Author Topic: An idea for drill sharpening jig  (Read 66246 times)

Offline sorveltaja

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Re: An idea for drill sharpening jig
« Reply #25 on: October 07, 2009, 01:12:38 PM »
The jig looks something like this, when finished. Only two fastening parts needs to be done:


... But there is (at least) one mechanical puzzle, that I haven't been able to solve. It relates to the pitch, that I mentioned earlier.

Took some photos of actual drills, but they were too blurry to demonstrate. Maybe this picture explains, what I mean:


Smaller one is half the size of the left one. Both have the same pitch, but smaller has also half of the axial length(red lines) on its cutting surface :scratch:.
Anyway, drill bit doesn't seem to be so simple as it looks :smart:.

...On the other hand, that can't stop me to finish, and test the thing. Many drill bits are just waiting to be the test pieces :thumbup:.

Offline sbwhart

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Re: An idea for drill sharpening jig
« Reply #26 on: October 07, 2009, 03:49:56 PM »
Hi Sorveltaja

Real nice job your making of that jig, I've been watching your progress with interest,  :clap: :clap: :clap: could your puzzle  :scratch: with axil length be due to the difference in diameter in the two drills.

Have fun

Stew

A little bit of clearance never got in the road
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Location:- Crewe Cheshire

Offline Bernd

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Re: An idea for drill sharpening jig
« Reply #27 on: October 07, 2009, 03:53:46 PM »
That picture reminded me of what the Drill Doctor drill sharping machine looks like.

Bernd
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Offline sorveltaja

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Re: An idea for drill sharpening jig
« Reply #28 on: October 07, 2009, 05:48:21 PM »
sbwhart: Yes, I'm on the same track, that the drill diameter is (one of) the key factor(s).

Possible (although laborious)solution: To make different size guides (the cylindrical brass part, see my previous posts), that have diameter, that matches certain drill sizes, all having 4.65 mm pitch.

Other solution might be to use an eccentric jig, whose eccentricity depends on the drill size. Smaller the drill, the more eccentric the jig.
Let's take a 10mm drill as a reference, that's eccentricity is 0. It takes ~90 degrees turn to sharpen using the jig.

With 1mm drill, it has to be eccentric, if same size jig is used, as on 10mm drill. If 10mm drill takes ~90 degrees, 1mm takes only ~9 degrees.
During that ~9 degrees, it has to rotate ~90 degrees, just like the 10mm drill does.

---------------------------------
Bernd: It's not intentional. I admit, that I have examined the Drill Doctor -devices patents, among many others, but haven't got the grasp of any of them.
That's the main reason, why I'm going to make and test this thing in a hard way. Be it failure or success. If success, I'll be glad to share it. If total failure, it means food for my future projects. 

Offline Joachim Steinke

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Re: An idea for drill sharpening jig
« Reply #29 on: October 07, 2009, 06:29:43 PM »
Hi Sorveltaja,

as I’m concerned with the drill subject too I will take the chance and try to explain a little bit about the mysteries of the helical tool called drill, hoping not to jam your interesting and already started article here?

Your idea of using the pitch of a special thread as a guide for grinding the relieved surface of drill tips sounds interesting, some commercial drill grinder use a similar technique in form of axial control curves embedded in the drill fixture bearing. But I think it is a little bit too complicated, there are much more simple techniques to achieve a really good performance at home.

But first of all, the pitch of the flute (helix) has nothing to do with the relief angles, it only generates the rake angle (if this angle is not corrected or changed by extra grinding the cutting face for non standard boring tasks). This will come obvious if you compare a drill with the front cutting edges of an end mill, end mills are only the special case of the hole system “helix tools”, the case with the point angle 180deg.

The relief or clearance angle is more or less independent of the drills geometry, naturally this angle must nevertheless follow the rules of making chips….a first clearance angle in the range of perhaps 8 to 15 deg makes sense for our several metal drilling jobs.

In principle there are two major techniques for grinding drills, the four or more facetted relief flanks method and the conically shaped flanks method, normally you will find the conically type on most of all standard drills at your tool store.

But the conically drills don’t make a better job, I think it’s easier for industrial manufacturing having only one process on each cutting edge than several passes like you will need on the more facet types. So to my opinion, it’s up to your free choice what grinding technique you will prefer at home.

