recently we made a video called clever tricks with forstner pits and it's been pretty popular i think for good reason if you haven't seen it yet i encourage you to click the link below this video and check it out you'll be glad you did but it also led to a lot of questions about how to sharpen forstner bits when they become dull or in the case of cheap bits right out of the package because they seem to come pretty tall from the start we dealt with this subject about five years ago but we've gained a lot of new viewers in that time and i think it's worth revisiting the subject because a dell forstner bit can be very frustrating to use fortunately it's not difficult to sharpen them at all if you just know a few tricks so in this video i'll show you how to sharpen the most common types including toothed rim bits and wavy or continuous rim bins so let's begin with the toothed bit for this i'm going to use a 600 grit credit card style diamond tone these are widely available and they come in various qualities as well as various prices i'll link to the one i prefer below this video all forstner bits feature some type of outer guide rim to sever the fibers around the perimeter of the hole in this case it's a sawtooth style as well as two chippers which cut out the bulk of the waste in the hole both the rim and the chippers must be sharpened but they have to be done evenly if you take more steel off one chipper than the other the other will be doing most of the future cutting likewise if you file some of the teeth along the rim down more than others the others will be doing all the cutting there the key is to keep everything even and that's the trick i'm going to show you so let's start with the chippers first this involves these two flat surfaces i like to use some lapping fluid to keep the metal dust from clogging up the grid on my home then i place the card on the corner of my bench so i can lay the flat chipper surface on the card i can feel when i have it flat and i want to keep it that way as i move it back and forth five times that's it just back and forth strokes five times using only enough pressure to keep it flat on the card i find that putting the card on the bench and holding the bit on top helps me keep it stable as i work however some bits have a bevel along the edge of the chipper rather than a large flat surface so in that case you'll have more success holding the bit in your hand and angling the card as needed to work the edge of that chipper by hand now i'll do the other chipper with the same five back and forth strokes why five strokes because while i try really hard it is still humanly impossible to absolutely ensure that i'm applying the exact same amount of pressure with each stroke over just a few strokes those small variations won't add up to much but over many strokes they can and i may end up with uneven cutters five just seems to be the sweet spot to restore a bit that's moderately dull without letting those variations accumulate when i'm done with the chippers i do something very similar to the edge of the teeth around the rim the edge of the card won't fit all the way down into the sharp corners between the teeth but it will catch on the top half and that's enough for our purposes i'm doing the same five back and forth strokes on each tooth face note how i'm only sharpening the vertical faces between the teeth i'm not touching the sloping tops of the teeth there's no need to mess with those it will just double any chance for accumulating air this bit is now sharp and ready to use again i can do this two or three more times before the bit will start to become too uneven and then it will have to be replaced but by then i've tripled or quadrupled its life span the process i just demonstrated for sharpening the chippers applies to all types of forstner bits the differences are found when you sharpen the guide rims continuous rims have a circular knife like edge and my favorite wavy rims have a rippled knife-like edge these are sharpened by touching up the inner bevel not the outside of the rim that would change the size of the hole it cuts you don't want to do that just sharpen the inner bevel along the rim since this is a curved surface you need a curved tone i normally use this diamond file which has one flat side and one convex or curved side i'll link to it below an alternative may be to just wrap some 600 grit wet dry sandpaper around the dowel won't be as handy but it'll get the job done either way the process will be the same apply some lubricant then place the curved part of the file upon the bevel on the inside of the rim and then tilt back just to be sure you're working along the cutting edge use moderate pressure and begin moving the hone back and forth around the rim i can't really count my strokes in the same way as i did before instead i just try to keep things moving and i try to maintain consistent pressure this is why you don't want to let your bits become hopelessly dull before you sharpen them it's a lot easier to restore a moderately dull bit evenly than it would be to work on a fully blunt wood smoking piece of scrap metal and that's all there is to it don't forget to use the links below if you need a diamond file or hone and i'll see you next time for the last several years i've been replacing my cheap drill and forstner bits with quality bits from fish tools they're a family-run company that still forges their bits the old-fashioned way try replacing your most used bits with fish bits using the links in the notes below this video and you'll see why i love them so much
