Sharpening fostner bits

dlbristol · Post by **dlbristol** » Fri Dec 05, 2008 11:54 am

I have a new set of bits, and I have learned from you guys ( and sad experience) they need to be sharpened. Can someone give me some direction on this project. I can see some way to do the cutters, but the rims are a total mystery!! Thanks and Merry Christmas!

ryanbp01 · Post by **ryanbp01** » Fri Dec 05, 2008 12:15 pm

For what it's worth, I'd like to see that too!! While we're at it, is there a thread on how to sharpen brad pint bits?

BPR

doug45601 · Post by **doug45601** » Fri Dec 05, 2008 12:34 pm

I've had good luck using a Dremel grinding wheels with a fine point.. Can't really justifiy if this is the right way to do it or not but has worked for me!:D

drl · Post by **drl** » Fri Dec 05, 2008 2:37 pm

FYI there is a "question & answer" on sharpening Forstner bits In American Woodworker September 2007 #130 page 10. It is not all inclusive as it does not address bits with the sawtooth type rim. Article recommends a flat diamond hone for the chippers and convex diamond hone for the rim. Diamond recommended because it cuts faster and therefore lessens the chance to change the original geometry. I don't know if I can legally scan and post the page or not. I need to sharpen some of my bits as well but haven't tried it yet.
Regards,
Dwight

dlbristol · Post by **dlbristol** » Tue Dec 09, 2008 11:03 pm

I did manage to find a few ideas on line, but for the most part they were pretty much based on " this is what I do" and very dependent on personal skill. I finally used an old,small whet stone that I used to use on braod heads in my archery hunting days. It is small enough to get into the flutes. The rims seemed to be more forgiving than I thought. I made a U shaped jig to hold the bit, mounted it to the floating table. I clamped my Dremel to the extention table and adjusted the height and angle to the rim angle. I used a Dremel bit with a cone shape and By turning the bit in its cradle, I did get some degree of help. This was on a 1in bit, and I can't imagine doing it with a bit less than 1/2 in.

It seemed to me that the flutes are the most important part of the problem. I will keep looking, there has to be a better way! Doug, How do you set up the Dremel?

a1gutterman · Post by **a1gutterman** » Tue Dec 09, 2008 11:24 pm

dlbristol wrote:I have a new set of bits, and I have learned from you guys ( and sad experience) they need to be sharpened. Can someone give me some direction on this project. I can see some way to do the cutters, but the rims are a total mystery!! Thanks and Merry Christmas!

I'm sorry dlbristol, if this seems an odd question, but, you did post that you had a NEW set of forstner bits. Why wood they need sharpened?

charlese · Post by **charlese** » Wed Dec 10, 2008 2:32 am

I bought a set of of Forstner bits, they were sharp enough to cut but a little touch up did wonders. I used diamond cards (fine) and stroked only on the sloped, straight cutting face on most bits. On others there were small ridges on the small edge adjacent to the slope. There is usually a recess in the rim to accommodate a file or diamond card to make a few strokes here.

So far I've never had to mess with the edges of the rims. Since the rims (or teeth) are at the same level as the cutting edge, they shouldn't need to be sharpened at all. Only the front edge of the rim does any cutting. The rest of the rim merely slided around the circle.

Has anyone found that sharpening a rim has any effect on the sharpness of the bit?

a1gutterman · Post by **a1gutterman** » Wed Dec 10, 2008 3:52 pm

Hi Chuck, I do knot doubt that you can touch up a factory sharp forstner bit to improve it's performance, but, hey, these are knot lathe tools; forstner bits should be sharp out-of-the-box, so to speak. dlbristol should expect to receive new forstner bits as sharp as needed!

dlbristol · Post by **dlbristol** » Thu Dec 11, 2008 12:50 pm

After reading the last posts, I went to the box of bits and tried several of the other bits. As some of you said, the other new bits worked ok. I think I may have a bad bit in the set that needs to be replaced. This was not a cheap set and I did expect them to be sharp. I can't tell now if the bit was bad, because I've worked on it. I can see some things that make me think it was defective. The angle on the flutes seem to be much flatter that on the other bits. Bad bit was 1in and the next smaller one was 7/8.
That said, I have had to touch up many new tools in the past. ( some of you told me that when I had issues with mortise chisels)
There is some question about the rims as well. Several places I looked at are adament about the rim being 1/64 in longer than the flutes so that the hole is cut before the stock is removed. I was able to get a better cut after sharpening only the flute. I will say this, the effort and time it took to set up the dremel to do the rims was probably not really worth it. I think I will keep looking. Perhaps I have found my "million dollar idea". If it fails, I can park my jet and drive my little Ford Focus to DC and get a baleout!Thanks guys.

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Sharpening fostner bits

Sharpening fostner bits

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