How to sharpen Forstner bits and twist bits

[Todd Williams]

I have a set of Forstner bits ranging from 1/4" to 3". I use the middle range often, and they seem to be dull. How do I sharpen them? I bought a set of diamond hones, but I am not sure they are doing much good. One friend who makes a lot of pepper mills says he just buys a new bit when the old one gets dull. I would rather reuse if possible. Any ideas? What do other people do?

And as a bonus, I have an old Sears Craftsman twist bit sharpener which worked great until the sharpening stone got grooved. No replacement can be found. Does anyone have a recommendation for a good twist bit sharpener?

 

[Randy Anderson]

There are some good youtube videos on sharpening forstner bits. Look for Stumpy Nubs for some good info on both toothed and wavy edge bits. I touch up the edge on mine regularly. Can make a big difference on a forstner bit. You may know already but speed is key for forstner bit drilling, especially end grain for hollow form pilot and depth holes. Faster is not better usually. My typical speed for drilling with them is around 400-450 with a bit of adjustment as needed. Faster generates more heat which is not good for the bit edge. For twist bits I have one of those drill dr cheap things that does an OK job. Old so may be a newer version of it. I can do twist bits by hand but not very well.

 

[Gerald Lawrence]

Sharpening does wonders to Forstners . Some brands do well with a touch up when new. I have a Drill Doctor and it has saved many a bit from the scrap pile.

 

[David Wrate]

I freehand sharpen any bit over 3/16”. It’s pretty easy to do and once you learn the motion takes only a few seconds. Smaller bits are tossed when they dull. I’ve looked at Drill Doctor units but I have never jumped on one.

 

[Vincent Vogel]

I have a drill doctor and it does a good job from 1/8" to 3/4". Smaller sizes not so good.

 

[Kevin Jenness]

The drill doctor is decent for larger bits. You can do a reasonable job by hand using a bench grinder with care. The main thing is to reproduce the cutting angles accurately and maintain clearance behind the edges. For small twist bits I find it more effective to just buy lots of 10 from McMaster Carr.

Carbon steel forstner, brad point and auger bits are best sharpened with an auger bit file. file High speed steel bits need tougher hones like diamond (or cbn if you can find them). You can speed things up with a Dremel grinding bit if careful. The main factor in cutting effectiveness is the sharpness of the primary cutting edges. Spur sharpness has more to do with clean entry.

I have a couple of high quality carbide forstners , 35 and 40mm, for Euro hinge drilling. They stay sharp a long time in abrasive materials. I send them out to a sharpening service when they get dull. I can hone them but it is slow and the service does an excellent job for about $10.

 

[john lucas]

I love my Drill doctor for anything larger than 3/16" twist drills. For Forstner style bits just do a google search. Lots of good info. I just use diamond hones.

 

[Todd Williams]

Thank you so much for all your responses. I watched some videos and I am already doing what is suggested. Perhaps I have not been aggressive enough with my sharpening strokes.
BUT it is interesting that there appears to be a wide spectrum of opinions as to which edges of a Forstner bit should be "touched". The only agreement is that the large flat surface should receive the most attention.
For twist bits, Drill Doctor is the only brand mentioned. I will check it out.
Happy Turning!

 

[robo hippy]

Project Farm does a review of drill bit sharpeners, which I think is excellent, as are all of his 'test videos'. He is not sponsored by any one, and his reviews tend to be very objective. As for forstner bits, I take them to a saw shop.

robo hippy

 

[hughie]

John Lucas has some very good info out on this subject. In the past I often hard issues with dull Forstner bits and could never quite get to cut that good. Then it dawned on me the Forstner bits just dont preform on the hardwoods I was regularly using. As for drill bit its all about technique and once shown it takes all the mystery out of it. I routinely sharpen by hand and have done so for many years with out any issue.

 

[Barry Richardson]

I used to resharpen a lot with a file or diamond stick, I mostly use forstners to start the center hollowing on hollow forms, often through end grain, and they dull fast. but since I have discovered these, I do it a lot less, although these can be easily sharpened with a diamond stick too. These clear chips very well and are kinder to my tailstock..

 

[hughie]

I used to resharpen a lot with a file or diamond stick, I mostly use forstners to start the center hollowing on hollow forms, often through end grain, and they dull fast. but since I have discovered these, I do it a lot less, although these can be easily sharpened with a diamond stick too. These clear chips very well and are kinder to my tailstock..
View attachment 47327

same here, love em

 

[Mark Jundanian]

I used to resharpen a lot with a file or diamond stick, I mostly use forstners to start the center hollowing on hollow forms, often through end grain, and they dull fast. but since I have discovered these, I do it a lot less, although these can be easily sharpened with a diamond stick too. These clear chips very well and are kinder to my tailstock..
View attachment 47327

Make and model?

