I have a tormek T7 that I bought 2 years ago. I used this machine to sharpen long and thin kitchen knives. So far I find the results very good. Recently I started to get in the knife making hobby. For my first initial offering I made two models. A small knife with a 3 inch Wharncliffe blade and a survival knife with a 5 inch drop point blade. This two knives are made in D2 steel and has a 3/16 inch thickness. The angle I choose is 30-35 degrees since this two are both sporting knives.
Now, one problem that I have noticed is at this angle the knife has a high risk of throwing back at the operator. It has happened so many times already that some times it will put a damage on the stone. When this happen, I fix the wheel with a truing tool. Is there a way to fix this problem? Am I push the blade to hard on the wheel? :'( :'( :'( :'(
Welcome to the forum!
What does the surface of your grindstone look like?
Is it smooth and even?
Are there any irregular, pitted or depressed areas on the wheel?
I had a bad grindstone that had areas that would grab a blade and pitch it back. These areas had a different color than the rest of the wheel, and became quickly pitted even after dressing the grindstone.
When a blade would hit those areas, it would grab the blade and pitch it back. Very scary with a big, sharp knife!
Can you feel the stone grab the blade at different areas as it revolves?
Tormek, to their credit, replaced the grindstone with a new one and the problem went away.
That may or may not be what is happening for you. I was not trying to sharpen @ 35 degrees.
One option is to sharpen horizontally with the rotation of the grindstone rather than vertically, into the grindstone. That will probably resolve your problem, but there may or may not be some other issue happening.
Welcome to the forum! :)
I fully agree with Grepper, the reason of your issue is not clear, but sharpening away from the edge may resolve your problem. When sharpening high quality steel blade, like your D2, I always try to do it with little pressure.
The other thing I would like to mention is your blade thickness. The Tormek Knife jig works symmetrically for blade thicknesses from 2 to 3 mm (1/10" with some margin). For your blade thickness 3/16"= 4.8 mm you cannot expect that after turning the knife jig upside-down you will get exactly the same bevel angle as on the first side. You can correct it with the adjustable stop.
Good luck!
Jan
(https://s14.postimg.org/7xwisxdv5/image.jpg) It usually grabs the knife back when it hits the " A " portion of the blade . At the " B " portion it is fine. This usually happen at 30 degrees up. The higher the degree the most likely it will grab :'(
As mentioned above, use as little pressure as possible. If you increase it the risk of the knife digging into the stone is quite severe.
Have you done some experimenting on fitting the jig in the second position and turn the T-7 around so the stone rotates in the opposite direction?
Some times when I resharpen knives that has been broken in two and big amounts of steel needs to go I rotate the machine so I can apply a greater pressure and lower the risk of kickback from the knife.
Quote from: Magnus Sundqvist on October 07, 2016, 10:55:51 AM.
Have you done some experimenting on fitting the jig in the second position and turn the T-7 around so the stone rotates in the opposite direction?
Is it done on this position? How do I measure the angle?
(http://i5wcpsycgxhp7wi5.zippykid.netdna-cdn.com/wp-content/uploads/2014/06/photo-60.jpg)
I saw this one sharpening on reverse...
https://www.youtube.com/watch?v=BKjMilG9LWY
Yes, the position is correct. The angle is set with the AngleMaster WM-200. It works for both grinding directions. ;)
Jan
I will try it tomorrow and see how it works :-)
Quote from: angpanday on October 07, 2016, 06:03:24 AM
Now, one problem that I have noticed is at this angle the knife has a high risk of throwing back at the operator.
Are you forgetting to halve the angle? For example, if you want a 40° edge angle on a typical knife you'll sharpen each side at a bevel angle of 20°.
Quote from: Herman Trivilino on October 07, 2016, 10:32:11 PM
Quote from: angpanday on October 07, 2016, 06:03:24 AM
Now, one problem that I have noticed is at this angle the knife has a high risk of throwing back at the operator.
Are you forgetting to halve the angle? For example, if you want a 40° edge angle on a typical knife you'll sharpen each side at a bevel angle of 20°.
