Knife Jigs Solution

[RickKrung]

Correctness of my value 1.25 mm was not confirmed by Tormek.

Jan

It would be most helpful if Tormek would chime in here with their design offset values, rather than us trying to reverse engineer them.

Rick

[cbwx34]

Thanks for all the work and update.

But this thread really shows the need for a self centering clamp. 

Hopefully Tormek is paying attention... and will come out with one, like many of the other clamped sharpening system have.... 

(... and fix that crazy wide jig stop too). 

Exactly what i've been thinking for years now.
Sometimes i think i have to buy a KME knife clamp and modify that for use on the Tormek.

If you haven't already seen... have done just that.



Takes little more than rearranging the parts and adding a small washer to pivot on (and maybe that top nut, can't remember if it was already on the KME).

Not perfect, but works well (better than the Tormek Jig in most cases)... definitely a step in the right direction, IMO.   

[RickKrung]

Rick, attached there is an image of the static knife jig clamp. The surface is not planar. One feature is the threshold denoted C. Other features are the two very slightly raised strips denoted as A and B. The area D between those stripes is below the level of the point E! (I am describing a new zinc jig.)

What we really need is to measure the spacing between the centreline of the jig shaft (at a place where there is the jig stop, not at a point E) and the slightly raised strip A or B near the bottom of the knife clamp.

To make such measurements reliably and repeatedly was beyond my limited possibilities and that was the reason for my adoption of the spacing 1.25 mm.

Jan

I can appreciate that.  I do have the ability to measure accurately, so here is what I found.

I measured the height of the several points on the flat side of the fixed jig jaw using a precision height gauge that reads at 0.001".  I placed the jig on its back side on parallels on a precision granite surface plate.  First, I stoned the parallels and measured them.  They were about 0.0005" different, the narrower one was placed under the front of the jig jaw (on the right in the photos). 

Zooming in on the height gauge in the photos below and referring to Jan's location callouts, point E measured 0.499" ("zero" on the gauge is the center of the set screw hole, which would be 0.500" in this case).  The height gauge could not reach point C, so I measured a point about equa-distant between point E and A, measured 0.499".  Point A measured 0.498".  Point D measured 0.4895", but I'll call it 0.490", about 0.008" - 0.009" lower than E, E-A and A.

I further checked the recess (area "D") with a feeler gauge - 0.010" went in, but 0.011" did not. 

I also measured seven locations of the flat with my micrometer (Mitutoyo, reads to 0.00005" with an uncertainty of measurement of 0.000044", according to the Certificate of Inspection)  The values ranged from 0.35185" to 0.35245".  Point E was 0.35145", Locations E-A and E-B were 0.35220". Rounding to the nearest 0.0001" there is a range of 0.0007" difference of the flat surface.  Pretty dang good for a casting and every single one will be different.  We can all come to our own conclusion on where to measure the thickness while attempting to determine the magnitude of the offset. 

Rick

[wootz]

Rick, and again thank you so much for your time and all that hard work you do for us.
The fact is that your last measurements have added precision to my jigs offset estimation.

Our jigs static part is polished to the recess, designated as D in this thread

Tormek knife jig out of the box (right) compared to ours.


Calculations of the offset by your method are done at the point E
Your estimation that the recessed area (point D) is lower than the point used for the offset calculation (point E) by about 0.008" (0.2mm) has added precision to our jigs offset number.

For example, having calculated the offset of my jig by your method as 1.1mm, at the recessed area that is actually clamping the blade spine it will be by 0.2mm lower, i.e. the true offset is 1.3mm

This doesn't apply of course to unchanged jigs.

[Jan]

Rick, thank you very much for posting the important results of your measurements! You have done a very good job. 

I have a question. When you calculate the spacing, do you assume that the centreline is parallel to the plane in which the flat side of the fixed jig jaw is embedded? 

Wootz, thanks for your values.

Jan

[RickKrung]

Wootz, yes, I concur with your estimation of the offset of your polished jig as being 1.3mm.  I recall someone saying they were concerned about the jigs causing scratches on their customer's knives.  Is that the reason for polishing the jigs?

Jan, yes, I do assume it is parallel, but as I've said, "trust but verify".  I did look at it.  I held a straight edge on the flat and examined how it lined up with the parting line on the shaft.  It appeared very much parallel. I also examined how "flat and parallel" the surface of the flat appeared and it did appear that way.  If it wasn't, all those fancy measurements would not have meant much. 

And thanks, both for your thanks.  Why to I do to such extremes?  It is like dogs...  Why to dogs lick their ...   Because they can... 

Rick

[Jan]

I am happy that the spacing value 1.30 mm is very near to my value 1.25 mm deduced without any measurements! 

I am firmly convinced that Tormek was also guided by the symmetry requirements when designing the Small Knife Holder with the 2.5 mm thick guide bar.

The symmetry concept is the most powerful tool of today's physics. It is almost evident the all laws of nature have origin in symmetries. May be it is guiding principle of the universe. 

Jan

[wootz]

Yes Jan, I also found it amazing that the offset to the recessed area in the older version of the knife jig is practically the same 1.25mm we've been using.

However, being honest to ourselves, the real offset in unchanged jig, which is clamping at those raised borders that you designated as A and B is 1.1mm and we unwillingly introduced asymmetry in our attempt to eliminate it.

I understand very well the purpose of those raised borders - they facilitate clamping of a tapered spine.
But unfortunately they are also the main source of scratches left on the blade, and that made me grind and polish them off.

[RickKrung]

Resurrecting another old thread, but one which has great value and utility, if one is inclined to go so far...

