Forstner bit sharpening??

[Paul.J]

I have a cheapish 50mm FB and have drilled about 30 holes into side grain Laburnum and its done a pretty good job but now it needs a sharpen,so what is the best way to do it.??
I have tried with a slip stone on the round cutter parts and a Trend diamond on the flat parts and although the edges feel sharp it is not cutting like it was from new.
Cheers.

 

[nev]

about as far from professional as one can get - i just touch mine on the blue grinding wheel, seems to work

 

[DTR]

I do mine with a saw-sharpening file.

When you say the round parts, you do mean the insides of the spurs, don't you? (hammer)

 

[Billy Flitch]

I do mine exactly the same as Dave inside of spur with a saw file.

 

[Eric The Viking]

Wot Dave and Billy said.

Mine yew, the cheap Forstner bits I have won't keep an edge for seconds, never mind minutes, no matter how much I fettle them.

I have a couple made of better steel, mainly intended for cabinet door hinges (30mm), and they're much better, although they have a steeper angle of attack and you can only really use them in a drill press (not yer actual Forstners at all, really).

I'm going back to the "only buy what you need" approach, and getting better ones next time.

E.

 

[custard]

I do mine with a saw-sharpening file.

When you say the round parts, you do mean the insides of the spurs, don't you? (hammer)

Like DTR said, you mustn't ever touch the outside of the circular cutter section, or it really won't cut properly ever again because it will then be cutting a hole with a fractionally smaller diameter than the actual size of the drill bit.

 

[gregmcateer]

Paul,

This helped me - look at the videos - someone on here directed me to it.

http://www.trend-uk.com/en/UK/produ..._credit_card_double_sided_diamond_stone_.html

HTH

Greg

 

[Paul.J]

Thanks for the replies folks and the link Greg. :wink:
I did see the one video but it was for a saw tooth bit,mines the ordinary style.
I don't touch the outside of the cutter that would be easier to do than trying to get an edge on the inner which is the difficult part to do,but might try a fine file?

 

[Eric The Viking]

Does anyone know what the titanium nitride coating is supposed to do, apart from hide imperfections)?

I've got some morticer chisels and forstners that are coated, and I've also seen it applied to cheap twist and masonry drills. I've not noticed any improvement in performance over ordinary tool steel (or carbide tips). It looks like a gimmic. I'd prefer better quality steel/machining, I think.

On sharpening Forstners: you have to take any burr off the outside, obviously. You can't win on the dimension thing, as they're slightly conical anyway. On balance a very slightly undersize hole is OK, as you can't make it smaller afterwards.

I'm going to try Fischer next time, or something similar.

E.

 

[Paul.J]

I haven't a clue why E,was it summat to do with keeping the cutter cooler longer??
but i'm glad to say that the file and the Trend diamond credit card worked on my FB,and the bit is cutting like new again,so now i know how i will keep on top of the sharpening when doing my next batch of drilling.
Thanks everyone

 

[yetloh]

I haven't tried this http://on.aol.com/video/how-to-sharpen-forstner-bits-with-a-rotary-tool-302212014 but it is the method I think I will use when I get round to sharpening mine.

Jim

 

[Paul.J]

That looks easy enough to do,i will have to find out my Lidl dremmel type tool to try it.

 

[Eric The Viking]

I wonder if the end result is actually sharper though. I do mine with a bit of emery cloth on something as close to diameter as poss., and I move it radially, not circumferentially.

I'd be a bit nervous of burr/wire edge with the method he uses, and you can see the mess it makes of the two chisel blades (I use a cheap diamond needle file usually for those). If you can hold the grinder so that it cuts across the edge , rather than along it, it might be fine.

E.

 

[yetloh]

I wonder if the end result is actually sharper though. I do mine with a bit of emery cloth on something as close to diameter as poss., and I move it radially, not circumferentially.

I'd be a bit nervous of burr/wire edge with the method he uses, and you can see the mess it makes of the two chisel blades (I use a cheap diamond needle file usually for those). If you can hold the grinder so that it cuts across the edge , rather than along it, it might be fine.

E.

I don't see any problem with circumferential sharpening. In principle it is no different from what many freehand sharpeners do when they register a bevel on a stone and sharpen by drawing the bevel along the the stone with the bevel parallel to its long edge, for the extra stability that gives when compared with sharpening across the narrow width of the bevel. I have recently been trying out the American made Sharpskate honing guide http://hmsenterprises.com/webstore/getsharpercom-sharp-skate which uses exactly this principle, which the makers call side sharpening. They claim that side sharpening actually produces a better edge because the edge consists of a continuous strip of metal when viewed under a microscope rather the relatively jagged edge produced by the series of microscopic grooves given by the ends of the scratch pattern produced when the blade is drawn along a stone at right angles to the edge. I think this idea has some theoretical logic although I could not detect any discernible difference in the sharpness of edges produced conventionally and by side sharpening.

Jim