Let’s talk about Drill bits, specifically twist drills.

[samuel heywoodParticipant @samuelheywood23031]

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.

[samuel heywoodParticipant @samuelheywood23031]

[Ady1Participant @ady1]

Backing off the trailing edge makes things easier

**LINK**

[samuel heywoodParticipant @samuelheywood23031]

….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.

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.

[Kiwi BlokeParticipant @kiwibloke62605]

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

Let's keep it simple. 4-facet (or 6-facet, if you want to be fancier) points are the answer for most (of our) applications. They can be elaborated to split point (as Ady1's link shows) if you want to make re-sharpening more difficult. The chisel point on 'conventional' bits just makes things difficult, especially on less-than-rigid machines.

As for 'step drilling', try to avoid the need – it's a tricky operation at best, and a drill-bit breaker at worst.

Oh, and don't start drilled holes with a centre drill – use a 4-facet pointed spotting drill.

That's all I know…

[Ramon WilsonParticipant @ramonwilson3]

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

[Simon CollierParticipant @simoncollier74340]

I hate drilling. Something that helps with difficult materials like brass on my SX3 mill drill is to lock the quill and wind the head down. It can’t grab and pull in. It can bind and spin in the chuck! But not likely with brass.

[SillyOldDufferModerator @sillyoldduffer]

Posted by samuel heywood on 12/12/2022 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 10000/diameter in mm, so a 2mm drill works best at about 5000rpm, 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

[Anonymous]

Posted by Kiwi Bloke on 12/12/2022 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

[BazyleParticipant @bazyle]

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 2040.

[Neil WyattModerator @neilwyatt]

Posted by Andrew Johnston on 12/12/2022 10:37:03:

Posted by Kiwi Bloke on 12/12/2022 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.

It's rather sad… my Dormers are so nice, I tend to use cheaper drills so that the Dormer ones stay sharp… 🤣

Neil

[Ramon WilsonParticipant @ramonwilson3]

Posted by Bazyle on 12/12/2022 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 2040.

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

[HopperParticipant @hopper]

LOL yes I do the same with my "good" set of 1 to 12mm in .1 increments. Looking through all sorts of sets of drills and boxes of loose ones and conversion size charts to rough it out to the last few thou undersize then use the "good" drill for the final pass to get it to size.

But yes, drills always/usually drill a bit oversize. Nothing you can do about that, except perhaps stone a small radius on the tips of the cutting edges (lips). Then they do reasonably well, most of the time, sometimes.

To do a hole "properly", toolmakers are taught to drill first for rapid but rough metal removal. Then bore for location, concentricity, and parallel. Then ream for final size and finish.

But it is horses for courses. Dowel holes between two pieces of a die will be just drilled and reamed. Bolt holes will be just drilled. Punch die holes etc will be just drilled then bored to final size in a specialist jig boring machine, with great precision and finish.

[bernard towersParticipant @bernardtowers37738]

I agree that the lip length is THE most important thing for accurate sized holes, I use 4 facet sharpening with a secondary point angle on sizes above 6mm as it is believed to keep the hole straighter and give a better finish and just stone the front for brass.

[BazyleParticipant @bazyle]

Thanks for the tip about drilling bronze Tug. I may have missed it in some ME article but maybe Neil could pop it into one of the 'hints and tips' lists.

[samuel heywoodParticipant @samuelheywood23031]

Posted by Kiwi Bloke on 12/12/2022 04:09:31:

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

Absolutely inviting comments.Already learned a little more.

Enthusiasm can go a long way but it's no substitute for experience.

I'm quite sure there's many collective years experience on the forum, with probably more than a few individuals possessing a whole lifetimes' engineering experience.

Thought my post might be helpful for someone, could be the thread might prove much more helpful.

[derek hall 1Participant @derekhall1]

 

sorry do not know how to delete my own post….

 

 

Edited By derek hall 1 on 12/12/2022 15:09:46

Edited By derek hall 1 on 12/12/2022 15:10:28

[Anonymous]

Posted by Ramon Wilson on 12/12/2022 11:49:40:

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.

