Perfectly ground Twist Drills every time.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Neil Wyatt on 04/05/2014 10:20:49:

Michael,

The cuttting edge of a twist drill isn't truly radial. Is the best angle at 90-degrees to the cutting edge or tangential to a circle at the point where it crosses the edge. And if the latter, at what point on the cutting edge? Half diameter? Half way along? Outer end? Inner end?

I expect a detailed finite element analysis of the forces on the cutting edge by 4:00pm

Neil

.

Nice one, Neil

Of course, in an ideal world the grinding marks would be radial to every point on the curved cutting-edge [limited only by the pitch of the furrows made by the grit of the grindstone] … don't think I'll bother.

MichaelG.

.

P.S.  Finite Element analysis is [by definition] a digital approximation.

Edited By Michael Gilligan on 04/05/2014 14:51:02

[WALLACEParticipant @wallace]

A further thought – assuming were going with the direction of grinding at right angles to the cutting edge – would it make any difference if the drill ( or other tool to be sharpened ) is fed into the wheel with the cutting edge leading or trailing ?

W.

[chris stephensParticipant @chrisstephens63393]

Hi JohnS,

"Modern technology has proved time and again what we were taught by rote and everyone since has repeated parrot fashion is not always the correct way."

Ain't that the truth.

Chris, the other John Stephens' son

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Michael Gilligan on 04/05/2014 10:06:43:

At the microscopic level, even the best grinding marks are like the furrows in a field [first illustrated by Robert Hooke, in Micrographia]

.

… He also describes it beautifully

… There's a good transcript here.

MichaelG.

[John Stevenson 1Participant @johnstevenson1]

Posted by Graham Meek on 04/05/2014 15:04:54:It apparently induces micro-cracks in the drill, I for one have always done this as this was the way I was taught, but I shall not from now on.

Gray,

 

Had to smile at this one Gray, another teaching by rote.

 

Some years ago I was in the gear cutters and they were machining some big blanks from some form of alloy steel. Chpipings coming off dull red and 3' deep on the floor. I asked why they didn't use coolant. The reply was similar to yours unless in this case you can absolutely flood the work which on this old unguarded manual lathe would have been impossible or messy best not bother as part cooling just cracked the inserts.

 

The bit that made me smile even more was knowing this I still dunk my drills like you. Old habits die hard.

Edited By John Stevenson on 04/05/2014 15:43:18

[chris stephensParticipant @chrisstephens63393]

Hi Gray,

As to how to quench, I always do it from the cold end, so there is far less thermal shock than plunging the hot bit first, and as I don't like the smell of burnt fingers I shall still have a bucket of water handy, besides flood cooling might be a bit messy on my B&D 8 inch .

ATB

chriStephens

[John Stevenson 1Participant @johnstevenson1]

Posted by Graham Meek on 04/05/2014 15:04:54:

I have been grinding my drills with the cutting edge trailing, the keenness of the edge produced feels considerably better than a a brand new drill of equivalent size, you do get a small frazzle of a burr thrown up but this is easily removed with a piece of soft wood.

Gray,

Gray,

Query please from the statement above.

Using the jig you show and having the edge trailing you run the grinder in reverse ?

[BazyleParticipant @bazyle]

Won't this also depend on which end of a double ended grinder you use?

[John Stevenson 1Participant @johnstevenson1]

Sorry Graham you have lost me.

Regardless of whether it's the edge or heel making contact first the wheel is always going in one direction, usually down and I don't see how the cutting edge can trail unless it goes up.

Am I missing something ?

[John Stevenson 1Participant @johnstevenson1]

Posted by Graham Meek on 04/05/2014 16:30:29:

Unless of course you don't include those who advocate using the periphery of the grinding wheel and grind concave facets, who tend to use the left-hand wheel for some in-explicable reason.

John, the drill makes contact with the wheel at about 10 o'clock at the moment, if the wheel makes contact with the heel of the facet first and the cutting edge last, then surely the cutting edge is trailing. If the cutting edge made contact first it would be the heel that was trailing, at least that's how I see it.

