Another idea for pivoting the knife jigs

[GKC]

In order to match the jig to the curvature of the knife tip, the length of the jig should be variable, equal to the radius of the curvature, and in any case longer than it is now.

Hmmm.  You make an interesting point, Ton.  If I understand what you saying, it is that the curvature of some blades describes an arc with a radius that is greater than the projection available from the current SVM jigs, such that accurate pivoting is already compromised.  If this is so, then any projection lost by adding pivot points in front of the SVM collar would further compromise that accuracy.  If this is a material concern, then we are best with something like the Pin Pivot Collar or the Triangular Pivot Stop, which at least preserve as much projection as possible from the shaft length of the SVM jigs.

[RickKrung]

Hmmm.  You make an interesting point, Ton.  If I understand what you saying, it is that the curvature of some blades describes an arc with a radius that is greater than the projection available from the current SVM jigs, such that accurate pivoting is already compromised. 

I believe you are correct, except that the radius of the blade is more often less than the projection available.  And I think this is why lifting is still required, even when using any type of "pivot" stop.  If the radius is greater, I think, moving the pivot point closer to the curvature can sometimes at least partially mitigate this by making the radius of the projection more closely match the radius of the blade arc. 

If this is so, then any projection lost by adding pivot points in front of the SVM collar would further compromise that accuracy.  If this is a material concern, then we are best with something like the Pin Pivot Collar or the Triangular Pivot Stop, which at least preserve as much projection as possible from the shaft length of the SVM jigs.

I take it differently.  I think it isn't a matter of losing projection due to something in front of the standard collar.  In fact, I think use of such "addition", one would move the collar back to put the pivot point at the correct projection.  Thus, the type of pivot collar is irrelevant as long as the projection is the same. 

I think the real upshot of Dutchman's statement is that, with existing collars/pivot stops, pivoting alone is not enough, that some amount of lifting is still required.  Where and how much will depend on the curvature of the blade and how the contact point of the bevel on the stone deviates from the "Line of Contact" (LOC), with or without pivoting.

His statement, to me, suggests that if a jig had a stop device that provided variable projection distance, then pivoting alone might be enough.  We do not have any such device at this point, that I am aware of.   

I've sure someone will correct on this if it is needed. 

Rick

[GKC]

Yes, I can see that lifting could compensate when there is insufficient projection, or when the radius of the arc of the blade changes along the length of the curve (most blades I encounter have a varying degree of curvature along the curved part of the blade).  In theory, lifting (alone) should work for many blades.

(A few weeks ago I sent a very precise question to Tormek support about Tormek's information on the geometry and trigonometry of pivoting and lifting, and got back a disappointing non-answer along the lines of "do either or both at once, see what feels right".  That might be a realistic answer, but I was hoping for some guidance on the theory even if the theory is not easily translated into practice.  Some engineer in Tormek will know this stuff cold, but it seems that they just won't divulge it.)

Perhaps Ton will come back online to clarify, but I took his comment (that the length of the jig should be "longer than it is now") to be indicating that the jig sometimes has too little projection, and this seems intuitive to me for blades with only a gentle curve (thus requiring long projection). 

It is doubtless true, as you say, that "the type of pivot collar is irrelevant as long as the projection is the same", but mounting things in front of the SVM collars reduces the available projection (before you fall off the O ring) by the thickness of the thing you mount (about 10mm in the add-on I posted in response to Drilon's jig).  I think my only point is that one preserves more projection capability (if needed for a longer radius) with the Pin Pivot Collar and the Triangular Pivot Stop.

I have tried to imagine a jig with projection that changes, during the sweep of a sharpening pass, to match the curve of the blade, but the complexity makes my head spin.  Ultimately, experience leading to the ability to do "what feels right" might be the only solution.

Gord

[jwv162]

I am new to the tormek and having the same problems with the knife holds. The adjustment knob turns while you pivot the knife.  I guess for the money we pay for the tormek, why should we have to redesign their holders?  A great deal for them, sell us junk and than have us fix it.  So far not to impressed with tormek.

[GKC]

I have a different impression: While in some areas I wish Tormek would introduce new design elements, I am very impressed with the quality of Tormek equipment. 

The Tormek knife jigs were not designed for pivoting: indeed, the large collar on the SVM-45 and SVM-140 knife jigs are there in order to help the user keep the blade perpendicular to the wheel; that is, to help the user avoid unwanted pivoting.  Curves in the blade can usually be accommodated by lifting the handle rather than pivoting, and the Tormek knife jigs allow the freedom to lift while staying square to the wheel.