If you like it conically a simple swinging fixture will work fine. In fact the cheap fixtures from your tool warehouse use the correct technique, but most of them are not build precise and tough enough for holding the drill exact in the axis of rotation. And they have problems with indexing the both cutting edges precisely from 0 to 180 deg when changing to the other cutting face…..therefore a lot of frustration for there users is preprogrammed….ha ha ha….

So you can buy a reliable and expensive fixture from a serious tool grinding machine builder like Cincinnati or Deckel or you  have to build your own device.

To achieve the needed clearance face by swinging the drill in front of a grinding disk the rotating base of the tool fixture has to be arranged with a defined offset distance to the axis of the drill, the shifting vector of this off set is pointing in the direction away from the cutting edge. The principle of the conically method is easier to present by changing the moving systems, here, contrary to reality,  the drill stands still and the grinding disk is performing a conically rotation:





The drawing shows two of many possibilities for arranging the rotating base in relation to the disk surface (90 and 70 deg), they both works fine and only need some different calculation of the setting parameters.

This is a drawing from the last year when I was starting to design my second grinding fixture:





And here an intermediate result of this in the mean time further enhanced fixture:





Some details like the graduation of the rotating base and the fine indexing of the tools axis  are not really necessary for only drill operations, but I designed this for additionally grinding all forms of d-bit routers.

But very important is the precise and rigid mounting of the tool, my choice was an ER20 system. And we have two linear adjustments, in tool direction for setting the cone radius in relation to the disk surface and perpendicular to this axis the off set value, together both parameters define the relieving characteristics of the desired clearance.

A good method for evaluating the clearance angle is having a frontal look at the drills chisel. As evident the chisel line rotates clockwise in direction towards the cutting edge, more rotation means a higher value of clearance. Number 1 and 2 are related to the numbers in the first picture above, as you can see, the different setting angels of the rotating system make no great difference to the result of the clearance value.





Okay, further details and the description of the other method (four or more facetted) could develop in to a really large article and my concentration needed for writing and translating at the same time is going to fade away for this night…..ha ha ha…..

I will try to continue as soon as possible in the next days, and I hope the stuff is not too dry presented, don’t wont to bore you with too much theoretic.


Bye from Achim

Offline sorveltaja

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Re: An idea for drill sharpening jig
« Reply #30 on: October 07, 2009, 07:46:46 PM »
Joachim Steinke: No worry, you have excellent presentations of the subject. So much information, that it might take some time for me to digest.

Feel free to post more.



Offline sbwhart

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Re: An idea for drill sharpening jig
« Reply #31 on: October 08, 2009, 02:24:27 AM »
Hi Achim

Very interesting post your quite right about the problems with shop bought drill grinders, not including the drill doctor in this because I have never seen or tried one.

My father taught me many years ago to grind drills by hand, which I'm quite good at, but hand grinding can never be as good as a jig grinding, the action you described is exactly the action, It's easy to demonstrate but difficult to describe.

Sorveltaja

Drill grinding and geometry when you get into it is a complicated subject this is a great thread you've started.

I'll watch progress with interest.

Cheers
 :beer:
Stew
A little bit of clearance never got in the road
 :wave:

Location:- Crewe Cheshire

Offline Joachim Steinke

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Re: An idea for drill sharpening jig
« Reply #32 on: October 08, 2009, 08:12:14 AM »
Hallo, only a short message in between,

this may be a little off topic, but as the “Drill Doctor” has already been mentioned above…….

I, similar to Stew have never operated with the relative famous Drill Doctor myself, but I have a friend who works with this Vertex Drill Grinder:

http://www.vertex-tw.com.tw/products/products_list.php?language=_eng&cid=591#pro

I took the chance to test it by myself and the little machine is astonishing well and rigid build (okay, it’s Vertex from Taiwan and not as bad as the most Chinese machinery), very smooth and quiet running and does a really good job on standard drills.

They use special made and inverted mounted ER collets (a clever idea) and axial control curves build in the circumference of a particular collets chuck. This curve is in contact with a corresponding curve in the mounting opening of the machine housing and generates the desired axial movement while rotating the drill in front of the grinding wheel.