Ever since first reading of Wootz's modifications to the SVM-45 Knife Jigs to address problems with asymmetry of the resultant bevel widths, I had been wanting to do the same.  But I only had two -45s and not enough "need".  Since starting with the farmers market work, I was sharpening knives of varying width, but none over about 4mm (0.157") (or if greater, I ignored it).  But...  This week, a customer returning for the third time brought two HUGE hunting knives, one an incredible work of Damascus steel art that looked to be 5-6mm thick.  I had already decided to take the plunge and had just received the day before, two more SVM-45s and another SVM-140, so that I could mill the recesses (0.5 and 1.0mm) on the fixed jaws of two of the -45s, so I had to tell the customer to bring his beautiful knives back next week when I would have the right jigs to deal with the blade thickness. 

I have just completed milling the recesses on the two -45s and am very pleased with the results.  Also, in preparation, I had ordered and received two SS feeler gage sets, labeled in both inch and MM.  I cut down one set for use with the -45s and saved one set full sized for use with larger knives and the -140s. 


I wanted four -45s and two -140s so that I could mount six knives at once and run them all through one stone/wheel at a time before having to change knives in jigs, so I really needed the modified -45s to be usable with thinner knives as well as thicker ones.  I developed a spreadsheet giving the shim thicknesses needed for various thicknesses of knife spines.  I initially worked it up in 0.001" increments, but for brevity and functional utility at a farmers market bench, summarized it into 0.005" increments (~0.13mm).  I figured +-0.005" is close enough and definitely much better than no compensation at all.  (A PDF of the shim chart is attached below)


The images below show a "thin" knife 0.062" (~1.6mm), that fits in an unmodified jig (Jig#1) and the shims needed for both Jig#1 and Jig#2.




I have used Jigs #2 and #3 for sharpening two large hunting knives (very cheap Schrades) that I bought a long time ago to practice sharpening long and thick knives but had never touched until now.  Results are excellent with bevels from side to side being so identical that I cannot discern any difference.  My bevels are still wider at the tip than in the straight body, but that is a lacking in my technique, not with the modified jigs. 

One happy puppy.  Thank you Wootz for the inspiration. 

Rick

[Jan]

Rick, in my understanding your chart was calculated assuming that the Tormek knife jig works perfectly for 0.1"spine thickness. Correct?

When I have to use shim(s) I often have difficulties to mount the blade in the knife jig symmetrically, so that the bevel angles are the same for both sides. The shim slides on the blade and makes the montage difficult. Do you have some trick how to overcome it?

Jan

[wootz]

Dr. Werner N. from Germany shared his shim holding with us:
"When I need a shim I use two small but strong Neodymium magnets to hold the shim in place, still being able to move it around. After I clamp the knife and shim I remove the magnets."


I use shims when the blade has a wedge profile, otherwise use layers of cloth tape to bring the clamping site thickness to the ideal for the given knife jig.

Dr. Werner also shared his other gimmicks, e.g. for setting the grinding angle with our applet he advised the depth caliper as on the photo, and we use them now.

[RickKrung]

Rick, in my understanding your chart was calculated assuming that the Tormek knife jig works perfectly for 0.1"spine thickness. Correct?

When I have to use shim(s) I often have difficulties to mount the blade in the knife jig symmetrically, so that the bevel angles are the same for both sides. The shim slides on the blade and makes the montage difficult. Do you have some trick how to overcome it?

Jan

Jan,

Yes, that is correct, 0.1" spine thickness.  I wasn't thinking of it exactly like that, rather 0.050" offset of the fixed jaw from the jig centerline, but that is the same. 

I've only used shims on a dozen knives since modifying the jigs.  I have not had much trouble with the shims sliding.  I insert the knife with the fixed jaw up and then slide in the shim and snug it so the knife can still move slightly.  Turn it over and use your (I think) projection template for positioning the edge perpendicular a tighten.  Then I use a device similar to the one Wootz uses to set the projection, a modified woodworker's marking gauge, which I'll address in response to Wootz's reply. 

Rick

[RickKrung]

Dr. Werner N. from Germany shared his shim holding with us:
"When I need a shim I use two small but strong Neodymium magnets to hold the shim in place, still being able to move it around. After I clamp the knife and shim I remove the magnets."

I use shims when the blade has a wedge profile, otherwise use layers of cloth tape to bring the clamping site thickness to the ideal for the given knife jig.

Dr. Werner also shared his other gimmicks, e.g. for setting the grinding angle with our applet he advised the depth caliper as on the photo, and we use them now.

Nice trick, using magnets.  I had not thought of it as my first reaction is "stainless steel is not supposed to be magnetic" since so many of the knives we deal with are stainless.  I know some stainless alloys have some magnetic response. Are knife alloys of that sort? 

I probably haven't used shims enough yet to recognize the need for shimming to compensate for taper in the knife spine.  I was just happy with this much.  I do have some cut-of shorts of the shim set I trimmed down.  I was wondering what, if anything, I could do with them. 

I really like the projection setting depth caliper idea.  I had found an attachable foot for my digital calipers but didn't really like it. 


More accurately, I didn't like the flimsiness of the Depth Rod that sticks out from the caliper.  Before finding the caliper foot and what I still use is a pattern maker's marking gauge, that I modified by replacing the cutter with a washer.


I use calipers to set the marking gauge projection and then use that to set projections of the jigs.  I use only 139mm so it stays set at that and I check it now and then to be sure it hasn't moved. 


I might have to look into a longer depth caliper, tho.  It might be better for setting the USB height than the marking gauge I currently use (different on than for setting knife jig projections) as it would allow direct setting rather than secondary - setting the gauge then setting the USB height. 

Rick

[Ken S]

I believe the Veritas marking gage uses 5/16" rod for the shaft.

Ken

[RickKrung]

Yes, it does use 5/16".  I do not understand your reason for commenting on it.   

Rick