Building a better mousetrap: Drill bit sharpening jig

strantor

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I'm needing a way to sharpen twist drills (lots of them) quickly and consistently. I won't be doing the work myself; I have an unskilled helper doing the chore. I've tried to teach him how to do it by hand but I suck at it myself so I can't hold it against him, but his results are less than stellar. I've looked into purchasing a jig/machine but there seems to be only two kinds: 1. Cheap crap that doesn't work, and 2. Really expensive production-oriented fixtures that have more axes than a CNC robot and more adjustments than two lathes together. They also mostly use a collet system so I would need a drawer of doodads, one for each size of bit I would conceivably want to sharpen. I don't like my options. I want something of acceptable quality (or at least acceptable results) and simple enough that a Liberal Arts major can use it. Necessity is the mother of hairbrained ideas and ultimate folly. Here's what I'm thinking...

(By the way, I'm posting this for peer review. Any and all criticism is welcome. Shoot holes in it, don't hold back. I can't find examples of anything close to what I'm about to describe so that means it's either a horrible idea or revolutionary. Most likely horrible. But at the same time, the pictures are just conceptual; only enough detail convey the point. the end result wouldn't look anything like this.)

I drew inspiration for this from knife sharpening jigs such as this:

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The stone is held at the end of a long rod which pivots about (and slides through) a fulcrum of adjustable height. The long distance between the knife's edge and the fulcrum point allows the setting of precise angles with relatively crude hardware.

My jig is the same concept but in reverse. The "stone" (grinding belt) is held stationary and "knife" (drill bit) is mounted on a mobile rod. The slot plates are interchangeable and with the plates shown, should produce general purpose 118deg 4-facet bits.

1.PNG

The image above depicts the jig fitted with a 1/2" 4-facet drill bit, grinding the relief edge.
The image below depicts the jig fitted with the same bit, but grinding the cutting edge.

2.PNG

Below is a top-down view from above the grinding belt. The drill bit is held in a cordless drill chuck which is mounted on the end of the paddle pole.
The belt is mounted to the plate behind, at an angle of 118 deg. This angle is adjustable. The belt assembly is mounted to its backing plate with linear slides, so it can be moved side-to-side for even belt wear.

3.PNG

The sequence of operations would be as follows:
[with belt off]
1. Loosen the locking collar and place paddle pole into slot plates A and B (cutting edge grinding position)
2. Insert bit to be sharpened in paddle pole chuck, with cutting edge 90deg to belt.
3. Slide paddle pole forward until bit touches grinding belt, slide locking collar forward until it touches slot plate A.
4. Back locking collar off [some small distance*] from slot plate A and tighten.
* this small distance sets the amount of material to be removed. it will depend on the size of the drill and condition. If only a touch-up resharpening is desired, then maybe use a few thousandths of shim stock to set the depth.
5. Back paddle pole away from belt, energize belt.
6. Slide paddle pole gently in towards belt, and continue to apply gentle pressure until locking ring bottoms out against slot plate A and the belt stops cutting.
7. withdraw paddle pole away from belt, carefully remove paddle pole from slots, and without adjusting the chuck or locking ring, flip it over and put it back in the slots.
8. Feed paddle pole forward, gently grind 2nd cutting edge until locking ring bottoms out and belt stops cutting.
9. Withdraw from cut, remove paddle pole, place in slot plates A and C (Relief grinding position). loosen locking collar.
10. Paying close attention to cutting edge thickness, feed paddle pole into grinding belt until desired cutting edge thickness is achieved.
11. Set locking collar up against Slot plate A and tighten.
12. withdraw paddle pole away from belt, carefully remove paddle pole from slots, and without adjusting the chuck or locking ring, flip it over and put it back in the relief grinding slots.
13. Feed paddle pole forward, gently grind 2nd relief edge until locking ring bottoms out and belt stops cutting.


So, by utilizing the locking collar to feed forward to precisely the same distance on both sides, this should ensure precisely the same length of cutting edge on both sides, if my logic is correct. A perfectly symmetrical grind at precise angles. And with taking most of the "art" out of the task, maybe it now makes sense to sharpen smaller drills rather than replace.

The slot plates B and C are drawn appropriately for a 1/2" drill bit, but would be made to extend in both directions (up & down) with multiple stops within the slots, to achieve a variety of cutting edge & relief angles for different sized bits (and those stops could be marked in drill bit sizes for simplicity, ex: "use this position for 5/32 & 4mm bits")

Ok, take your shots. Why won't this work?
 
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Maybe I missed it, but what provision is there for keeping the cutting edges the same length?
 
I think you are over thinking this, but of course, that is what we do as Hobby Machinists, and are proud of it!

Get yourself a sharpening jig and a bench grinder, and learn how to use it. This type:
1547223780626.png
They are quite inexpensive new, and can often be found dirt cheap, lightly used by people who did not read the instructions and think beyond them.

Has been sold by many companies under different brand names, and it works just fine after you understand how it works, including beyond the dumbed down instructions that come with it. You seem to understand the concept, and have skills good enough to post a very nice graphic post of what you have in mind. The jig above will do what you want, with a whole lot less investment in time and effort. It is designed to do what you are trying to do in your post, and it gives nice results -- if you are smarter than it is... It also has adjustments for several drill point angles.

I have ground several hundred drills in this type of jig before buying a Drill Doctor, which also works very well after you understand how it works and how to get there. They all turn out fine once you understand the setups and adjustments and know what you are looking for with various drilling operations.