 

[RichColvin]

The best reference for this is The Complete Guide to Sharpening by Leonard Lee. I really recommend getting a copy of this excellent guide.

 

[Barry Richardson]

Make and model?

I believe the ones I have are Roman Carbide brand, but I have seen identical looking ones by other sellers, Chinese made. google carbide router bits and they will pop right up, Amazon sells them too....

 

[Pat Patterson]

Make and model?

These are available from several vendors on Amazon https://www.amazon.com/gp/product/B07G5HDH3Y/ref=ox_sc_saved_title_3?smid=A1THAZDOWP300U&th=1
Pat

 

[Bill Boehme]

The best drill bit sharpener by far is the drill sharpening fixture for the Tormek, but it is also the most expensive by far if you don't already own the Tormek machine. The thing that sets it apart from the others is that it puts a four-facet point on the drill which means that it won't walk and it cuts a rounder and straighter hole than the standard drill point (which doesn't actually have a point).

 

[Doug Rasmussen]

The term "forstner" seems to be applied to a number of bit styles these days. The concept is the outer circular rim that cleanly severs the wood fibers with the secondary flat cutting edge that clears the bulk of the material.

The picture shows what I've known as an original Forstner. With the circular rim these bits will drill half a hole on the edge of a board.

 

[Bill Boehme]

Doug, I frequently see the term "Forstner style" used in ads for bits that are variations of the true Forstner bit that you have pictured.

The ones with a sawtooth edge must be a cross between a Forstner and a hole saw.

 

[Dennis Weiner]

View: https://youtu.be/Qeop38i3gbo

or

View: https://youtu.be/bV4rZUn0WGY




I sharpen my Forstner bits with diamond files and cards. I bought a complete kit from Trend with 180,300,600,1000 grit cards, lapping fluid, and cleaner with instructions. Done...Finished! I also take these cards on the road to sharpen my turning tools. (SHARPEN as well as hone).

 

[Doug Rasmussen]

Doug, I frequently see the term "Forstner style" used in ads for bits that are variations of the true Forstner bit that you have pictured.

The ones with a sawtooth edge must be a cross between a Forstner and a hole saw

Bill, I've always heard the heard the toothed ones called machine spur bits.

Here's a picture of one that might be called a half-Forstner that was made by Stanley. I don't think they're made any more. With the long center point these could be used in hand drills since the center kept them from wandering until the hole was started.

Previously you mentioned the 4 facet bits done on your Tormek. That sounds like what is called a split point bit. Those usually have a 135 degree tip angle as opposed the standard 118 degree on regular bits. I have a very expensive Darex grinder that does nothing but split points.

 

[RichColvin]

Split point geometry is different from 4-facet grinding, but a similar concept. The document, Drill Bit Geometry, by Joseph Mazoff is a truly great reference about drill bit geometry. Joseph noted that split point geometry (he calls it modified split point) is best to use for machining operations with bits larger than ½”.

Leo St. Clair wrote a book in 1952, Design and Use of Cutting Tools, which also gets into sharpening for industrial use. Both he and Joseph focused on tool efficiency (work required to use the cutter) and cutting edge life in an industrial setting. I believe the Darex grinders are targeted at that environment. Great tools to have around, but as you noted, they are quite expensive.

I find the best value of the 4-facet grind in its addressing a different need though. Having a point on the end instead of a spinning flat makes the bit less apt to wander when starting a bore. It also seems to wander less on a deep bore, especially a problem with wood where the grain is not straight.

And, the secondary facets help evacuate chips better from hard woods. This really helps control heat buildup. I’ve lost some small pieces which split due to heat when I was in a hurry and didn’t pay enough attention. So every bit can help.

The point angle is not a differentiator. I just ground a bit yesterday with a 4-facet grind and an 82° point angle.

 

[Doug Rasmussen]

Interesting stuff Rich. A couple points, I can see the 4 facet might last longer than a split point in production and is an easier point to grind. But I consider the harder to grind split point better and takes less force. Also, I don't recall often seeing 4 facet drills as an option when shopping for drills. Typically choices are 118 degree jobber drills or screw machine length 135 degree split points. Parabolic flute drills too which do a better job of chip evacuation on deep holes.

I have to wonder if the 4 facet is a better tip why would Darex have made grinders specific to 135 degree split points like my Darex SP2500 (odd to note that grinder back in the day cost the same as its model number, $2500).

I didn't read all of your first reference. One big issue with drills is web thickness. I don't know if he addressed that. In production drilling we used spotting drills to locate holes because they have a very narrow web that doesn't wander even though they have a chisel point. Having the thin web, spotting drills are a bit fragile. Many times 60 degree center drills are used to spot holes which is a really bad idea.

