First results

[Hatchcanyon]

As a newbie on machine sharpening - we, my wife and me - own a T 7 for 2 month. We both are no professionals simply hobbyists. She is turning, I like to construct jigs and shop equipment, sometimes some furniture.

Some pictures from the results of using the T 7:




Chisels polished with the SJ stone


24mm chisel machined with the SG stone


Same 24 mm chisel after using the SJ stone (sorry about some blur)




Same iron other perspective

Using a paper kitchen towel for cleaning the iron invariably leaves particles on the irons surface.


Backside - could be better

After sharpening this chisel with a setting of 25° - actually after calculating the hollow grinding it comes out as only 23° - I used the iron on a piece  of Douglas Fir, damaging the edge with the first cut....


Douglas Fir


Damaged edge


regrinded to 30° - actually about 28°. That works well on the fir!


Grinding a short spoke shave iron


The sharpening workplace

Rolf

[Ken S]

Sehr gut! You are up and running. Nice photos, also.

Keep up the good work and keep posting.

Ken

[Jan]

Sehr gut gemacht, Rolf! 

Thank you for posting your very nice sharpening results. The mirror finish of your chisel's bevels is really impressive!

Please do not be afraid about the size of the edge angle. The hollow grinding does not influence the edge angle because only the edge is directly involved in wood chiseling/mortising. If you set the universal support for 25^o using the angle master you will get an edge angle of 25^o on your chisel. 

For more information please read the topic "hollow vs flat grinding thoughts"http://forum.tormek.com/index.php?topic=2413.0

Jan

[RobinW]

Very impressive finish!

I'm even more impressed (with my warped sense of humour) with the numbering included - that's clever.

Your photographs also are a good representation of what happens at the edge and detailed in, I think, Hermann's previous posts using a x40 lens; and Jan's comments about stress at the edge if grinding is not fine enough.

I was concerned about the small spokeshave blade - it's a real pain in backside trying to hold a blade like that and get a decent finish - I've been there, done it, rub and cut my fingers etc and collected the T-shirt. So may I refer you to a post I made in 2013 "Spokeshave Challenge" where I made a jig for such blades. If you go right through the post there was a wooden trial jig, followed by a machined metal jig, and a detailed drawing.

Here's the details:-

http://forum.tormek.com/index.php?topic=1620.0

[Ken S]

Robin,

The front surface of the SE-177 has been redesigned to hold shorter tools like spokeshaves. i will put a spokeshave blade in during my next trip to the shop and report.

Ken

[Hatchcanyon]

Thank you for the comments!

The first pictures of the mirror chisels were not usable. The things reflected were far out of focus. The setup shown reduced the difference between the bevel and the mirrored item.

Personally I don't have any difficulties sharpening these spoke shave irons. The method shown works fine for me. But I use both hands while grinding to holt the iron onto the SVD 110. For taking the picture the other hand was temporarely used to trigger the camera.

Hollow grinding is not always a problem but it can be. Here is a formula for calculating the angle deviation from a wanted angle.

D = Stone diameter in mm
s = Thickness of the iron in mm
α = Angle setting
β = Angle deviaton from ideal

sin β = s / D x sin α

The iron shown above has a thickness of 3.7 mm, the stone diameter measures 248 mm, the angle setting is 25° (sin 25° = 0,4226)

sin β = 3,7 mm / 248 mm x 0,4226 = 0,0353 >> β = 2,02°

Angle deviation comes to about 2° - resulting cutting angle = 23°.

(Closer to the handle the iron becomes thicker. (5.5 mm) resulting to a ircreasing deviation of about 3°.)

Rolf

[Jan]

Rolf, thanks for posting your formula.  I would probably need a sketch to understand where you measure the so called deviation angle beta.

Please, can you measure your resulting cutting angle with a Protractor (Angle Meter) and let us know if it is in compliance with the results predicted by your formula or if it is equal to the edge angle properly set using the Angle Master?  Please measure the angle near the cutting edge not the of the chord angle.

Thank you in advance, it is really quite important issue for many members of this forum.

