Mission: Grind Secondary Point Angles (SPA) on Drill Bits

[RickKrung]

I am on a personal mission, to grind secondary point angles on drill bits.  I have mentioned several times in my posts that sharpening drill bits was a major factor in my decision to purchase a Tormek (T8) and more precisely, the grinding of four-facet points was the deciding factor. 

Last summer (2017), I had purchased a Drill Doctor, for the second time.  I didn't like it the first time I had one, but now they advertised being able to vary the drill point and relief angles, and to sharpen up to ¾" drills.  So I gave it a try.  No joy.  It did generally work as advertised, for drill point and relief angles.  But, the grind quality was so coarse, I could just not get comfortable with it, especially compared to factory grind quality with which I was accustomed. 

Factory Two Facet Drill Point


Drill Doctor 180 Grit Two Facet Drill Point

         
In my search for a more satisfactory alternative, I came across the Tormek.  It was in watching their videos on drill bits that I first learned of the four-facet point grind and I was very excited. I also liked very much the quality of the grind pattern.  That plus the fact that the Tormek was the very same machine the guy that I took my knives to used, and the Tormek's huge versatility, was enough for me to take the plunge.  I have not looked back.

My first four-facet drill bit sharpened on the Tormek


It was after joining the Tormek forum and reading posts on drill bit sharpening that I was introduced to the six-facet drill point geometry, or more correctly, Secondary Point Angle (SPA), via the very informative article by Joseph Mazoff, referenced in a forum post by Rich Colvin:

https://forum.tormek.com/index.php?topic=3263.msg19351#msg19351

Elden posted regarding the benefits of SPAs:

https://forum.tormek.com/index.php?topic=3265.0

Janne is the only member I am aware of who has actually ground an SPA, but he didn't really go into much detail about how he did it:

https://forum.tormek.com/index.php?topic=3265.msg19491#msg19491

Now it is my turn to give it a go, which is what this multi-stage thread will begin being about, in a fair bit of detail.  The trial victims will be a group of ¾" drill bits that a good friend of mine has beat the heck out of, hogging through ¼" steel plate on a large lathe using power feed with a drilling attachment on the carriage.  See example photos below.  Some have split points, but all are worn out and some have significant damage to the outer lip corner.  Solving this latter problem is one of the key benefits of secondary point angles. 

The next installment will be about setting up two slightly used Norton 3X 8" high speed grinding wheels on the Tormek. 

Rick

[Elden]

That is great Rick! I did get as far as getting the pivot (fulcrum) point drilled into the DBS-22 for doing the six facet grind but never posted pictures of that modification. Also I never tried it out after doing it.

[RickKrung]

This post is about mods to the DBS-22 jig to allow for setting the angle for grinding the Secondary Point Angles (SPA). 

The Joseph Mazoff article on drill point geometry, referenced in my first post and in other's posts, discusses the myth of the 118º drill point angle as being a good compromise and good all around point angle.  It is an interesting article if you are interested, but I wasn't at first.  Very recently, on the second and third reading, it started really sinking in.  For my immediate purposes, the five ¾" drills and my friend's drilling needs, a much broader point angle of 140º would be more suitable, especially with addition of the secondary point angle of 70º (half of the primary angle).

Unfortunately, great as the DBS-22 drill bit jig is, it only allows setting of angles down to 90º.  I needed a way to set it to lower angles in order to grind the SPAs.  At the time, I had not noticed Janne's mentioning of adding a second pivot hole (not shown in either of the two following photos) to the left of the original.  Instead, I reasoned that it was necessary to add a second locking hole (larger holes at the top) to the right of the original.  I am glad I did, as it preserves the arch of the jig and allows addition of angle markings and setting the angle as low as 45 º. 

   
One benefit of moving the pivot to the left, as Janne did, is that it keeps more of the moving plate over the stationary plate, but may cause an excessive amount of protrusion compared to the route I took. 


Since the jig was only designed for setting angles down to 90 º, rotating the plate further to set lower angles causes the bottom edge of the moving plate to protrude significantly.  What is shown in the first photo below is the protrusion for a setting of only 70º.  Rotating the plate further to the right, as far as 45º really exacerbates the protrusion and it looks much more like the photo above representing Janne's pivot location (and shown in the second photo below).  Using the default USB distance of 14mm from the stone surface, set by the hole in the angle setting tool causes the extra protrusion of the moving plate to interfere with the stone.