As to web thickness, drill webs are tapered thicker toward the shank end. If a drill gets broken off to half length it can't be resharpened to original performance without web thinning of the end.

 

[RichColvin]

Doug, this is my presumption and not based on any research. That said, I believe the Darex grinder was made for the machine shop to make resharpening of drill bits fast and accurate, and with no strong skill required by the sharpener (i.e., vs. the machinist who sharpens by hand). For that, it works remarkably well, and achieves a very good edge quickly.

My understanding of the split point grind is that it effectively achieves the same cutting end as the 6-facet grind (the tertiary facets are extra relief behind the secondary facets). It also allows for a larger primary facet.

The pictures below show a drill bit from the end. The bit would revolve counter-clockwise when viewed from this angle.

The Secondary Facet has a clearance angle of 7-14 degrees. The Tertiary Facet would be 20-30 degrees or so from the Secondary Facet.



I broke a drill bit recently and tried to regrind the remaining part to be a short bit. What I found was that the center was not as hardened as the outer part, and the result was a bit which had to be discarded. It was like a piece of punky wood at the center of the heartwood.

What surprises me is that the Darex does not also grind a secondary point angle. Joseph Mazoff documented how that additional grind reduced the power required for drilling. Possibly better materials in tooling has reduced the need for such.

By the way, the latest-and-greatest Darex is a CNC machine which retails for $30K!

---

I must add one thought about sharpening of drill bits. The benefits of doing this are certainly that you can get more life out of your investment in good drill bits. But one must also look at the real benefit to the materials.

When I am boring very expensive or rare woods, I always ensure the bits are sharpened and honed. This helps to prevent the build-up of heat, and helps to reduce the chance of blow-out as I exit the piece. For these materials, I will sharpen the drill bit(s) on the diamond wheels, finish on the Japanese stone, and then hone the flutes on the leather wheel.

As Bill Boehme noted, this is very doable on a Tormek with the DBS-22 jig. It is not cheap, but no where near the cost of a Darex.

As a retiree, my time is cheap; excellent wood is not.

 

[Bob Vaughan]

The outer perimeter of a Forstner is a cutting surface besides the straight wedges. I'll usually chuck it up in the wood lathe and rotate by hand. I'll use a Dremel sanding drum to sharpen the inside bevel. It takes a deft touch that isn't hard to learn.
Multi-spur bits and "Forstner" bits with cutting teeth around the perimeter are super simple to sharpen with a file or hone.

 

[Bill Boehme]

As Bill Boehme noted, this is very doable on a Tormek with the DBS-22 jig. It is not cheap, but no where near the cost of a Darex.

I’ve only had the drill sharpening attachment for about two months, but I am really impressed by the four facet profile compared to the standard twist drills with the wandering dull bump across the web. I am pleased that I am not limited to just a 135°tip angle. The tip angle can be set anywhere from 90° to 150°. The range of drill sizes is ⅛ inch to ⅞ inch (plus a bit).

The maximum drill size was listed as ⅞ inch, but I was pleased that I was able to sharpen a 29/32 inch drill with MT2 shank that had been rendered unusable by its previous owner.

 

[Don Wattenhofer]

Bill, I've always heard the heard the toothed ones called machine spur bits.

Back in the 60's and 70's when Irwin was selling that style bit and maybe even manufacturing them, I believe they were calling them multi-spur bits.

 

[Bob Vaughan]

I’ve only had the drill sharpening attachment for about two months, but I am really impressed by the four facet profile compared to the standard twist drills with the wandering dull bump across the web. I am pleased that I am not limited to just a 135°tip angle. The tip angle can be set anywhere from 90° to 150°. The range of drill sizes is ⅛ inch to ⅞ inch (plus a bit).

The maximum drill size was listed as ⅞ inch, but I was pleased that I was able to sharpen a 29/32 inch drill with MT2 shank that had been rendered unusable by its previous owner.

Any remote chance this Tormek rig can sharpen drill bits specifically intended for wood boring since this a woodturning forum? Can a Forstner bit rim be sharpened on it?

 

[Doug Rasmussen]

Don, you're probably right, it may well have been "mult" and not "machine". I am pretty sure they were not called Forstner or Forstner style as now seems common.

 

[RichColvin]

Brad point bits and Forstner bits can't be sharpened on the Tormek, or at least I've not found a way to do that. But, I use the standard twist bit in wood quite a bit. Far more than on any other materials.

 

[Doug Rasmussen]

Any remote chance this Tormek rig can sharpen drill bits specifically intended for wood boring since this a woodturning forum? Can a Forstner bit rim be sharpened on it?