The pivoting jigs have been developed by more specialized users to allow a different movement, not because the Tormek jigs are deficient for their intended use.

The movement of the collars of the Tormek knife jigs is a result of Tormek's decision to use the friction of an "O" ring instead of the previous locking screw, which held the collar better but (some thought) got in the way.  This is not a bad design, just a design with a different priority.

I have never had a problem with my collars moving, but if I did, I would just install a locking screw.

Gord

[RickKrung]

I am new to the tormek and having the same problems with the knife holds. The adjustment knob turns while you pivot the knife.  I guess for the money we pay for the tormek, why should we have to redesign their holders?  A great deal for them, sell us junk and than have us fix it.  So far not to impressed with tormek.

I have to agree with you at one level and disagree on another.  First, the "O-ring" collar does turn at times.  I did not like this, so I replaced them with locking screws.  Second, the Tormek is definitely NOT junk. 

I've never heard or read this idea, but perhaps the turning of the O-ring collar is a matter of too much pressure of the collar on the USB.  The USB is just a guide.  An unpracticed hand needs to keep good pressure of the collar against the USB.  I would ask of those who use the unmodified collar, with practice, are you able to apply less pressure because your muscle memory is keeping it in place and thus the lesser pressure does not cause the collar to rotate?  If that is not it, what do you do to keep the collar from rotating? 

I would add that the very high level of design and ingenuity shown with the machine and jigs is astounding and the quality of the castings and machining is equally astounding.  These are anything but junk.  I have heard, but have no first hand experience, that some of the knockoff imitations can be junk. 

I suggest you work with the machine and jigs for a while before deciding.  If you do decide it is junk, I've been wanting a second machine, so would entertain buying that junk off your hands at at commensurate prices. 

Rick

[cbwx34]

I have a different impression: While in some areas I wish Tormek would introduce new design elements, I am very impressed with the quality of Tormek equipment. 

The Tormek knife jigs were not designed for pivoting: indeed, the large collar on the SVM-45 and SVM-140 knife jigs are there in order to help the user keep the blade perpendicular to the wheel; that is, to help the user avoid unwanted pivoting.  Curves in the blade can usually be accommodated by lifting the handle rather than pivoting, and the Tormek knife jigs allow the freedom to lift while staying square to the wheel.

The pivoting jigs have been developed by more specialized users to allow a different movement, not because the Tormek jigs are deficient for their intended use.

The movement of the collars of the Tormek knife jigs is a result of Tormek's decision to use the friction of an "O" ring instead of the previous locking screw, which held the collar better but (some thought) got in the way.  This is not a bad design, just a design with a different priority.

I have never had a problem with my collars moving, but if I did, I would just install a locking screw.

Gord

Actually, the collar rotates when you rotate the jig, not when you pivot it.

I am new to the tormek and having the same problems with the knife holds. The adjustment knob turns while you pivot the knife.  I guess for the money we pay for the tormek, why should we have to redesign their holders?  A great deal for them, sell us junk and than have us fix it.  So far not to impressed with tormek.

I wouldn't say "junk"... but definitely a bad redesign from their previous version, IMO.

Just a bit of FYI... most of the "redesign of the holders" is for other reasons... pivoting, self-centering, etc.  About the only thing done to avoid this issue, is putting tape on the jig under the collar, or "re-adding" a locking screw.

...
I've never heard or read this idea, but perhaps the turning of the O-ring collar is a matter of too much pressure of the collar on the USB.  The USB is just a guide.  An unpracticed hand needs to keep good pressure of the collar against the USB.  I would ask of those who use the unmodified collar, with practice, are you able to apply less pressure because your muscle memory is keeping it in place and thus the lesser pressure does not cause the collar to rotate?  If that is not it, what do you do to keep the collar from rotating? 
...

I don't think pressure is the issue... I have a pretty light touch and mine would still move.  Adding tape under the collar or adding a locking screw solved it for me (I've done both).  Ok... pretty much quit using it is really what I've done....  

[RickKrung]

I don't think pressure is the issue... I have a pretty light touch and mine would still move.  Adding tape under the collar or adding a locking screw solved it for me (I've done both).  Ok... pretty much quit using it is really what I've done....  

I wonder if a fatter O-ring would help, if it would fit in the space.  The existing one can be difficult to get the collar over already.  O-rings are great for sealing joints, but are not meant for that kind of service (anti-rotation). 

