Knife tip grinding - To Pivot or Not To Pivot

[cbwx34]

This is how we do a curved tip:
- Mark the tip radius perpendicular to the edge.
- Clamp in the middle of the straight segment.
- Start at the bolster end, and grind the straight segment as usual, sliding across the stone with the knife jig perpendicular to the Universal Support till you reach the marked radius line.
- At this point fix the jig position at the US, not sliding laterally further.
Do the tip radius by pivoting the jig and raising the handle, till the radius line comes perpendicular to the US (i.e parallel to the wheel margin) - not any farther.

Thanks for the example.

I'm not sure "clamp in the middle of the straight segment" can be a guideline.  On longer knives, like in your example, it'll work, but the relationship of the clamp distance to the tip, as has been talked about before, plays a large part in the angle at the belly to tip area.  On a shorter knife... where you clamp can change the angle more.

I do think, one point worth mentioning is, pivoting to keep the grind line more perpendicular is an advantage to pivoting over just lifting to follow the curve.

Kavik was kind enough to send me a modified collar to try.  Haven't had a chance to yet, but just noting in the attached picture how much closer it stays to the LOC, seems to me an improvement.

(I'm jealous of your stone rack in the background).   

[Kavik]

Glad to see it arrived, usps tracking never updated for me to even say the shipment existed lol
That's a great comparison shot you took, thanks for that!

One thing to keep in mind when you do get a chance to test it. I was setting my tip projection to match the blade protection like we talked about, but using the side of the shaft as the base reference, not the center of the shaft. Play around with different projections (I'm sure you will anyway), but my idea was for knives whose shapes don't allow the tip to stay on the LOC, it should end up slightly above rather than below, allowing you the option to lift to compensate

Feel free to shoot me a pm or follow up here if you run into any issues. But based on your pic, it looks like you're already pretty close to on target with it 

[cbwx34]

I've had a chance to try Kavik's modified collar... and have already told him... he's not getting it back.   

With the "sides" of the collar removed,  I get a nice fluid movement from straight portion -> belly -> tip.

I'm not much on videos, but tried to make a couple of short ones... just to give an idea.  Note how close the knife stays to the (imaginary) LOC on the stone...

https://vimeo.com/234061935

https://vimeo.com/234061995

... in the 2nd video,,, even a blade that is basically curved the entire length, is a nice smooth movement.  As a bonus, where the knife is set in the jig appears to be less of an issue... having the pivot basically in the same location gives a nice consistent bevel.  (I tried to keep my hands out of the way a bit more in the 2nd video, so maybe you could see the pivot area better.. and showed the shape of the knife at the start).

I thought there might be a problem, since the "stop" is so smooth, it might "ride over" the USB... but maintaining the same pressure needed to keep the jig on the USB... this didn't occur.  Also, not an issue keeping the straight portion of the blade parallel to the stone.

Works great... I like it.      (I'm not much on making videos... but hoped this would at least give some idea of how well it performed).   

As a double bonus... wootz allowed me to beta test his new Android version of the app for setting the USB height to set the angle.  Honestly, when I first read it on his website, I thought it would be no easier than the AngleMaster... man, was I wrong.  It's great too... makes setup easy and very accurate.  Highly recommended. 

[Kavik]

So glad it's working for you man! 
Sounds like you had the same experience as me, it makes the whole motion just feel much more fluid and natural, in addition to keeping closer to the LOC

Not saying it's the be-all-end-all solution to everything or anything like that,  but i know which jig I'll be using from this point on 


Only other think I might try some day is putting a concave curve on the end of one, rather than convex. See if i can pull the pivot point directly on center instead of just closer, but it's probably not necessary  (unfortunately didn't think about this until just this minute)

[wootz]

...
I'm not sure "clamp in the middle of the straight segment" can be a guideline.  On longer knives, like in your example, it'll work, but the relationship of the clamp distance to the tip, as has been talked about before, plays a large part in the angle at the belly to tip area.  On a shorter knife... where you clamp can change the angle more.
...

To remind of the context, we are talking of a special case of a steep curved tip.

To estimate effect of the clamping position, we ground an identical SWIBO knife from our rental pool the same way and at the same edge angle, but clamped closer to the tip, at 1/3 of the blade length from the tip.
-   Start at the bolster end, and grind the straight segment as usual, sliding across the stone with the knife jig perpendicular to the US till you reach the marked radius line.
-   At this point fix the jig position at the US, not sliding laterally further. Do the tip radius by pivoting the jig and raising the handle, till the radius line comes perpendicular to the US (i.e parallel to the wheel margin).

Then compared both knives, looking at the bevel height and measuring edge angle with a laser protractor in the straight segment, and at the tip radius.

