I have sharpened two of my kitchen knives (8" chef and 6" slicer) on my Tormek.Both easily caught on my thumbnail and cut paper.
Both failed to function properly on my cutting board.
Ron Hock addresses the problem in his sharpening book. Leonard Lee and Steve Bottorff do not. The Tormek Handbook does not include it. Not even Jeff's otherwise well done knife demo video mentions it. (Sorry, Jeff.)
The problem is quickly and easily diaganosed. The knife is held with the cutting edge against the cutting board. The blade is allowed to rock back and forth. Any light shining through between the edge and the cutting board indicates a hollow spot in the blade. That part of the blade will not cut completely; things like green onions will not be cut through.
Such a knife will probably be returned to the sharpener as unsatisfactory or taken elsewhere.
The problem is the curve of the blade has been compromised by incorrect sharpening. This creates the flat or hollow spot. The bolster may also need to be ground back.
I followed Ron Hock's suggestion of repairing the first knife using a belt grinder. This method is quite satisfactory. I repaired the second knife (with less of a problem)using my Tormek. I am not an experienced knife sharpener. I consider my Tormek repair to be barely satisfactory and somewhat hit or miss.
I believe the Tormek is capable of handling this problem better in more experienced hands. I would welcome suggestions. (A more in depth knife sharpening video would be most welcome.)
I believe mastering this problem is essential for anyone who wishes to sharpen kitchen knives for professionally, as a restaurant owner, or for a home kitchen.
Please help.
Ken
I believe this issue has been discussed in a different context here in the forum.
The general issue, to my way of thinking, is the reshaping of the edge. This comes up when, for example, the tip of a knife has broken off, or as you mention here in this thread Ken, there's a section of the edge that's concave.
The easiest way to fix it is to reshape the edge by grinding at an edge angle of 90o in the places where it's needed. Then sharpen as usual.
The other comment I have is that the problem you mention, Ken, may not be noticed by people who use a slicing motion rather than a rocking motion. As I recall Ron Hock mentions this, too, in his book.
Herman, I will check my copy of Ron Hock's book about slicing instead of rocking.
I did a forum search of "broken tip". The only post which popped up was your last response. My point was that the solution to the blade curve problem shouldn't be something buried in a somewhat related post which does not emerge from a simple search. The Tormek related media make knife sharpening look like zip zip, and you're done. That's true with a new knife or with one which has been very carefully sharpened in the past. That leaves a lot of unprotected territory. If the Tormek is designed and marketed as a tool for the sharpening professional, and I believe it is, than the training should cover such things.
This post is mostly an extension of my belief that Tormek manufactures a fine product, but does not fully support the purchasers with proper training options. From time to time, we read posts by new or prospective buyers who plan to start a sharpening business. Someone who sharpens kitchen knives professionally should not ever deliver a knife which can't cut properly.
Ken
Sharpening knives of any kind is certainly an interesting subject of which I know very little about. I can understand that there are many different types of edges for different types of knives. I sure would like to learn more about them and how they should be sharpened on the Tormek.
If I needed to re-true a knife edge, I would probably skip the electrics (unless it was tremendously out of shape) and use a bastard file with the knife chucked in a vise. I'd think this would afford greater control and result in removing the least amount of steel necessary so as to preserve the life of the tool.
At the 21:30 mark in this video, you can see an example of using a file for re-shaping, but on an axe. I've used this method and can tell you it will re-shape an edge in mere seconds.
https://www.youtube.com/watch?v=Xz3rs-eaN3E
Having said that, I've been looking very hard at how to justify a KMG belt grinder lately. :)
Good thought, Mike. In truth, I have a large drawer in my mechanic's chest dedicated to files. The mill files get used a lot for all sorts of utility duty. They have never let me down.
Ken
Quote from: Ken S on August 10, 2013, 10:39:51 PM
I have a large drawer in my mechanic's chest dedicated to files.
That's the best tool to use to make sure the blade on your kitchen knife is everywhere convex. Once that's done you can take it to the Tormek and get it sharp.
Having used the HK-50 now to sharpen dozens of knives I think it far better suited to the task than any method I've tried.
My final modification was to add a piece of adhesive backed felt to the surface. The thinnest I could find was also the cheapest and available any place where they sell craft and hobby supplies.