Edit: By the way, the setup in the photo above is wrong, WAY too much overhang of the drill beyond the end of the holder...
 
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Why not try a drill doctor? I don't have one but have heard they work pretty good.
 
My first thoughts on your design were as follows.....Why does it need to be so big, are you sharpening Industrial Giant sized drill bits?
By trying to simplify it in the manner you have outlined with the plates and multiple positions, I think you will end up with an over complicated settup (at least not something a Lib Arts major wont have trouble with, lol).

Wouldnt a few "protractors" somehow attached to a few adjustable "Joints/Knuckles/shaft assemblies" be much more effective without the need to take up half of your floor space?

Edit: lol i started typing when there where no replies and by the time i finished i I was beat to the punch....I really Suck at typing, lol
 
Maybe I missed it, but what provision is there for keeping the cutting edges the same length?
When you feed in on the first side until the locking collar bottoms out, and then you flip it over and again feed it in until the locking collar bottoms out, that's where you get your symmetrical grinds. In (my) theory, anyway.
 
Why not try a drill doctor? I don't have one but have heard they work pretty good.

I think you are over thinking this, but of course, that is what we do as Hobby Machinists, and are proud of it!

Get yourself a sharpening jig and a bench grinder, and learn how to use it. This type:
View attachment 284552
They are quite inexpensive new, and can often be found dirt cheap, lightly used by people who did not read the instructions and think beyond them.

Has been sold by many companies under different brand names, and it works just fine after you understand how it works, including beyond the dumbed down instructions that come with it. You seem to understand the concept, and have skills good enough to post a very nice graphic post of what you have in mind. The jig above will do what you want, with a whole lot less investment in time and effort. It is designed to do what you are trying to do in your post, and it gives nice results -- if you are smarter than it is... It also has adjustments for several drill point angles.

I have ground several hundred drills in this type of jig before buying a Drill Doctor, which also works very well after you understand how it works and how to get there. They all turn out fine once you understand the setups and adjustments and know what you are looking for with various drilling operations.

I've spent an appreciable amount of time reading & watching reviews for Drill Doctor and the inexpensive sharpening jigs. I have no doubt that I could make them work with enough practice and figuring out the finer points of how they work. But I don't intend to do any of this myself. I've already wasted enough time teaching myself (with marginal success), and then my apprentice (unsuccessfully), how drill bits work, the geometry behind them, and how they should be sharpened. This is 50% personal and 50% business (I own a small business and it isn't a machine shop but we do use drills) so I can't treat it the same way I treat my pet projects. It has to make sense money-wise. I want something I can hand off to someone else, who doesn't have the same technical background as I do, and have it "just work" (idiot proof). If I can't have that, then I need to just move on. Maybe send the bits off for sharpening. Or forget about them, hang on to them for the next 35 years until I retire.

I don't even intend to build this jig myself. If I can believe in it enough to go forward, I'll model some patterns and have my apprentice cut out his own sharpening jig and assemble it, probably out of plywood.

Edit: By the way, the setup in the photo above is wrong, WAY too much overhang of the drill beyond the end of the holder...

Point taken. I'll address that before I make anything. Maybe put a V-plate up by the belt as the final resting surface for the end of the bit.
 
My first thoughts on your design were as follows.....Why does it need to be so big, are you sharpening Industrial Giant sized drill bits?
By trying to simplify it in the manner you have outlined with the plates and multiple positions, I think you will end up with an over complicated settup (at least not something a Lib Arts major wont have trouble with, lol).

Wouldnt a few "protractors" somehow attached to a few adjustable "Joints/Knuckles/shaft assemblies" be much more effective without the need to take up half of your floor space?

Edit: lol i started typing when there where no replies and by the time i finished i I was beat to the punch....I really Suck at typing, lol

It doesn't need to be big, it's just that... ok, so the angle of the drill, the angle of the sanding belt, and their relation to the floor form a triangle. The more distance there is between the 3 points of the triangle, the more accurate the angle can be, utilizing crude materials and construction methods. Also, it minimizes error in setup and use. This is probably going to be made out of plywood and built by my apprentice. I can't justify spending any time on the clock machining parts for it. No machining, quick & dirty. That's why it's big. If it works as I hope, and I find there to be any market for it than anyone would be interested in purchasing something along these lines, I could make machined versions much smaller.
 
Point taken. I'll address that before I make anything. Maybe put a V-plate up by the belt as the final resting surface for the end of the bit.
On that 'specific' drill grinding jig, the overhang should be about half the drill diameter beyond the "tooth" that engages the flute of the drill, for a 'standard' 118 degree drill, so the drill has the correct clock orientation to the grinding wheel for making a proper grind. However, different point angles, different twist rates of the drill, and what the drill is intended to be used for, all come into play and require changed settings for best results.
 
There are at least dozens, if not hundreds of differently designed drill jigs available on the new and used market, from under $5 to thousands of dollars. They all work if used properly, some better and more quickly and easier than others. Drills are used in many industries and in many home shops, so there is a huge market, but it is already pretty saturated with products that do the job if the operator does his job correctly. Drills can also be ground to a proper point without any jig at all, just eyes, brain, tool rest, and bench grinder. It is done all the time, some far better than others. I grind all my drills 3/4" and above by hands and eyes to a good result, checking them with a drill gauge. Drill bit grinding tooling has been studied, better mouse trapped and improved, and new products put on the market for well over a hundred years now. The market is mature, and may well be considered saturated. Please keep us informed with what you end up with. There is always room for a better product at the right price.
 
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