Gray,

Ok see your explanation but in my book the only way a cutting edge would trail is if the wheel is throwing the burr off the edge hence the question about direction.

Another question.

What is wrong in using the periphery of a wheel ?

For one thing wheel manufacturers do not condone using the side unless it's a wheel specifically made for this like a cup wheel.

Many cutters are hollow ground for clearance and some profession tool and cutter grinders hat keep the spindle horizontal at all times use the periphery and distances above centre to get the required angles. The Boxford G200 even includes a table giving wheel sizes and at what distance above or below centre to achieve a certain angle.

If we get down to the nitty gritty [ is that a pun ? ] on a 6" wheel with a land of 0.100" wide the curve is 0,00042"

Hardly earth shattering.

[John Stevenson 1Participant @johnstevenson1]

See your point but it's cosmetic anyway.

The heel does nothing only provide clearance you could put that on with an angle grinder if necessary.

In fact on some of the bigger stuff I have resurrected from scrap yards like 2 1/2" diameter drills to save time and prevent too much undue heat I have sliced back an inch or so on damaged drills with an angle grinder.

[John Stevenson 1Participant @johnstevenson1]

OK I can see where you are coming from, I was thinking more along the lines of the drill lying across the wheel so the lines were at 90 degrees to the edge and the curvature would be minimal.

However even though on a 1" drill this is 0.37 of a mm curvature does it matter ?

Where is it written in stone that a drill land has to be a straight line? In fact drills made especially for very soft aircraft alloys are ground more like a corner rounding endmill than a drill, they have a real radius on the land.

[John Stevenson 1Participant @johnstevenson1]

No not meant to cover special purpose drills only asking if a straight line was absolutely needed.

However this has spiked my interest in that these jigs have been around for literally century's but for obvious reasons industry cannot use them so what do they use ?

Even semi industrial units like the Darex still swirl the drills round a wheel.

Do a patent search on the latest Swiss drill grinders, the big industrial ones and you will get a pleasant surprise in that although they are CNC the actual mechanism once the servo motors are removed hasn't changed form the 1950's and is absolute simplicity itself.

[_Paul_Participant @_paul_]

Gray, et al absolutely fascinating thank you.

I must ask, why bother with the original base at all? if you are going to the bother of machining an extension wedge why not ditch the original low quality casting and knock up a replacement steel base with a 14* hole and perhaps even a nice brass bush for it to rotate in.

Paul

[WALLACEParticipant @wallace]

A very interesting thread !

Thank you Gray for starting it off and to everyone else who contributed !!

W.

[John Stevenson 1Participant @johnstevenson1]

Gray,

Sorry think I have unwittingly confused you by mentioning CNC.

The modern Swiss made ones basically have had the mechanical bits changed to servo's, smartened up a bit, bunged in a big box with fancy logo's on but underneath they are still the same design as the 1950's models.

They are hopper fed and thru feed the drills after grinding so high speed, can't see how many per hour but that obviously depends on size. The brilliant thing is they are so simple and no weird geometry to have to understand.

I'm simply amazed than none of the smaller industrial players have latched on to this, can't be patents because the idea is so old.

[_Paul_Participant @_paul_]

Gray,

You do have me hooked, I must try and find the thing now.

My replacement base will probably be around 3" x 2" x 1-1/2" and in steel so the mag table on my aged Norton T & C grinder has something to grab onto.

Paul

[LynneParticipant @lynne]

Hi , MEW 176 &177, drill sharpening jig, by John Shepherd; well worth a read.

Lynne.

[VersabossParticipant @versaboss]

To bring this thread back to on-topic:

Graham, would it be possible for you to produce and present a drawing of that new part on the foot of the jig (visible in pictures 2 and 4 on the first page)?

Although I have no problems with the wedge, I'm completely lost with this. Obviously I'm the only one – but that's no big news for me.