KSMike, thanks much for that link. Very interesting and I learned a lot from it. At my age I'm not too interested in using axes, but the video answered a lot of questions about axes that I have long wondered about, but maybe not enough to actually search the net. I did split green logs earlier with axe and wedges, which I learned from a green woodworking book by Mike Abbot, and English woodworker. I was surprised at how easy it was to do, and I got a lot of good turning pieces that way.
You're welcome Mike, I'm glad you enjoyed it. I never had the slightest interest in axes until someone else posted that video a couple of years ago. I was fascinated by the history of the axe and the process of maintaining them. I've used it as a guide to re-hang a double bit of my own, and have a new appreciation for the tool. I even had a chance to put my double bit to use not long ago when I got my chain saw stuck while felling a mature pear tree in my yard.
I lived on my grandparents farm in Minnesota for a year during WWII when I was five years old Mike. All of the men in the family except my uncle who had health problems was in the military. My job was to split firewood for the wood stove in the kitchen. Thinking back, it must have been a pretty small axe considering that I could use it. The wood was Birch from our own woods, and it was probably only about 4" in diam. That stove did all the cooking and baking and also heated the whole house. I can't remember seeing the axe sharpened, but we had a big stone sharpening wheel not far from the front door, and the axe always worked well for me, so I guess my uncle kept it sharp, or at least sharp enough. I didn't mind that chore, as I thought it was fun and it made me feel useful.
I'm no regular user of the ax, but I do know that a splitting ax doesn't need to be anywhere near as sharp as a felling ax.
I learned a lot watching that video and found it very interesting.
Mike, I suspect that during a Minnesota winter, they were glad to have anyone split as much wood as they were able!
"Any light shining through between the edge and the cutting board indicates a hollow spot in the blade. That part of the blade will not cut completely; things like green onions will not be cut through."
Use less time and pressure in the middle of the blade. Requires some practise but then the edge will have a perfect line.
I bought some expensive Japanese knives that came with an convex edge. They were sharp but my wife asked me to sharpen them after 5 days. And off course i did.
On those knives its impossible to feel any difference from convex to concave. I have some other good knives that came with a concave edge and all I do with all my knives is sharpening once a year and honing 2-3 times a year.
In my high school days, I used to work in a delicatessen. They were kind of famous for their health salad and as a result, they made mountains of it.
Once a week, a grinder would come with a set of sharp knives and collect the dull ones. When he came, the cook would pounce on him and check all the chef's knives to make sure there were none with a concave edge. If she found one, she's read him the riot act in German, pointing to the space between the middle of the blade and the cutting board insisting he take the knife back out and regrind it. The grinder was Italian but he got the message loud and clear. He would resharpen the offending knife and it only happened a few times in the time I worked there.
Very often, when I would be eating lunch in the kitchen, Tessie would be making health salad. She was like a machine the way she could chop everything into quarter inch pieces and made it look effortless. The action was half rocking and half forward motion and she could do it all day.
I always think of Tessie when sharpening a knife.
Good thought, Stig. Thanks; I will work on it. I do think it would be valuable to keep a straight piece of wood near the Tormek to check the edge curve of kitchen knives.
Funny story, Koolingit! It reminds me of growing up in New Jersey. Good for Tessie! We need more Tessies to keep the knife sharpeners honest (and knowledgeable).
Ken
Once the edge becomes convex it's very difficult to straighten it back out without a file. On the other hand, once the concave shape has been established, Stickan is correct in that if you're careful to not spend too much time on any one spot it'll stay convex.
The moral of the story is sharpen it correctly from the start.
Ken
I've found reprofiling a convexed blade to be flat a frustrating experience and was actually going to post here and ask if anyone is good at it.
On the T7 I've tried pressing harder and/or just spening more time on the on either side of the convexity (call it the "high" parts), but that never worked very well. I'd end up with an uneven bevel and when I continued sharpening the convexity returned.
I've used a file to flatten the blade by just removing high parts. That did not work so well either because as the now square edged high parts got sharpened, so did the convex part, and so the convexity returned. Very frustrating.
The width of the Tormek wheel, about two inches, makes this more difficult for me on knives where the convexity starts less than that distance away from the bolster. I find it extremely difficult, if not impossible to sharpen only using half the width of the wheel.
I think what you have to do is to flat file the entire length of the blade to the same dulness or in other words the same cutting edge thickness. That way when you resharpen, the entire edge sharpens at the same rate. I've done this, and it works.
I suppose that there might be some way to do it using the edge of the wheel, or maybe the rounded edge of the wheel?