Jan

[Herman Trivilino]

D = Stone diameter in mm
s = Thickness of the iron in mm
α = Angle setting
β = Angle deviaton from ideal

sin β = s / D x sin α

Note: I'm editing this post for clarity, but not changing the essence. All subsequent comments are still entirely relevant.

What you are calling ß is actually what Lee calls α, the angle between the tangent line and the chord. The angle between the tangent line and the back of the tool forms the edge angle, and that is the angle measured with the Angle Master.

[Jan]

Thanks for your sketch, Herman, it is helpful. 

Rolf's formula is surprisingly simple, and so I am wondering, if it is exact expression or an approximate one. The other thing I am wondering about is whether the chord is constructed for the whole thickness of the chisel or only to the midpoint of the tool. Sometimes the terms edge angle, mid angle and heel angle are used to describe the hollow grinded chisel bevel geometry.

Numerically Rolf's angle deviation beta is almost equal to the difference between the mid angle and the cutting edge angle. 

For the time being I do not have enough time to derive the Rolf's formula, but I believe it will not be too complicated.

Jan

[Hatchcanyon]

Thank you very much for the drawing. It depicts the situation exactly .

I found the formula years ago in the book "The complete guide to sharpening" from Leonard Lee (The Taunton Press 1995, ISBN 1-56158-067-8) on page 62. Leonard Lee is the founder of Lee Valley and Veritas Tools.

At this time I was more interested in sharpening by hand but this has changed considerably.

I'm sorry but I do not own a tool to measure the edge angle very exactly. The problem is its change due to the circular shape of the bevel.

Rolf

[Ken S]

Good post! Leonard Lee's sharpening book has been a staple on my bookshelf for many years. I like his accompanying DVD, also. Good sharpening advice with a sprinkling of dry humor; two thumbs up.

"It should be part of every serious sharpener's library."

Ken

[Jan]

Thanks for your prompt response, Rolf. 

Unfortunately I do not have the book  , but I am sure that other members have it and will be able to consider the assumptions under which the formula was derived. 

My understanding of the Tormek Handbook is that correct edge angle setting using the Tormek Angle Master WM-200 results in chisel cutting edge angle exactly equal to the angle set by the Angle setter of the WM-200.

Jan

[Hatchcanyon]

My understanding of the Tormek Handbook is that correct edge angle setting using the Tormek Angle Master WM-200 results in chisel cutting edge angle exactly equal to the angle set by the Angle setter of the WM-200.

Jan,

I don't think so.

The deviation from a wanted angle is a function of iron thickness. Thick irons produce large deviations. The WM 200 only sets the angle desired and does not know anything about the thickness of the iron it is rinding on.

Herman decribes the essential things. The chords angle is what is set with the WM 200 but the tangent line sets the angle of the of the bevel at the very edge.

A "dramatic " example: I own some Kirschen mortise chisels whit irons 1/2 inch thick. Trying to sharpen these irons the normal way on a desired angle of 25° leads to a deviation of 7° or a real angle of 18° only. More or less unusable. (Grinding the first millimeters behind the edge only is one solution.)

Rolf

[Elden]

Jan,

The deviation from a wanted angle is a function of iron thickness. Thick irons produce large deviations.

A "dramatic " example: I own some Kirschen mortise chisels whit irons 1/2 inch thick. Trying to sharpen these irons the normal way on a desired angle of 25° leads to a deviation of 7° or a real angle of 18° only. More or less unusable. (Grinding the first millimeters behind the edge only is one solution.)

Rolf

Rolf (Hatchcanyon),

   I have been down the path of measuring with a machinist style of protractor. As you are stating there is a deviation. However, the deviation is in the opposite direction. It has to be added instead of subtracted. There have been several discussions in regard to that here on the forum. To the best of my recollection, I do not remember anyone else actually measuring with a machinist protractor to verify Jan and Herman's statements of that being true. The protractor affirmed the truth of their statements.

[Jan]

Elden, thank you for posting your results. 

Rolf (Hatchcanyon), in the topic "hollow vs flat grinding thoughts" as reply #26 there is a statement from Stig, Tormek AB concerning the function of the Angle master. http://forum.tormek.com/index.php?topic=2413.15

Jan