Knife tip grinding - To Pivot or Not To Pivot

[Jan]

With the platform jig I grind towards the knife and find that it doesn't tend to lift if you do it correctly. It just takes some practice. On the other hand, more experienced sharpeners prefer other methods. Some don't use a jig at all. It's a matter of preference.

Herman, you are correct, practice is sure important, but I hope to understand why you do not experience the lift tendency when grinding towards the edge.

In my thinking the explanation is following: on your steeply inclined platform your hand keeping the knife is sliding down towards the grindstone like a movement on an inclined plane.

In my case it is different, I have to be proactive in pressing the knife against the grindstone. I have found that my "contact" force is not the same during the pass/passes which to some degree influences the bevel grind.

I still use my horizontal platform, but it has not replaced the knife jig especially when sharpening expensive knives. I am not sharpening for money and so I have enough time to mount the knife in the knife jig and to check that it was clamped symmetrically. For batch sharpening and small blades I of course use the platform. 

My motivation to build the horizontal platform was twofold:
1) similarity to the way how freehand sharpeners work,
2) very simple bevel angle setting.

Jan

[cbwx34]

I have horizontal platform for sharpening in both directions...

Jan

Was gonna mention this before... if you ever sold your setup as a kit.... I'd be first in line.  Nice setup.

[Jan]

Thank you, CWBX.  I am pleased about your interest in my set up! I tried to build it as solid as the Tormek machine. 

Jan

[Ken S]

With the platform jig I grind towards the knife and find that it doesn't tend to lift if you do it correctly. It just takes some practice. On the other hand, more experienced sharpeners prefer other methods. Some don't use a jig at all. It's a matter of preference.

There's a discussion in the Tormek manual about platform jigs, and their philosophy is that it's a useful technique only when the edge angle is blunt such as on a scraper. Note that when using the Tormek Tool Rest jig, which is a platform jig, the edge angle must be blunt because the platform is too far from the Universal Support rod. The idea is that for shallow angles the operator has to apply more force to a platform than to the grindstone. I don't agree. The platform can be used as a guide where very little force is applied to the platform. After all, you can freehand with a Tormek, in which case there's no force at all applied to a platform and the edge angle can be rather shallow.

Using the scissors jig base to mount a platform lets you get the platform much closer to the grindstone so you can grind shallower angles.

I find it fascinating that people whose Tormek expertise I respect often have different approaches. Steve Bottorff, my knife sharpening guru, regrinds bevels freehand with the grinding direction trailing with his Tormek. For uniform bevels, Steve's first choice is the Tormek knife jigs. Incidentally, US Tormekers can thank Steve for convincing Jeff Farris to import the 140mm long knife jig. Originally, it was only available in Europe.

I value Herman's thoughts on his small knife jig with the same high regard. Herman designed the jig and probably has more hands on shop time with it than anyone else on the planet. If he states that something can be done with his jig, I believe him.

Herman's jig is designed for a different function than any of the Tormek jigs. His jig was originally designed to sharpen small knives, such as pen knives. It is not limited to this work, but was originally designed for it. Tormek has never made a jig for this purpose. The classic handbook technique for sharpening small knives is freehand. Tormek's platform jig works very well for its intended purpose, sharpening large turning scrapers. Tormek's knife jigs work very well for sharpening their intended purpose, sharpening larger knives. Tormek's small blade tool works very well for its intended purpose, sharpening small carving knives with substantial wooden handles. (Look at the photos). It is clumsy with small pocket knives. Herman's jig is not.

The function of the smaller width, matching the thickness of the grinding wheel, is to allow both bevels to be ground full length without needing to readjust the jig. The thinner leading edge of Herman's jig allows the jig to be placed closer to the grinding wheel.

Incidentally, Herman got it right by using the scissors jig platform. I made two (one each for the T4 and T7, by cutting a platform jig in half. With a higher center of gravity, these do not work as well as Herman's design.

I will restate my belief that a well equipped Tormek knife sharpener should have one of Herman's jigs. This should be in addition to the Tormek jigs, not instead of them.

Ken

[cbwx34]

No thoughts on the differently profiled collars?

I have a thought on it this a.m....  it might be better to reduce the size of the collar (considerably).

I've been working with the clamp from the KME sharpener... this morning I just used a small washer so that I could pivot the blade with as little interference from the collar as possible (basically keeping the pivot point near center, and held it against the USB with my thumb)....



... as you can see in the sample picture... keeping the pivot point small, and properly positioning the clamp (still necessary of course), allows the blade to pivot with little position change as a result of the collar.  (Feels more comfortable too... across a variety of knives).

