel.
• Diamond-Like Carbon (DLC): A black-colored coating that provides superior hardness and wear resistance. It is best used for drilling non-ferrous metals and plastics.
• Zirconium Nitride (ZrN): A copper-colored coating that provides high wear resistance and low friction. It is best used for drilling aluminum and other non-ferrous metals.

Types of Drill Bits

When it comes to drilling, there are various types of drill bits designed for specific materials and applications. Here are some of the most common types:

• Twist Drill Bits: These are the most commonly used drill bits and are suitable for drilling holes in wood, plastic, and metal. They have a spiral shape that helps to remove the material being drilled and prevent the bit from getting stuck.
• Brad Point Bits: These bits are designed for drilling clean and accurate holes in wood. They have a sharp center point that helps to start the hole and two cutting edges that make clean cuts along the sides.
• Auger Bits: These bits are designed for drilling deep holes in wood. They have a long, spiral-shaped flute that removes chips from the hole as it is drilled.
• Spade Bits: These bits are designed for drilling large holes in wood. They have a flat, paddle-like shape with a pointed tip that helps to start the hole.
• Forstner Bits: These bits are designed for drilling flat-bottomed holes in wood. They have a flat, circular shape with a center point that helps to start the hole and cutting edges that create a smooth, flat bottom.
• Hole Saw Bits: These bits are designed for cutting large holes in wood, metal, and other materials. They have a circular shape with a saw-toothed edge that cuts through the material.
• Step Drill Bits: These bits are designed for drilling holes in metal and other hard materials. They have a stepped design that allows for drilling holes of different sizes with one bit.
• Masonry Bits: These bits are designed for drilling holes in concrete, brick, and other masonry materials. They have a carbide tip that can withstand the hardness of masonry materials.
• Glass and Tile Bits: These bits are designed for drilling holes in glass, tile, and other fragile materials. They have a carbide tip and a specialized design that reduces the risk of cracking or chipping the material.
• Countersink Bits: These bits are designed for drilling pilot holes and countersinks in wood and other soft materials. They have a tapered shape that creates a conical hole and a flat bottom for screws or other hardware.
• Drill Bit Sets: These sets include multiple types and sizes of drill bits for various applications. They are a great option for those who need a variety of drill bits for different materials and projects.

Each type of drill bit has its own unique features, suitable applications, advantages, and disadvantages. Choosing the right type of drill bit is essential for achieving accurate and efficient results in drilling.

Maintaining Drill Bits

If you want your drill bit to function optimally and improve its longevity, proper maintenance is a must.

Proper Storage

• Store drill bits in a dry and clean location
• Keep them in their original packaging or a designated storage container
• Use a rack or pegboard to organize and prevent damage
• Avoid exposure to extreme temperatures and humidity
• Label the storage container for easy identification
• Sharpening and maintenance techniques

Sharpening and Maintenance Techniques

• Use a file or grinder to sharpen dull drill bits
• Keep the bit cool while sharpening to prevent overheating and damage
• Remove any burrs or chips on the cutting edge
• Check the bit regularly for signs of wear or damage
• Use lubricant or cutting oil during drilling to reduce friction and heat buildup
• Avoid applying excessive pressure during drilling, which can cause wear and damage to the bit.

Common Mistakes to Avoid When Using Drill Bits

When it comes to using drill bits, mistakes are not uncommon. These are some of the most common mistakes that you should avoid to ensure safety:

• Using the wrong drill bit: Choosing the wrong type or size of drill bit can damage the material being drilled, the drill bit itself, or even the drill. Always use the appropriate drill bit for the material and project being worked on.
• Applying too much pressure: Applying too much pressure on the drill can cause the bit to bend or break, damage the material being drilled, or cause injury to the user. Let the drill do the work and apply gentle and steady pressure to avoid damaging the bit or material.
• Overheating the bit: Overheating the bit can cause it to become dull and ineffective, or even melt and break. Use the proper speed setting for the drill, and apply lubrication or cooling agents to reduce friction and heat buildup.
• Neglecting to use safety gear: Failure to use proper safety gear such as safety goggles, gloves, and earplugs can lead to injury or long-term health problems. Always wear the appropriate safety gear when using a drill to protect yourself from flying debris, loud noises, and other hazards

Drill bits are essential tools used in various applications, from woodworking to metalworking and construction. Choosing the right drill bit for the task at hand can save time, increase efficiency and ensure safety. It is crucial to consider the type of material to be drilled, the desired hole size, and the required precision. Additionally, understanding the different types of drill bit coatings, design features, and maintenance techniques can extend the life of your drill bits and save you money in the long run.

