When is a new 90 degree drill not 90 degrees?

[Mark RandParticipant @markrand96270]

Forgive me for being picky, but with that width of chisel edge, is isn’t a spotting drill unless it’s specifically made for spotting with much larger drills.

82° is a perfect angle for most spotting drills, the main drill will normally have that angle, so will start with no tendency to wander or chatter.

Yes, it’s left-hand. No it isn’t a spotting drill. No it isn’t 90°.

Time for a chat with Presto?

[Bill PhinnParticipant @billphinn90025]

That’s a fair point, Mark.

The chisel point on the present 12mm drill is 2.65mm wide. A new 16mm Sherwood 120 degree spot drill I have has a chisel point of 2mm.

I suppose I should ask whether recognised international standards call for chisel points to be wider on spot drills with steeper angled tips than on flatter ones of the same cutting diameter, or whether it’s the other way round…or neither.

On another note, I’m not quite sure I follow when you say “the main drill will have that angle”, i.e. 82 degrees. A countersink might well do, but a twist drill…?

[jimmy bParticipant @jimmyb]

At work we frequently have special tooling made by modifying existing tooling.

Rarely do we get around to identifying this on the original packaging……

 

Private sellers on ebay could be selling tooling liberated from work (as car boot sellers may do)

 

Please note the word “could” has been used, so as not to offend any genuine private seller with lots of brand new tooling for sale…….

 

Jimb

[JasonBModerator @jasonb]

The private sellers also often buy job lots when a business closed down so it could have come straight from the stores after having been modified. This would explain no signs of use.

 

Spot drill ends do vary, I tend to use the Keo brand which have a thinned web so the end is quite narrow compared with other spot drills of the same diameter. Keo closest to camera

[Mark Rand]

On Mark Rand Said:

82° is a perfect angle for most spotting drills, the main drill will normally have that angle

Please could you unpick and expand that phrase for those of us whose understanding is slow.

As I understand it, most standard drills have a 118 degree point angle, with some using 135 degrees.

I do not understand the connection between 82 (or 90) and those numbers and how the perfection is thus achieved.

—

Another option (jimmy b as above) is that these were a custom order by a manufacturer from a specialist tool grinding company. The grinding company orders the nearest standard item from Presto, which comes with its standard markings and standard box, applies its professional grind to the tip and sends them off to the customer.

At some extremely fussy level of quality control, the fact that the etching does not correctly describe the tool might matter, but in this case it would not have done so.

[ChrisLH]

On ChrisLH Said:

[…]

I am still curious as to why 82 degrees was chosen by the Americans but perhaps this is considered excessive subject drift.

Me too, Chris …so I asked ChatGPT for the history:

.

.

MichaelG.

 

[Michael GilliganParticipant @michaelgilligan61133]

Here is that report [276 page download]

https://www.govinfo.gov/content/pkg/GOVPUB-C13-fe2d83f32c7ce5613e947331f0221c3b/pdf/GOVPUB-C13-fe2d83f32c7ce5613e947331f0221c3b.pdf?utm_source=chatgpt.com

 

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

[DC31k]

On DC31k Said:

On Mark Rand Said:

82° is a perfect angle for most spotting drills, the main drill will normally have that angle

Please could you unpick and expand that phrase for those of us whose understanding is slow.

As I understand it, most standard drills have a 118 degree point angle, with some using 135 degrees.

I do not understand the connection between 82 (or 90) and those numbers and how the perfection is thus achieved.

 

Severe brain fart!

I was reading 82° as 118°

Mea culpa, mea maxima culpa.

[not done it yet]

On not done it yet Said:

I would think that left-handed ‘spot’ drills are not a regular item?

It appears that left hand versions of Jason’s go-to brand of spot drill are available in many (imperial) sizes and a choice of finishes.

Crucially, however, these Keo left hand spot drills are not available in 82 degrees, which makes the theory (advanced by several people here) that this batch of drills was professionally modified prior to use seem all the more plausible.

While we’re on the subject of spotting, spot Grainger’s howler in that link about the cut direction of left hand drills.

[Kiwi BlokeParticipant @kiwibloke62605]

That’s a surprisingly wide chisel edge, isn’t it? Four-facet pointed spotters are available, and work so much better than chisel-ended types – at least in my experience.

Can anyone suggest why spotting drills are a lot more expensive than jobbers from the same manufacturer? Being a smaller mass, and requiring less grinding, one might think they should be cheaper. Or is it rip-off New Zealand pricing at work yet again?

[edit]  Oops, failed to read previous comments about chisel edge width…

[alecsParticipant @alecs]

With its 82 degree chamfer its probably not a spotting drill but more likely a countersink drill for 82 degree wood screw heads, used where there is already a hole for the screw shank existing. Hence no need for narrow point.

Why would it be left hand? Possibly for CNC mass production use, in either wood or metal. Reverse spindle rotation is often used on such machinery to control chip direction or on old cam-operated screw machines because the slow speed rotation for tapping was slow and high speed was reversed due to gearing.

What it says on the package is possibly irrelevant due to packaging error, which could possibly be why it ended up on eBay.

Or the moon could possibly be made of green cheese.