Accommodation to the drills diameter is made by using a preset fixture (left side of the machine) where the drill is pre mounted in the collets. As the back rotation angle of the existing cutting edge (relative to the fixtures coordinate systems abscissae) has an effect on the relief characteristic in direct dependency to the tools diameter this single collet chuck can be used to a wide range of drill diameters with one and the same control curve.

This all is very similar to the technique of the Drill Doctor, but Vertex made the wear parts out of hardened steel and hard steel castings, so the well known wear out problems of the Drill Doctor (drill chuck partial made from plastic) should not appear.

As Vertex delivers the machine with a CBN grinding wheel you have a relative constant plane surface on the wheel over a long operation period, dressing the wheel is not necessary.

But this neat little machine is really expensive (just under 900,- Euro here) and you can grind only one type of relief form. It would devinitely do a good job in the commercial shop for daily use, but for unfrequent home grinding it might be a little bit too overshooting….ha ha ha….

Bye from Achim

Offline Bernd

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Re: An idea for drill sharpening jig
« Reply #33 on: October 08, 2009, 08:19:30 AM »
Joachim,

A bit  :offtopic: here. I've been to your web site and find it very interesting. One question. Is the material you use to make all those nice looking tools brass?  Thanks.

Bernd
You can't fix "STUPID".

Offline Darren

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Re: An idea for drill sharpening jig
« Reply #34 on: October 08, 2009, 10:51:58 AM »
Hi Achim, I have a drill doctor and I believe Bernd has one as well. I must say I am very impressed with it. I have sharpened about 200 drills so far with mine and it was second hand when I bought it. The result is without a doubt a better finished point than when purchased new. Nice smooth drill with little or no chatter. If the relief option is used (split point) the effort in drilling is remarkable esp with larger diameters.

Just my take on the tool. A big improvement on my freehand grinding  :doh:
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

Offline Bernd

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Re: An idea for drill sharpening jig
« Reply #35 on: October 08, 2009, 04:15:23 PM »
I have to second what Darren has said. Although mine was new.

The intersting thing about yours is the way you plan on rotating the drill.

I'm hoping this experiment will work out for you. I will keep watching your progress. I figure when my Drill Doctor doesn't work any more I'll build one like yours.

Bernd
You can't fix "STUPID".

Offline sorveltaja

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Re: An idea for drill sharpening jig
« Reply #36 on: October 09, 2009, 02:40:53 PM »
I tested the jig with 4 mm drill. Result: that ~4.7mm pitch is way too long. Meaning, that the axial feed is also too high.
Seems that if this method is in use, there should be matching thread for every size drills. Without doubt, it wouldn't be simple, or even practical.

I guess that it needs some kind of compromise to simplify whole thing. Assuming, that requirement isn't industry-level cutting speeds for the drills.

Anyway, next I'm going to try with milder, 1mm pitch, which should be closer to what I'm looking for :borg:.

Offline tinkerer

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Re: An idea for drill sharpening jig
« Reply #37 on: October 09, 2009, 03:09:34 PM »
I believe 0 pitch is what will be required.
Tink

The desire accomplished is sweet to the soul.
Prov 13:19

Offline sorveltaja

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Re: An idea for drill sharpening jig
« Reply #38 on: October 09, 2009, 04:00:38 PM »
0 pitch.. hmm. If burnout of the drill is desired, that would be fine. With cutting oil you would get even nice smoke cloud.

Since I'm not going to make any smoke signals(at least not from drilling) in the near future, I'll rather prevent myself from using 0 pitch.

Offline tinkerer

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Re: An idea for drill sharpening jig
« Reply #39 on: October 09, 2009, 04:31:11 PM »
I am speaking of pitch as in a screw. You must be talking about rake, or I just have no understanding of which aspect of the drill you are changing from 4.7mm to 1mm. My not understanding may be attributed to everything on a drill bit except diameter is usually presented in degrees. It appears to me that as you turn the bit 180 deg, you are also moving it in a screw like action. If I am wrong please accept my apologies and I will continue to follow your process.
« Last Edit: October 09, 2009, 05:13:50 PM by tinkerer »
Tink

The desire accomplished is sweet to the soul.
Prov 13:19

Offline sorveltaja

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Re: An idea for drill sharpening jig
« Reply #40 on: October 09, 2009, 05:14:23 PM »
Yes I meant the screw pitch, that is to be used on the jig. My use of the term "pitch" might not be the most correct way, when describing things on a metric system.