I was wondering that and if you were lifting the handle or tilting the handle.
https://www.youtube.com/watch?v=fYURcwkKGPs
QuoteI was wondering that and if you were lifting the handle or tilting the handle.
https://www.youtube.com/watch?v=fYURcwkKGPs
I just lift the handle.
QuoteAre you forgetting to halve the angle? For example, if you want a 40° edge angle on a typical knife you'll sharpen each side at a bevel angle of 20°.
Isn't it that you only half the angle on thin knives with a small bevel? My knife is 3/16 thick and the first bevel is wide....I don't divide the angle setting.
https://www.youtube.com/watch?v=BKjMilG9LWY
I did the horizontal sharpening today and so far the result was okay. I was able to sharpen the knife at a 30 degree angle and the result was okay. ...It was razor sharp :-)
Is there any disadvantages when sharpening on the horizontal position?
Angpanday
You raise a most interesting point. The Tormek handbook is probably one of the most comprehensive in the industry. That said, however, for all that is covered, much is either not covered or only sparsly covered.
The issue of grinding direction is mentioned in a general sense on page fifteen of the handbook. You have posted a link to the best source I know of for using the horizontal position with the wheel moving away from the knife edge, Steve Bottorff. Steve and I both live in Ohio (several hours apart). I have been most fortunate that Steve has taken me under his wing and taught me a lot about knife and scissor sharpening. Inspired by Steve, I generally use the horizontal position. I have not noticed a problem with grinding speed, and I like the feeling of having more control. In fact, a lighter touch with the horizontal position actually cuts faster with the SB-250 blackstone.
The handbook, in my opinion, seems to favor one method of working. It mentions the possibility of other methods. There may be a belief that showing one good method simplifies things for beginners.
I also suspect the vertical position evolving as the preferred method may have been influenced by the fact that it pointed away from the demonstrator and toward the audience. Unconsciously, this may have influenced the handbook author and video presenters.
I use the handbooks (I have several editions, including a very early edition.) for reference. I use these as working tools. I highlight, underline and make notes. They are no longer pristine collectors' items. I think my additions make them more useful, if not more valuable. I am grateful for all the good information in the handbook, and hope it will be expanded in future editions. The Tormek is continually evolving. Newer jigs have both improved its efficiency and increased its scope. The handbook and company videos have not kept pace with these innovations at this point.
Thanks for asking your question.
Ken
Thanks Ken :-) I really like the tormek, It is the most versatile and well built sharpening system in the market today. However, there are still a lot to be discovered to maximize its use ;) specially in sharpening knives.
I agree, we have not reached the full potential of the Tormek. Even in the few years (since 2009) that I have used a Tormek, the developments have been amazing. The EZYlock stainleaa steel shaft; the SB and SJ grinding wheels; the DBS-22 drill bit jig; T4; T8; several redesigned jigs. Development is ongoing.
Some of the advances in knife sharpening that you might envision in the future are already here. Google Steve Bottorff and Robin Bailey. Both are forum members as well as very experienced knife sharpeners and teachers. Robin has designed and manufactured a well designed oversized universal support. Steve has written a book on sharpening and has produced an excellent DVD package. He has generously posted some parts of his DVD on the forum and on you tube.
I think you will be pleasantly surprised to read about some of the knife jigs and techniques post be forum members. Ideas get bounced around and improved by various members.
Please feel free to learn from our ideas and add your own thoughts.
Ken
Quote from: angpanday on October 09, 2016, 08:57:28 AM
I don't divide the angle setting.
That's the source of your problem.
Quote from: angpanday on October 09, 2016, 09:12:26 AM
I did the horizontal sharpening today and so far the result was okay. I was able to sharpen the knife at a 30 degree angle and the result was okay. ...
If you set the Angle Master at 30° and sharpened both sides, you have an edge angle of 60°. That's appropriate for a cleaver or machete.
QuoteIs there any disadvantages when sharpening on the horizontal position?
It doesn't remove steel as fast, but many prefer it because you have more control. I prefer to use a homemade platform jig and sharpen towards the edge.
Herman's small knife tool started out as a better way to handle small knives than the Tormek platform jig. In fairness to the Tormek platform, it was never designed for small blades. The constraint is the width of the jig. It is wide enough that one side of the knife can not be ground full length. Herman's jig is the width of the grinding wheel, so it works well with both sides.
