Drill bits , what do I do wrong ??

[One of Many]

Another peek and I would suspect the secondary relief is not a flat angle grind, but a radius of the wheel where in the runout(near tangent, but not quite) meets the heel of the primary grind while it also reduces the negative rake at the web center blend of the opposite flute.

The center may not neccesarily cut, but it could help stablize the drill from wander?

DC

[Deusrexmachina]

Hello to all, this is my first post. :þ

You've to also forgive my crappy technical explanations if there'll be something I won't express properly, mainly because I've never learned these exact terms in my almost 8 years as a CNC lathe operator starting from scratch, and on top of it my past school background differs from my job, so what I've learned is grounded directly from the workshop.
We've recently changed two supervisors, and our working methods have changed for the better, providing us -finally!!- with appropriate tools. Some past techniques still remain though, like grinding drills by hand and/or using the grinding machine in a slightly different way. I've learned, for instance, to sharpen unevenly the cutting edges; the result is to have a bigger hole from a minimum of 0.05 [mm] up to 0.4 [mm]. It's good for deep drilling so the diametrical cutting edge of the drill bit doesn't friction during the path, wearing it and in the worst case destroying it.
Example:
Material 1.2311, drill Ø8 x 83 [mm], drilled automatically with the lathe (can't recall the feed nor the rpm, sorry); I've drilled 54 pieces without the need to sharpen more than once (before starting); the hole wasn't important so it could have been almost up to Ø9.
Sometimes if drills are too precise, well, they just don't fit for the job. Of course I'm not talking about those modern bits with inner refrigerant holes, eh?

Erm, didn't want to show-off nor be a smart-ass, just wanted to share a little info I THINK might be useful.

[chipsinpan]

Is That an old Gallmeir Livingston grinder ? Looks a lot like mine .
Anyway , that jig in your photo is not meant for drill grinding . I think you are just grinding a cone that "looks" like a drill point .At best , you are grinding an end mill with a tapered end . Suggest you get a cheap drill grinder , like a drill doctor and see how it gyrates the drill to get a variable angle that changes from the point , out to the O D lip. You will be able to split a point , or do a facet grind on a masonry bit with this setup , but you will never get consistant results as a properly ground drill.

[Mcgyver]

I think you are just grinding a cone that "looks" like a drill point .At best , you are grinding an end mill with a tapered end . Suggest you get a cheap drill grinder , like a drill doctor and see how it gyrates the drill to get a variable angle that changes from the point , out to the O D lip. You will be able to split a point , or do a facet grind on a masonry bit with this setup , but you will never get consistent results as a properly ground drill.

chips, why do you say that? most I've heard or read says the faceted point is as good or better than a conical point, which has also been my experience. imo a cheapo drill doctor can't hold a candle to a properly done T&C ground 6 faceted point. the good conical point sharpeners are thousands and still don't do a better job.

Pat, couple of things,

i take it from your explanation that you are moving the univise instead of indexing the drill 180 degrees? This is a bit problematic in that it's difficult to set the univise with any angular precision, meaning that the two sides might not come out exactly the same. much better to be able to index the drill.

I designed a drill holding head to go onto a univise to do this - to be able to hold any sized drill, index via a tooth rest and have find adjustments on both tooth rest and the longitudinal position of the drill. here's some pics.

http://bbs.homeshopmachinist.net/sho...t=25540&page=2

Finally, the first picture you posted, is a 6 facet cut. Note the acute corner of the drill lip has been ground down a bit. This is not essential, but does make the faceted grind a lot tougher, probably better tracking. What sort of accuracy are getting with the holes? i still impress the hell out of myself with 1" drills that only cut 2 thou over.