15th Sep 2009, 12:34 PM #1
How Do I Sharpen Solid Carbide Drill Bits?
How Do I Sharpen Solid and Other Carbide Drill Bits?
Can any of the machinist experts please tell me how to sharpen –
1 Solid Carbide Two Flute Twist Drill Bits (with angles to cut hard metal)
2 Carbide Tipped Masonry Bits (for rotary and rotary+impact work in masonry)
3 Artu brand type carbide tipped twist drill bits for metal.
Need to know point angles, relief and relief angles, grinding wheel types, grinding area fpm past the drill point (or wheel RPM), etc.
I assume that diamond is best for sharpening, with silicon carbide second?
I have a General drill sharpening jig, so I can regrind bits with a resaonable accuracy, but it is the "angles" question on which i need to ask advice.
I have heard that I need to grind a secondary cutting edge on solid carbide drill bits, at an angle almost axial with the drill bit, so as to avoid micro-chipping of the edge., and subsequent poor drilling performance and premature drill bit failure. Is this correct? My ARTU drills have a reverse angled cutting edge; what should this angle be for metal cutting?
My solid bits will be used to drill stainless steel, high tensile bolts, and hardened steel, but not HSS nor tool steels.
I have yet to find a website with a good “how to grind” section on grinding solid carbide twist drills.
Does anyone know of any such websites with good material?
Sorry about the multiple questions, but my primary question is about the solid carbide drills.
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15th Sep 2009, 05:20 PM #2
Silicon Carbide is the way to go and then you may just use a hand diamond to lap the edge.
P.S I found it best, as you mentioned, to grind a secondary edge (very small) in negative rake.
As for the angles I can't help you as it just comes natural over 30 years or so experience but I'm sure someone will bob up shortly with the text book details.
17th Sep 2009, 07:29 AM #3
Attached is an interesting article on Drill Point Geometry.
11th Oct 2009, 07:53 AM #4
Thanks for the replies, but I am still searching for some advice on how best to sharpen these solid carbide drills.
Has anyone got any more to offer please?
One thing I did find in research is that the dust from grinding most tungsten carbide drills etc contains Cobalt, used as a binder for the material in manufacture of cemented carbides, and it is highly dangerous. At least one worker in the industry has died from inhalation of dust when grinding carbide cutting tools.
I will be much more safety conscious when I eventually get around to grind my carbide tools.
I wonder how many others like me knew nothing about this aspect?
Cobalt poisoning - Wikipedia, the free encyclopedia
12th Oct 2009, 08:39 PM #5
It is always a good idea to wear a slip on dust mask when grinding or sanding anything as the fine particles fly around.
No dust particles of anykind are good for you.
I would rather die from grinding than die from boredom.
All I know is that you can use Green coloured Silicon Carbide wheels for grinding Tungsten carbide.The volume of a pizza of thickness 'a' and radius 'z' is given by pi z z a.
12th Oct 2009, 11:21 PM #6
Check out this site here.
You can use a drill point angle of 128 degs .or 130 degs. And the carbide will work just fine. As suggested by Chips, use a Silicon Carbide wheel to sharpen the drill. Dont even thing of using an Aluminium Oxide wheel for this job. These wheels chip and breal the carbide, they do not cut as a silicon wheel will. By far the best is a diamond wheel but they only have a narrow face. After shaping and sharpening the carbide, do use the diamond lap to finish the cutting edges. For drilling hard steel, SS and hard metals, cut a flat on the lip of the drill the same as you would a HSS drill for brass. See the attachment for details. All masonry drills have the cutting edge beveled at about 45 degs. This is to stop the cutting edge from chipping and also gives it strength.. Cement and rock crumble and powder easily but the edge must be angled back.
I use drills that have straight flutes and they sink into SS like a knife into butter. These drills must have a sharp cutting edge and a minimum of clearance as shown in the drawings. Even though the attachment refers to HSS drills, if you keep to the above angles everything will work for you. For drilling Stainless Steel, use a good cutting oil and plenty of it. Use WD40 or kero or diesel on the diamond lap for best results.
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