RUN 1 - clamped at the middle of the straight part
Naked-eye increase in bevel height to the tip; the edge angle is almost the same in the middle of the blade and at the tip radius... maybe by less than 0.5 degree larger at the tip, hardly detectable by the portable CATRA laser protractor.




RUN 2 - clamped at the tip 1/3
The bevel is of pleasantly even height all along the edge; the edge angle at the tip radius is larger by +4 degrees (per side) compared to the angle in the blade middle.



Before you ask, I measured the manufacturer's edge angle - SWIBO are very well made knives, probably the best in their class, of 56-58 HRC and 120-130 BESS score out of the box; the bevel is of even height all along the edge, and edge angle at the tip is by only 1 degree larger than in the middle of the blade.

[Ken S]

Wootz,

I like your idea of using protective paper on your knife in jif photo. I am starting a new topic with a question for you.

Ken

[cbwx34]

To remind of the context, we are talking of a special case of a steep curved tip.
....

We might have gotten our wires crossed a bit... I was more stating as a "general rule" don't use "clamp in the middle"... not your specific example.

Thanks for the post though... good information as always, and good info on what to look for in setting the knife in the jig.  (Also, a good example of what I'm now calling... the "Collar Effect").     (Your setup effectively deals with that too).

[wootz]

A thought once uttered becomes untrue without the context

[Ken S]

Good thought, Wootz.

Ken

[troflog]

I've had a chance to try Kavik's modified collar... and have already told him... he's not getting it back.   

With the "sides" of the collar removed,  I get a nice fluid movement from straight portion -> belly -> tip.

I'm not much on videos, but tried to make a couple of short ones... just to give an idea.  Note how close the knife stays to the (imaginary) LOC on the stone...

https://vimeo.com/234061935

https://vimeo.com/234061995

... in the 2nd video,,, even a blade that is basically curved the entire length, is a nice smooth movement.  As a bonus, where the knife is set in the jig appears to be less of an issue... having the pivot basically in the same location gives a nice consistent bevel.  (I tried to keep my hands out of the way a bit more in the 2nd video, so maybe you could see the pivot area better.. and showed the shape of the knife at the start).

I thought there might be a problem, since the "stop" is so smooth, it might "ride over" the USB... but maintaining the same pressure needed to keep the jig on the USB... this didn't occur.  Also, not an issue keeping the straight portion of the blade parallel to the stone.

Works great... I like it.      (I'm not much on making videos... but hoped this would at least give some idea of how well it performed).   

As a double bonus... wootz allowed me to beta test his new Android version of the app for setting the USB height to set the angle.  Honestly, when I first read it on his website, I thought it would be no easier than the AngleMaster... man, was I wrong.  It's great too... makes setup easy and very accurate.  Highly recommended. 

Is it possible to put these videos on Youtube?

[cbwx34]

https://vimeo.com/234061935

https://vimeo.com/234061995

Is it possible to put these videos on Youtube?

The above links should work now... (I somehow had set them to private).

BTW, Rick's "Pin Pivot Collar" is a bit better solution, if he has any left to sell.

If not, and if you have a spare collar, you can just cut the collar down to size... I did it here.  (It wasn't the prettiest job, which is why I "censored" it), but it worked.

[Ken S]

We are fortunate to have a good source for spare parts. Extra parts, plus the courage to risk needing them, help drive our innovative spirit.

Ken

[troflog]

https://vimeo.com/234061935

https://vimeo.com/234061995

Is it possible to put these videos on Youtube?

The above links should work now... (I somehow had set them to private).

BTW, Rick's "Pin Pivot Collar" is a bit better solution, if he has any left to sell.

If not, and if you have a spare collar, you can just cut the collar down to size... I did it here.  (It wasn't the prettiest job, which is why I "censored" it), but it worked.

Thank you very much. This is a great forum. I think I will try to make one myself by grinding down the standard collar. But I will try only to grind the sides if it is possible:)

[Ken S]

In fairness to the Tormek engineering team, we should acknowledge that we forum members do not have many of the constraints that they have. We do not have the ever presence of various safety  commissions examining our work. We do not have the accounting and marketing departments pressing us for a single "one size fits all" cost effective solution. We do not have the experts bemoaning that our designs require the end users to raise their level of skill by 3.17%, thus limiting the market.

The standard issue Tormek knife jigs do a commendable job for most knives at a very reasonable cost for most users. However, I am proud to be one of those in pursuit of a more commendable jig.

Keep on innovating!

Ken

[Hogdog6]

I have one of Rick's pivot pins and along with the information here in this post it has completely changed how much I enjoy my Tormek. Thanks to Rick and all of you for making my Tormek better than it ever was.