I'm definitely OCD regards drill bits.I've probably acquired way too many, but still crave more.

I had much trouble drilling with the mini lathe when i started out. Small bits flexed alarmingly, mid sized bits seemed ok…ish, larger bits wanted to waggle the tailstock quill!

Turned out my headstock/tailstock alignment was poor…if your having problems drilling on your lathe then start there….but i'm jumping ahead of myself,

As a novice i just didn't know…..this lead to many hours internet research in search of the truth & a solution.

"Drilling is not a precision opperation"~ one quote i found on the internet which deflated me somewhat.

Seems on further inspection if you want a precisely round, precisely sized hole you need to bore or ream it.

But we still want drilled holes as precise as we can make them?

Oft times a drilled hole is 'good enough.'

Try as i might, on my mini lathe or mciro mill an X mm sized hole always seems to come out about 4 thou (0.1mm oversize) I now have various "point 9" drills for the common mm sizes.

"Drilling is the most efficient metal removal opperation"~ another internet quote.

So, given we are using small machines, at least compared to industrial ones, Drilling is your friend in terms of time saved machining.

Drill to remove material whenever possible one might say.

Drilling may not be a precise opperation, but it certainly seems to be a mature & vast one.

Look at a humble twist drilldrill, it may be 118 or 135 deg point angle, it may be split point or conventional point or one of many variations ~ Racon point anyone?

It may have a thin web or a thick web, it may have light or heavy lands.

It may be a rolled drill bit (generally black finish) or a ground bit ( generally bright finish)

It may be coated or uncoated, it may be HSS eg M2 or a cobalt tool steel

All this will influence how it cuts & in what material.

Goodness i'm giving MYSELF a headache.

Then we have fast, normal & slow helix drills…..personally iavoid fast helix drills, i consider them the work of the devil, but if you like Ali, maybe not.

On my search for an accurate drill i discovered stub drills~ shorter should be more precise right? Ok up to a point, but not a solution with a wonky tailstock.

Stub drills could have been tailor made for the home engineer~ with our limited center to center distances / head to table height~ these short bits are a oft times a godsend.

What is frustrating is that generally you pay.more to get less material!!

Now, back to those drill points.

Conventional drill points ( 118 deg non split ) are great for the hobbyist,

These you can sharpen yourself. Money saving.

I'm not the best @ this but can get the job done.

Everyone should give this a go.

My non machinist, keen DIYer friend was ecstatic when i gave him a sharpening gauge~ he seems to have got the knack of it very quickly.

….What i'm less keen on is with conventional drill points you need to pilot/ center drill first.

They do seem to work better for step drilling however IMO.

Split point drills, particularly those with a larger point angle require less power to drill a hole.(major boon for small machine tool users)

If you don't believe me try drilling a 1/2" hole with a conventional drill then with a split point.

On the negative side there doesn't seem any easy way to resharpen them. You could resharpen as a conventional point but as they usually have a heavty web this may be less than satisfactory,

I guess some enterprising individual has found a way to resharpen these at home.

Ground or rollled drill bit?

From my pre engineering days i always found ground seemed to cut a little better.

However, though i am at a loss to explain this, once resharpened, Rolled bits, even quality ones SEEM to cut better than new???

Additionally a little tip i picked up was to gring a secondary steeper angle on the drill point edges~ this seems to make the drill cut truer & closer to size~ google it if your interested.

I do like cobalt bits, however if truth be known standard HSS of good quality are probably all most hobbyists will need.Stainless?~ no problem, slow speed high feed.

Drilling Brass~

In my pre engineering days i chewed up a good few drill shanks drilling brass. How was i to know standard drill bits are not so good for brass.

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Correct procedure is to use a slow helix angle drill (i have a few odd sizes of these but still, less than impressed)

Or, dub some old bits (google it) I did try this with a couple of old Hss-R bits but must have got something wrong as they refused to cut brass or any other material.

My proccedure for drilling brass with standard drill bits is as follows~

Generally below 3/16" aint a problen

I find sharp split points best.

NEVER EVER EVER step drill brass with standard drills. Ok…go do it,if you gotta learn the hard way,

Select slow speed, slowly feed drill bit in, it may squeal a bit till full width of bit is engaged, then you can up speed & feed a bit.