Herman based his design on the platform with the scissors jig, which sits lower than the platform jig. The jig is still usable with scissors. Herman has sharpened a machete with his jig. Its use extends far beyond small knives.
I think one of the small knife jigs should be part of a well equipped sharpener's kit. (For the record, I feel the same way about Tormek's small blade tool, which works differently.)
Ken
Angpanday, I think you are in a difficult situation because:
1) the knife blade is too thick for the knife jig and
2) the knife blade tappers towards the edge. ???
The hardware solution of the issue ad1) was described by Wootz. This issue has to be resolved because such a thick knife is not correctly centred in the knife jig.
The solution of the issue ad2) is in your hands without any hardware changes. When setting the desired edge angle using the AngleMaster whose setter is touching the primary bevel, you have to correct for the tapering angle of the blade.
Because your knife is thick the angle of your blade (primary bevel edge angle) may be some 20° or more. If your desired edge angle is 30° you need to set 30° - 20° = 10° on the AngleMaster. ;)
In my understanding until now you were ignoring the blade tapper and so unintentionally sharpening an edge angle 30° + 20° = 50° which could resulted in throwing the knife back at the operator when sharpening towards the edge.
Jan
P.S.: I have assumed you set the edge angle as shown in the handbook picture.
Jan, yes I measure the angle from how it is shown on the book. From my observation using the angle master. If I set the angle at 25 the knife will not throw back at me, but once I go above 30, it has that tendency to happen. The 30 degree angle will show a nice looking cutting edge ( around 1 to 1.5 mm ). Below 30 will show a much wider cutting edge ( 2-3mm ) which is not appealing when you plan to sell the knife :-(
The reason why the cutting edge is wide for angles below 30° is too small angular difference between primary and secondary edge angle.
Imagine that your primary edge angle is some 24° and you set the secondary bevel angle for 26°. Than you will get wide cutting edge. When you enlarge the secondary bevel angle to 28° you will get significantly narrower cutting edge. ;)
Good luck! Please keep us posted. :)
Jan
Quote from: Jan on October 11, 2016, 05:27:43 PM
Because your knife is thick the angle of your blade (primary bevel edge angle) may be some 20° or more. If your desired edge angle is 30° you need to set 30° - 20° = 10° on the AngleMaster. ;)
In my understanding until now you were ignoring the blade tapper and so unintentionally sharpening an edge angle 30° + 20° = 50° which could resulted in throwing the knife back at the operator when sharpening towards the edge.
Jan
(http://www.tormek.com/images/jigs/svm45/edge_angles_knives_en_530.png)
Your formula is very confusing????
I also use the Tormek T7 to sharpen thin kitchen knives ( 2-2.5 mm ). The angle I use 25 degrees. With that angle from the Angle master it will create a nice cutting edge. Around 2mm wide on both side.
Now with the thick 3/16 blade. At 30 degrees it will create a 2mm wide cutting edge. However, it will have an unbalance cutting edge. One side will be 2mm the other will be around 2.5mm . Now if I do the mods on the jig I think it will fix that problem.
If I will follow your formula and set it to 30-20 = 10 degrees on the Angle master. How big will the cutting edge be 5mm? or even more...
Yes, the formula is confusing at first glance. The formula is valid when the AngleMaster setter is touching the wide primary bevel, shown blue in the sketch below. It was my attempt to explain your issue. ;)
If the AngleMaster setter is touching the secondary bevel, shown red, than no correction is necessary. It is a standard situation described in the handbook. :)
Jan
Except for agreeing with all above I would add my experience.
D2 and alike hard metals have to be handled with very light pressure and slow move. Otherwise the metal will cut into the stone when used against the wheel. I prefer this method as u can see the water getting up on the blade and know that you are parallel to the stone. Also the sharpening position works better for me and it's easy to leave the knife with the jig when measuring the angle with the WM-200 that I use frequently.
Don't forget to deduct the first bevel angle when you measure with the WM-200 as it is optimized for straight primary bevel.
I have never worked with D2 steel. I have found that I have more efficient grinding with HSS by using a lighter touch. (I usually grind away from the tool, too.)
