Drill bit sharpener

by mgx, published

Drill bit sharpener by mgx Sep 20, 2015

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I've researched many existing approaches to drill bit sharpening but did not find one that I like. I like simple and utilitarian designs. This is one of those: a one-piece guide for sharpening drill bits on a Dremel or similar rotary tool that uses an M19-2 thread.

There are 3 guides included: 90, 118 and 135 degrees. The majority of people will need the 118* and for that the adapter comes in two sizes such that it can easily fit both small and large diameter drills, as well as different diameters in cutting/grinding disks.

The adapter prints in one piece without support and is threaded to screw right onto the Dremel (I've tested it on my Dremel 285, 8000 and generic Alltrade tool which all happen to be 19mm thread size). It's also designed to accommodate mandrel upgrades.

Addressing some comments:
Doesn't FIT - check your printer calibration, x/y/z steps/mm and slicer settings (filament factor or extrusion multiplier especially). Print a 20mm calibration cube and measure with precision calipers. Also check your material settings, many materials (esp ABS and PETG) tend to "tighten" when you print inside circles. Maybe resize it a bit (1-2%)?

No Relief Angle - Yes I'm aware of the flaw. I'm going to try to re-design it some day, I wasn't expecting this to become so popular amogst the specialized people. I was in fact aware of the drill bit geometry and relief angle at the time of the design, it's actually a bit more complex than a single angle, but at the time decided to keep it simple and figured I'll add the relief by hand, you can actually see me doing it in the video.

Feel free to tweak but note the non-commercial use, please contact me for a separate license if you are interested.



I printed mine out of PLA, 0.2 layer, 33% infill. I printed multiple ones on multiple printers and seem to fit well, however printer calibration is critical.

If you are worried PLA melting, then you're overheating your drill bit anyway (iow remember to quench the bits in water if they get too hot at the tip)

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Threads not compatible with dremel 300

Double-check your printer calibration (both slicer settings and firmware x/y/z steps/mm). This is using an M19 thread which is supposed to work on Dremel 300.

My calibraton is more than ok (0.01 mm error and that is inside my digital caliper error so...) I Print threads all the time and they work. Other users here also have reported the thread not working on the 300 model. May be the 300 has different threads. My new one definitly doesnt work with your thread. I have measure the thread step in your model and the caliper shows is not the same step as the dremel's

Didn´t work with my old dremel Multipro 395

Do you happen to know if that's an M19-2 thread size?

It needs to cut a clearance at the top. This can be done by making the arm that holds the drill bit lean a couple of degrees to the side.

Thanks for confirming!

But it somehow does :)

Now seriously - it won't compete with the $$$ drill sharpening machines, but it should be better than some of the cheap sharpeners I've seen in retail (esp the flimsy ones with cylindrical grinding stone).

There are several sellers there, some haven't even bothered to use their own pictures :(

It is almost good, but you must think on the negative cut, otherwise it will not drill, just melt together.
The heel must have negative angle, about 5-10 degree.

I'm going to address that in the next revision. When you buy retail bench grinders with drill guides, you add the relief by hand as well. I'll see if I can make it guided somehow.

This is true, drill bits do need the back/heal be lower than the leading edge (face) to be effective. I guess it is still a little better than a totally dull bit though.

What is important is the number of likes, not that it works :).

Made, and works with my dremel 4000, with first print. If you have problem then it means you have to calibrate your printer better, Extrusion multiplier. I am using Simplify 3D and printed 0.2 layer high. Very useful tool, Thank you.

Thanks for confirming

Not luck with it working on my Dremel 4000 unfortunately. Hopefully someone can remix to work.

it works fine on dremel 4000 its ur printer.

I have been trying to remix this with the proper threads, but have had trouble getting the correct size for my Dremel.

Dremel 4000 should be an M19 thread, it's probably the printer/slicer settings, check the tips above.

I'm not sure if it's a problem in the gcode or what it is but I tried to print one twice and both times when it got to a certain hight its like it went back down to try to put another layer on the base and ended up one popped off the bed by the extruder pushing against it and the other was stuck to the bed so good it almost jammed my printer.

Just printed out one and it fits my Craftsman rotary tool. Haven't tried to sharpen anything yet...

Has anyone remixed this to fit on the Dremel flexible shaft thing ? it has a smaller thread .

Has anyone remixed this to fit on the Dremel flexible shaft thing ? it has a smaller thread .

Nice build. Put relief on bit after sharpening. Hack saw cut through threads solved install issue.

Thanks. Yes, definitely lots of pressure on the relief angle (pun intended :) ), I'm going to fix that. You shouldn't have to use the hacksaw, is the printer/slicer perfectly calibrated and the tool using an M19-2 thread?

OK, I just got to say.. for the "nay sayers" .... is this going to bring a bit back to new.. no it's not!! Can it make a bit at least drill a hole again? yes yes it will.. I just did. I have a wood bit a moron thought he could drill through concrete with. It wouldn't even bite at all, just spun and burned on wood.. 2 mins touching it up on this and it went through a 2x4 like a champ.. is it like new, no way, but it's usable again. I'll be bringing it (and the other models) to job site to save those trips to the store for a stupid bit that dull!! for a happy home owner/tinker.. it'll work just fine to revive a dead bit.

