Long Knife Jig asymmetry problem

[Jan]

Vadim, could you please estimate the size of the asymmetry before modifying the clamp? I think how much wider (in mm) was the bevel on one side than the other side?

If I knew the bevel angle, blade thickness and the radius of your wheel, I could try to calculate it. This would allow to understand better the source of the bevel asymmetry. 

Jan

[Jan]

There can be only one knife thickness for which the bevel angle will be the same on both sides of the knife. A thinner knife will have a wider bevel on one side, a thicker knife on the other side. Thus, it's possible to accommodate a thicker knife by removing some metal from only one side of the jig, but only up to a limit. At some point a knife that's thicker yet will need to have additional metal removed from the other side, too.

Herman you are correct. 

Today I have carefully measured the dimensions of the knife jig and came to the conclusion that the fixed side of the jig is 1 mm (2.5/64") below the longitudinal jig axis, around which the adjustable stop revolves.

So the knife jig is perfectly symmetrical for 2 mm (5/64") thick knife blade. The accuracy of my measurements is +/- 0.2 mm.

Jan

[carvingcat]

I had this exact same problem with the Tormek SVM-100 that came as part of a kit with my 1206 bought a few years ago, and after trying it out once (on one of my cheaper 8" chef's knifes) I found the results so bad (my knife sliced diagonally after!) I put the jig away until recently, putting it down to my novice sharpening skills. I use my Tormek almost exclusively for sharpening my carving gouges and so I forgot all about the SVM-100 until recently when I thought I'd have another go before selling it.

Looking at it again it is clearly offset, and the only option is to reset the angle for each side of the blade - it is a bit of a hassle but I've now had some reasonable results, I'll try to upload some images to illustrate.

[carvingcat]

Here's the jig holding my thinnest knife (kai shun 8" chef's), you can see the knife is not inline with the jig, even the larger cast part of the jig appears to bend away from the shaft...


,




And here it shows how much the angle changes when turning the jig over...






The only difference in the two images above is that the jig has been turned over, the angle has changed significantly

[Jan]

Welcome to the forum carvingcat. 

In this thread we have discussed mainly the Tormek knife jig SVM-45 and I am not quite sure if we can apply the conclusions also to your SVM-100 jig.

Based on Wootz experience the usage of the knife jig SVM-45 for thick knives (more than 3 mm) results in uneven bevel angles. He solved this problem by filling away 1 mm from the static clamp.

Based on my measurements the knife jig SVM-45 works perfectly symmetrically for 2 mm thick knife blade.

Because it is hardly imaginable that your knife is substantially thinner than 2 mm, it is probably necessary to look for the fault in the jig, or in the way the knife is mounted into the jig. When the blade is tapered and the jig grips only 2 or 3 mm of the knife's blade, than the knife is often not sufficiently firmly mounted in the jig.

Jan

[Edwe]

Hia All

This is very sad to read and I think Tormek must ansver this and fix it.
I am not in the skill for sharpening on freehand and is very dependent on the jigs.

In Swedish
Tormek ni måste fixa detta, antingen byta ut jiggarna mot fungerande eller föreslå en lösning.

Best regards Edwe

[Ken S]

I have never had much luck with the anglemaster on very shallow surfaces. (Chisels and plane blades are fine.) I would substitute something thin and flat like a plastic gift card. Then, make a cradle to hold the jig with the  knife. With another block of wood, mark the position of the knife edge. Flip the jig over and note the knife edge location difference. Add a shim of half the difference in thickness.

Sorry, this needs photos or a video.

Ken

[stevebot]

For a look at another sharpener's solution to this problem, see
http://amktactical.com/epages/3c926a50-9aba-43a5-9571-098ee03f1288.sf/en_US/?ObjectPath=/Shops/3c926a50-9aba-43a5-9571-098ee03f1288/Products/24
Watch the video from about 1:30.