Some experimenting may pay good dividends.
Ken
Quote from: Jan on October 12, 2016, 06:37:26 PM
Yes, the formula is confusing at first glance. The formula is valid when the AngleMaster setter is touching the wide primary bevel, shown blue in the sketch below. It was my attempt to explain your issue. ;)
If the AngleMaster setter is touching the secondary bevel, shown red, than no correction is necessary. It is a standard situation described in the handbook. :)
Jan
Jan, if there is already an existing cutting edge on the knife. I think the best thing to do is just regrind the existing bevel. Now from the existing cutting edge I will be able to know what angle it already have.... then from there I will just chase it to the desired angle.
I agree with you, Angpanday! :)
I personally use for setting the cutting edge angle the kenjig concept, which is based on geometrical relations, and which is immune to blade tapering problems. It works also fine when the secondary bevel is very narrow. ;)
Jan
Thanks, Jan. It means a lot to me that you, with your formidable math background, recognize my practical little tool. :)
Ken
Quote from: angpanday on October 12, 2016, 02:53:41 AM
Jan, yes I measure the angle from how it is shown on the book. From my observation using the angle master. If I set the angle at 25 the knife will not throw back at me, but once I go above 30, it has that tendency to happen.
If you set the Angle Master at 30° and sharpen both sides, you have an edge angle of 60°.
In Reply #22 you posted a chart showing edge angles. The largest is 40°, which is appropriate for a butcher knife.
Why are you sharpening your knife at 60°? That's an appropriate edge angle for an ax, machete, or cleaver.
Quote from: Ken S on October 13, 2016, 02:01:20 AM
Thanks, Jan. It means a lot to me that you, with your formidable math background, recognize my practical little tool. :)
Ken
Honour to whom honour belongs, Ken. You have recognised the potential of Ton Nielsen paper Grinding Angle Adjustment for our forum and suggested your practical little tool – the kenjig. :)
This geometrical concept removes all difficulties with setting an edge angle for thin knives and knives with tapered blades provided the blade is properly centred in the jig. ;)
Jan
Thanks for your kind words, Jan.
My original motivation for the kenjig was to assist an older member who was having difficulty using the Anglemaster because of his eyesight. Improving set up time has been a nice by product. The Anglemaster, while an essential accessory, can be difficult to use in poor light and with small bevels. Unless some sort of presets are used, it also must be used with every tool to be sharpened. This can be tedious.
The admonition in the handbook to use good light should be in large bold type! I experienced this epiphany years ago when I set up my Tormek on a Workmate outside. The light was bright and soft that day. I was on the north side of my primitive garage/workshop. I was astounded how much easier the Anglemaster was to see. Since that day, I have strived to improve the task lighting in my new shop.
The difficulty with small bevels is improved with a black marker. It can be eliminated by using a substitute target. I made up a substitute target out of a rectangular piece of steel 25x40x3mm. Grind a single bevel from the long side to less than fifteen degrees. For greatest accuracy match the ideal thickness of the jig jaws (2.5mm). Measure the protrusion of the knife in your jig. Replace the knife in the jig with the steel substitute target set to the same protrusion. You now have an easy to measure large, flat target.
Standardizing the Distance between the universal support and the grinding wheel AND the Protrusion of the tool in the jig from the universal support has several advantages:
1) It simplifies sharpening for beginners and infrequent users. This allows the user to focus on the actual grinding.
2) It eliminates the tedium of continual remeasuring with each tool to be sharpened.
3) It makes set up very fast for busy sharpeners.
4) When Prutrusion is carefully chosen (I chose 139mm), it allow very quick changes between knife sizes (paring to chef to slicer) with little or no jig adjustment and no Distance changes. The Distance remains constant. The Protrusion needs only occasional tweaking to bring it to 139mm. (I use three jigs and a small blade tool for efficiency. I could do it all with just one regular knife jig.)
Again, thanks for your kind words, Jan. You fully understand the process.
Ken
Ken, you are welcome! :)
For your single bevel substitute target I would recommend a thickness of 1.25 mm = 0.05" which would guarantee that its edge is centred with respect to the jig axis.
