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05-14-2005, 01:50 PM #1
I will try to explain this as best I can. Every countersink at work has been ground up, by someone trying to make a chipbreaker on them. These countersinks are MAO Ford uniflute 90 degree design. What someone did is grind a small groove on the inside of the cutting edge(cutting edge flute), and this makes them cut like crap. When I learned to grind drills I was taught that grinding the face will bring the cutting edge to a nice sharp edge. Is this correct, it makes since to me. I was taught that you only grind on the cutting edge if your making a split point drill. This is driving me nuts because I have gone over this issue with a few coworkers and they dont think I am right. Can someone settle my mind and tell me if you think this is correct, I hope i explained this well enough.
05-14-2005, 02:00 PM #2
I think I can visualize what your talking about,
the only time that ever helped anything in
my small world was using them to hand champher
asome of the softer plastic like materials like clear ultem, brown delrin etc,...but for
cutting steel, aluminum, etc that practice
does not help, it makes them cut with too
05-14-2005, 02:41 PM #3
i know where you're coming from. years ago....
when i worked for someone else's shop, there was
a moron who insisted he could grind a "pilot"
on his drills....well, he F'd Up every tool he
got his dirty mitts on.
there's always some "expert" out there who thinks
he knows more about tool geometry than Greenfield,
brubaker and niagara..........
anyway...get some of the zero flute c-sinks with
the round hole in the side...the douchebag
tool expert won't know what to do.
05-14-2005, 03:02 PM #4
Grinding on the cutting side of a drill bit, countersink, end mill, or tap is a big no-no, unless you have the knowledge, skill and capabilites to not screw up the tool's geometry. I daresay, most shop workers do not meet these requirements. Uniflute countersinks are ground with a slight positive rake on the cutting face. By trying to freehand grind a chipbreaker into the face, the rake has probably been changed to negative. I imagine they now raise more of a burr than they remove. Travers sells a simple sharpening jig for uniflute countersinks (about $100), which allows the tool to be rotated against a surface grinding wheel with an eccentric radial motion, giving it the required heel clearance to prevent rubbing. This is the only acceptable method for accurately and consistently sharpening uniflutes.
Stupidity like this rates right up there with those 'experts' who freehand drill bits, without using a drill gauge. I used to work with a guy who did that; after he reground a drill bit a few times, it was closer to 90* than 118*!
05-14-2005, 09:25 PM #5
M A Ford also makes & sells a Uniflute grinding fixture http://maford.com/
If you really want to have some fun, bring in one or two Severance Inside Chamfer Mills. These are guaranteed to drive anyone crazy if they try to sharpen them. BTW, they are fantastic in thicker wall pipe & mechanical tubing.
05-15-2005, 06:12 PM #6
We do a lot of deburring and chamfering with a countersink in a drill press. So these countersinks become really frustrating to use. No we dont need a gringing fixture since we all ready have one. I think I am going to find any countersinks that havent been molested and hide them, save them? On a side note another coworker had a very nice six flute carbide countersink, big bucks. That he allowed another coworker to borrow under strict guidelines. Well it came back hacked up, after he tried to do him a favor by sharpening it.