Author Topic: Primary Bevel Only Strategy  (Read 360 times)

Offline Regdop

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Primary Bevel Only Strategy
« on: March 25, 2019, 07:07:56 am »
Guys, just bought my first Tormek. a T8. I’ve watched all the videos and have an idea of sharpening using only a 25° primary bevel.. and that’s all... ok. What happens when that edge goes blunt... do I have to do it all over again?     Surely a 30° secondary touch up bevel is more efficient? Please help me to understand the theory / strategy of single bevel only... cheers Gary!

Offline Ken S

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Re: Primary Bevel Only Strategy
« Reply #1 on: March 25, 2019, 12:00:39 pm »
Welcome to the forum, Gary.

The reason for having a single or multiple bevels is what is propeling the sharpening. Secondary or micro bevels are considerably less labor intensive. For someone sharpening with hand powered bench stones, this is a real factor. The edges are no sharper; they are just less laborious.

With the Tormek, the power comes from the motor. Using multiple bevels offers no labor advantage.
In fact, resetting the jig for the micro bevel actually requires more time.

With a water cooled Tormek, you can do complete grinding up to and including raising a burr. The tool stays cool and does not overheat. Preliminary work with high speed dry grinders normally stops before raising a burr. At this point, the edge is very thin and can easily be overheated. Careful workers do the final grinding by hand. "slow speed" grinders (1725 RPM instead of 3450 RPM) are still at risk of overheating.

The ideal strategy with any sharpening method is to sharpen lightly and frequently. When you are doing something like hand cutting dovetails, you can feel when the chisel begins to lose sharpness. Cutting becomes more laborious. That is the time to resharpen. Do not wait for the chisel to become blunt; limit your sharpness range to quite sharp to just off quite sharp.

A logical strategy is to have two chisels of the most used size(s). You will probably use a second half inch chisel much more than an 1 3/4” chisel. The second chisel means you only have to stop work to sharpen half as frequently.

Chisels are fun to sharpen. Enjoy!

Ken

Offline RichColvin

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Re: Primary Bevel Only Strategy
« Reply #2 on: March 25, 2019, 01:00:24 pm »
With the Tormek, the power comes from the motor. Using multiple bevels offers no labor advantage.

I almost never disagree with Ken, but I do on this.
  • For woodworking bench tools, I grind the primary bevel using the traditional SG stone.  Then, I switch to the Japanese SJ stone and add a micro / secondary bevel.  The smaller micro bevel angle is quick to do and using the Japanese stone on the whole edge would take too long and really adds no value.
  • For metal lathe tools, the reason for doing one is different and the terminology is different but the effect is the same.  This is especially used for cemented carbide tools. (For these tools, it is a Relief Angle vs Clearance Angle:  this is explained in more depth on my Sharpening Handbook).
Hope that helps.

Kind regards,
Rich
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Offline RichColvin

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Re: Primary Bevel Only Strategy
« Reply #3 on: March 25, 2019, 01:02:20 pm »
Gary,

One more thing, consider using different angles for different purposes.  I’ve outlined this in my Shapening Handbook.  The link is in my footer.

Kind regards,
Rich
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You are born weak & frail, and you die weak & frail.  What you do between those is up to you.

Offline Ken S

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Re: Primary Bevel Only Strategy
« Reply #4 on: March 25, 2019, 05:27:59 pm »
Rich,

I don't disagree with you, however, I think a new user would be better advised to learn the basic technique before venturing farther afield. Once one masters the basic technique, he is in a better position to experiment with different angles and grinding wheels.

Ken

Offline Herman Trivilino

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Re: Primary Bevel Only Strategy
« Reply #5 on: April 09, 2019, 05:13:47 am »
Guys, just bought my first Tormek. a T8. I’ve watched all the videos and have an idea of sharpening using only a 25° primary bevel.. and that’s all... ok. What happens when that edge goes blunt... do I have to do it all over again?     Surely a 30° secondary touch up bevel is more efficient? Please help me to understand the theory / strategy of single bevel only... cheers Gary!