Jan
P.S.: Your 3 mm thick substitute target will not cause a large error in edge/bevel angle but it is breaking the knife jig flip symmetry. ;)
A most interesting thread !!! Apparently, I've been doing this all wrong. Several times in this thread there has been reference to "halving the angle" as measured on the Angle Master for a double bevelled blade. I sort of missed that the first time around. I prefer using the written manual for these things, and upon review, I cannot find any reference to this concept in the owner's manual. They use a single bevelled tool as the primary object of the discussion.
I then went back to the video and, sure enough, right at the very end, they briefly refer to this concept.
Am I correct that this is not mentioned in the written word (owner's manual)? If I am in error, I would appreciate being straightened out. If I'm not, this definitely needs to be elaborated on in the owner's manual. I can't find it, but HEY, I'm old and it's early.
Anyway, I think I have it now. When determining the blade angle of a double bevelled blade, you set the Angle Master at 1/2 of the desired final angle. Someone please confirm for all of posterity. Thanks. Great thread. R
Apologies ...... I just found one brief reference to this (see previous post) on page 55 of the Owner's Manual, under the Knife Jig SVM-45 chapter, under "thin knives". As this appears to be a fundamental concept for the use of this machine, I still feel it is under emphasized. But that's just me. Anyway, I think I have my answer. I've been doing this all wrong. It's hard to be cool when you don't read the fine print !!! Things should be more better from now on. R ;)
The "halving the angle" method on p.55 is used for thin knives and also for knives with small bevels where the bevel is too short for alignment of the angle setter. The "halving the angle" method works as described in the handbook when the sides of the blade are parallel, but it requires correction when the blade tappers towards the edge. ;)
Jan
Thanks, Jan. This is a bit ahead of my learning curve right now, but at least I'm aware of it. I'll try and read up on it some more. Thanks again. R
Quote from: Jan on October 13, 2016, 02:32:26 PM
Ken, you are welcome! :)
For your single bevel substitute target I would recommend a thickness of 1.25 mm = 0.05" which would guarantee that its edge is centred with respect to the jig axis.
Jan
P.S.: Your 3 mm thick substitute target will not cause a large error in edge/bevel angle but it is breaking the knife jig flip symmetry. ;)
Jan,
You are correct. The substitute target works best if the thickness is on the center axis of the knife jig, 1.25mm. That was my intention from the start. Thanks for assisting my math.
Rem,
I think we can all benefit from a quiet morning or afternoon with an insulated mug of coffee or tea, a highlighter, a dark pencil, and the Tormek handbook. I try to do this periodically, and have benefitted everytime. I will continue to to this.
Unfortunately, we have no guided path for the learning curve. An indepth basic training video from Tormek would be a great help. The top email on the Tormek General subforum was my attempt to do this. The topic grew too much. I still think a 3/4" chisel is the best training tool to learn the basic Tormek, even if the user never intends to sharpen chisels. The chisel is a great trainer. Most of the initial difficulties we all experience with the Tormek seem unnecessary to me with some good training. Hang in there. You will soon be doing fine.
Ken
Quote from: Rem on October 13, 2016, 03:48:37 PM
Thanks, Jan. This is a bit ahead of my learning curve right now, but at least I'm aware of it. I'll try and read up on it some more. Thanks again. R
Rem, I think that being aware of certain pitfalls is the right approach. :)
It is not good to study in advance all possible future difficulties. "For everything there is a season, and a time for every matter under heaven: ..."
Jan
REM,
This is why I still recommend JF video's, even for a new Tormek owner (T-8). The tool may have changed a bit, but what he teaches is technique and he covers things so well, that stuff will get missed the first time viewing. I watched it the first time, and then the first time I went to do a knife, I had the jig and knife with me, and caught his video, telling to put the edge of the jig, parallel with the edge of the blade, NOT the knife back. Makes a world of difference.
Guys, it is way easier to set grinding angle by the Universal Support height than with the WM-200 AngleMaster.
As a matter of fact, I haven't used the AngleMaster since I developed a computer script for this.
And since you are reading this you also have a computer and can use this script.
Using this method you needn't bother about the blade taper.
The method was elaborated here http://forum.tormek.com/index.php?topic=2969.0 (http://forum.tormek.com/index.php?topic=2969.0)
Despite the topic caption, you can use it to set a desired grinding angle even if you use only one grinding wheel.