Rick

[GKC]

As I noted, I haven't had a problem with my collars moving, could it be that Tormek has increased the O ring size or composition (my purchase was fairly recent)?  Or, perhaps as my O rings wear down, the problem will surface.  I have quite a good machinery parts supplier near me, and I know they carry thin and fat O rings for the same inside diameter, I will see what happens with a fatter O ring.  But I agree that a locking screw is the real answer when this issue surfaces.

Gord

[cbwx34]

...You might call it a wedge collar.

The governing factor in this design was simplicity in fabrication: I am no machinist and I wanted something that could be made by anyone with a hack saw and file (and drill press, for the holes).  Also, I wanted to design something that someone could make out of plastic, either by shaping it or by using a 3D printer, and so it had to have more reinforcing bulk than Rick's pin collar.

I find this wedge collar very easy to use.  The fingers (of the hand you are using to hold the knife jig) can slide up comfortably behind the wedge; you can leave off the disc supplied with the SVM-45 and SVM-140.  The pivoting is very fluid, and the range of pivoting is more than sufficient for the knives I have tried it on.

As I said, I wanted this to be easy to make.  It is made from a 2" length of a 1" square bar of aluminium, which I drilled and then cut to a triangular shape. 

Stainless steel would be better than aluminium: less friction and wear, but I haven't noticed the friction from the aluminum, and machining stainless steel would require tools I don't have.  A block of UHMW plastic should work, and might be nicely slippery on the USB.  I don't know much about 3D printing, but the wedge seems like a simple project, perhaps with the holes being done after.  Of course, wood would be easiest, but there are drawbacks when wood is used around water.

Gord

I like it!!

...
Rick, after seeing your great tool I was looking for a way that I can test this method. That was my intention to make the cheap copy. If I come to the conclusion that I like it and use it often I most probably will purchase your professional tool as now offered by Knife Grinders, Australia.

Thank you!
Drilon

Yours is also a good idea!  As long as it holds... it'll work just as good as the "original".


The main thing with all these ideas, is simply to reduce the pivot area of the collar on the USB.

In order to match the jig to the curvature of the knife tip, the length of the jig should be variable, equa; to the radius of the curvature, and in any case longer than it is now.

This I will have to think about.... do you mean the distance by adjusting the collar (screwing it in or out more... vertically)?  In my mind, it's more of the distance created by how far away you clamp the belly/tip area (more horizontally).  Vertical (for me) provides "maneuvering room".

[harivney]

Hey Gord, that's really slick! Thanks for sharing the idea and instructions.

Are there any additional instructions for Gordon's jig other than comments in his post? Knife grinders stopped selling Ricks design. Are there any similar jigs available that can be ordered?

[cbwx34]

Are there any additional instructions for Gordon's jig other than comments in his post? Knife grinders stopped selling Ricks design. Are there any similar jigs available that can be ordered?

Go join the Tormek Group on Facebook... and have a look around.

[RickKrung]

Hey Gord, that's really slick! Thanks for sharing the idea and instructions.

Are there any additional instructions for Gordon's jig other than comments in his post? Knife grinders stopped selling Ricks design. Are there any similar jigs available that can be ordered?

Hanns Plag, a member of the Facebook Tormek Users group is producing Gordy's jig, in Germany.  There is a link to his web page in his post about it.  If one selects the jig and puts it in their cart, at checkout the site indicates it cannot ship to the USA, but conversations with Hanns on the FB page modifies that to where he allows that he can probably just ship by normal postal methods.  One would have to PM him to work that out. 

Rick

[harivney]

Hey Gord, that's really slick! Thanks for sharing the idea and instructions.

Are there any additional instructions for Gordon's jig other than comments in his post? Knife grinders stopped selling Ricks design. Are there any similar jigs available that can be ordered?

Hanns Plag, a member of the Facebook Tormek Users group is producing Gordy's jig, in Germany.  There is a link to his web page in his post about it.  If one selects the jig and puts it in their cart, at checkout the site indicates it cannot ship to the USA, but conversations with Hanns on the FB page modifies that to where he allows that he can probably just ship by normal postal methods.  One would have to PM him to work that out. 

Rick

Thanks. Expensive shipping. Surprised no one in the USA makes one. What is the mm diameter of the tormek knife holder shaft (I dont have tormek yet)

[harivney]

can someone please tell me the diameter of the shaft on Knife Blade Sharpening Jig Tormek SVM-45? I don't have tormek yet.