I suspect the correct way to do it is to file the entire edge to the same flatness and then resharpen.
Maybe I just don't know how to do it, and/or it requires practice, but completely resetting the edge worked for me.
Quote from: grepper on August 13, 2013, 07:37:13 PM
The width of the Tormek wheel, about two inches, makes this more difficult for me on knives where the convexity starts less than that distance away from the bolster. I find it extremely difficult, if not impossible to sharpen only using half the width of the wheel.
I don't understand this part. If the first inch or two of the blade next to the bolster is straight, just keep it straight. If it's concave you have to grind away the edge near the bolster. Removing some of the bolster itself will likely be necessary.
As to the other problem you mentioned about having to spend more time on the parts of the edge that you ground flat, well, if you watch what you're doing closely with good light I don't see it as a problem. I suppose you could use a marker to color the knife edge and make sure that you grind into the colored portion only in places where the edge was flattened with the file.
I guess the trick is to make sure the convexity is large enough that you reduce the risk of making it concave.
And yes, Ken, it's best to not ever end up with a concave edge to begin with, but sometimes we inherit them. ;)
Yup. I understand what you are saying Herman. In theory it seems very simple. Grind on the areas that are not concave.
Where I had problems was when the part that was not concave only went half way across the wheel. In theory you could just lay the blade across the wheel and it would only remove steel from the part that was not concave. Should work.
What happened to me several times was that as the part that was not concave was ground down very close to the part that was concave, the wheel started hitting the concave part too, thus maintaining the concavity.
I suppose it's what you suggest, that I just need to pay closer attention, take more time and practice at it. Nonetheless it gave me problems on several knives.
I've inherited a bunch of knives like that. Seems to be a pretty common problem with how folks sharpen knives. I try really hard not to let that happen because it's a pain to deal with it!
Quote from: grepper on August 14, 2013, 12:44:54 AM
What happened to me several times was that as the part that was not concave was ground down very close to the part that was concave, the wheel started hitting the concave part too, thus maintaining the concavity.
Can't you just tilt the knife a bit so only part of the edge makes good hard contact with the grindstone?
QuoteI've inherited a bunch of knives like that. Seems to be a pretty common problem with how folks sharpen knives. I try really hard not to let that happen because it's a pain to deal with it!
Lucky you! I can see how knives end up that way. People get frustrated with dull knives and try everything they can think of to get them sharp. It's really better to pay someone to sharpen them, then invest in a good steel to keep them sharp. But you have to know where to go to get them sharpened, drop them off, then pick them up. It's really much easier to just go out to the workshop and turn on the Tormek. ;)
Yes, Herman. :) I can tilt the knife and apply more or less pressure, etc.
Nonetheless, I find it a amazingly challenging to get a perfectly flat edge on an 8" chef knife what has been badly concaved. Especially ones with a heavy bolster that extends to the cutting edge.
To place the thing on a cutting board and and see a good 6" of perfectly flat edge contact with no light at all passing under the blade, (a wet spinach leaf), is difficult... for me at least. A good strong light behind the cutting board is very telling.
I've sharpened a lot of knives now, and I'm ok at it. But still, getting a perfectly flat long edge is challenging. Guess I just need to practice some more.
Getting a straight edge is very difficult, I agree. Getting a convex edge is much easier.
Grepper,
You need to work on getting a feel for where to cut and where to relax. It sounds like you're trying to keep your pressure even and consistent. That doesn't always work. Like Kenny Rogers sings, you have to know when to hold them and know when to ease off --- or something like that.
Oh great, now that's stuck in my head.
Good thoughts, guys. In this age where major crimes are solved on television in less than an hour, becoming really proficient in knife sharpening requires concentrated experience. (It makes me appreciate my old friend the chisel!)
I spent a long time and hard work flattening my grandfather's oilstone years ago. Today I would try to do it on a diamond flattening stone, but back then it was rub rub rub on glass with carborundum powder. Since then, I am very careful to try to use the surface of a stone or grinding wheel evenly. I will also be sure to know when to hold and when to fold.
Any thoughts on thinning the bolster when needed (other than just do it)?
Thanks.
Ken
I've ground off the bottoms of bolsters, but I've never thinned one. Why would you want to do that?!
Quote from: Herman Trivilino on August 14, 2013, 08:05:23 PM
I've ground off the bottoms of bolsters, but I've never thinned one. Why would you want to do that?!
