D2 planer blade... Grinding hollow grind bevels on a knife blade

[Elden]

http://forum.tormek.com/index.php?topic=2527.msg13054#msg13054

[Ken S]

Excellent work (again), Eldon!

That topic is actually later than the original, and has thoughts which more prove more useful than the original. Rustygunn, I suggest you study both.

I finally gained access to my main computer. (My grandson is asleep. )

Here is the original article:

Expanding the Scope of the Tormek

The Tormek is not a static machine.  The original Tormek used a natural stone of approximately 220 grit. Over a decade would pass before  the leather honing wheel was added. The grinding wheel switched from being a natural stone to a man made stone, which allowed the concept of the stone grader to work. Now the Tormek had both 220 and 1000 grit capabilities plus the leather honing wheel.

Later the blackstone and 4000 grit Japanese stone were added, making the Tormek capable of working with harder steels and making very polished edges possible.

The BGM-100 was introduced, allowing those who had only a dry grinder to have the flexibility of the Tormek jigs. This allowed faster reshaping of tools. However, this came at a cost. The dry grinder, while fast, does not provide the Tormek protection against overheating the tools. Nor does it operate free of dust and sparks.

I searched for a way to combine the speed of the dry grinder with the cool reliablilty of the Tormek. Several years ago I read a post on the Tormek forum where the poster tried mounting his cheap dry grinding wheel on the Tormek. He was impressed with the cutting speed, but apparently lost interest and moved on. This fascinated me, and the fascination remained.

I have a forty year old six inch dry grinder. Many years ago I replaced one wheel with a friable white wheel, which helped the problem of overheating tools. Eventually I replaced the second wheel with a Norton 3X 46 grit wheel. The 46 grit wheel worked like a champ when I needed to remove extensive mushrooming on two splitting wedges. I was curious to know how the 3X wheel would work on my Tormek T7. The six inch wheel is too small to work with the T7 (ten inch diameter wheel).

When I acquired a T4, I decided to renew the tests with the six inch 46 grit wheel. Although not the ideal diameter for the eight inch (200 mm) Tormek T4, the 46 grit 3X wheel removed a surprising amount of steel from a bolt and left a surprisingly smooth surface. The bolt remained quite cool during the grinding process.

The eight inch diameter Norton wheels come with bushings with the smallest being 5/8".  I had previously made a business card shim for the half inch bushing on the six inch wheels. Norton would not sell me a spare 5/8" to ½" reducing bushing for safety reasons. These concerns are with high speed grinders, not the Tormek.

I found that a short piece of schedule 80 water pipe could be adapted to make a bushing. The Outside Diameter is 5/8". The original 7/16" Inside Diameter is too small for the 12mm Tormek shaft. Not having a 12mm drill bit, I used a 31/64" drill bit in my drill press and reamed out the inside diameter. This is easily accurate enough for coarse grinding.

I thought the 46 grit wheel might be too coarse to be practical with the Tormek. My next step was to purchase a Norton 3X eight inch diameter 80 grit wheel in the harder K grade. My first test was to grind away at a metal lathe tool bit. The bit is at least High Speed Steel and designed to be hard enough to cut steel. In a five minute timed grind, the 80 grit wheel removed a surprising amount of steel. At this point, I knew I was onto something.

My second test was to measure the amount of steel removed from the side of the lathe tool bits. (I had ordered an eight inch diameter 3X 46 grit  wheel for the test.)
I made sure that both bits were the same steel. I ran three timed tests (for one minute). The previous test was run with the universal support bar in the horizontal position (trailing) position. This test was run with the universal support bar in the more agressive vertical position. I ground the bit surface paralled to the face of the grinding wheel and the full one inch width of the wheel for one minute. I tested both the 46 and 80 grit wheels this way. I also tested the Tormek SG-200 wheel graded coarse with the bit across one inch of the width of the wheel. I measured all ground surfaces with a micrometer, averaging several readings to determine how much steel had been removed by each grinding wheel in the same one minute. The coarser wheels showed slightly more metal ground away, however, the test time was too short to be a good indicator.  The weak link was my fingers.

I switched to placing the metal lathe tool bits into the SE-76 and adjusting the jig and support bar to procuce a thirty degree bevel. I used identical bits and ran the tests for five minutes.

The 80 grit Norton wheel ground a bevel almost the entire thickness of the 5/16" (8mm) bit in five minutes. The 46 grit wheel ground the same bevel depth in four minutes.

The Tormek SG-200 grinding wheel ground a bevel between half and two thirds of the tool bit thickness in the alloted five minutes. The coarser Norton wheels cut noticeably faster, although the Tormek wheel put in a surprisingly good performance.

The Tormek wheel's ground finish was visually smoother than the coarser wheels, but, again, the difference was less than expected.

