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:
(http://hatchcanyon.eu/Navigation/Sonstiges/Holz/Tormek/DSC07400_9.jpg)
(http://hatchcanyon.eu/Navigation/Sonstiges/Holz/Tormek/DSC07401_9.jpg)
Chisels polished with the SJ stone
(http://hatchcanyon.eu/Navigation/Sonstiges/Holz/Tormek/DSC07446_9.jpg)
24mm chisel machined with the SG stone
(http://hatchcanyon.eu/Navigation/Sonstiges/Holz/Tormek/DSC07458_9.jpg)
Same 24 mm chisel after using the SJ stone (sorry about some blur)
(http://hatchcanyon.eu/Navigation/Sonstiges/Holz/Tormek/DSC07464_9.jpg)
(http://hatchcanyon.eu/Navigation/Sonstiges/Holz/Tormek/DSC07476_9.jpg)
Same iron other perspective
Using a paper kitchen towel for cleaning the iron invariably leaves particles on the irons surface.
(http://hatchcanyon.eu/Navigation/Sonstiges/Holz/Tormek/DSC07486_9.jpg)
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....
(http://hatchcanyon.eu/Navigation/Sonstiges/Holz/Tormek/DSC07481_9.jpg)
Douglas Fir
(http://hatchcanyon.eu/Navigation/Sonstiges/Holz/Tormek/DSC07479_9.jpg)
Damaged edge
(http://hatchcanyon.eu/Navigation/Sonstiges/Holz/Tormek/DSC07483_9.jpg)
regrinded to 30° - actually about 28°. That works well on the fir!
(http://hatchcanyon.eu/Navigation/Sonstiges/Holz/Tormek/DSC07378_9.jpg)
Grinding a short spoke shave iron
(http://hatchcanyon.eu/Navigation/Sonstiges/Holz/Tormek/DSC07575_9.jpg)
The sharpening workplace
Rolf
Sehr gut! You are up and running. Nice photos, also.
Keep up the good work and keep posting.
Ken
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 25o using the angle master you will get an edge angle of 25o on your chisel. ;)
For more information please read the topic "hollow vs flat grinding thoughts"http://forum.tormek.com/index.php?topic=2413.0 (http://forum.tormek.com/index.php?topic=2413.0)
Jan
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 (http://forum.tormek.com/index.php?topic=1620.0)
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
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
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
Quote from: Hatchcanyon on May 27, 2016, 06:32:34 PM
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.
(http://i1291.photobucket.com/albums/b553/htrivilino/chisel%20angles_zpsbuf7c7s0.png) (http://s1291.photobucket.com/user/htrivilino/media/chisel%20angles_zpsbuf7c7s0.png.html)
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
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
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
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
Quote from: Jan on May 28, 2016, 01:47:22 PM
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
Quote from: Hatchcanyon on May 28, 2016, 05:10:09 PM
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.
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
Quote from: Hatchcanyon on May 28, 2016, 12:40:38 PM
Thank you very much for the drawing. It depicts the situation exactly .
When you are using a tool to cut into a piece of wood, it's the edge angle that determines how well the tool performs. This is the angle between the two planes of steel that meet to form the edge. The angle that the chord makes with the back of the tool is far less relevant; especially for thinner tools, smaller edge angles, and larger radius grindstones. It is therefore the edge angle, the angle measured by the Tormek Angle Master, that's of primary importance. The difference between this edge angle and the angle the chord makes, what you are calling ß and Lee is calling
α, is not a measure of any "error".
Rolf's post echoed in my memories more info on edge angle reduction from the Experiments on Knife Sharpening by Verhoeven.
"The predictions of this equation are shown in Fig. A9 for the 10 inch Tormek wheels on blades having thicknesses of T = 1/8, 1/4 and 1/2 inches.
It is seen that the values of ∆β become fairly significant for common grinding conditions used on chisels, with β angles of 20 to 40 degrees and blade thicknesses of 1/8."
[and an example]
"The iron shown above has a thickness of 3.7 mm, the stone diameter measures 248 mm, the angle setting is 25°. Angle deviation comes to about 2° - resulting cutting angle = 23°."
(http://home.exetel.com.au/dropbox/edge_angle_reduction.jpg)
(http://home.exetel.com.au/dropbox/edge_angle_reduction%202.jpg)
Quote from: Jan on May 28, 2016, 12:35:04 PM
Rolf's formula is surprisingly simple, and so I am wondering, if it is exact expression or an approximate one.
I have verified that it's at least approximately correct. I'm still working on trying to prove that it's exact. No luck so far, and Lee is no help.
Quote from: Hatchcanyon on May 28, 2016, 05:10:09 PM
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.
Rolf, the WM-200 Angle Master sets the angle of the bevel at the very edge. This is what Tormek calls the bevel angle
ß. Note that in the case of a chisel or plane iron, as discussed here, it's equal to the edge angle. For a traditional knife ground on each side with a bevel angle
ß, the edge angle is 2
ß.
Quote from: wootz on May 29, 2016, 12:17:38 AM
"The iron shown above has a thickness of 3.7 mm, the stone diameter measures 248 mm, the angle setting is 25°. Angle deviation comes to about 2° - resulting cutting angle = 23°."