[David George 1Participant @davidgeorge1]

When at work in a toolmaker shop I had the use of a drill grinder machine which was so simple to use. As we made parts for arospace for the US as well as UK we used to regrind the angle on spot drills to suit US angle and UK angle or specials which could be 60 deg inclusive as well for valve seats. You just set the angle of drill point put in drill to pre set stop and rotate to it stops rotating and tighten the collet. you would start the grinding wheel and rotate a small handle which rotates the collet spindle untill you hear a slight grinding noise. when it stops cutting stop machine and remove the drill and it is a perfect ground  drill point and looks just like a new drill at set drill point. There is a cam action inside the machine which puts on corect cutting edge clearance etc. This machine had diferant camms which could grind 2 3 or 4 cutting edge countersiks as well but I was never allowed to use it for other than plane drill or spot drill sharpening.

David

[Michael GilliganParticipant @michaelgilligan61133]

That sounds like the perfect machine for producing Bill’s mystery item, David.

I sense some ‘Armchair Research’ coming on !

… do you remember the maker’s name ?

MichaelG.

[duncan webster 1Participant @duncanwebster1]

Aldi has a universal sharpening machine on sale at present. Claims to do drills. No idea if its any good, and I have enough stuff already

[noel shelleyParticipant @noelshelley55608]

What David is describing sounds like a Brierley drill grinder, or one of the specialist drill grinding machines. It takes only a minute or two to set the machine up for any type or angle of drill and once set takes seconds to grind/regrind a drill to suit the job. I have one, a joy to use.  Noel.

[Michael GilliganParticipant @michaelgilligan61133]

Thanks, Noel

… This looks a good place to start my education:

https://www.lathes.co.uk/brierley-drill-grinders/

MichaelG.

[duncan webster 1]

On duncan webster 1 Said:

Aldi has a universal sharpening machine on sale at present. Claims to do drills. No idea if its any good, and I have enough stuff already

Had a quick look on Aldi’s website and couldn’t see it, but I suspect it will be the same, or similar to, the one I bought a few years ago. It does sharpen drills, but I had to make a few modifications to get it to work reliably (gluing on some spacers, replacing a self-tapper with a nut and bolt, etc.). I wouldn’t use it for anything smaller than 4 or 5mm, and the grinding wheel is quite coarse, being one of those carbide-encrusted items. I wouldn’t buy another.

Rob

[alecsParticipant @alecs]

When I was an apprentice we had a drill sharpening attachment that could be sat on the magnetic table of a small surface/T&C grinder, the type used for sharpening small press tool punches etc.

From memory it was simple to set up — must have been because it was a job for second year apprentices fresh out of the works training centre. Like the Brierly above, it had a crank handle that rotated the drill bit in a carefully calculated wonky manner that gave the perfect tip angle, clearance and equal lip length. Drills ranged up to 2″ diameter, so took some sharpening. I remember sharpening milling cutters on the same machine, but not sure if it needed a different attachment.

I can’t remember the name of the grinder or attachment. We never took much notice of such things. It was just what was there. I hated it anyway, sitting there all day long cranking the handle and feeding the slide over by hand. Day after day for weeks and weeks until the leading hand took pity and gave some other sucker a turn.  The joys of apprenticeship!

[noel shelleyParticipant @noelshelley55608]

With the Brierley the WONKY movement Alecs refers to is generated by one of a set of over 10 different cams that give the form needed. Red cams give a lefthand form and green ones a righthand. The workhead can be rotated round the wheel to give the required angle even 180* for spot facing.

If it seems to be making a strange edge or wrong clearance angle then there is a good chance the timing between the cam and work head have slipped – easy to reset when you know how !

The Clarkson T&C grinder attachment uses cams of a sort but the 2 cutting lips are done separately as is the case with some of the cheaper tools and this is where the skill/luck comes in. The Brierley rotated the bit around it’s centre in one setting giving equal length cutting lips.

The Clarkson will do upto .625″, the Brierley ZB 25 = 1″ and the ZB 32 = 1,25″ and there are bigger units that go to over 3″

For those of you who like me cannot abide blunt drills and can travel to me I will happily regrind bits for you more or less while you wait (if I’m at home) WITH IN REASON, not like the fellow who turned up with a box of over 30. Shanks can be parallel, 1,2, or 3 morse.  I have a ZB32.  Noel.

[alecsParticipant @alecs]

LOL. Wonky = technical term. I dont know how else to describe it. The shank of the drill went around in a large circle whilst the tip stayed on centre. Thd drill rotated about its own axis simultaneously, giving the basic conical tip shape to both cutting edges and surrounds. Must have been some camming action inbuilt to get the relief angle. Wonky as anything!

[Martin ConnellyParticipant @martinconnelly55370]

I think I would try them on a bit of aluminium and see what the result is. As the two cutting edges are on parallel planes and not in the same plane it’s possible you will get an error measuring the angle in the manner shown.

Martin C

[JasonBModerator @jasonb]

Just tried 3 different size 90deg spot drills against a tri-square and they all fit without a gap. So seems a reasonable way to measure them.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, if it is a Brierley, like Noel says, they are a really good machine. The I last place where I worked had one, and although I never used it myself, as it was in the machine shop, one of the machinists would sharpen up my drills.

Regards Nick.

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