Thanks MGX for the simple design!! it works and I'll be using it.

Thanks for the nice words and support! Yes, that's exactly what this is for. I've broken lots of drill bits and revived them with this. If I could make it bring drill bits to brand new, I would probably not make it available for free :)

Your drill bits should not get more than warm while sharpening them. If they're getting hot enough to melt PLA or they're changing color, then you're destroying the temper.

Comments deleted.

this drill jig has a major flaw. Since the V-groove in which the drill bit sits is in the same plane as the dremel axis your relief angle is zero. That way the drill will not penetrate the material easily. No good for drilling metal. Styrofoam might still work...You should study the proper angles of a drill bit tip like tip angle, relief angle, rake angle. Lots of sources in the internet. If you tilt the V-groove by 10 degrees out of the dremel axis plane the bits will cut much better.
A precision grinding jig has 4 features:
1) an adjustable or fixed guide for the 118° tip angle, (present in your design)
2) an adjustable or fixed guide for the 5-15°relief angle. (present, but at disfunctional 0°)
3) an adjustable length stop for the bits. The adjustment screw allows to feed the bit into the grinding disc. (missing)
4) a means to lock down the bit's own rotation axis and allowing it to be rotated by 180° for the opposite cutting edge. (missing)
With those 4 features the tips will become perfectly symmetrical i.e. the point is exactly in the middle.

Hi Rol,
I got inspired by your constructive comment and made this http://www.thingiverse.com/thing:2006453.
Despite the simple design, it should have all the nice features you listed (though it has nothing to do with Dremel).
Please feel free to comment, especially on the "Guide line to help with bit positioning": I got the input here http://www.instructables.com/id/Sharpen-Your-Drill-Bits/step18/, but I am not sure how to use it and if it is fully correct.

Drill bit sharpening block with relief angle
by paolo68

Hi Rol,
I got inspired by your constructive comment and made this http://www.thingiverse.com/thing:2006453.
Despite the simple design, it should have all the nice features you listed (though it has nothing to do with Dremel).
Please feel free to comment, especially on the "Guide line to help with bit positioning": I got the input here http://www.instructables.com/id/Sharpen-Your-Drill-Bits/step18/, but I am not sure how to use it and if it is fully correct.

Drill bit sharpening block with relief angle
by paolo68

I was wondering if relief angle was built in. Bummer

Smart design and it printed nicely but the threads doesn't fit my Dremel (model 395).

the 118° one does not seem to fit my Dremel 300; i might need to test some more.

Thread didn't fit either of my Dremels so I drilled the threads out to 3/4" and it fits tightly enough to still be useable.

I love this idea, so simple and so useful.

Okay with my Dremel 3000.
Very easy to print and very easy to use !
Thank you !

Hey, how did you get the dimentions for the thread on the top of the dremmel? It screws in really nice, but i can't figure out how people get the slope of the tread and all that? Could you tell me your secret? :)

look forward to making one

I think you are missing something here. When a drill is sharpened, you have to give it "relief" towards the back edge. As nice as this design may look, it's no more than a glorified pencil sharpener. It may melt a hole through with friction, but that's about it. Sorry to be the bearer of bad news. The drill has to be twisted as it is rotated to put "RElIEF" on the back edge.

The video is bad quality (focus ) and I'd have to redo it, but at around 1:15 mark there is a point where I give the relief angle. You have to do this free-hand though. I did think about making it complete and have rotating axis for the relief angle, as well as a perfect centering mechanism (for now you need to use a drill stop), but I decided in the favor of keeping the design as simple as possible. The intent was not to compete with the $200 drill bit sharpeners on the market (at least not in this revision :) ), but to make drill bit sharpening a bit more scientific that the completely random approach I was using before where I would free-hand the Dremel and wasn't even getting the same angle between left and right cutting edges.

Man, you just saved me at least an hour of arguing with Solidworks. I absolutely love having a replicator!

Works perfectly well, I've just brought my collection of drills back to live. Thanks a lot.

Be careful how much wear you put on the grinding disc. These discs (as well as thick grinding wheels) are meant to be edge loaded, not side loaded. Wear through the side of the disc too much, and the disc could "let go", into your eyes! Great design, but looks risky how the disc is loaded.

I would think everybody would use safety glasses whenever they use a rotary tool. And safety glasses should be sufficient to protect from a thin grinding disc. When bits of a broken grinding disc fly and hit my hand, the impact doesn't feel that strong--I would assume that safety glasses in good working condition would be sufficient to protect the eyes.

Whats worth more your eyesight or a 2 dollar twist drill ??
safety glasses or not these cut off disks are NOT meant to be side loaded... EVER! They are not designed to allow side loading and its often where the centrifugal reinforcement is.
This design has a "hospital smell" about it

The picture looks like the reinforced cutting disc, in any case it is not meant to be used like that. I used the sanding discs, which is the far thicker one. Yes, excellent designs! Save me so much effort 'trying' to align the sanding of drill bits manually haha.

Always wear protection, irrespective of the load direction. The discs can shatter when loaded on the edge as well.

I saw this and actually came here to say the same thing as davesuniquedesigns. It is a clever idea though. If you brought it out a little more and angled it more you could use a cylinder grinding bit to get the same effect but much safer. It would also give you the ability to use different grit bits to work on bits which are more heavily damaged.