How to sharpen Krenov style drill bits??
I had recently read in The Fine Art of Cabinetmaking about James Krenov sharpening an ordinary twist drill bit in a certain way that cut better for him. I’ve looked at the picture and it looks as though his method produces a bit similar to a brad point drill bit. I’ve tried to duplicate his sharpening, but haven’t been successful, I usually end up with something that looks more like a regular brad point drill. His cutting edges seem to have a gentler, smoother curve. My question is, has anyone been able to sharpen bits like he recommends? If so, do they cut cleaner? How do they compare to a regular brad point bit or a standard twist drill? I’ve been using brad points and regular twist drills for home repair type projects and woodworking and they seem to work fine. I’ve recently given up on hand grinding my twist drills and purchased a Drill Doctor. It does a great job for general use bits, but I can’t help but wonder if I would have better results if I could learn to sharpen bits like he recommends. Given his experience he must have good reason for taking the time to grind them that way, maybe I should too. Any advice is appreciated.
Replies
Anyone out there see this? Any experience with this type of drill bit??
dp,
i haven't the slightest idea how our beloved james sharpens his drill bits. yesterday,while driving home and fanticizing freely, i imagined owning some sort of device with which i could sharpen my extensive collection of dull drill bits. the drill doctor came to mind. i determined to post a question regarding its qualities and then this morning i stumbled upon you post. and, although i apologize for not knowing krenov's technique, i would very much like to know what you and others think of the drill doctor. i'm not intending to hi-jack your thread and i do hope someone who knows the answer to your question writes in.
thanks,
eef
I am very happy with the Drill Doctor. It is easy to use and the bits are as sharp as new. I was never able to get really good freehand grinding. The conventional shape of the twist drill works fine for most everything I do. I still wonder why Krenov sharpened his bits differently, and how to do it. I'm sure he had a good reason.
I believe his reason was just as you have described, his technique resulted in a brad point drill. That's all. Drills ground for metal working don't give anywhere near the control that a brad point does in wood.Rich
I never saw Krenov sharpen a drill bit while I attended school there (although that doesn't mean he doesn't). That was left up to David Welter (shop guru). It was great having numbered and lettered bits sharpened to a brad point tip. I wish I could do it myself. I've tried a few times but ended up trashing the bit each time. Essentially you're supposed to grind the center to a point while cutting down the flute on either side. How he does it I couldn't tell you. Take a summer class up there and he might show you.
Another option is to not worry about it. Buy a good set of brad point bits (Lee Valley sells an excellent set) and keep them sharp as need-be. Spend all that extra time working wood.
I'm sure that with enough time invested, someone with good mechanical skills could figure out how to turn a car axle into a pretty good lathe. The question is, unless you are McGyver, why would you want to??
Enjoy your woodworking.
Jeff
The point :) however, is that Lee Valley does not sell a complete line of numbered and lettered brad point bits (although they do have a few lettered bits for pen making.) When looking for a very precise fit, lettered and numbered bits are most handy.David Finck, as a part of his one of his workshops, covers grinding a metal working bit to a brad point, if memory serves.Regards,
Dick
"My question is, has anyone been able to sharpen bits like he recommends? If so, do they cut cleaner? How do they compare to a regular brad point bit or a standard twist drill? "
That cutting edge shape is not unique to James Krenov. It certainly drills wood better than the standard twist drill shape which is intended primarily for metals. It also cuts cleaner than regular brad point drills which are shaped with an emphasis on the aspect of drilling straight and fast rather than ultra smoothly.
To do this grind you need to have a thin wheel and the means to shape the wheel so that the periphery is nosed or u shaped-that makes grinding that curved cutting edge much easier.A multi cluster diamond wheel dresser is the tool required.
But I agree with others-unless you are adept at this sort of thing it is better to buy a set of brad points and forstner bits . But if you are keen it is essential to be able to re-shape your wheel-and I suggest you buy a few twist drills say in the size range 8, 10 12 ,15mm to practise onPhilip Marcou
Edited 11/9/2008 4:56 am by philip
Pete Galbert has a series of posts on his blog that talk about bit grinding. I don't know how Krenov grinds his bits but it sounds like a similar result to what Pete gets. Here are the links:
http://chairnotes.blogspot.com/2007/05/here-is-close-up-photo-of-grind-that-i.html
http://chairnotes.blogspot.com/2007/05/bit-grinding.html
http://chairnotes.blogspot.com/2007/05/final-cut.html
I have tried his method and gotten pretty good results, though it does take some practice.
Jeff
Jeff,That's a great link. Thanks.Rich
When I was at the school they showed us to use the corner of the grinding wheel to cut a 90 degree area spanning from the tip to the end of the flat area where the twist begins.
Use the corner of the grinding wheel to cut out the flat area of the twist drill. Rotate the drill to grind a relief the same as if you were grinding a twist drill for steel.
When were you there?
Summers of 1987 and 1988
Edited 11/13/2008 11:37 pm by gb93433
ahh. the early years.
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