Bob, I can't speak as an expert on Tormek. But, I do know those wood those type bits you show are usually ground on tool and cutter grinders. I don't believe there's enough market for grinders specific for those type tips. The picture here shows one variety of spur bit grind, not quite as sharp a spur as your bits. I did this on my tool and cutter grinder with an almost square corner wheel. The bit is a 13 mm standard HSS metal drilling bit. You can do these free hand, to be effective though the center point has to be on center and the spurs nearly equal. With a little trial and error it can be done.



I'm not sure whether Bill and Rich are recommending the 4 facet grind as done on the Tormek for wood boring. I would not consider that a wood boring bit, more for metal.

 

[Bill Boehme]

Any remote chance this Tormek rig can sharpen drill bits specifically intended for wood boring since this a woodturning forum? Can a Forstner bit rim be sharpened on it?

You have a choice of tossing them or sharpening them with a four-facet grind. That initially means grinding a lot of metal to get past the brad point, but that isn't a big deal. My opinion is that the four-facet grind works at least as well as the brad point drills, probably better because they leave a clean exit hole as well as a clean entry hole

I'm not sure whether Bill and Rich are recommending the 4 facet grind as done on the Tormek for wood boring. I would not consider that a wood boring bit, more for metal.

I think that Rich already mentioned that the four-facet grind works quite well in wood. You can adjust the tip angle as well as the lip clearance angle based on the drill size and the material being drilled.

 

[Todd Williams]

I bought the General Model 825 Drill Bit Sharpener. However, I have only one grinder, which is already set up with a Wolverine Sharpening jig for gouges. The right hand wheel is 120 grit and used most of the time. I want to set up the Model 825 to use the outside, flat surface of the wheel for touching up drill bits. The problem is that the Wolverine jig mounting "bar" sticks out to the right so far that I cannot get the Model 825 mounting plate close enough to the grinding wheel. The single hole to accommodate a mounting bolt is supposed to be 2.25" from the wheel surface, and I can get it no closer than almost 3". The grinder shaft is not long enough to move the wheel to the right relative to the Wolverine bar.

I have not been able to find any information on the Web about this circumstance.
Has anyone else faced and solved this problem? Thanks.

 

[David Wrate]

I bought the General Model 825 Drill Bit Sharpener. However, I have only one grinder, which is already set up with a Wolverine Sharpening jig for gouges. The right hand wheel is 120 grit and used most of the time. I want to set up the Model 825 to use the outside, flat surface of the wheel for touching up drill bits. The problem is that the Wolverine jig mounting "bar" sticks out to the right so far that I cannot get the Model 825 mounting plate close enough to the grinding wheel. The single hole to accommodate a mounting bolt is supposed to be 2.25" from the wheel surface, and I can get it no closer than almost 3". The grinder shaft is not long enough to move the wheel to the right relative to the Wolverine bar.

I have not been able to find any information on the Web about this circumstance.
Has anyone else faced and solved this problem? Thanks.

I had one of those and it was just far too much fuss and bother. I sold it and sharpen all my twist drills freehand.

 

[Todd Williams]

I love my Drill doctor for anything larger than 3/16" twist drills. For Forstner style bits just do a google search. Lots of good info. I just use diamond hones.

John, did you read my post about interference between the Drill Doctor and a Wolverine jig? Any ideas how to mount them both on the same grinder? Thanks.

 

[Brian Gustin]

John, did you read my post about interference between the Drill Doctor and a Wolverine jig? Any ideas how to mount them both on the same grinder? Thanks.

Maybe thinking of a different drill doctor? only one I'm familiar with is a self contained unit with its own motor and wheel - That is Drill Doctor brand..... It won't interfere with wolverine since it doesn't even hook up to a grinder...

 

[Russ Braun]

View: https://youtu.be/Qeop38i3gbo

or

View: https://youtu.be/bV4rZUn0WGY




I sharpen my Forstner bits with diamond files and cards. I bought a complete kit from Trend with 180,300,600,1000 grit cards, lapping fluid, and cleaner with instructions. Done...Finished! I also take these cards on the road to sharpen my turning tools. (SHARPEN as well as hone).

James Barry is great! He sure shows how easy it is to sharpen things….way easier for him than me, lol!!

 

[Don Wattenhofer]

I bought the General Model 825 Drill Bit Sharpener. However, I have only one grinder, which is already set up with a Wolverine Sharpening jig for gouges. The right hand wheel is 120 grit and used most of the time. I want to set up the Model 825 to use the outside, flat surface of the wheel for touching up drill bits. The problem is that the Wolverine jig mounting "bar" sticks out to the right so far that I cannot get the Model 825 mounting plate close enough to the grinding wheel. The single hole to accommodate a mounting bolt is supposed to be 2.25" from the wheel surface, and I can get it no closer than almost 3". The grinder shaft is not long enough to move the wheel to the right relative to the Wolverine bar.

I have not been able to find any information on the Web about this circumstance.
Has anyone else faced and solved this problem? Thanks.

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