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Post by Staffordshirechina on Jan 5, 2009 9:41:47 GMT
Correct drjohn! The big one is 1.5"dia. They were done to illustrate a talk on drill sharpening. Unfortunately if you try to show small drills to most ME's they are all reaching for eyeglasses, binoculars etc. So I did these jumbo size ones.
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Post by drjohn on Jan 5, 2009 10:08:27 GMT
So tell me, as I haven't mastered sufficient chinese to ask the local supplier ;D what is that "rake-off" on the left hand drill - I have a few like that, even down to 2.5mm and I don't really know why they're like that - presumably some form of swarf / chip clearance, but as the end is usually in a hole, I can't see how it works - and to me, seeing is believing  DJ |
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Post by weldsol on Jan 5, 2009 17:59:22 GMT
DJ Try drilling some perspex
Sorry having a flippant moment
Paul
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Post by Staffordshirechina on Jan 5, 2009 18:11:19 GMT
On the drill in the photo, the rake is for clearance of the second angle. It is not immediately obvious until you try a 4 facet drill larger than about 1/2" against the hole in say, a washer. Above this size the back end of the second angled face starts to rub on the hole and needs extra backing off. Hence larger size drills need to be 6 facet sharpened.
The drills you mention are sharpened by the newer way that manufacturers seem to have adopted. There is a subtle difference between them and 4 or 6 facet points. The 5th and 6th facets are arranged so as to overlap the cutting edge and give a small pair of pilot cutting edges, almost like a twin corkscrew effect. It is a bit difficult to see on small drills. This makes for very good pilot hole drilling even with bigger sizes that you would normally drill small then middle then large.
It is not too easy to duplicate this point geometry when you come to re-sharpen them.
However, by experiment, I have managed to sharpen some of my drills this way by modifying the 6 facet point. It is one of those things that is easy to see but hard to explain!
I have one drill at 1.25" that is sharpenened this way and use it for drilling 'the hole before the boring bar'. I centre drill then wack in the 1.25" drill all the way with no pilot very easily.
It cuts very true to size too.
Sorry I haven't got a photo in stock of that one yet.
Les
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Post by drjohn on Jan 6, 2009 9:26:38 GMT
DJ Try drilling some perspex Sorry having a flippant moment Paul Tried that paul but it goes all cloudy and I still can't see what's going on. ;D So I'll accept the Staffordshirechina (wot a name!?) explanation as I have neither the drills nor the rigidity to try a 1.25" hole - I bore once it's over 5/8"  DJ |
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Post by weldsol on Jan 6, 2009 10:35:33 GMT
DJ Try drilling some perspex Sorry having a flippant moment Paul Tried that paul but it goes all cloudy and I still can't see what's going on. ;D So I'll accept the Staffordshirechina (wot a name!?) explanation as I have neither the drills nor the rigidity to try a 1.25" hole - I bore once it's over 5/8" DJ Turn the suds off |
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Post by Staffordshirechina on Jan 6, 2009 17:41:27 GMT
Staffordshirechina is our Ebay and website trading name. We are purveyors of teapots to the gentry. We also sell them to Americans.
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