Might be the route to take.

[Kavik]

Very interesting, though it would require creating an entire collar from scratch, threads and all. Quite a bit more complex than my original thought of having different pieces to slap on abov the existing collar, hmmm.....

I wonder if the width on the original had anything to do with helping inexperienced users keep the jig from pivoting unintentionally when working along the flat of the blade?

[Ken S]

One of the several ideas in my thought stage is to order several more adjustable stops as spare parts. I would glue a flat piece of round plastic to the front (no radius). This would assist lifting the blade without pivoting.

Ken

[cbwx34]

Very interesting, though it would require creating an entire collar from scratch, threads and all. Quite a bit more complex than my original thought of having different pieces to slap on abov the existing collar, hmmm.....

I wonder if the width on the original had anything to do with helping inexperienced users keep the jig from pivoting unintentionally when working along the flat of the blade?

Maybe substitute the collar for something smaller in diameter... just to see if you notice the difference?  I'm not sure the radius of a substitute would be that critical... especially if the collar wasn't much bigger than the jig part it would be screwed onto. 

(I'll see if I can find something and test the actual Tormek jig).

[Kavik]

Honestly, I still don't have enough experience to make a good test subject myself yet

Can you test that theory by just threading your stock collar on backwards?

[Herman Trivilino]

In my thinking the explanation is following: on your steeply inclined platform your hand keeping the knife is sliding down towards the grindstone like a movement on an inclined plane.

Good point, Jan. I hadn't thought of that. My arms are at about the same angle as the platform, so applying force along the direction of the platform is a natural and productive direction.

[Herman Trivilino]

Tormek's small blade tool works very well for its intended purpose, sharpening small carving knives with substantial wooden handles. (Look at the photos). It is clumsy with small pocket knives. Herman's jig is not.

I've never used the SVM-00, but looking at the picture I see what you mean.

Thanks for your exhaustive list of the benefits of my platform jig. It is also good for machetes. Tormek doesn't have a jig for that, so your only option is freehand.

[Ken S]

You are most welcome, Herman. Your small knife jig is a well designed and useful tool. You have also stuck with it long enough to really master. As I have said before, I think it should be part of every knife (and machete) sharpener's kit.

It is easy to be complimentary about a good tool.

Ken

ps Any chance you could delete the annoying photobucket images and replace them using the forum attachment program?

[cbwx34]

Honestly, I still don't have enough experience to make a good test subject myself yet

Can you test that theory by just threading your stock collar on backwards?

Actually, you might make a better test subject... no preconceived ideas. 

Can't really thread it backwards... the internal stop is at the other end of the collar.

I did make a comparison both with and without the collar... using a reference line on the stone as a guide...



... in the top row, you can see the '0' on the knife jig stays pretty much on top of the USB.  But with the stop collar, it pulls it well below the line.  So if the width of the collar was reduced... this factor would be nearly eliminated.

Without the collar, you actually can still use the jig to maintain the angle... as long as you keep the blade at the same reference point/line.  (Sort of a "guided freehand").

Obviously, some of this depends on the knife length.  Longer kitchen knives, knives without much 'belly' etc. won't be influenced as much.  But I tend to sharpen more EDC/pocket knives, small hunting/camping knives, etc. where this is seen more.

[Kavik]

Cbwx, your last post was rather interesting and got me thinking about a few things.  So I cut the top off one of my 3 knife jig collars and started experimenting as you did, with the machine off and focusing on the LOC drawn on the wheel.
I'm writing this up while giving my back a little break from standing over the machine, but I'll provide some detail a little later this evening.
So far is looking QUITE promising on 7 very different knives all using one specific combination of sliding,  lifting,  and pivoting to keep the LOC.

One thing to note: so far the only advantage I see to the stock jig collar is that the wide base stops the lock screw knob from contacting the USB while pivoting. A smaller knob, or a collar from scratch with the lock screw located closer to the base, would be the most likely solutions to this
Edit: it does also help keep straight along the main length of the blade, assuming you set it up properly parallel to the edge... But that's something that probably means a lot less after some practice

[Ken S]

Your last sentence brings up a situation. I am as guilty of this as anyone. I think we have a tendency to want to improve our tools before we have had enough experience with them to master them.

My own experience with the Anglemaster illustrates this. I was most of the way through redesigning it before I realized the difficulty I was having was due to poor light. I stumbled upon this realization one day after I set up my Tormek outside. With my personal technique, I rarely use the Anglemaster, however, I now hold it in much higher regard.

Ken