The DBS-22 learning curve

[Rob]

But don't you have to rotate the bit as you grind so that you produce two conical surfaces?

You do rotate them to exactly (by eye) half the circumference of the shaft to leave as you describe a cone before flipping over and repeating for the other half of the circumference.

[harvestbarn]

To sharpen my drills I use a jig I designed, I was finding it difficult to get the angles accurate by hand. I have just tried the base of the scissor drill set at 59 deg. To use you place the cutting edge at 90 deg and grind then push outwards and downward to cut the clearance. This worked on the Tormec but it was very slow cutting even though the wheel was course dressed on the 6mm dormer drill I tried.  Will send a picture of my jig shortly .

Garth

[harvestbarn]

Picture of Drill Jig

[Jan]

To sharpen my drills I use a jig I designed, I was finding it difficult to get the angles accurate by hand. I have just tried the base of the scissor drill set at 59 deg. To use you place the cutting edge at 90 deg and grind then push outwards and downward to cut the clearance. This worked on the Tormec but it was very slow cutting even though the wheel was course dressed on the 6mm dormer drill I tried.  Will send a picture of my jig shortly .

Garth

Garth, thank you for sharing your experience. 
It is highly inspiring for me because I do not have the drill bit attachment!

In my thinking the described procedure will lower the chisel cutting edge angle of the drill, but sharpening the lip clearance properly may be more important.

Jan

[harvestbarn]

One is aiming for an angle of between 10 to 15 deg  from the cutting edge to the end of the lip clearance while maintaining both cutting edges the same length.

This will only provide a chisel edge not the 4 facet point that the DBS-22 is capable, it has been very interesting hearing the comments from users thanks to all who have contributed.  I do not yet have a Blackstone Silicon grindstone which I suspect is needed for sharpening drill bits on the Tormek.

Garth

[Jan]

Thank you for reminding the size of the lip relief angels. 

In my thinking for small drill bit diameters and soft material we use high relief angels, while for large drill bit diameters and hard material we use low relief angels.

If I grasp your Tormek grinding procedure correctly, you rotate the drill bit with fingers, while pushing it outwards and downwards simultaneously. Is my understanding of this correct?

Jan

[Ken S]

Garth,

I would not delay drill bit sharpening because you do not yet have a black stone. I did a preliminary test comparing the SG regular grinding stone and the SB black stone. My test was not comprehensive, however, I did not notice any difference between the results of the regular and black stones. Further testing and the need to sharpen many drill bits on a regular basis might lean me more toward the black stone, however, at this point, I am quite satisfied with the regular stone for sharpening standard high speed drill bits. If sharpening high speed steel causes the SG stone to wear a little more quickly, I have no problem with that. I consider grinding wheels consumables, like brake shoes.

The Tormek DBS-22 is quite a nice jig. I consider it the most advanced and versatile of all the Tormek jigs. (It is priced accordingly.) The design and machining is very well done. It can handle many drill bit angle configurations. The four facet grinding is well beyond the standard grind. A serious drill bit sharpener will be well satisfied with this jig.

That said, I think the person who occasionally wants to sharpen a drill bit could self design a modification of the platform or scissors jig (much like the HK 50 or HK40) to do a basic sharpening of drill bits. Drilling a smaller pilot hole would help keep the bit with standard grind aligned. This is a standard machine shop practice.

Ken

[Jan]

To me it seems the process you describe, Rob, would produce two flat surfaces that meet near the center. But don't you have to rotate the bit as you grind so that you produce two conical surfaces? Moreover those surfaces aren't really conical as the cone angle has to decrease as you move away from the cutting edge. I've seen the practiced hand do this with ease and speed. My dad would do this on his dry grinder. When I inherited his bits I had to properly sharpen them all with my Drill Doctor. I think that as he got older his hand-eye coordination started to fail a bit.

Kind of like sharpening a knife by hand. If you're good at it you make it look easy.

It is a pleasant duty to properly sharpen all inherited tools, including old drill bits. 

When re-sharpening an old drill bit repeatedly, we inevitably form a longer chisel edge length, because the web thickness is usually increasing towards the shank of the drill bit.

Drill bit web does not contribute to the cutting process, on the contrary it consumes power and torque, and generates heat. The only positive thing on forming longer chisel edge is, that we move this drill bit to heavy duty category.

Jan

P.S.
Drill bit nomenclature and geometry is nicely described at http://neme-s.org/2005%20May%20Meeting/drills.pdf

[Elden]

Jan, that is excellent information. I missed seeing your post until today.

I have wondered about the difference between a split point and a four facet grind. It appears to be only that the four facet does not have to come entirely to a split point, albeit, it may. Split points have been around for years. Darex bit grinders, the maker of the Drill Doctor and more industrial models, have had this capability for years.

[Herman Trivilino]

Looking at the information Jan posted, it seems to me that as the web thickness increases the advantage of a split point increases.  Would this also be true of the four-facet grind?

[Jan]

Thank you Elden and Herman for your responses.    I am surely not a drill bit specialist.

Recently I saw Robert Gilman's video introducing Drill Doctor. I was surprised by his statement that the drill bit chisel edge is involved in cutting process. I my thinking the chisel edge does not cut, but penetrates the material. Chisel edge consumes part of power and torque, generates heat and for those reasons its length should be reasonably small. If the split point technique will reduce the total chisel edge length, than such a drill bit may be mechanically more efficient than the standard grinded drill bit.

Jan

[Herman Trivilino]

Jan, splitting the point, as I understand it, theoretically reduces the chisel edge length to zero. The intent is to reduce or prevent "wandering" of the bit when you begin to drill into something hard like steel.

[Jan]

Thanks for the explanation, Herman. 

I do not have neither the DBS-22 nor the Drill Doctor, so I am contemplating how to sharpen drill bits using T7 and a slightly modified Tool Rest. Because I am conservative, I plan standard drill bit grinding, as it was invented by Steven A. Morse in 1861.
I would like to master the knack of your dad!

Jan

[Ken S]

Jan,

Ernie Conover did an excellent you tube for Fine Woodworking about using standard metal drill bits for precision drilling of wood. Ernie just uses the standard biy grind. However, following good machine shop practice, he first drills a considerably smaller pilot hole. Next he enlarges the pilot hole with a drill bit just slightly smaller than his final diameter. The third hole is drilled with the actual diameter bit. It removes very little wood, and can drill a very accurate hole.

Ken

[Elden]

Herman, the picture you posted is a modified split point instead of a standard split point. This article, which has been previously posted, shows a split point (which they and Tormek call "four facet") as well as other kinds of points.

http://www.mmsonline.com/articles/choose-the-best-drill-point-geometry

It appears to me, a split point still has a portion of the chisel edge remaining from the primary bevel grinding, although it has been tapered off by the secondary bevel grinding. A drill bit with a thick web makes this very noticeable. I think the modified split point would help relieve it a little more and might require even a little less pressure than a normal split point. However, this is only supposition on my part.