Ok, so let's check these values in Lee's formula. We have
D=248 mm,
T=3.7 mm, and
Θ=23°.
Thus
T/(
D sin
Θ)=(3.7)/[(248)(sin 23°)]=0.03334.
Therefore sin
α = 0.03334 and
α=1.9°. So that's a match!
Note that we still cannot tell from this whether Lee's formula is exact. The round off error could have already been present.
Vadim (Wootz),
Please purchase an inexpensive machinist square (or an expensive one if you rather) and measure the chord angle of a chisel ground on a Tormek that was set to 25° with the Angle Master. One such as shown in this link is rather inexpensive here in the USA.
http://www.homedepot.com/p/General-Tools-Steel-Protractor-17/100349259?cm_mmc=Shopping%7cTHD%7cG%7c0%7cG-BASE-PLA-D25T-HandTools%7c&gclid=CjwKEAjwg6W6BRDn6v__7vzN9QkSJAC9l9C3l5R7yevUDSjADj53hSy9F-EX8FvFEs3evBjxxoRPmBoCddnw_wcB&gclsrc=aw.ds
I believe you will find out as I did that the chord angle will be greater than 25°.
The following link records the end of my measuring experiment at that time.
http://forum.tormek.com/index.php?topic=2413.msg12078#msg12078
Quote from: wootz on May 29, 2016, 12:17:38 AM
(http://home.exetel.com.au/dropbox/edge_angle_reduction.jpg)
(http://home.exetel.com.au/dropbox/edge_angle_reduction%202.jpg)
Wootz,
Thank you very much for posting the graph and sketch concerning the reduction of the edge angle due to the grindstone curvature. They perfectly illustrate the difference in edge angles grinded flat and hollow. :)
Please let us know if a formula for Δβ is available in the quoted source.
Jan
Already quoted Stig's statement concerning the Angle Master reads:
"The angle master WM-200 is very good and are measuring the tip of the edge. It is compensated for the hollow grind. If you use a regular "angle setter" or a protractor you will find that the degree will indicate that it's not the same as the anglemaster. A protractor are not compensated for a hollow grind but for a flat surface."
In my understanding it would be more accurate to say that WM-200 is compensated for the reduction of the edge angle due to the grindstone curvature. (See the sketch posted by Wootz)
Rolf (Hatchcanyon) is correct, when he mentions "The WM 200 only sets the angle desired and does not know anything about the thickness of the iron it is rinding on."
Rolf is also correct when he says "...the tangent line sets the angle of the bevel at the very edge."
The WM-200 works in the following way: it sets the selected bevel angle for the very edge of a tool. Via the Diameter compensator the WM-200 compensates for grindstone curvature.
The WM-200 has no info about the tool thickness and so cannot do predictions beyond the very edge.
I think that Rolf started very fruitful discussion which helps to deepen our understanding of this key issue for each Tormek sharpener. The question, how was the Lee's formula derived, remains still open.
Jan
Additional facts:
Measuring the bevel angle is not that easy with relatively thin irons. As a solution working for me I used a 1/2 inch thick mortising chisel.
Draw a straight line longer than the Iron on a sheet of paper, position the back side of the tool along the line.
(http://hatchcanyon.eu/Navigation/Sonstiges/Holz/Tormek/DSC07660_9.jpg)
Aligning the backside
Use a triangle:
(http://hatchcanyon.eu/Navigation/Sonstiges/Holz/Tormek/DSC07664_9.jpg)
Triangle across the bevel
(http://hatchcanyon.eu/Navigation/Sonstiges/Holz/Tormek/DSC07665_9.jpg)
Bevel angle is 28°
With this result I set the WM 200 to exactly the same value. The iron itself is mounted into the SVD 186 jig. This is only to hold the iron statically and not intended to use it for grinding (might be possible?). Positioning the iron is done with the universal support fine adjustment.
(http://hatchcanyon.eu/Navigation/Sonstiges/Holz/Tormek/DSC07667_9.jpg)
Aligning WM 200 and the iron
And now comes the insight!
Only the edge is riding on the stone. That means the angle setting of the WM 200 is always correct. Hollow grinding doesn't lead to a decreasing angle, it produces an increasing angle!
Guys, many thanks for the comprehensive discussion. I learned a lot!
Rolf
Quote from: wootz on May 29, 2016, 12:17:38 AM
(http://home.exetel.com.au/dropbox/edge_angle_reduction%202.jpg)
Note that ß-Δß is bevel angle set by the Tormek WM-200 Angle Master. Note that the ß shown in that figure is
not the the same as the ß shown in the Tormek literature.
Quote from: Hatchcanyon on May 29, 2016, 06:34:28 PM
Guys, many thanks for the comprehensive discussion. I learned a lot!
Rolf
Rolf (Hatchcanyon), you are welcome! :)
Jan
Quote from: Jan on May 28, 2016, 12:35:04 PM
Rolf's formula is surprisingly simple, and so I am wondering, if it is exact expression or an approximate one.
The formula is exact, Jan.