If you need to clear hole of swarf (peck drilling) disengage bit as normal but when feeding back in feed very gingerly until drill bit bites again as this is most likely time where you will get a dig in.

I've drilled 16mm holes in one in brass like this.

Well i'm sure i missed some stuff, I certainly don't know it all, hopefully someone that does will chip in.

Inncidently i read some of the drill bit threads~ selecting an initial drill set can be daunting when starting out.

I started with a 1-10mm in 0.5mm

Although i usually work in metric this wasn't the most useful for me.

1/16 to 1/2" set plus some odd metic sizes helped out a lot. Go figure.

Samuel,

As you have found in your search a drilled hole is not a precision item per se but it can be improved considerably with care and the right approach

Whilst I agree that step drilling brass with conventional drills is fraught with 'pull in' simply stoning the cutting edge to a very slight negative angle will improve matters considerably. Drawn Phosphor Bronze is another material to be aware of when drilling. That material and some stainless are those I steer clear of if possible.

I don't possess anything 'fancy' when it comes to drills only a set of jobbers drills in 1-10mm in .01 steps, a set of Number drills 0- 80 and 1/16 – 1/2" in 64ths and a set of letter drills. Though I used them at work I don't possess a spotting drill of any kind just conventional centre drills 1/8 – 1/2". All, when required, are sharpened by hand on a bench grinder. Centre drills are quite difficult to resharpen and not always successful.

I think it would be fair to say I've drilled a few holes at home over the years – never felt the need for anything more 'esoteric'. At work, of course, it was much more different

Best – Tug

Posted by samuel heywood on 12/12/ 00:24:03:

…

Goodness i'm giving MYSELF a headache.

…

Indeed! Welcome to the complicated world of drilling. My experience suggests it's a waste of time looking for the perfect accurate drill because the answer varies depending on what's meant by 'accurate', the material, hole-depth, and the machine. As noted, no drill in the world works properly in a mini-lathe with an offset tailstock. Another problem with mini-lathes is they don't spin fast enough for small diameter drills, and may not have enough torque at low rpm to cut with a big drill. Rule of thumb, approx /diameter in mm, so a 2mm drill works best at about rpm, twice typical top mini-lathe speed. So, drilling – which isn't a precision operation in the first place – is often compromised, either because the drill is too slow or torque problems force one into step-drilling. Step-drilling has many disadvantages, best avoided altogether, but needs must when the devil drives!

Twist-drills are quick and convenient, and the holes they make are accurate enough for most purposes. Text-books highlight their relatively poor accuracy and suggest reaming or boring when accuracy is important. That is the drill bangs out a hole of roughly the right size, which can be corrected by a reamer or by boring. Of the two, boring is best because it produces perfectly circular holes, of the right diameter, that are true – boring cutters don't wander off axis like twist-drills, which can't be trusted to stay straight for more than about 2.5 diameter deep.

One of my books insists that hand sharpening and accuracy are incompatible. The problem is the human eye and hand aren't good enough to cut two identical edges that meet at a point exactly on the drill's axis. Hand sharpening is done for cheapness, which is great if the resulting holes are 'good enough', but not acceptable when accuracy matters. Then the drill has to be resharpened by machine much more sophisticated than the type sold by ironmongers.

I've settled on mid-range ground HSS drills because they make reasonable holes. Below about 10mm I don't bother resharpening them. I keep one set for Brass and another for steel because Brass needs sharp drills, steel is less fussy.

I have 5 drills, all with strengths and weaknesses:

• Hand-held, is good for quick one-offs but not accurate.
• Hand-held power drill, good for repeat work, mostly DIY, not accurate.
• Bench pillar drill, moderately accurate if a centre-punched job is allowed to float into the drill's spinning axis. Good for several non-critically placed holes on largish jobs
• Milling machine, good accuracy when the work is clamped firmly, including X,Y,Z positioning within about 0.02mm. Most of my drilling is done this way.
• Lathe. Best accuracy, but can only take smallish jobs, and setting up a 4-jaw or faceplate for other than drilling dead centre is finicky. Fortunately most drilling is done dead centre in a 3-jaw.

Years of fun ahead!

Dave

Posted by Kiwi Bloke on 12/12/ 04:09:31:

Not sure whether you're inviting comments, or just casting pearls…

I'm not sure either, seems a bit over-complicated?

My everyday drills, 1 to 10mm by 0.1mm, are Dormer 4-facet. Imperial, number and letter drills are conventional, but don't get used that often. I expect drilled holes to be within 1 to 2 thou, usually oversize. For better accuracy I bore or ream depending on size and machine in use.