   
 

Offline tinkerer

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Re: An idea for drill sharpening jig
« Reply #41 on: October 09, 2009, 05:24:33 PM »
I am sorry, I was editing the previous post as you were answering. A drill bit does not have pitch from one side to the other. Each flute forms an equal angle from the point that is measured from the center of the bit. Any deviations in angle from one side to the other will result in only one flute cutting and the other just following along. Swarf (I love that word) should be removed equally down each flute when cutting.

I may still not understand the process and will follow with interest. I do believe you have a great design in the tooling if you take the pitch out and just provide rotation. It may take two grinding heads, one for the angle and another for the rake and that could be difficult to incorporate.
Tink

The desire accomplished is sweet to the soul.
Prov 13:19

Offline sorveltaja

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Re: An idea for drill sharpening jig
« Reply #42 on: October 11, 2009, 11:23:05 AM »
The brass piece, before I turned the 4.7mm pitch threaded part off:

Next I made 2 point thread with 1 mm pitch to it. It's barely noticeable in the photo, so demopicture instead about it:


With that, test-sharpening a 3mm drill gave a lot better result. The angle (in the picture) was quite small, allowing only slow feed, when I test-drilled aluminum, brass and mild steel.


Next thing to test would be to increase the jig's guiding thread's pitch to 1.5-2mm, to get closer to average cutting speed, when drilling.   

Offline Joachim Steinke

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Re: An idea for drill sharpening jig
« Reply #43 on: October 12, 2009, 05:31:59 PM »
Hi Sorveltaja,

I spent some time over the weekend thinking about your helical grinding method, but I don’t know if something wise had come out of my brain….ha ha ha….okay, let’s try it….

First of all your pitch problem, you wrote that your last testing version made too little relief angle, as you already mentioned the helix pitch is too low.  

The calculation of the helix angel is still quite simple, you only need to unwind the surface of the cylinder and so the angel for a given diameter (D) and a give pitch (s) follows the equation    

                                         tan alpha = s / (pi * D).

So one and only helix curve of a multi purpose grinding fixture should become a problem, variations of the drill diameters will require a wide range of pitch value. Here for example the pitch table for a relief angle of 10deg at the circumference of the tool:





And here, for a constant pitch of 2mm the table of the variations of relief angles you would get for the various diameters from 1 to 10mm, you see, the range is really wide:





As evident, alpha is inverse depended to the helix diameter, large diameter means a small helix angle. This in fact also will create an increasing relief angle from the circumference to the center of a drill. Within limits this effect is helpful and even desired, but if the value of variation on one and the same drill is too heavy it might become a problem.

So I consulted some articles from the web and then tried too visualize the theory for Helical Drill Point Grinding by my self a little bit further. What came out is a schematic model for a Universal Helical Grinder System, which, depending on the highly manipulable axis system can create all imaginable relief surfaces on a helical drilling tool.





This model can create all sorts of grindings, quadratic surfaces as well as planar like the multi facet method, so planar is only a special case of the whole process.

To simplify the system, some parameters like the distance S and B can be fixed during the operation. But the problem of rotate the tool along the pitch of a helicoid (H) under the implemented angel PHI and with the distance S relative to the tool axis (index of rotation) can not be solved with a collet fixture collinear to a single helix curve like this:





If the axis of rotation and indexing (toolholding) coincide you will have no influence on the relief characteristics distribution on the flank surface from center to circumference. But I might be mistaken, that is only a first glimpse on this geometrical problem. For a real calculation it is really not quite a simple task, for it is complex vector analysis of a multi determined 3D system, I don’t do that normally every day…..ha ha ha……

I just tried to simulate the simplified process in AutoCAD and the results were not satisfying, had some problems with boolean operations on complex sweeped bodies. So I should try it with Inventor in the next days.

