Setting 25 degree edge angle with TTS-100

[Jan]

Ken inspired me to think about the usage of TTS-100 for setting the edge angle of a tool mounted in the square edge jig SE-76. The results of my research shows that it is well possible.

First, mount the tool in the square edge jig with the protrusion 44 mm (1.73").

Second, set the position of the US using the inner hole (B) of the TTS-100.

Third, these two steps ensure the edge angle aproximately 25 degrees.

I have checked the edge angle setting with the angle master. I have got 25.5 degrees.
This setting should almost not depend on the grindstone diameter. 

Jan

[Ken S]

Jan,

I use a slight variation of this. I adopted TTS-100 hole B as my standard distance from universal support to the grinding wheel (just like you did). I placed a blank strip of white label tape in one of the shree slots. With the us to gw distance set at hole B, I used the anglemaster to set the projection length of my chisel at 25 degrees. I then used a fine black marker to make a mark at that length and labelled it 25 degrees. I did the same for 20 and 30 degrees on the same piece of label tape.

This both eliminates the need to compensate for wheel wear (including switching between a T4 and a T7), it also eliminares future need for measurement. This was actually my inspiration for the kenjig for knives. It all started for me with chisels.

I use hole A when I want longer tool projection, such as when I want to add camber to traditional (thinner) plane blades.

Ken

[Jan]

Ken, I know from your previous posts that you use the TTS-100 for chisel edge angle settings. Please let me know your protrusions for the 20, 25 and 30 degrees edge angles.

From the geometrical point of view the tool setter TTS-100 together with the square edge jig SE-76 works perfectly only for one value of protrusion, which defines one size of the edge angle.

The ideal protrusion, for the set of TTS-100 and SE-76, is 42 mm (1.65"), which corresponds to an edge angle of 28.5 degrees, assuming we are using the inner hole (B). 

Small variations of the protrusion/edge angle are surely possible, but they will cause that the edge angle slightly varies depending on the grindstone diameter. (Tormek also allows some protrusion change when the TTS-100 is used with SVS-50 jig.) 

Jan

[Ken S]

Jan,

Here are my markings on the label tape:

25 degrees 44+ mm
30 degrees 40mm
35 degrees 32+mm
40 degrees 38+mm oops, make that28+mm

These are pencil lines based on angle master readings and are somewhat approximate (as opposed to just approximate)

Ken

[Jan]

Thank you Ken for sharing your protrusions. 
Congrats to the carefully selected values.
(I assume a value 28 mm for 40 degrees instead of yours 38+mm.)

I am confident, that the values for the edge angles 25 and 30 degrees will work almost independently of the grindstone diameter.

What concerns your protrusions for 35 and 40 degrees, I expect systematic increase in the actually grinded edge angle with decreasing grindstone diameter.  Based on my considerations, using fully worn grindstone (160 mm diameter), you should get 50 degrees edge angle instead of the desired 40 degrees. Please be so kind and check it, if you have such a small stone.

It is the inherent property of the set TS-100 and SE-76, that it sets the edge angles independently of the stone diameter only for angles from narrow vicinity of its principal angle, which is some 28.5 degreees. 

Jan

[Ken S]

Jan,

You caught my "fumble fingers" (English idiom for hitting the wrong key by mistake.) I do proofread, but sometimes the typos can be very elusive.

I will accept you caveat about angles>28.5 degrees.

I can check with the T4 stone, which is 200 mm. I plan to replace my SG-250 when it wears to approximately 200 mm. At that time, I will reserve my present stone for rougher work.

Ken

[Ken S]

Jan,

Just to start a good conversation, how precise do we need to be? For example, with a mortising chisel like the one you have inherited from your grandfather. Assuming me ng it was sharp, how much difference would a few degrees in the bevel angle make? I am not being argumentative or promoting sloppy technique. I merely wonder if the end result, mortises, benefits from more precision than an experienced craftsman like your grandfather would have used in hand sharpening by eye.

Ken

[Jan]

You are correct Ken, in some situations a few degrees change in the edge angle is not important.    A heavy duty mortise chisel is a good example. For such a chisel we have to increase the edge angle to 35-40 degrees. But I am sure an experienced craftsman will not be satisfied with a chisel ground with a 45-50 degrees edge angle.

I have checked your protrusion 28 mm for setting an edge angle of 40 degrees on mine grindstone with a diameter 240 mm.  Everything worked fine. Then I went to the honing wheel (220 mm) and have seen, that this protrusion sets an edge angle 42 degrees. This would dull the edge. That was the reason why I have mentioned, that with decreasing wheel diameter, the actually grinded/honed edge angle will increase. In this real situation, I think, we need a 0.5 to 1 degree precision. The simple marker method surprisingly can provide this precision.

Jan

[Ken S]

Good points, Jan.

Looking back at my original inspiration, I wanted a reliable and repeatable method for sharpening my bench chisels. I actually have a set of mortise chisels, but have never used them. So, the higher angles were just transferred from a bench chisel.

It is good to have the flexibility of knowing several methods.  It is also good to know when we need more accuracy. Keep up the good work.

Ken

[Jan]

Currently the heavy duty mortise chisels are being replaced by chain mortisers, which are ideal for timber framing. Only a smaller part of joints is made by chisels. In this country the standard width of a mortise and tenon joint for home building is 40 mm (1 5/8"). Because so wide mortise chisels are not manufactured, the craftsmen use carpenter chisels or firmer chisels to cut the mortises. Sometimes you can find broken chisels on the construction site. I collect the broken tools and reshape them as a butt chisel. 

Jan