For general work 4-facet drills start, on the vertical mill, without needing a centre, provided the work is smooth and flat. If I need to be assured of positional accuracy I use a carbide spot drill first. Never got on with using centre drills for spotting. I only use centre drills in the lathe.

Stoning drill edges never worked for me so I have a small set of slow helix drills for use on copper alloys. Bronze and gunmetal are worse than brass for pulling in. I also have a few fast helix drills, but I don't machine much aluminium these days.

Carbide drills are used for tough materials, like tungsten, and are also stiffer than HSS. So small carbide drills are less prone to wander than HSS.

I would agree that drilling is a good way of removing metal. I have a good selection of Morse taper drills (all secondhand) for opening up holes before boring. Biggest drill is 1-7/8".

Although hand sharpening is easy, and I have a Clarkson T&C grinder for conventional and 4-facet drills, by the time my drills need sharpening they're not in great overall shape. It's much simpler and cheaper to buy new drills.

I also have a good selection of LH drills, and centre drills, for use on the repetition lathe.

My only problem drilling is with gauge plate. In it's supplied state it ought to be fine, but it seems to eat my HSS drills.

Andrew

The reason your holes are oversize is that the two drill lips are different sizes, even from new, and once used the outer corners of the cutting edge unevenly worn. Step drilling helps with this, and ensures the little lathe is not overloaded.
If you read old ME articles drilling is always done in stages but recently there seem to be a brigade of "I was a toolmaker for 50 years" who can't grasp that a minilathe can't shove a 2inch bit through steel in one go like their 20 HP industrial machine did in the blacksmiths shop where they really worked.
The reason for using a centre drill not a spotting drill to start is that is it is rigid but your tailstock must also be firm, the barrel not sloppy, and of course on centre. Make sure there is no residual burr to throw off the next stage drill which is why you go in to just start using the coned part of the centre drill.
Each drill in the steps needs some metal to work on so choose steps appropriate to the size of lathe so that the chisel is well cleared and there is at least 1mm for the edge to work on.
The reason new drills do not have a secondary clearance is that the area of that back slope stops the drill spiral trying to pull it in too fast. Amateurs putting on a secondary clearance actually make performance worse, which is not helped by the tailstock thread backlash allowing it to snatch.
Hand ground drills whatever those "toolmakers" claim are always out of true as it is a physical impossibility for a wobbly flesh hand to hold a constant angle, let alone duplicate it for the other lip. Even lightweight hobby tool and cutter grinders cannot achieve this,
A good Model Engineer eventually learns all the limitations of their equipment and compensates. I hope to get there in about .

Posted by Bazyle on 12/12/ 11:01:12:

The reason your holes are oversize is that the two drill lips are different sizes, even from new, and once used the outer corners of the cutting edge unevenly worn. Step drilling helps with this, and ensures the little lathe is not overloaded.
If you read old ME articles drilling is always done in stages but recently there seem to be a brigade of "I was a toolmaker for 50 years" who can't grasp that a minilathe can't shove a 2inch bit through steel in one go like their 20 HP industrial machine did in the blacksmiths shop where they really worked.
The reason for using a centre drill not a spotting drill to start is that is it is rigid but your tailstock must also be firm, the barrel not sloppy, and of course on centre. Make sure there is no residual burr to throw off the next stage drill which is why you go in to just start using the coned part of the centre drill.
Each drill in the steps needs some metal to work on so choose steps appropriate to the size of lathe so that the chisel is well cleared and there is at least 1mm for the edge to work on.
The reason new drills do not have a secondary clearance is that the area of that back slope stops the drill spiral trying to pull it in too fast. Amateurs putting on a secondary clearance actually make performance worse, which is not helped by the tailstock thread backlash allowing it to snatch.
Hand ground drills whatever those "toolmakers" claim are always out of true as it is a physical impossibility for a wobbly flesh hand to hold a constant angle, let alone duplicate it for the other lip. Even lightweight hobby tool and cutter grinders cannot achieve this,
A good Model Engineer eventually learns all the limitations of their equipment and compensates. I hope to get there in about .

I don't know how many times I've used the phrase 'Horses for Courses' on here in the past but where any machining is concerned it doesn't – shouldn't – take much to realise that whatever you do has to be within the limit of the machines at your disposal. Andrew's ability to use his larger machines is a whole world from a mini lathe. Likewise using kit at work. Watching blue chips hit the back of the lathe tray like bullets is one thing there but forcing the Super 7 to emulate it is not, in my mind, a viable option.

