sharpening Forstner bits, easy, hard, or fuggedaboutit?

Roger Tulk

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St. Catharines, Ontario, Canada
I tried to make some dog holes in a new portable workbench top today, and found the bit stopped about ½" into the 3/4" pine. It just wouldn't go any further. So, I finished the job with a spade bit, which went through the pine almost instantly, but left the bottom very messy. So, can these things be sharpened, and is it worth it when I can pick up a new bit for about $15?

TIA.
 
Personally, I just replace the bit when it gets dull. It might be worth it to have the larger sizes sharpened by a service but like you say, the smaller sizes can be replaced for $10-$15.
 
It's not hard. There are two edges to sharpen, the outside rim and the edge that does the cutting. Sharpen the lip with a small file, be careful to match the existing cutting angle. The outside rim can be sharpened with a Dremel with a stone chucked in it. You grind only on the inside of the rim.
 
On my larger 1 3/4, 1 9/16 etc I use for drilling my pepper mills, I'll sharpen them on a 1" belt sander... match the flat edge angle to the sander belt and touch up the edge a little... works for about 3 or 4 sharpenings, then toss it for a new one. Smaller bits I toss and replace.
 
Bigger ones are expensive. I once took one to a professional. He reversed the belt on a 1" grinder and sharpened freehand. He knew what he was doing and it came out fine. Takes practice, I'm sure. Fortunately they don't need it very often.
 
I wanted to move ahead wth the project, so I bought a bit ($13). I have a Dremel type tool, and a box full of stone grinding points that will probably work, as well as a diamond file. The new bit is too large for the nice box the set of bits came in, and I hate to break up a set, so I'll have to sharpen this one.:rolleyes: I also got a blade for the small Surform, which was pretty good, as I went into HD doubting that they would carry either of those.
 
I ran a cheap HCS set that I got from Woodcraft for better than 10 years. One becomes quite proficient at sharpening them. I now run higher quality HSS ones that require sharpening much, much, much less. I did have to up my sharpening game though as the bits just laugh at the box-tie file I used on the High Carbon bits. DMT diamond files are my new best friend. They work great for router bits too.
 
In the middle of driling dog holes for my work table tops, the new Forstner bit seemed to be getting a little tired. I grabbed my diamond file and quickly touched up the chippers, and it improved the performance. Later, I took the older bit and touched up the chippers. The bit didn't have a rim, but more of a spur, about 3mm on top, which was easy to sharpen with the same diamond file. Its performance improved too. I suspect this was a cheap set, dressed up in a wooden box to make it look higher quality. I have used them for drilling out stuff on the lathe, and will continue to use them for that. I was surprised at how little time I had to spend on the touch up.
 
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