Because if you have gotten to the point where you need to grind off the bottom of the bolster, you have sharpened away enough steel to where the edge will be too thick.
True on why you would thin a blade, but it's not always the case that a blade needs thinning if you have to grind away the bolster. I've see a bunch of chef's knives like this one, http://tinyurl.com/mdacxvx, where when the knife is new the bolster is even with the edge. In this case if any metal is removed from the edge when sharpening, the blade will never lay flat unless the bolster is also ground down.
Quote from: grepper on September 12, 2013, 04:13:27 PM
True on why you would thin a blade, but it's not always the case that a blade needs thinning if you have to grind away the bolster. I've see a bunch of chef's knives like this one, http://tinyurl.com/mdacxvx, where when the knife is new the bolster is even with the edge. In this case if any metal is removed from the edge when sharpening, the blade will never lay flat unless the bolster is also ground down.
The funny part is that people make knives with those extended bolster primarily because that is the way that Pierre and Klaus always did it. Some of the German knives are not even drop forged from a single bar of steel anymore. The 2 bolster pieces and that one small part of the strip blade steel are heated with an induction coil and are forge welded together and then stamped out. There is a Wusthof video out there showing them doing it. The selection of steel is driven more by how they have to manufacture the knives than by the performance of the specific alloy. The Japanese bolstered knives often have the bolsters TIG welded onto the blade and they are sometimes hollow. They rarely, if ever have an extended bolster even iof they are actually forge completly. Bolsters do not mean better quality. They just mean that it is a western style knife. Even if I forge an integral bolster knife, it will never have the extended bolster.
This topic needed to be revived. It is very useful for knife sharpeners, with some much needed, solid advice. I also had a good laugh reading koolingit's delightful comment.
Ken
I encounter this problem often. Many times caused by pull-through type sharpeners that cannot
reach all the way to the back of a stamped blade, or by repeated sharpening of a forged blade without reducing the bolster.
For stamped blades, I use 80 grit Zirconia on a Viel and lightly run the blade up the belt (blade standing up directly on the belt) as it is running away from me until the blade is true.
Use a flashlight behind the blade and look for any light or test by chopping chives or parsley. For forged blades, reduce the bolster first, and the do the above if necessary.
You may lose some or all of the bevel depending on how bad the damage. Use the same process for chipped knives.
Then put a new bevel on using the tormek. The 80 grit zirconia doesn't generate much heat as long as you are careful.
Best Wishes
Tim
Good post, Tim
I have now recurved knives with several methods. First, I used a handfile, which works very well. While my Tormek is my go to sharpening tool most of the time, my collection of handfiles sees frequent use.
Second, like Tim, I restored the blade curve and lowered the bolster with a Viel belt grinder. In my opinion, the Viel is a very useful complement to the Tormek. As this is the Tormek forum, I do not wish to discuss the Viel extensively.
Most recently, I needed to grind the bolster on my slicing knife. I was trying out the T2. I worked on the bolster handheld with the T2 snd DWF-200. The T2 did the job with flying colors. I arrived at this proficiency by a roundabout path. The Tormek videos were no help. I knew I could do the job with the Viel. I was able to rethink the operation to the Tormek. Using the Viel is perhaps a small bit faster. Doing the entire job with the Tormek is definitely more cost effective, assuming one already owns a Tormek and not a Viel.
I believe a skilled sharpener should be flexible enough to be proficient with multiple techniques.
Ken
Tried it this way with a stamped knife using only the Tormek. Hold knife perpendicular to a flat surface.
Run a fine point sharpie up between the 2 surfaces. Set my angle at 30 deg. and only
ground where I saw sharpie mark. Repeat as necessary and reduce your angle as you
come closer to a true edge. Done in under 5 minutes. Would still recommend reducing bolster
first on a belt grinder for a forged knife.
Best wishes
Tim
Tim,
Regarding which tool to use to reduce the bolster, having done it with both the Viel and the Tormek (T2 hand held), I would prefer whichever was handier........
To restore the blade curve, I would definitely use the Tormek if I did not own a Viel. :)
Ken
Wondering how the T2 wheels hold up to heavy
work like reducing a bolster. Do they maintain their
effectiveness.