Rather than reading through the lengthy concept, just copy the script from that thread to the Notepad on your PC, save, and change the file extention from .txt to .vbs
Double click to run, and follow the prompts to get the Universal Support height.
For a double-bevel knife the "target grinding angle" is your desired knife edge angle divided by 2, e.g. to get a 30 degree cutting edge, the grinding angle is 15 degrees per side.
The script will calculate the Universal Support height from the Tormek case top to the top of the Universal Support bar for a given edge angle.
Then set the US height with the help of a callipers depth probe, or a combination square.
(Note that constants in this script are for T7. For T2000, T4 and T8 you have to measure and edit values of the ConstantHorizontal and ConstantVertical.)
I validated this method with laser goniometer on so many custom knives... you can trust it.
T7 has its peculiarities and limitations in knife sharpening, but all have been addressed in this forum; older threads are well worth studying.
Yes, the Wootz approach is another geometrical method to set an edge angle. I have tested it carefully this spring and can confirm that it works correctly. It is immune to blade taper problem. I can definitely recommend it. :)
From the geometrical point of view it is another successful application of the cosine rule to Tormek grinding geometry. Wootz approach is based on setting the edge angle through the USB height over the Tormek housing while the kenjig approach is based on setting the edge angle by the distance between the USB and the grindstone *. Both methods depends on the grindstone radius. ;)
There is only one edge angle setting approach which does not depend on the grindstone radius – the modified TTS – 100 jig. Currently it exist for a predefined set of bevel angles and fixed protrusion 139 mm.
http://forum.tormek.com/index.php?topic=2639.30
http://forum.tormek.com/index.php?topic=2639.60
Jan
* P.S.: The kenjig concept is based on the original Dutchman approach which involves small approximation concerning the way we measure the distance between the grindstone and the USB.
Wootz approach is not burdened by this small approximation. For this reason Wootz script provides even more accurate results than the Dutchman tables. :)
Quote from: Jan on October 13, 2016, 03:38:00 PM
The "halving the angle" method on p.55 is used for thin knives and also for knives with small bevels where the bevel is too short for alignment of the angle setter. The "halving the angle" method works as described in the handbook when the sides of the blade are parallel, but it requires correction when the blade tappers towards the edge. ;)
Regardless of the method used, the shape of the blade, or the thickness of the blade, the bevel angle will be half the edge angle on any conventional knife that is sharpened on both sides.
Quote from: wootz on October 14, 2016, 05:51:48 AM
Guys, it is way easier to set grinding angle by the Universal Support height than with the WM-200 AngleMaster.
As a matter of fact, I haven't used the AngleMaster since I developed a computer script for this.
And since you are reading this you also have a computer and can use this script.
Using this method you needn't bother about the blade taper.
The method was elaborated here http://forum.tormek.com/index.php?topic=2969.0 (http://forum.tormek.com/index.php?topic=2969.0)
Despite the topic caption, you can use it to set a desired grinding angle even if you use only one grinding wheel.
Rather than reading through the lengthy concept, just copy the script from that thread to the Notepad on your PC, save, and change the file extention from .txt to .vbs
Double click to run, and follow the prompts to get the Universal Support height.
For a double-bevel knife the "target grinding angle" is your desired knife edge angle divided by 2, e.g. to get a 30 degree cutting edge, the grinding angle is 15 degrees per side.
The script will calculate the Universal Support height from the Tormek case top to the top of the Universal Support bar for a given edge angle.
Then set the US height with the help of a callipers depth probe, or a combination square.
(Note that constants in this script are for T7. For T2000, T4 and T8 you have to measure and edit values of the ConstantHorizontal and ConstantVertical.)
I validated this method with laser goniometer on so many custom knives... you can trust it.
T7 has its peculiarities and limitations in knife sharpening, but all have been addressed in this forum; older threads are well worth studying.
So you measure to the center of the support bar, or the bottom or top of the support bar?
The calculated Universal Support height is in mm from the top of the support bar down to the housing.
