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Perfectly ground Twist Drills every time.

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Chris Trice13/05/2014 11:04:58
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1362 forum posts
9 photos
Just in case anyone is looking to find offence where no offence is intended, my comments are directed at those who feel intimidated about posting photos of their work for fear of what others might think. "Good enough" refers to reaching a standard that the builder is satisfied with. Like the car analogy, people want different standards so where some would not settle for anything less than a BMW, many are happy with any car that stops, starts and steers. The whole point of aiming high is to get better at the craft as a whole and engineering is about precision so this is a good thing. Commerce is about doing a sufficiently good job as cheaply as possible whereas hobbyists have the luxury of doing the best they can just for their own satisfaction and the art. The pleasure is looking at something you made and being proud of it and not letting other people wind you up.
Chris Trice13/05/2014 11:13:14
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1362 forum posts
9 photos
Just as an aside, there's a guy at work who boasts and genuinely believes he can regrind a drill by hand as good as a jig. Maybe in his head and not to the standards I'd be happy with but it's not worth getting into it with him.
Gray13/05/2014 11:44:01
1038 forum posts
13 photos

Gray,

it is sad that the comments of a few have made you feel this way, maybe perfect was not the best choice however, perfection, like beauty, is in the eye of the beholder, your post demonstrated your desire to strive for perfection, your workmanship also demonstrates this, and as others have said, gives us all something to aim for, I strive for perfection and in my eye sometimes achieve it, on other occasions, I settle for the best I can achieve with the equipment I have to hand, learn from it and try to do better next time.

Please do not stop posting your work, it is an encouragement to us all.

Kind regards

Graeme

Gray13/05/2014 13:13:12
1038 forum posts
13 photos

To add to my last, a 'perfectly ground' twist drill is one which meets the specifications, i.e. it drills a hole with the appropriate effort required to a dimensional tolerance specified by the manufacturer, therefore, if Grays modifications to the drill jig achieve this then he has encapsulated the title of his thread.

if a 12mm drill produces a 12mm hole +- the manufacturers specified tolerance, or better, then this is PERFECT

The fit, finish etc of his implementation of the modifications are not for us to question or comment - other than to praise for the exemplary standard of such.

jason udall13/05/2014 14:23:53
2026 forum posts
41 photos
Would someone please let me know whem this thread gets back on topic
Harold Hall 113/05/2014 16:07:00
418 forum posts
4 photos

I agree Neil that there is much to be desired with the very common drill grinding jig but in my estimation 90% of the failings are in the instructions received. It has been mentioned on this forum, and I have receieved similar comments by mail, that the contributor has had one stored away for years having found it impossible to achieve adequate results. However, having read my article in MEW, or on my website, have rescued it, tried to use it once more, achieving acceptable results.

I do though agree that there is room for improvement in the device itself, having made one of my own. I do though particularly like Graham's superior pivot arrangement and will endeavour to find time (unlikely) to make the modification to my jig. However, I must go back and read Graham's explanations as I am unsure as to the reason for the tapered packing under the jig's base, is it to correct an error in the angle being ground?

Should anyone like to take a look at my pages on drill sharpening, including using the common drill grinding jig for the purpose. It can be found here **LINK**

Harold

jason udall13/05/2014 18:22:53
2026 forum posts
41 photos
Gray
.If you could. .and even if you feel like doing by pm
Rather than here
Test grind a plane rod ..ie no flutes. .and post a photo of the sharp end.

.I am trying to "understand"..
It seems to me that the jig will grind two cylindrical faces on the end ..and the flute combined generates the cutting face..
The only way I can grind is what I call four facet..more like a spear point drill..than the conventional bought in result....
Is the reason for the cylindrical face a production compromise ...or is there an advantage?
Regards Jason
Chris Trice13/05/2014 19:02:40
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1362 forum posts
9 photos

You get a stronger cutting lip than if you grind two simple flats because there is more 'meat' behind the cutting lip at the cutting lip while still giving clearance.

Neil Wyatt13/05/2014 19:11:46
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18232 forum posts
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Thank you for bringing this thread back on topic Harold and others.

Any off-topic comments will be deleted.

Neil

Oompa Lumpa13/05/2014 21:47:38
888 forum posts
36 photos

Like everyone else I too had one of these jigs. Unlike many I didn't put it under the bench it went in the bin.

Looking at the photographs though, it wouldn't take much to actually make one of thee from bits.

graham.

jason udall13/05/2014 22:14:45
2026 forum posts
41 photos
Ah Chris..so it is superior. .A easier to generate. .B stronger..
And further study shows that the intended "face" is two faces each part of a cone........
Well I can make ( just) the spear point work..but am still looking into the geometry. .btw how does the flute helix effect setting..some of my carbide drills have faster than "normal" helix..and some pcb drills have slower helix. .slow =less turns per inch
jason udall13/05/2014 22:16:32
2026 forum posts
41 photos
But then those pcb drills are sub 0.3 mm so might be tricky to grind..just wondering
Gordon W14/05/2014 09:49:22
2011 forum posts

Just to confuse things even more- yesterday I was putting a few holes in some aluminium , the only drill I had was damaged. So dug out my Silverline sharpener with a coned grinding wheel chugging away. The drill bit, 6.5mm ,came out with the end looking like a ball -nosed end mill. In despair I tried it and it worked ! Drilled clean holes in ally sheet better than ever.