The USB would need to be set further away from the stone for the plate protrusion to clear the stone, or some of the plate would have to be removed.  I did not want to do the latter, as it is a bearing surface for the sliding drill bit holder part of the jig.


Once the modified jig, with a drill bit in place, was placed on the fixed platform and on the USB support plate, even with the USB set at 22mm rather than 14mm, the knob on the drill bit holder interfered with one of the USB knobs on the T8 base.  This can be remedied by using a 6mm set screw instead of the knobbed locking screw. 


For my purposes, I wanted the primary point angle to be 70º, which was set with the angle setting tool.  But the additional distance of the USB and the very acute angle of the drill bit holder requires a longer protrusion of the drill bit out of the front of the holder.  I assumed the same additional distance as was used for the USB would work for the drill protrusion (I have an email in to Tormek support to confirm this assumption).  The Primary and Secondary facet adjusting screw on the moving plate appears to have enough travel to accommodate the acute angle and additional protrusion. 

I had planned on posting about adapting the two Norton 3X grinding wheels to the Tormek, but the mods to the DBS-22 jig seemed more appropriate.  The Norton 3X adaptation was completed a couple weeks ago and they have been waiting to be used and a close observer might notice one of those wheels in the last photo above.  More on that later.

Rick

[Ken S]

Great project, Rick. You are just the person to take it on. This will be another example of another good idea from the Tormek engineering team refined by the forum. (To be fair to the Tormek engineers, we do not have the constraint of having to appeal to the larger general purpose market.)

When I get some quiet time, I want to carefully study your work, as well as the suggestion Elden forwarded. I predict my DBS-22 will soon have some more holes!

Keep up the good work and keep us posted.

Ken

ps The 3X wheels have found their proper home.

[RickKrung]

Thanks, Ken. 

I received a response from Tormek Support:

"The setting of the US and the protrusion of the drill bit does no effect the angle. You can chose your preferred position of US and drill protrusion and still use the angle setting template: Mats Wuolo, Production Technician".

That is pretty much what I figured out.  I have the first 3/4" drill bit partially done for the first four facets. 


I have to say, it is taking longer with the 3X wheel than I expected, but I can say that the grind finish left by the 64 grit Norton wheel is far superior to that of the 180 grit Drill Doctor diamond wheel.  I could almost be satisfied with it, but am anxious to see what the SB and SJ wheels do.  I have my doubts about putting too much of a polish on the primary facets using the SJ wheel, sort of, is it better to leave a more durable edge ("toothy" ?) rather than too finely finished but possibly less durable edge. 

Rick

[RickKrung]

Adapting Norton 3X Wheels to the Tormek

Once I had the T8 with the standard SG stone, I was anxious to try out sharpening drill bits.  I was very pleased with the initial results, at least as far as the finished drill points were concerned (see the third photo in my first post).  However, I didn't like how long it took.  Even though the drills I sharpened were not damaged and didn't require grinding off a lot of metal to get to where the primary and secondary reliefs could be ground, it still took a long time, primarily to grind the secondary relief.  I was a bit put off on drill bit grinding for a while.

Then came along the SB stone, which was intended for grinding HSS, which my drill bits are made of.  I didn't get an SB stone right away, but even once I did, it still seemed like it took a long time.  I wanted something for taking off metal faster and leaving only the finish grinding for the SB stone.  I first planned on setting up a USB on my high speed grinder, with its very old (30yrs), 6" worn grinding wheels.  Then, a fellow forum member offered me his two used but no longer in service Norton 3X 8" grinding wheels (64 and 80 grit).  These were designed for use on high speed grinders, but had been used on a Tormek for slow speed, water bathed grinding. 

I wanted to mount them in a way that would maintain concentricity of the wheels, once trued on the Tormek but taken off and put back on repeatedly.  So I machined stainless steel bushings with 12mm reamed holes, which were glued into the 3X wheels. 


I also machined some large diameter and thick aluminum flange washers which were also reamed to 12mm in an effort to hold the wheels as perpendicular as possible, to reduce lateral runout.  The effort was partially successful, with the 80 grit running true, but the 64 grit not so much. I will say that this latter effort was probably not really necessary as standard grinding wheel flanges would probably have worked fine.


Once the wheels were mounted, they needed to be trued.  The coarser wheel (46 grit) was the worst, most out of round and with a significant groove in the middle. Both wheels were trued using my motorized truing tool.