Quote from: Herman Trivilino on October 15, 2016, 03:30:22 PM
Regardless of the method used, the shape of the blade, or the thickness of the blade, the bevel angle will be half the edge angle on any conventional knife that is sharpened on both sides.
Herman, considering a blade in Tormek knife jig, than your statement is correct, if the blade thickness is circa 2.5 mm. :)
If the blade is thicker or thinner than 2.5 mm than the knife jig is not symmetrical with respect to upside-down flip. This results in asymmetrical bevels with slightly different bevel angles β1 and β2. The edge angle is the sum of β1 and β2, but in this situation we cannot say that the bevel angle is the half of the edge angle. ;)
The unpleasant think is, that bevels asymmetry is often visible at the first glance, as described by Wootz. Fortunately Wootz suggested how to overcame this difficulty. :)
Jan
Quote from: Jan on October 15, 2016, 06:48:45 PM
If the blade is thicker or thinner than 2.5 mm than the knife jig is not symmetrical with respect to upside-down flip. This results in asymmetrical bevels with slightly different bevel angles β1 and β2. The edge angle is the sum of β1 and β2, but in this situation we cannot say that the bevel angle is the half of the edge angle. ;)
I make no reference to the Tormek knife jig, Jan. If one is not careful, regardless of the jig or method used, it is possible to come up with unequal bevel angles. Some exotic knives are perhaps intended to be sharpened in this way. But a conventional knife has equal bevel angles on each side, and thus the bevel angle is half the edge angle.
When using any jig, measuring method, or sharpening tool, there are shortcomings to be overcome. Getting bevel angles equal on both sides of a knife using the Tormek knife jig is an example. Regardless, once you accomplish the task, the bevel angle is half the edge angle.
I appreciate the fine work done by this forum to raise the standard of knife sharpening excellence. It is valuable and remarkable.
I would also like to point out that using standard issue Tormek equipmennt and methods will consistently produce excellent sharpness in a cost and time effective manner. A busy sharpener, while being aware of such advanced techniques, would not reasonably be expected to produce such sophisticated edges on a day to day basis at moderate prices. However, for those knife users and collectors who appreciate (and will pay for) the very best, the advanced techniques developed and advocated on this forum are sure to please.
Ken
Quote from: Herman Trivilino on October 16, 2016, 11:14:09 PM
I make no reference to the Tormek knife jig, Jan. If one is not careful, regardless of the jig or method used, it is possible to come up with unequal bevel angles. Some exotic knives are perhaps intended to be sharpened in this way. But a conventional knife has equal bevel angles on each side, and thus the bevel angle is half the edge angle.
When using any jig, measuring method, or sharpening tool, there are shortcomings to be overcome. Getting bevel angles equal on both sides of a knife using the Tormek knife jig is an example. Regardless, once you accomplish the task, the bevel angle is half the edge angle.
My laser goniometer measures the bevel angles with an accuracy better than 1° so I know how often the bevel angles are different, even with new blades. ;)
Even when sharpening a knife, which thickness is suitable for the Tormek knife jig, we can get unequal bevel angles. It is often in the case when we are grinding one side until burr forms but on the other side, where the burr appears quickly, we do not grind enough to get a symmetrical edge. Based on my experience it is more often when sharpening large edge angles (40°).
To minimise the asymmetry I frequently flip the jig upside-down. In my understanding in this way less steel is removed to get a sharp edge.
Jan
P.S.: Dotted area in the picture A shows the steel removed in the when grinding one side until burr forms. Dotted area in the picture B shows the steel removed when flipping the jig frequently.
Quote from: Jan on October 17, 2016, 10:53:22 AM
Even when sharpening a knife, which thickness is suitable for the Tormek knife jig, we can get unequal bevel angles.
Of course we do. And even when the bevel angles are the same, that's no guarantee that the bevel width is the same on both sides because the edge is not always centered on the blade.
Regardless, if the bevel angles are equal, then the bevel angle is half the edge angle.
The attached sketch shows a blade with different bevel angles β1, β2. The edge angle α = β1 + β2.
The half of the edge angle has no relevant meaning in this case. May be it was the desired bevel angle.
Example: If β1 = 24°and β1 = 16° then α = β1 + β2 = 24° + 16° = 40° and α/2 = 20°.
Jan