Harold Hall 114/05/2014 09:53:28
418 forum posts
4 photos

Cannot comment Jason regarding carbide drills as I have none to see if the flute has a different shape to those on a high speed drill. However, where HSS drills are concerned they are made with a differing helix for different tasks. If these are ground at the wrong angle then the cutting edge will become curved, convex if too pointed for the drill being sharpened and concave if too flat.

See Photo 6 here (left hand drill) and the associated text on that and the following page. **LINK**

Harold

Harold Hall 114/05/2014 10:18:14
418 forum posts
4 photos

I do not know the sharpener you mention Gordon but you must have placed the drill into the device with the cutting edge wrongly orientated. The same will happen with the jig being discussed here. If the cutting edge is not upright the point will take on a curved shape, becoming more extreme the greater the error in placing the drill. See Sk6 here **LINK**

Still, it goes to show that things are not as critical as often unfortunately implied, something I try to avoid doing.

Harold

John Stevenson14/05/2014 10:19:33
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Moderator
5068 forum posts
3 photos

Gordon,

Often times things that work, or should in theory don't and the opposite works in practice.

Inside a piano there are two extruded aluminium rails that all the action parts are screwed to. Its a quite complex shape in section view as are a lot of extrusions and the easiest way to extrude this is to use an alloy that contains a high percentage of treacle, or so it seems.

I think we have all come across this material where it's easier and cleaner to punch a hole thru than drill.

These had something like 160 holes drilled in them in a line on an automatic machine. The guys running these used to grind their own drills. If you used a normal drill or 4 facet it worked but you got a spelching or massive burr on the underside that wasn't acceptable because there was no second operation to clean up.

If you ran a wing and spur wood drill you got a brilliantly clean hole but the turnings were of such a shape that they just clogged everything up and broke the drill but it's a good trick to use at home for the odd holes in this soft alloy.

Over time they developed their own shape that gave a clean hole, no underside burrs, and the drills lasted.

Basically it was a swept point as is being discussed here but ground on a convex wheel, BTW we are only talking about 4.2mm drills here, which gave a concave shape to the drill.

Best way to describe it was if you held it up to the light it would look a gear cutter or the space between two teeth on a gear.

Now in my extensive reading of engineering books over the years and talking to people I have never seen that shape shown or mentioned, I'd even go as far as to say if you tried to teach this the theorists or theoretical terrorists would soon shout you down but it works.

Long - short is not everything is a correct in books for certain applications.

jason udall14/05/2014 12:56:34
2026 forum posts
41 photos
At the risk of siding with anyone...I don't think we are in the "business" of making drills or grinding them..we work /sharpen drills to achive a result..a hole , round..parallel. ..straight..smooth..low or no burr..reasonable cutting load.and at right postion....I for one find shortening drills a trial..but a jig or even those horrid plastic drill sharpers gets me closer.....perspnally I work pilot hole..ream
..seams to work...
Btw spotting drills are fantastic. ..but don't look as sophisticated as normal twist drills..wonder why the difference..
Chris Trice15/05/2014 10:54:52
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1362 forum posts
9 photos
Well this demonstrates how threads like this promote interest in the subject. I just bought one of these jigs (early sixties) second hand with a view to tweaking it.
WALLACE15/05/2014 11:21:44
304 forum posts
17 photos
Absolutely.

Made me click on the links, read Harold's and others MEW articles and stretched my brain cells a bit.

I'm happy it's done that, even if my jig remains on the shelf ( but open to reasonable offers. ...).

W.
AndyP15/05/2014 20:54:24
189 forum posts
30 photos

Ok so this thread prompted me to go out and buy one of these jigs to modify because I definitely can not hand sharpen drills and I can't afford to get enough practice.

The Draper jig is significantly different from that which has featured so far.

pivotangle.jpg

The angle of the pivot seems to be about 6 deg but not a big issue.

angle.jpg

The drill holder sits at 34 deg which I think is going to grind a drill with 112 deg point.

offset.jpg

This is where the differences get bigger, the offset between the end of the trough and the centre line of the pivot is around 13mm. The photo has the jig mounted with it's pivot in the lathe chuck and measuring to a tailstock centre.

setting2.jpg

Setting the jig as per the instructions with the drill protruding by half it's diameter as measured from the tip of the lip stop seems to show a slight mis-match in point angle.

setting1.jpg

This the jig set up allegedly ready to grind, somehow I expected the cutting edge to be vertical, certainly nothing like the angle shown here.

Some of these differences are easy to fix but the offset difference is huge, any thoughts anybody?

Andy

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