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Thread: Drill Geometry

  1. #1
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    Default Drill Geometry

    Purchased a set of Dormer UK metric drill bits when passing through Singapore, but did not look at then closely at the time. However now I see the secondary clearance angle looks to be excessive, but maybe this is just the new trend. So wondering if anyone else has seen such and any comments / suggestions. First photo (I hope) is relative to an off the shelf drill bit. Thanks, Alan.

    drill13.jpg

    drill12.jpg

    drill11.jpg

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    Quote Originally Posted by C-47 View Post
    Purchased a set of Dormer UK metric drill bits when passing through Singapore, but did not look at then closely at the time. However now I see the secondary clearance angle looks to be excessive, but maybe this is just the new trend. So wondering if anyone else has seen such and any comments / suggestions. First photo (I hope) is relative to an off the shelf drill bit. Thanks, Alan.
    Yes I have. Milwalkee Thunderbolts, and another Milwalkee set I purchased a couple of years ago. I believe they have a 135 deg cutting angle. They also have the split point / 4 facet grind. I have used them almost exclusively since I bought them. Mainly because they are complete sets of drills capable of drilling stainless steel and alloy steels.

    Some years ago I read quite a bit of information regarding the drill cutting angle and there were a number of people who felt that the larger angle was beneficial to cutting as it provided a shorter length cutting edge and so less required effort. It was also felt that the 118 deg angle was just a random value. Maybe just a happy medium.

    Dean

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    I do a far amount of drill work on small stainless, diameters -mainly 304.
    I use 4 facet 135 degree drill bits solely for stainless and will not use 118 bits ever again on stainless. Couple with the correct operating specs and a modicum of common sense and you will have no trouble.

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    There is a fancy name for that (point splitting). Really, the material behind the cutting edge only supports the edge so can be relieved quite a lot.

    Michael

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    Hi C-47,

    I would not see it as a problem. This sort of split point is fairly common and the exact angle of the relief and amount of material removed seems to vary by manufacturer according to their marketing blurb. The 135 or 140 degree angle grinds seem to be good for harder materials. The 118 degree points seem good for softer stuff. TiN coating also helps with harder stuff and reducing wear.

    Cheers

    The Beryl Bloke
    Equipment er.... Projects I own

    Lathes - Sherline 4410 CNC
    Mills - Deckel FP2LB, Hardinge TM-UM, Sherline 2000 CNC.

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    I bought a set of Sutton Viper drills a couple of years ago the had the same tips.

    Ratty 05/2004 -05/07/2010 COOPER 01/08/1998-31/01/2012

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    I can see no reason for that sort of clearance behind the lips other than marketing, and a speedy replacement of the bit. As soon as you have sharpened the drill once or twice you will need to grind back a diameter or more just to re-establish a new cutting edge.

    Cheers Phil

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    Thanks to all for the responses, I won't have to bin them now . Maybe I need to visit the tool shops more often to see what's trending, sure I can explain that to the money minder. Alan.

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    Quote Originally Posted by Michael G View Post
    There is a fancy name for that (point splitting). Really, the material behind the cutting edge only supports the edge so can be relieved quite a lot.

    Michael


    It could possibly act as a heat sink though.
    Gold, the colour of choice for the discerning person.

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    Quote Originally Posted by 12bolts View Post
    I can see no reason for that sort of clearance behind the lips other than marketing, and a speedy replacement of the bit. As soon as you have sharpened the drill once or twice you will need to grind back a diameter or more just to re-establish a new cutting edge.

    Cheers Phil
    No you don't. Either you re-grind them to the same angles or you grind them to a traditional constant backoff angle. Whichever works for you. I do both depending on what I want to do. The split points tend to self-centre a bit better than the smooth relief grinds IME.

    PDW

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    Quote Originally Posted by 12bolts View Post
    I can see no reason for that sort of clearance behind the lips other than marketing, and a speedy replacement of the bit. As soon as you have sharpened the drill once or twice you will need to grind back a diameter or more just to re-establish a new cutting edge.

    Cheers Phil
    Phil, as Michael said, that grind is a way to achieve a split point. I have some that are ground that way and it seems to be the trend these days. Splitting the point is not a marketing product and is definitely noticeably better, especially to start. I split the points another way, but the effect is the same.

    There's also no need to throw them away if they need sharpening, you will just lode the point splitting unless you regrind it also.

    Alan, Singapore + Dormer, I bet I know where you got them

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    Hi Guys,

    I agree with all the points made here, I will add that, I now grind all my drills four facet split point, particularly since I made John Moran's 4 - 6 Facet drill grinder. One other comment is that I grind both 118 and 125 degree tip angles. I find that the sharper angle is better for harder materials.
    Best Regards:
    Baron J.

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    Pete F
    Yes I think I know the source as well, I hope that Alan's drills are the real thing not like the fake Presto ones I brought a few years ago from the same place. I have an assortment of Dormer taps,end mills from the same supplier and they are all good quality.Are Dormer products still made in UK.The extra clearance is supposed to reduce the downward pressure when drilling especially on larger diameter drills.I agree with Baron J a four facet grind with a split point is a joy to use.
    Bob

  14. #14
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    Bob and Pete,
    I reckon probably the same place on Rowell Rd, have always had good stuff from there, so far anyway. When I brought this lot was offered made in UK (coated) or for a bit less (un-coated) made in Brazil, I chose the former as previous stuff made there has been good. Alan.

  15. #15
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    Hi Guys,

    I don't think that Dormer make anything in the UK any more ! It seems to come from Brazil and Czechoslovakia

    http://www.dormerpramet.com/en-gb/co...our-production

    The drills used to be made in Shefield. Somewhere I still have a couple of long (12") X (1/8") inch split point specials that they made me, for a particular deep hole job.

    I recall that compared to todays prices, they weren't all that expensive either.
    Best Regards:
    Baron J.

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