Before truing, high side of the wheel.


Before truing, low side of the wheel.


Norton 3X wheel mounted on the Tormek. Notice the groove in the center of the wheel.


After truing. No more groove.


Freshly trued wheel showing aggressive grit.


Video showing trued surface.
https://vimeo.com/265109338

Rick

[RickKrung]

...snip...

I have to say, it is taking longer with the 3X wheel than I expected, but I can say that the grind finish left by the 64 grit Norton wheel is far superior to that of the 180 grit Drill Doctor diamond wheel.  I could almost be satisfied with it, but am anxious to see what the SB and SJ wheels do.  I have my doubts about putting too much of a polish on the primary facets using the SJ wheel, sort of is, it better to leave a more durable edge ("toothy" ?) rather than too finely finished but less durable edge. 

Rick

I have figured out what the problem was with how slow the 3X wheels were grinding.  I had them graded too fine.  I had used the Truing Tool to true them and ran it at a fairly slow rate across the wheels, much like for the Tormek wheels.  I am pretty sure that left them without the aggressive grit they were designed for. 

I figured this out by using a Lee Valley diamond grading tool that Ken S. had recommended. 


The difference in performance was dramatic.  Much rougher sounding grinding process and much faster material removal.  This is much more like what I was expecting.  Watch the videos of using the grading tool and then grinding one of the SPA facets and listen. 

Grading the wheel:
https://vimeo.com/267692261

Grinding a secondary relief facet:
https://vimeo.com/267692242

With the "refreshed" 3x 64 grit wheel, I quickly finished roughing the secondary facets and was ready to move on grinding the SPA facets. 


I am much happier with the 3X wheels and feel they will be a welcome addition to the toolbox. 

Rick

[RickKrung]

Grinding the SPAs

Next came rough grinding of the SPA facets.  Rotating the moving jig plate to the 70º mark required moving the USB substantially away from the grinding wheel and extending the drill protrusion, by 12mm, almost twice the stock values for the USB.  Because of the greater distances, the interference with the USB locking knob went away. 

Ready for grinding the SPA.


Roughed six-facet grind.


So, with jig mods complete and some kinks worked out, I think proof of concept has been made, at least for me.  I am now ready to put on the SB wheel and do some finish grinding.

Rick

[Ken S]

The groove in the 46 grit wheel was from a combination of reshaping a half inch turning gouge several times and not knowing how to true the wheel. I should have just done it, however, I was reluctant to use the TT-50 on the 3X wheel.

Rick, good tip about using the Lee Valley diamond T to restore the coarseness to the 46 grit wheel.

I think most users would be happy with just one of the grits. The 80 is probably fast enough. My test showed both wheels cut fast, with the 46 grit cutting in four minutes what the 80 grit cut in five minutes. Either is much faster than an SG or an SB.

The new diamond  wheels will be game changers, however, a 3X wheel can be purchased for $50 US. That's a lot of firepower for a small price. And, the cool, dust and spark free working environment of the Tormek is preserved.

Rick, you have done outstanding work on this project!

Ken

[RickKrung]

Thanks, Ken.  It has been interesting and quite educational for me. 

After all that, it took only about 45 min. tonight to complete the finish grinding of all facets on the SB stone.  I'm not sure just how it happened, but I recall "watching" it happen, but instead of this drill point being six-faceted, it turned out to be eight-faceted.  One extra set of relief facets.  I'll have to pay closer attention on the next one. 


Also, recall I mentioned interference of the jig when rotated over to 70º for the SPA during rough grinding and how it "went away" due to the additional distances of the USB and drill protrusion.  Well, that interference came back when the 2" wide wheel was put on.  The drill jig holder actually would contact the corner of the Tormek stone (any) and the tightening knob almost does on the USB locking knob. 


So, for now at least, for these 3/4" drills that will receive pretty heavy use, I am not going to try to put any polish on the primary facets using the SJ stone.  I also don't want to try to put that polish on the SPAs either, as I view it as a nightmare of trying to match angles in an application that doesn't seem to warrant it.  I'll save that exercise for simple four-facet points. 

Thanks for your attention and patience. 

Rick

[cbwx34]

Just to satisfy my curiosity...