If you have a secondary bevel of 30° that would be equivalent to a single 30° bevel, which would be more efficient provided you have the motor propulsion of the Tormek. The only advantage to a secondary bevel is that it makes it easier to hand sharpen, perhaps when you're away from your Tormek.
Origin: Big Bang

Offline Ken S

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Re: Primary Bevel Only Strategy
« Reply #6 on: April 09, 2019, 03:33:12 pm »
Returning to my logical solution of owning two identical chisels of the most used width, Why not sharpen one with a single bevel and one with a secondary micro bevel. If you are cutting dovetails, letting in hinges,or trimming tenons, repetitive work should provide practical information about sharpness usage. Let your work be your decision criteria.

Remember that certain steels like A2 are designed to be sharpened with a thirty degree bevel.

Please post your observations.

Ken

Offline Twisted Trees

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Re: Primary Bevel Only Strategy
« Reply #7 on: April 09, 2019, 05:47:19 pm »
The way the Tormek eats metal there is only one reason for a micro-bevel, that is a different grade of stone be it a different wheel or hand sharpening on an oil stone or whatever. the Tormek will remove metal as well over 4mm as it would over 2 or 1mm.



Offline john.jcb

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Re: Primary Bevel Only Strategy
« Reply #8 on: April 09, 2019, 07:02:16 pm »
I would be interested to hear how what I presume is a secondary bevel that is created when you hone at 1° to 1.5° greater angle using the FVB impacts sharpness. Is this not a secondary bevel?

Offline wootz

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Re: Primary Bevel Only Strategy
« Reply #9 on: April 10, 2019, 03:16:36 am »
I would be interested to hear how what I presume is a secondary bevel that is created when you hone at 1° to 1.5° greater angle using the FVB impacts sharpness. Is this not a secondary bevel?

Let me stress that our honing method is 2-step: 1st we remove the bulk of the burr, and 2nd we remove the root of the burr - we call it "differential honing" for that.
We hone at a a higher angle AFTER we have removed the bulk of the burr by honing at the edge angle.
Purpose of honing at a higher than the edge angle is to improve the edge apex stability; for mainstream knife steels it is typically +1.5-2 degrees per side higher. By doing so, we remove the root of the burr, and get a lasting sharp edge.

On the contrary, if you keep honing at the edge angle till you can no longer see and feel the burr, you will shape the burr root into the wire edge, that is sharp but short-lived. The wire edge may cut thin paper well, and shave your forearm, but on the BESS sharpness tester it mushrooms against the test line and shows over 300 BESS. As you start live cutting, the edge quickly turns dull as the wire edge rolls.

Answering John's question, the laser protractor can detect the microbevel from a higher-degree honing, seen as 2 dots on the scale
« Last Edit: April 10, 2019, 06:16:16 am by wootz »

Offline RichColvin

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Re: Primary Bevel Only Strategy
« Reply #10 on: April 10, 2019, 12:54:02 pm »
TwistedTrees Pete,

I have to disagree.

Many wood turning and carving tools greatly benefit from a micro bevel.  A skew chisel in particular has a very large ground surface — ½ inch or more is common.  A marking knife, especially a Japanese marking knife, has a huge ground surface, oftentimes over an inch!  Adding a micro bevel makes resharpening much faster, and gets me back to the work I’m actually doing.

And metal lathe tools with carbide inserts demand such an approach.  Carbide sharpening requires low grit wheels to get the work done.  But, when grinding the Side Clearance Angle, one should leave the top 1/16 inch unground (this is called the Relief Land). This is because the rough grinding of the carbide introduces cracks and makes it more brittle. By stopping short of the top, this is minimized. Then, when grinding the Side Relief Angle, a high grit wheel should be used to make the edge smooth with minimal cracks.  + 4º to +6º is what I have found to be necessary.  (More details are on my Sharpening Handbook web site).

Kind regards,
Rich
« Last Edit: April 10, 2019, 12:58:59 pm by RichColvin »
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You are born weak & frail, and you die weak & frail.  What you do between those is up to you.