I've had trouble using HSS milling cutters, too but carbide is no problem. It's almost as if the material hardens while being cut. A recent job was to make two simple blocks, with clearance thru holes, to act as drive dogs on the Int40 vertical attachment for my horizontal mill. The screws were 1/4" BSW. After spot drilling, and failing with a 6.4mm HSS drill, I drilled through 6mm using the carbide spot drill without a problem. Should be easy to open out to 6.4mm, right? Three fudged HSS drills later……

The tips of the drills are blunt, and blue, indicating that they are simply not cutting, just rubbing. Next time I'll take the advice and slow the speed right down.

Andrew

[Simon Williams 3Participant @simonwilliams3]

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

[Dave SParticipant @daves59043]

Posted by Bazyle on 12/12/2022 11:01:12:

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.

I disagree. The reason for using a centre drill is to put a centre in the end of a bar without having to use 2 (pilot and cone) drills. A spotting drill is exactly the correct drill to spot a drilled hole. They have very short flutes, often made of carbide, and no centre pilot tip to snap off. At least as stiff as a centre drill.

Spotting drills don’t create a 60 degree cone, but rather a more correct cone to guide the following drill. The centre drill cone doesn’t really guide well, as the corner of the cone can cause the lip to dig in and push the drill off axis

Youtube machinists seem to get this wrong, and a large audience follows them.

I have used a centre drill to spot, but then I doubt I am alone, at least I know it’s wrong – rules are for the obeyance of fools and guidance of the wise

Dave

[old martParticipant @oldmart]

Having both centre drills and spotting drills and using them in the right context does help greatly with drilling. Amongst my centre drills are a few with 90 degree angles, better for drilling purposes than the common 60 degree ones, I have not yot seen a dead or live centre with a 90 degree end. For precision work, solid carbide drills are better than any hss drill, but most of us can only afford a few and they need careful handling.

[Chris MateParticipant @chrismate31303]

For the lathe I bought some extra 2nd hand old drill bits up to 20mm, cut the rear ends on lathe so they run truer, use them to cut holes, I don't care just resharpen, before using a boring bar.

If I just want to cut a hole I used new ones in lathe.

If I want to drill a small hole op to say 6mm between two edges in the centre, without having DRO, I mark it accurately, then punch a smallest hole as I can using magnifying glasses, then work it from 1mm drill to the size, a bit time consuming(Chuck must run true).

I recently find that the carbide cutters I aquired rather like to plunge down and drll better if I just paint the cutter with cutting oil, wipe it off, and go ahead, the chips fly ou/evacuatet nicely, after many use nothing sticks to the cutter tips not even alinimium, unlike oyher cutter tips I have.. If I flood it with cutting oil by hand, the chips/swarf tends to stick around, and on replunging down, (CNC floodcooling probably properly solve that problem), it may wonder on previous chips before cutting. I am not sure if this is true for any carbite 4 flute endmil cutter. The cutters comes from Gesag base.
 

Edited By Chris Mate on 12/12/2022 22:10:45

[Neil LickfoldParticipant @neillickfold44316]

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.

[Mick B1Participant @mickb1]

Yes, learning the bench grinder to sharpen drills, and make and resharpen HSS turning tools and form tools of all types, is time excellently well-spent that repays itself for ever.

One useful point in favour of centre drills is that the pilot cuts on the side as well as the lip, which means 2 things:-

i) the centre hole is effectively bored – truly concentric on the rotation, irrespective of any minor misalignment, providing it's been allowed to cut till it idles, and

ii) you can use the pilot as a slot drill for narrow and shallow slots – it's at least as strong as a standard slot drill in those size ranges.

[derek hall 1Participant @derekhall1]

Did my apprenticeship in the 1970's, and although I was taught how to grind a drill by hand, I could never get the knack of it.

I eventually made a drill grinding jig to a design in the ME by "Duplex", works very well. I have never used spotting drills but using some drills already ground to 4 facet was a revelation!

Derek

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