Bye, Achim
« Last Edit: October 12, 2009, 05:39:48 PM by Joachim Steinke »

Offline tinkerer

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Re: An idea for drill sharpening jig
« Reply #44 on: October 12, 2009, 05:48:37 PM »
Achim,
Kind of what I was saying, only with science to back it up. Try with two grinding heads, one for the angle and one for the rake. May be too close proximetry to accomplish. Take the pitch on rotation out. Another solution could be two seperate tools, one for grinding the angle and one for grinding the rake. The back cut can be done by hand, as it is only needed on larger diameter bits.
Tink

The desire accomplished is sweet to the soul.
Prov 13:19

Offline sorveltaja

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Re: An idea for drill sharpening jig
« Reply #45 on: October 12, 2009, 06:13:16 PM »
Achim, that's an excellent interpretation of the idea :clap: :clap:. It describes clearly those different factors, that I have in mind, but didn't know how to explain or visualize them. 

Offline Joachim Steinke

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Re: An idea for drill sharpening jig
« Reply #46 on: October 12, 2009, 08:51:35 PM »
Tinker,

yes and no, the rake angle is actually not concerned in the whole process. Normally it is not necessary to grind this part of the cutting lip, unless you want to adapt the drill for special purpose. And with Sorveltajas fixture and operational base there is no way to realize this, I think he don’t want to do this either.

And the pronounced chisel between the two cutting edges is an accessory symptom of the helical grinding method. As you mentioned, eventually picking out material to minimize the chisel will help, but it’s only needed on larger drills. An alternative way to ease the chisel phenomenon a bit is to leave the helical method and generally switch over to the four and six facet grinding, the reduced chisel generates less pressure and the drill is nearly self centering.





And I think two grinding wheels are really not necessary and would make the things highly complex to adjust and operate too.

If  Sorveltaja wants to build a universal fixture based on the real helical curve motion he should design a collet based chuck housing with a not collinear, angel adjustable swivel axis and an adjustable off set feature. The helical curve then has to be placed in the axis of the swivel motion, like shown above, and should have a variable pitch, which is naturally no easy job to design and build. Nowadays the machine designer are used to solve such problems with NC moved axis, with the pure conservative method it will become really complicated.

But by the way, the advantages of such complex possibilities for modelling a perfect and highly task optimized relief surface are not necessary for just average home use. This are methods of industrial production for use on high effective machine tools and for people who have to earn money with them.

So an alternative could be coming back to a relative simple swivelling fixture, like the design for my Mini Bonelle. It does the job really good and  build with adequate precision you can grind drills even down to 1mm diameter (with additional Schaublin miniature collets) with very good performance.





Since I have added a second, differential dividing system which operates independent from the main indexer I am able to position the cutting lips in precisely repeatable orientations to the main axis system which produce very reliable results.





Bye, Achim

Offline sorveltaja

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Re: An idea for drill sharpening jig
« Reply #47 on: October 13, 2009, 04:48:16 PM »
I have decided to test 2mm pitch next, and already started making an extra gear for my lathe, that is required for the task.

While making that gear, another crazy idea popped to my mind, relating to this very subject of drill sharpening . :med:

It appears to be an alternative method, since it would use gear(s) instead of thread(s). I'm not sure at all, would it be any simpler mechanism in practise, than the current one. But enough for that. Maybe I'll start an another thread about that thing.

Offline sorveltaja

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Re: An idea for drill sharpening jig
« Reply #48 on: October 17, 2009, 03:15:37 AM »
Finally got the 2mm pitch made. Did some test sharpening, resulting quite asymmetrical cutting surfaces. The problem appears to be the chuck, that just isn't precise enough to keep the drill concentric.


Using mandrel(s) instead would be an ideal solution, but rather expensive one.

Anyway, back to stomping bugs :dremel:.


Offline sorveltaja

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Re: An idea for drill sharpening jig
« Reply #49 on: October 19, 2009, 05:17:43 PM »
This may be an :offtopic:, but it loosely relates to this project.

To make that chuck little more precise, I fastened it just enough that its 3 jaws touched the abrasive element, that was fastened on tailstock.
   
It's one of those cheap diamond-coated things, having 4mm diameter ballhead.

Next the chuck was fastened to lathe's chuck. While lathe is on, ballhead is fed back and forth, to grind chuck's jaws. Resulting this:

All jaws have nice and even grooves in them. It improved the chuck a little, but not enough. Maybe most certainly due to lack of dial indicator.
If the centering is done properly, results would be even better.

« Last Edit: October 19, 2009, 05:21:25 PM by sorveltaja »