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An idea for drill sharpening jig

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sorveltaja:
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. 

Joachim Steinke:
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

sorveltaja:
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.

sorveltaja:
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:.

sorveltaja:
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.

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