Just keep in mind that the bevel angle
ß as defined by Tormek and measured on the WM-200 Angle Master appears nowhere in that formula.
sin
α =
T/(
D sin Θ).
Tormek's bevel angle
ß = Θ - α.
Quote from: Jan on May 29, 2016, 12:44:19 PM
Wootz,
Thank you very much for posting the graph and sketch concerning the reduction of the edge angle due to the grindstone curvature. They perfectly illustrate the difference in edge angles grinded flat and hollow. :)
Please let us know if a formula for Δβ is available in the quoted source.
Jan
Jan, Experiments on Knife Sharpening by Verhoeven can be downloaded as PDF from https://www.wickededgeusa.com/wp-content/uploads/2012/10/knifeshexps.pdf (https://www.wickededgeusa.com/wp-content/uploads/2012/10/knifeshexps.pdf)
See Chapter 5 on Tormek.
Quote from: Herman Trivilino on May 29, 2016, 10:13:42 PM
Quote from: Jan on May 28, 2016, 12:35:04 PM
Rolf's formula is surprisingly simple, and so I am wondering, if it is exact expression or an approximate one.
The formula is exact, Jan.
Just keep in mind that the bevel angle ß as defined by Tormek and measured on the WM-200 Angle Master appears nowhere in that formula.
sin α = T/(D sin Θ).
Tormek's bevel angle ß = Θ - α.
Thanks for your message, Herman and congratulations to your successful reverse engineering of the Lee's formula. :)
It is nice to know that the formula is valid and exact. I like simple and elegant formulas.
Jan
Thank you very much Wootz, for posting the link to the valuable study of professor Verhoeven from Iowa State University. I look forward to go through it carefully. :)
From the appendix 2, page 52 it is now clear how the parameters in the formula were defined and it is also clear that the formula is exact, as confirmed by Herman.
(http://img21.rajce.idnes.cz/d2102/11/11771/11771137_37021e568ec44478b9ce7dc74d286378/images/ExperimentsonKnifeSharpening.jpg?ver=0)
Having this sketch and explanatory text it is relatively easy to derive the formula. The back engineering task performed and reported by Herman was much more difficult! ;)
Jan
A couple years ago I tried regrinding the bevel on one of my chisels from twenty five to thirty degrees. I use this chisel for rough work and wanted to find a way to reduce the nicks. I originally planned to reshape the entire length of the bevel, but wisely stopped halfway through. I had inadvertently stumbled upon the chisel equivalent of making chef's knives into paring knives with a sandstone wet wheel.
The Tormek makes quick work of sharpening an existing bevel. Changing entire bevel angles can make quick work of reducing chisels to mini chisels with large handles. I believe there is room in Tormek technique for micro bevels.
Ken
Quote from: Hatchcanyon on May 29, 2016, 06:34:28 PM
And now comes the insight!
Only the edge is riding on the stone. That means the angle setting of the WM 200 is always correct. Hollow grinding doesn't lead to a decreasing angle, it produces an increasing angle!
Rolf (Hatchcanyon),
Thank you for the well done pictorial and verbal presentation of your journey to the culmination of your thought process!
More work on hollow grinding. As shown in an earlier posting the WM-200 gives a correct setup and the edge of the iron touches the stone first.
(http://hatchcanyon.eu/Navigation/Sonstiges/Holz/Tormek/DSC07667_9.jpg)
The edge touches first
But what happens if the iron is set to contact the stone at first in the middle of the bevel?
(http://hatchcanyon.eu/Navigation/Sonstiges/Holz/Tormek/DSC07681_9.jpg)
First stone contact of the bevel at its middle
Clearly visible - the edge and the upper end of the bevel are not contacting the stone. That means the stone will work itself into the middle of the bevel first. How about the resulting angle?
Lets ask the WM-200:
(http://hatchcanyon.eu/Navigation/Sonstiges/Holz/Tormek/DSC07682_9.jpg)
Reading is about 22°
The value corresponds nicely to Leonard Lee's formula. (6° reduction for an angle of 28°, an iron thickness of 12,8 mm and a wheel diameter of 250 mm) The bevel angle will be reduced of that amount on the edge and the same amount will be added on the farther end.
Now lets go extreme and position the iron to contact the wheel at first with the upper end of the bevel.
(http://hatchcanyon.eu/Navigation/Sonstiges/Holz/Tormek/DSC07683_9.jpg)
First wheel contact on the far end of the bevel
(http://hatchcanyon.eu/Navigation/Sonstiges/Holz/Tormek/DSC07684_9.jpg)
WM-200 reads 15°
This is a further doubling of angle reduction due to hollow grinding but is was expectable by Lee's formula. The edge would be weakened to 15° or by 12-13° On the other hand the bevel angle will increase the same amount with the first setting where the edge touches first (up to 40-41°). With a relatively thick iron this might not be desirable too. Grinding such long bevels only partially seems to be the solution.
With other words: The complete modification in angles is double the value Lee's formula predicts. The user decides how to distribute the modification, but it always will be there with the same value.
Result. The WM-200 AngleMaster can also tell about hollow grinding angles. I like the tool! ;)
Rolf