Large Drill Grinding Jig

taycat

taycat

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just aquired box load of large drill bits going up to two and a half inch.
some are mt3/2 others are reduced shank.
need to get plans for grinding jig but cant find anything for that big.
anyone help pls?
will be using a mk1 clarkson tooling and cutter grinder for sharpening them.
cheers
 
I use jigs for drills up to 3/4" and then switch to hand/eye/drill gage/bench grinder for anything larger, because I don't have a jig or dedicated grinder for large drills. It is all I have, and it works fine, after studying, learning, and practicing the techniques and skills. Large drills are much easier to hand grind than small ones, in my experience. It is easier to see what is going on, the grind progresses more slowly, so it is harder to make gross mistakes, and slight errors are less of a problem than with smaller drills. The other issue is that I do not do enough grinding of big drills to make a jig or dedicated grinder cost and storage space effective. I barely do enough of them to keep proficient at hand grinding them.

Edit: Having a box load of them will give you plenty of material to learn and practice on!
 
Get you an upright belt sander with either a 2" or 6" wide sanding belt. About 60 grit. This is the way to go on larger drill bits, 3/4" and larger. As Bob said, practice, practice, practice and you'll get good at it. Ken
 
Using a Clarkson? I like Ken's suggestion. I don't have an upright belt sander - but I do have a 20" sanding disk, and it is awesome for drill bits, especially those over 1/2". With a zirconia disc, it can seriously take off some metal, and also gives a very nice surface finish (select your surface speed by how far out you are on the table). With the table set down at your preferred angle (say 31°), then one of the drill point criteria is taken care of - letting you concentrate on the other features. With less than 1 hours practice I had drills making very nice twin curls and pretty close to size.

I find with "free bee" drill bits (I have about 10 pounds of 3/8" to 1" to work through), the land has often been chewed back from folks pushing a dull drill bit, then sharpening it and pushing it some more - the land can't take it. Just measure across the lands - you have to cut it off back to near full size. If you just sharpen the drill with out cutting it back, the surface finish will be horrible, everything gets hot - generally not good.

Do not hesitate to cut the drill back (abrasive cut off saw) - but it means a full reprofile - not a big deal, but it sure helps if you have a machine that can rough it out in a reasonable length of time.

My days with the 20" disc for sharpening are probably about done:
http://www.hobby-machinist.com/threads/pine-drill-grinder.48556/

Okay, I apologize for the little gloat. I got the drill grinder very cheap and it is another piece of iron in the shop (which is always a good thing). When it comes right down to it, the 20" disc removes the material faster, is quicker to set up and produces a good result without a much fussing (you can work 10 drill bits at a time, letting them cool as need be). The Pine Grinder is good and the two cutting edges are pretty well right on, however it is a bit fussy to set up, easy to make a mistake on, is pretty slow if there is a fair amount of material to remove from a large drill bit. Strictly speaking, a drill bit is a roughing tool and in most applications there is little to be gained in getting it "perfect".

Now it you are thinking about a 4 or 6 facet drill grinder (see various posts here and other web sites for "precision drill sharpener") the Clarkson may be a great platform to start with. That seems like an improvement in drill performance (on my bucket list to build).
 
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