Let it be said clearly 'I am not a toolmaker' – nor would I ever claim to be but I have been machining both at work and home for many years. I do grind my drills by hand and I do get results. Like anything else though – practice makes for better results. I was fortunate to be shown early on in my ME 'career' by some one who was a highly respected toolmaker and though those first results were pretty poor if it didn't cut I reground it till it did. Grinding the end off a perfectly good drill to drill a flat bottom hole and then repointing it was the only way in early days.

Like any other workshop practice learning how to do something pays off in the end. For instance it's handy to be able to grind one flute longer than the other to aid drilling phosphor bronze to head off the inevitable seizure then return it to normal. No of course it isn't 'machine ground' accurate but certainly good enough for 95%+ of the holes required.

As has been stated if an accurate sized hole is required then it requires reaming – if an accurately sized and positioned hole is required then it needs boring after drilling too as a reamer will always follow a drilled hole.

I don't have, nor keep, separate sets of drills for anything – just work what I have to suit the occasion.

Agree with the gauge plate issue though – not an easy material to work at the best of times so I I always keep the speed well down on any cutter including drilling.

Best – Tug

In a previous galaxy, far far away, I found myself drilling second hand Morris Minor rear springs for a centre bolt. I was cutting them down in length to make trailer springs for a range of two axle trailers I made for a while. I wanted an 8 mm hole but found I couldn't drill this in one take, I needed a pilot hole because I couldn't put enough pressure on an 8 mm drill to keep it cutting. I don't know the exact metallurgical provenance of Mr Morris' spring steel, but it was tough stuff. Ford Transit springs were even tougher – I couldn't drill those.

I found that a 3 mm pilot was too fragile and the drill snapped, a 5 mm drill was a little on the large size and I couldn't reliably keep it cutting but a 4.5 mm drill was a good compromise whilst leaving enough meat for the following 8 mm drill to cut through without grabbing. If you let the drill skate then you might as well throw that leaf away – this was before the days of carbide drills as we now know them. I did experiment a bit (no pun intended!) with re-shaped masonry drills, but it was more trouble than it was worth.

Drills needed to be sharp, with not too much front clearance – hand ground was perfectly adequate. I doubt if the drills were anything other than bog standard Dormer jobber drills. They had a hard life! They needed to be run really slowly and with water or soluble oil coolant with as much down pressure as you dared.

But the moral of the story is that drilling hardened or hardenable steels is about enough pressure on the drill to keep it cutting.

FWIW I think 01 tool steel is lovely stuff to work with!

Seasons greetings

Simon

When I did my apprenticeship, drill sharpening was essentially the apprentice job to keep them sharp and on drills all over 4mm. Under 4mm they were discarded. So I got a lot of small drills free. Now days , people don't like learning, and anything that seems like hard work is avoided as there are now drill sharpening tools that do a very good job in a timely manor. Often the home shop does not have the best grade of wheel for sharpening drills on, as often they come with hard wheels , suitable for general grinding of soft steel. Few know about using diamond dressers to re dress a wheel, and if they need a fine dress or a course dress. Touching up a dulled bit is easily done with a fine dressed white wheel. But a drill with chips or heavy edge rounding will be best if started with a course dressed wheel as it cuts cooler. Some my be lucky enough to have fine or course desic CBD wheels to sharpen drills on. But that is what often the serious wood turner has at their disposal and sometime come up for sale at a very good price.

One thing I do, is use a basic clearly graduated rule, I like the small Toledo ones, and measure the length of the drill sides. In general they will be about 1/2 the diameter of the drill or so, and of equal length to drill an on size hole, assuming that they are held at the same angle to the wheel. After a while , you get used to making your hands the fixture to get the angles even and adjust the back off to suite the material and rate of drill advance etc.

When you have a drill, and the hole is oversized, the side with all the chips is the one doing all the work. So just take a little more off the side with no chips to get it back closer to cutting evenly on both edges to get it back to size.

Another trick, when we did not have reamers, was to radius the outer cutting edges with a stone, and run that through at a slower speed, to get a very close to size hole. When done with castor oil, it would be very close to the drill size. This was for things like odd sized ejector pin holes in plastic dies etc.

Where ever possible, would drill the hole with the largest closest drill we had, up to 1.5 inches or 38mm diameter. Just start with a spotting drill, or centre drill, and in with the drill. This is when you find out, how important web thinning is.

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