I think it would be easier than waiting for the day when something shows up in MEW (Or the other one, unmentionable here…?)

Greetings, HansR.

[John Stevenson 1Participant @johnstevenson1]

No Graham, you have got fixated because I mentioned CNC.

Try doing a search for patents on the 1950's pre CNC [ if I dare mention that ] They are the virtual same machine as regards the mechanics of the grinding process.

I must admit that I didn't have any joy only finding the later patents hence the mention of [ no we wont mention that again ]

[Howard LewisParticipant @howardlewis46836]

I have one of these grinding jigs, and gave up using it, because it was so imprecise.

I am unhappy with locating the drill flute against a stop, as any axial movement changes the angular position.

(Which is why I am not happy with the Hemingway Mk2 drill grinding accessory. Sorry Mr Jeffree, otherwise your design is excellent)

Instead, I now four facet grind using an ER20 collet holder mounted on the Hemingway 31 degree base for the Worden Cutter Grinder, setting the drill edge vertical. Four facet grinding is good, but I find it slow to set up.

The Worden has a tapped hole in the base ready to take this "Picador" type attachment, and I think that Tony Jeffree did design a base which allows precise advance of the device.

So PLEASE Graham, do publish the drawings for your improvement. I am sure that your version improves the gadget to the point, where mounted on a base with graduated advance, it can sharpen drills accurately and consistently.

Howard

[Tony JeffreeParticipant @tonyjeffree56510]

Posted by Howard Lewis on 05/05/2014 16:28:59:

I have one of these grinding jigs, and gave up using it, because it was so imprecise.

I am unhappy with locating the drill flute against a stop, as any axial movement changes the angular position.

(Which is why I am not happy with the Hemingway Mk2 drill grinding accessory. Sorry Mr Jeffree, otherwise your design is excellent)

Instead, I now four facet grind using an ER20 collet holder mounted on the Hemingway 31 degree base for the Worden Cutter Grinder, setting the drill edge vertical. Four facet grinding is good, but I find it slow to set up.

The Worden has a tapped hole in the base ready to take this "Picador" type attachment, and I think that Tony Jeffree did design a base which allows precise advance of the device.

So PLEASE Graham, do publish the drawings for your improvement. I am sure that your version improves the gadget to the point, where mounted on a base with graduated advance, it can sharpen drills accurately and consistently.

Howard

Howard –

Not guilty I'm afraid – I have built a Worden from the Hemmingway kit, and I did buy their drill grinding kit at the same time (and have failed as yet to build it), but I had nothing to do with its design, or the adaptation for the Picador device, for that matter.

Of course, if I had, it would work flawlessly

Regards,

Tony

[VersabossParticipant @versaboss]

Posted by Graham Meek on 05/05/2014 13:09:28:

…

The reason for the wedge is,

…

I'm so sorry Graham, it seems I could not express clearly what I meant. I said I have no problems with the wedge – meaning I understand its purpose.

What I really don't understand is the other part, which looks like a very substantial bearing for the small vertical stem of the jig. Maybe, instead of a drawing, you could try to tell in a few words how to make it? (length, thickness, the purpose of the tangential clamp(?) screw – which part is still movable when this really iy a clamp?). In the description you wrote something about 'dialling in the eccentricity…) Is there a scale somewhere?

Oh, how difficult to express ones thoughts when one has nothing than a photo…

Greetings, HansR.

[Neil WyattModerator @neilwyatt]

Hi Howard,

What angle do you use for the cutting and secondary clearance when you grind 4-facet drills?

Sir J.That video is worth a thousand words!

Neil

Edited By Neil Wyatt on 05/05/2014 20:32:40

[Michael GilliganParticipant @michaelgilligan61133]

For those with a penchant for Patents, this one from 1949 is definitely worth a look.

… Those with no interest, please just ignore it and accept my apologies for the intrusion.

MichaelG.

[Author]

Posts