That's a good question. I have no supporting data from Tormek. To the best of my knowledge, Tormek only promotes them for use with the T2 and with the T2 built in jig. However, I would be very surprised if the 200mm diamond wheels were of a lesser quality build than the 250mm wheels. Tormek promotes the larger wheels as suitable for carbide. This differs from the "suitable for touchups with carbide" claim with the SB-250 blackstone. Between those claims and the limited use I have given the DWC-200 with my T2 and T4, I would guess these wheels would work well with extended heavy work provided they were used properly. By properly I mean with light grinding pressure.
I believe more diamond wheels will be damaged by heavy hands than by heavy work. With light pressure and being used with Tormek's anti corrosion compound (diluted 1:25 with water), I would expect a long life. In fact, I believe diamond or CBN wheels may be the answer to efficient grinding of planer blades. (I have not tested this idea.)
Worst case scenario, the DWF-200 and DWC-200 each cost about twice the price of an SG-200. If they only last three times as long, you are money ahead. You are also time ahead, as they require no dressing and, in my opinion, cut faster. I predict the diamond wheels will last considerably longer than this scenario.
Ken
Quote from: Ken S on March 22, 2018, 03:52:58 AM
...
Most recently, I needed to grind the bolster on my slicing knife. I was trying out the T2. I worked on the bolster handheld with the T2 snd DWF-200. The T2 did the job with flying colors. I arrived at this proficiency by a roundabout path. The Tormek videos were no help. I knew I could do the job with the Viel. I was able to rethink the operation to the Tormek. Using the Viel is perhaps a small bit faster. Doing the entire job with the Tormek is definitely more cost effective, assuming one already owns a Tormek and not a Viel.
I believe a skilled sharpener should be flexible enough to be proficient with multiple techniques.
Ken
You should make a video! ;)
Or at least a bit more info... How much bolster did you need to remove? Do you grind them flat, or do you shape the sides a bit?
Quote from: bisonbladesharpening on March 24, 2018, 02:08:08 AM
Wondering how the T2 wheels hold up to heavy
work like reducing a bolster. Do they maintain their
effectiveness.
My .02... I see it in part, like maybe reshaping some of the woodworking tools?
Quote from: bisonbladesharpening on March 24, 2018, 12:25:02 AM
Tried it this way with a stamped knife using only the Tormek. Hold knife perpendicular to a flat surface.
Run a fine point sharpie up between the 2 surfaces. Set my angle at 30 deg. and only
ground where I saw sharpie mark. Repeat as necessary and reduce your angle as you
come closer to a true edge. Done in under 5 minutes. Would still recommend reducing bolster
first on a belt grinder for a forged knife.
Best wishes
Tim
That's a good idea.
Personally, I have better luck making repairs on the Tormek grinding at very high angles (which often means freehand), for things like tip repairs, and in this case removing recurves... the higher angle (or even perpendicular), keeps the stone from 'falling' into the recurve, plus I can see what I'm doing better. You're spot on doing the initial work setting a higher angle IMO.
Good post, CB. (Your last post came in while I was preparing mne. Must dash for now. I shall return.)
You are quite right; I should make a video. I have taught myself how to make them with my digital camera and ipad. I still have some learning to do with editing and posting them. I keep hoping that Tormek will make them. Tormek has decades of sharpening experience. They also have a studio. I do not understand their reluctance to make training videos. The getting started videos they made for the T7, T4, and T8 are very done, as are the DBS-22 video Alan Holtham did for them. The woodturning videos Jeff Farris did for them are, in my opinion, their gold standard.
If Tormek made these training videos, they would have content control. There are some very good videos online showing using the Tormek with other sharpening systems. A video by Tormek should show the Tormek doing all the operations. Video production appears to be low on the corporate priority totem pole.
With no false midesty, I can easily count the colsters I have reduced to the fingers on one hand, hardly a match for the factory. Incidentally, I also ground the sides of the bolsters a bit. The bolsters I ground were on the knives I use every day in the kitchen. The first one needed more work than subsequent knives. The first knife both focused my attention and gave me the confidence to do the job. Bolster work should be just a routine part of sharpening, as should minor curve correction. (I would add a surcharge for major curve repair.)
I agree, there will probably be more heavy grinding with woodworking tools. (How many bolsters does a farmers market sharpener grind on a typical Saturday morning? How many of those knives even have bolsters?
I have no expectations that a Tormek with a diamond wheel will match the grinding speed of a high speed dry grinder with a CBN wheel. However, I have been able to reshape a turning gouge on a Tormek with a CBN or Norton 3X wheel in only a couple minutes. That is plenty fast enough for me, and the Tormek cool, dust free environment makes the job pleasant.
Ken