[Elden]

   I like that, Steve. That is a quick and easy fix for the asymmetry problem that thin knives produce. The process could easily adapted to the Tormek knife jigs. For thick knife problems, one would still have to modify the jigs or flip the knife over in the jig. That electronic protractor is nice as well.

[grepper]

This is slightly off the off-center topic, but might save you a couple of $$.  I have a similar inexpensive digital protractor.  I think the one shown in the video is 0.1 degrees accurate:
http://tinyurl.com/hpbak5d

The one I have specs out to 0.2 degrees accurate:
http://www.amazon.com/gp/product/B006JR8XBG?psc=1&redirect=true&ref_=oh_aui_search_detailpage

I got it for hanging pictures.  I quit using it because I could tilt the picture frame and it did not register on the protractor.  I can plainly see level better than 0.2 degrees.  I get better results using a good quality bubble level.  0.1 degrees is 2X better than the one I have, but still I would rather use a bubble level.  It's amazing how well the eye can judge the short distance at the ends of a bubble.

Accurate digital protractors are far more expensive.  I though I could get away with a cheaper one, I was laboring under a delusion.  After hanging a picture I could easily see it was out of level even though the cheapo protractor indicated level.

Onion other hand, I suspect this one would be just fine:
http://tinyurl.com/jyo3fsb

[Elden]

   Thanks for the warning, Mark. I am sure you are right, you get what you pay for. While not being extremely accurate, I have used the dial type magnetic protractor before for other projects. Here is a cheap one.

http://www.homedepot.com/p/Johnson-Magnetic-Angle-Locator-700/100161689?cm_mmc=Shopping%7cTHD%7cG%7c0%7cG-BASE-PLA-D25T-HandTools%7c&gclid=CjwKEAiA8K20BRDetNv3p6DNhXwSJADSwa3t8oF9f0KKDDSAd6szOcRKMtkwK7XSZ-LvwX9ieR9lsRoCpBfw_wcB&gclsrc=aw.ds

[grepper]

And if you need to know the angle, like in the belt grinder video, a bubble is useless.

[carvingcat]

Welcome to the forum carvingcat. 

In this thread we have discussed mainly the Tormek knife jig SVM-45 and I am not quite sure if we can apply the conclusions also to your SVM-100 jig.

Based on Wootz experience the usage of the knife jig SVM-45 for thick knives (more than 3 mm) results in uneven bevel angles. He solved this problem by filling away 1 mm from the static clamp.

Based on my measurements the knife jig SVM-45 works perfectly symmetrically for 2 mm thick knife blade.

Because it is hardly imaginable that your knife is substantially thinner than 2 mm, it is probably necessary to look for the fault in the jig, or in the way the knife is mounted into the jig. When the blade is tapered and the jig grips only 2 or 3 mm of the knife's blade, than the knife is often not sufficiently firmly mounted in the jig.

Jan

Thanks Jan, the SVM-45 is identical to the SVM-100 apart from the width of the blade jaws which are 100mm on the SVM-100 and (I assume) 45MM on the SVM-45, they both function in exactly the same way. The knife I'm using here is exactly 2mm thick, and the more I look at the jig the more I think it could be a defective item.


In the first image you can see how the lower jaw deviates from the straight line at the arrow, the other images showing the angle refer to the blade angle (not the bevel), the anglemaster reading was taken from one side of the blade and not changed for the other - it is to illustrate the different angle of the blade resting against the stone, if the jig was accurate then surely the blade should be resting flat against the anglemaster (at 16 degrees) in both images, not just on one side.









Note the anglemaster is set to 16 degrees in both images;

[carvingcat]

I'm very tempted to just knock this so that it runs straight, but I'm worried it might break - any thoughts on the alloy?

[WolfY]

Hi guys, I'm new here and this is my first reply

The problem you describe about the angle change as the jig is turned 180 dgrs is of little concern to me too.
But let say for the regular user with the standard jig that use it for years and never got into this measurements, is it a real problem? Let say the sharpening angle difference is 2~3 dgrs.
How much tolerance will you accept?

Carvingcat, Is your jig bent or was it so originally?