...
Also, recall I mentioned interference of the jig when rotated over to 70º for the SPA during rough grinding and how it "went away" due to the additional distances of the USB and drill protrusion.  Well, that interference came back when the 2" wide wheel was put on.  The drill jig holder actually would contact the corner of the Tormek stone (any) and the tightening knob almost does on the USB locking knob. 

...

... and from earlier post...

...
I received a response from Tormek Support:

"The setting of the US and the protrusion of the drill bit does no effect the angle. You can chose your preferred position of US and drill protrusion and still use the angle setting template: Mats Wuolo, Production Technician".
...

... so can't you just extend the "protrusion distance" to avoid this interference? (Just curious).

Good info and pictures... you do great work.

[RickKrung]

Just to satisfy my curiosity...

...
Also, recall I mentioned interference of the jig when rotated over to 70º for the SPA during rough grinding and how it "went away" due to the additional distances of the USB and drill protrusion.  Well, that interference came back when the 2" wide wheel was put on.  The drill jig holder actually would contact the corner of the Tormek stone (any) and the tightening knob almost does on the USB locking knob. 
...

... and from earlier post...

...
I received a response from Tormek Support:

"The setting of the US and the protrusion of the drill bit does no effect the angle. You can chose your preferred position of US and drill protrusion and still use the angle setting template: Mats Wuolo, Production Technician".
...

... so can't you just extend the "protrusion distance" to avoid this interference? (Just curious).

Good info and pictures... you do great work.

Thanks. 

Yes, I believe you could just extend the protrusion, with some care.  First your drill would need to be long enough to still be held securely in the drill bit holder.  Second, with greater projection, any instabilities may be amplified, or instabilities not noticed before could become issues. 

What I mean is, the DBS-22 jig is a loose assembly of three pieces, the rigid base plate, the loosely fitted guide plate (movable) and the drill bit holder.  They basically rely on gravity and hand pressure to keep them firmly together and aligned.  They are not at all like the moving elements of a lathe with gibs closely adjusted to allow controlled sliding movement but without vertical, lateral or angular movement.  When the DBS-22 sliding plate is moved far enough to either side, it can tip, especially with the drill bit holder on top, lifting the drill bit from the stone or worse, changing the angle at which it contacts the stone. 

With the mod to allow further rotation of the guide plate, it is necessary to push the limits of stability of the guide plate.  I had to be extra careful to keep the sliding plate firmly planted on the base plate.  Adding extension to the drill bit would exacerbate that inherent instability. 

It is sort of like a step ladder.  Great to work on when on the lower rungs.  But there is a reason it says on the top rung "Do not work or stand above this level".  In the case of the DBS-22, it could be like standing on the top rung when the footing was unstable. 

In the case of working on the SPA facets, there was so little area being ground, it was not a problem using 80% of the SB stone surface. 

There is a third reason, which has to do with how well the drill bit is aligned in the drill bit holder.  I had problems with the 3/4" bit I was working with, aligning properly in the holder.  If you look in some of my photos, you may notice the multi-slotted tube in which the drill bit is held, within the drill bit holder.  Without that, the drill was always canted to one side.  Any mis-alignment of the drill bit in the holder would greatly be exacerbated with greater protrusion.  I plan on a separate post to explain the alignment problem and solution.

Rick

[cbwx34]

Ah... very interesting.  Thanks for the detailed reply.

[RichColvin]

Rick,

So how well did the newly sharpened, 8-faceted drill work ?

Rich

[RickKrung]

Rich,

Don't know yet. 

I am making the journey to Portland, OR (350mi.) this weekend to go to my friend's shop to find out just that.  I am hoping it works well, at least as far as the SPA goes.  I am not so sure about how well it will do on the center point, as it is not split-point, as all of his other drills are. 

I have a small knee mill and a drill press, but nothing that would put this drill through 1/4" steel very quickly.  I doubt he will be wanting to take the time to drill a pilot hole, opting instead to try to make it pilot itself.  The four-facet center point that the Tormek does is superior to the standard two-facet point with the wide flat chisel edge, but that is more for centering without walking.  I don't know how well it holds up under the kind of conditions he will subject the drill to.  I always put in a pilot hole, but he is focused on high rate production. 

I could split point it on the Drill Doctor that I have, but I'd want to try that out first on some not so important drills.  He has a precision drill sharpening machine that I've used in the past to put standard two facet points on many of my index drills.  He says it will split point, but it has to be done by hand. 

Rick