I repeated the same tests with the Tormek SG-250 and SB-250 grinding wheels on the T7. The SG-250 produced a bevel essentially identical to the SG-200 in cut depth and smoothness. This was not surprising, as the surface feet per minute is very close with the two sizes.

The bevel produced by the SB-250 was quite smooth, although it was the most shallow of any of the wheels tested. It was perhaps half the thickness of the tool bit. This was surprising, as the black stone is designed for hard steel. I am postponing any conclusions about the SB wheel until I do further tests.

Conclusions:

The two Norton coarser wheels were noticeably faster cutting than the standard Tormek wheel. However, the difference was not as much as I might have expected. I believe one or both of these coarser wheels would be a nice backup for a sharpening job involving removing a lot of metal from high speed steel (such as nicked planer blades).  If one did a lot of reshaping of turning tools, I would suggest including a coarser wheel in the stable. I would use it before the standard Tormek wheel and finish with the SG wheel for a smoother finish.

I believe the "Tormek advantage" from wet grinding with coarser wheels would prevent me from adapting my dry grinder to use the Tormek jigs. If I did not already own a Tormek, it would be a question of money. I still think I would favor the Tormek option.

In working with the T4, I have found it to be a stalwart. I am accostumed to the larger T7 wheel, although I find myself adapting easily to the slightly smaller T4 wheel. The T4 seems to cut as quickly as the T7. I have also not noticed much heat retained. I do not think any more about the "thirty minute" limit.

I have found the SG wheel works well with resharpening high speed steel drill bits. If I was sharpening high speed steel on a very regular basis, I would consider the black wheel (SB-250). My test with it is inconclusive at this point.

[RustyGunn]

Pretty extensive testing, more than I might have done. Thanks for sharing it.

[RustyGunn]

Update... Almost a year has gone by it seems. I finally worked on a few blades the past two weeks, with very pleasing results.
I made two small neck knives, with 1.75" blades, of a sheepsfoot design. My first blade was to prove to me the concept was sound. It is. Slow, but doable.
The second blade was to perfect the design and and to set up a custom jig. I intend to combine two Tormek jigs to create one that I want. This will be a project soon.
Then I will make knives to sell.
The only issue I have is the very slow hollow grinding of the blade bevel. To speed up the process I first flat grind the blade, then hollow that out on the T-7. The end results are impressive. I am very pleased with the T-7. I have a few pics on this cell phone, but I don't know how to post pics here. More to come. Slowly, but surely.

[Ken S]

We look forward to your future posts.  Good luck with this project.

Ken

[RustyGunn]

Thank you.
BTW I've used the T-7 to sharpen some knives and it works awesome. Blades come out sharp! I highly recommend a Tormek, they work very well.

[RustyGunn]

Lets see if this works. My first photo upload. This blade is a sheepsfoot style simply because its an easy knife to make. The bevel is an easy one to make for a newbie.
The blade profile was cut out with a Dremel cut-off wheel and ground on a 1x30 belt sander to shape. The bevel was then flat ground, then hollowed out on the T-7.

[RustyGunn]

I was able to combine the Scissor jig and a knife jig into a new-to-me jig, assuming Tormek makes one I haven't seen. I used two U-bolts to attach the knife jig via four holes drilled in the scissor jig.
This modification does not destroy either jig, except I had to remove the plastic sheeti g on the back of the scissor jig (I saved it, and can reglue it back on later). Both can still be used as intended once it it dismantled. I am using this modified jig to put the hollow bevel on a kiridadhi blade. The results are outstanding. I am very pleased with how this is coming along.
I was not able to post a pic, but will when I can.

[RustyGunn]

Here is a picture of the modified jig and blade.

[Ken S]

Rusty,

That is a very clever modification of the knife jig! I have thought of trying to remove the radius from the adjustable stop, however, your idea never occurred to me. Kudos for imaginative thinking!

Ken

[RustyGunn]

Thank you Ken. My initial thinking on this is to reduce the long term wear on the corner/edge due to the jig allowing the blade to "rotate" downwards at the edges. I didn't want to have to re-square the stone too often.
This jig greatly reduces this, and holds the blade level with the stone.
The problem that arises is that this jig wants to stick/stop due to the oblong hole drilled through the scissor jig plate. This oblong hole is a locking device when tightening the clamp screw.
Had the hole been round then the modified jig could slide back and forth easily.
Its not much of an issue though. I get outstanding hollow grinds. I will share a pic of the kiridashi blade later. Its almost done.

[RustyGunn]

My kiridashi neck knife with a hollow ground bevel done on the T-7. This blade now needs to be sanded on it's surface, followed by rounding out the profile edges.
Yes, a small knife can be made using a T-7. It just takes time. About five hours I think, to grind out the bevel. A bit long, but outstanding results.