Forstner Bits FAQ
What is Forstner Bit?
Forstner bits are a little bit different than most drill bits.
They have a centering bit which lets you get right on your mark and drill exactly you want to drill.
They have teeth on their outer edges (not always) which give you a nice clean cut on the sides of your hole.
They have a scraping edge inside between the centering bit and the outer teeth and that cleans out the balance of the holes. Because of that edge in the middle it gives you a nice flat bottom finish.
Where I can use Forstner Bit?
You can use it with:
- Handheld drill
What size Forstner bit for the cabinet, concealed and euro hinges?
You need to use 1 and 3/8 inches or 35 mm. size bit.
How to sharpen a Forstner drill bit
Sharpening with Diamond Sharpening Kit
I recommended this particular kit because is it high quality but it comes with a double-sided diamond card and a diamond file with one flat side and one round side. Together this two hones can be used to sharpen all sorts of things.
Common stagger toothed bit
For these, you need to use a diamond taper. It’s 600 grid which is ideal for our purposes. In one side it’s flat, in other side it convex.
Step 1. Put a little bit of the lapping fluid on the flat side.
Step 2. Take a file and place it against the flat of each tooth on Forstner bit.
Give it five back and forth strokes. Apply only little bit of pressure. We don’t want to remove too much material. Just enough to refresh the point of each tooth. And on each tooth counting out same number of back and forth strokes. When you combine light pressure with the same five strokes per tooth you’re ensuring that you aren’t removing more material on one than you are on another.
You also don’t want to sharpen sloping top surfaces of the teeth because you want all of them to stay on the same plane. So they all contact the wood and work together as the bit cuts.
Remember: five back and forth strokes per tooth, light pressure and only inside surface.
Step 3. Sharp the cutters.
These are just flat surfaces. To refresh them you place the flat of the diamond file against the cutter and stroke at an angle so you cover the entire cutter with one stroke of the narrower file. Do this back and forth, applying light pressure, five times then switch to the other cutter and repeat same five back and forth strokes.
That’s it. This process will work for all sorts of force ribbons.
Bits without teeth
Step 1. Use the rounded side of the diamond file
Step 2. Lay it in one of these concave ripples and tilt it back just a bit. It must be filling on a sharp edge
Step 3. Work back in forth very lightly all the way around the rim.
You can’t count the strokes in the same way as before instead just keep the file moving applying consistent pressure.
Step 4. Switch to another side of the rim and repeat the process.
Step 5. For the flat cutters check Step 3 in the previous part.
Sharp self-feeding Forstner bits
You can sharpen it using the same techniques. But a lot of productions shops prefer a coarse sharp edge. That meand they don’t want them honed to a fine 600 grid because the edge will actually last longer in their situation if it’s sharpened to 300 grid. Think about a bench chisel as compared to a turning gouge. Turning gouge take a beating and rarely honed as finely as bench chisels.
So for really aggressive cutting particularly it end grain or in production settings with very hardwoods a coarse sharp edge is preferable for extended durability.
To achieve this you need to use that credit card size stone that came in the same kit. One side is 300 grit which you need to use between the teeth.
And underneath those flat cutters.
Use the same technics as above.
Some of this self-feed bits do have a sharpened edge on the tops of the teeth. For those, you would have to use the rounded side of the file. Which won’t give you a coarse sharp edge because it’s 600 grit, not 300. But that’s not a big deal because the main cutters be coarse sharp really well.