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Thread: Burrs and drill bits

  1. #1
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    Default Burrs and drill bits

    Hiya

    I'm currently having two problems:

    1. When using very small drill bits (under 1mm) they break and often snap off in the piece of metal I'm working on which is a total pain to try and remove (or just ruins the piece). Any suggestions on why this happens and how I can stop it? I'm going to be flush setting some tiny diamonds soon and will be using a 0.5mm and a 0.8mm bit. Am I drilling too fast and overheating it?

    2. Every so often my round burrs don't cut nicely - they leave a rippled edge to the stone setting (looks a bit like the edge of a flan tin!). It doesn't always happen - in fact, it seems to mainly happen when I use Cut Lube which certainly makes the burr more efficient in terms of how much it cuts away but not with a good result. Again, any suggestions on why and how to avoid?

    Thanks!
    V

  2. #2
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    Make sure your drill bit is lubricated well, that should sort out your drilling problem, not sure about the other problem but at a guess I would think that the silver tube wall isnt thick enough. Just guessing and I am sure someone more experienced than me will give you a better answer later on.

  3. #3
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    Hi Victoria, small drill bits fractionally untwist in use, until they finally fatigue and break. Other factors are any slight bending movement while they are in use and of course too high a speed and lack of lubricant.

    It's a good idea to start with a punch mark made by lightly tapping a scriber, or by using a small round burr. The drill must turn at medium speed, lubricated with wax or light oil and frequently withdrawn to clear the swarf and avoid over heating. The tip should not turn blue, and to avoid fatigue fracture in tiny sizes they should be discarded after a set number of uses, which can be decided by experimenting on scrap until one breaks.

    You don't say how you use your drills, or what type, but I presume it is some sort of hand piece to hold mounted drills with a 2.35mm shank. There are several choices in the Cookson range, but my experience is that the HSS ones are the most brittle.

    As for the juddering of round burrs when making a seat for a stone, this is related to the speed for each size and is difficult to avoid with a motorised hand piece. Your alternative is to mount it in a universal handle (Cooksons 999AZM) and turn it by hand. You need a little oil and it will cut best slightly on its side, but it saves wear on the burr too.

    Regards, Dennis

  4. #4
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    Ok, well I got some of it right. Hahahaha.

  5. #5
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    We are using 0.7mm and 1mm bits all day
    1 fine drill bits don't bend so make sure you are not drilling at an angle. even a 1degree bend and it will snap.
    2 the juddering (and possibly the breaking) could be because your bit is not straight in the chuck. As you tighten the chuck jaws slide the bit in and out and the shank will align itself.
    3 such tiny bits go blunt if you blow on them. We reckon five pearls to a bit and I don't use a bit on a pearl after I had used it on metal. (we buy from the maker in 100s)
    we don't use lubrication and the drill we use is an old black and decker (a normal put up shelves drill)
    Author: Pearls A Practical Guide
    www.pearlsapractical.guide
    www.Pearlescence.co.uk

  6. #6
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    The other thing to remember is that you need to clear swarf. As soon as you're drilling 3x the diameter of the bit you're into deep-hole territory; the swarf won't clear the flutes as effectively and particularly with softer metals can jam the bit - and trying to clear that usually results in bending.
    Carbide bits are even less tolerant of bending BTW.

    A soak in an alum solution or used safety pickle overnight usually dissolves them out.

    If you're using the shanked bits I'd save them back and learn to sharpen them - not purely from a cost point of view, but shorter drill bits are less vulnerable.

  7. #7
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    Thanks all. It sounds like largely I just can't use the bits as much as I thought...and I need to be more patient and clean out swarf, etc

    How do I learn how to sharpen drill bits? Sounds really useful for prolonging their life a bit as otherwise I will be getting through quite a lot!

    For info, I'm using a Foredom drill and the swiss or busch drill bits/burrs on cooksons (I'd noticed hss weren't as good too). I'm using 998 021 to lubricate the burrs - though I swear the ripple effect is worse when I use it! The burr isn't juddering as such (I can't see obvious movement/wobbline), but there's a higher pitch squeaking noise when I use it...!

  8. #8
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    Yes I sharpen mine, and a bonus as Peter has pointed out, is that shorter drills are less stressed and do not break as easily.

    If you look at the cutting end of a twist drill, you will see that there are two facets and two cutting edges facing the same way. I use a good quality diamond disk mounted on a screw up mandrel in my hand piece. I say good quality, because the cheapo ones I have tried are too coarse.

    I rest my handpiece horizontally on the hand piece stand, but a block of something would do, and steady it with my left hand. Then with the disk running fairly slowly, I touch the facets of the drill against it, with my right hand, first one and then the other, trying to maintain the angles.

    It is not critical to achieve the exact angles on small drills, but when done, the cutting edges should feel much sharper to the touch. With very little practice, this can be done quite quickly. Of course your drill selection will end up all different lengths. Dennis.

  9. #9
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    To shorten the bit just push most of it into the chuck.
    As you have noted, lubrication not needed unless you are drilling through very thick metal (if then)
    to clear swarf simply out and in the drill bit occasionally and look at the bit. You can see if the lines are clogged. Pick out clogging with pin or whatever to hand.
    Author: Pearls A Practical Guide
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  10. #10
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    Did you know you can make your own drills from needles? when I was an apprentice, one of my regular jobs was to visit a tailor's supply shop in Soho and buy many packs of needles, mostly ones that were sized 8 Sharps. Then when I returned to the workshop I used to make the needles into spade drills using an oil stone, it only took a few minutes to make each drill and I made hundreds as one of the jobs I had to do was drill holes in KCB Stars and other British Empire order castings, each KCB star had over 450 holes to be drilled which meant a lot of drill breakage so we used cheap needle drills and they worked fine. I just checked online and a packs of 20 sharp needles sizes 5 to 10 (0.70mm. to 0.50mm. diam) are only 0.75 per pack, that's 4 pence per drill.
    If you are interested the stars had to be drilled so that we could punch an even design on their backs, I have added a photo of a KCB Star below to show what I mean. Sorry if I have posted these sketches about making spade drills before. I use the pin tongs and oilstone method when sharpening twist drills also.
    Click image for larger version. 

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    James
    Last edited by Goldsmith; 08-06-2014 at 01:27 PM.

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