Thread: How do I sharpen forstner bits?

A file or diamond stone on the flat of the cutting edges. For my cheaper forstner bits a normal file works fine. If the steel is a bit harder, use a diamond file.

Originally Posted by TassieRob

A file or diamond stone on the flat of the cutting edges. For my cheaper forstner bits a normal file works fine. If the steel is a bit harder, use a diamond file.

The bits I have range from 6mm to 22mm, what grit should I use?, any recommendations on what to buy to get these thing sharp again?.

You are really trying to restore an edge rather than hone. There is really no purpose in trying to hone a very fine edge on a drill bit.

There are YouTube videos showing multiple methods - usually either a Dremel, diamond paddles if you have flats, or a roundle file or round hone. No-one I've seen has ever suggested you need anything other than a coarse grit.

Originally Posted by EagerBeaver71

This things as blunt as a foot to the face, how should I go about sharpening it?:

IMG_9130.jpg IMG_9131.jpg

They're Freud so pretty good quality.

If you have ever sharpened or touched up the teeth of a backsaw, you will understand when I say that you need to imagine that the forstner bit is much the same. I use 240-, then 600 grit diamond paddles. The aim is simply to polish the flat faces on the inside of the bit - never the outside. Count your strokes to give each face the same number. You want to keep the cutting edges level.

Regards from Perth

Derek

The sharpening tips are good.

One thing to consider - how did they become blunt?

Many users abuse forstener bits, well all drill bits, by operating them at very high drilling speeds, which becomes more of an issue with our Australian hardwoods and the typically high silica content of the wood.

drill-speed.pdf (carbideprocessors.com)

great thread very helpful!

Originally Posted by derekcohen

If you have ever sharpened or touched up the teeth of a backsaw, you will understand when I say that you need to imagine that the forstner bit is much the same. I use 240-, then 600 grit diamond paddles. The aim is simply to polish the flat faces on the inside of the bit - never the outside. Count your strokes to give each face the same number. You want to keep the cutting edges level.

Regards from Perth

Derek

Hi Derek, Thanks for the sound advice mate. At the moment I have no sharpening gear at all, so if you have any advice on what and where to buy I'd really appreciate it.

Regards - Sam

Sam, look up DMT dia-sharp mini hone.

I just clamp the bits into a vise and work the faces. Keep the hone flat and make sure you can feel the wire.

Regards from Perth

Derek

Originally Posted by derekcohen

Sam, look up DMT dia-sharp mini hone.

I just clamp the bits into a vise and work the faces. Keep the hone flat and make sure you can feel the wire.

Regards from Perth

Derek

What do you mean, "feel the wire"?.

Sam, have you any experience sharpening blades (chisel or planes)? It sounds not.

When one hones across the bevel face of a blade, a wire edge is created at the back of the bevel. This is an indicator that you have indeed honed the full face. If you do not achieve a fine wire, the bevel edge has not been sharpened. It is possible to polish up a bevel face with it actually remaining dull.

The edge of any blade sharpened with a hone is the same - be it forstner or knife or chisel.

Regards from Perth

Derek

Originally Posted by derekcohen

Sam, have you any experience sharpening blades (chisel or planes)? It sounds not.

When one hones across the bevel face of a blade, a wire edge is created at the back of the bevel. This is an indicator that you have indeed honed the full face. If you do not achieve a fine wire, the bevel edge has not been sharpened. It is possible to polish up a bevel face with it actually remaining dull.

The edge of any blade sharpened with a hone is the same - be it forstner or knife or chisel.

Regards from Perth

Derek

Its all totally new to me, I've not so much as sharpened a chisel!. I'm guessing I will need to learn a new skill set before I attempt it on my expensive tools!. Thanks for all you're valuable advice Derek.

Originally Posted by EagerBeaver71

Its all totally new to me, I've not so much as sharpened a chisel!. I'm guessing I will need to learn a new skill set before I attempt it on my expensive tools!. Thanks for all you're valuable advice Derek.

Good response, EB.

Your next priority now should be to learn to sharpen. You cannot do anything good with blunt tools, no matter how expensive. May I guide you towards researching sharpening techniques:

• Derek Cohen's website, and
• sharpening Forum on this Forum.

Probably the best (and cheapest) way to get started is with "scary sharp" method - just need a honing guide (optional, but recommended), 4 or 5 grades of sandpaper and a flat plate. The first time a "wire" appears is transformational. You are now a sharpener! Later, when you are more experienced and can make an informed decision then you can consider other options - diamond plates, water stones, CBN wheels, etc. Many, many viable options.

Originally Posted by GraemeCook

Good response, EB.

Your next priority now should be to learn to sharpen. You cannot do anything good with blunt tools, no matter how expensive. May I guide you towards researching sharpening techniques:

• Derek Cohen's website, and
• sharpening Forum on this Forum.

Probably the best (and cheapest) way to get started is with "scary sharp" method - just need a honing guide (optional, but recommended), 4 or 5 grades of sandpaper and a flat plate. The first time a "wire" appears is transformational. You are now a sharpener! Later, when you are more experienced and can make an informed decision then you can consider other options - diamond plates, water stones, CBN wheels, etc. Many, many viable options.

Thanks for the advice Graeme , I'll be sure to check out everything you have mentioned.

Thanks,

Sam