Author Topic: SVM-45 optimal blade thickness?  (Read 3672 times)

Offline cbwx34

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Re: SVM-45 optimal blade thickness?
« Reply #30 on: April 07, 2018, 12:15:30 am »
Adjusting the collar used to be necessary for fine-tuning the angle, but that was before the micro-adjust feature was introduced. The SVM-45 is an ancient jig, but it's not clear how the suggested improvements could be engineered. The Tormek will allow one to easily adjust and measure the edge angle to within a couple degrees or more, and for me that's more than enough precision. I usually change the edge angle on a kitchen knife by 5 degrees if I want to alter the way it performs.

Slicing papers and arm hairs is all for show, although it does indeed demonstrate sharpness. It's the amount of roughness on the surface of the bevels that determines how a knife will perform in the kitchen. Sometimes you want the edge polished; but sometimes you want it rough, with a "tooth" to it. The Tormek allows for this variation well enough for me.

The collar still turns, so if the micro-adjust made it unnecessary... seems they could have locked it in place?  There are numerous examples of the suggested improvements (although Tormek would probably  have to come up with its own variation).


No one is saying that the micro-adjust made adjustments of the collar of the SVM-45 unnecessary. It is still needed for some adjustments, but the micro-adjust makes it not critically necessary for fine adjustments of the angle.

Quote
As for precision, look no further than examples in this forum, where some are measuring in tenths. ;)

No one has ever demonstrated that they can use the SVM-45 to create an angle that's uniform to within a tenth of degree along the length of an edge. Not even close. I would bet that the best, most experienced sharpeners couldn't even achieve one degree, probably a few degrees is the best they could do.

Making a measurement that's accurate to within a tenth of a degree is not the same thing as being able to reproduce something to that level of precision.

I guess I read "used to be necessary" as "no longer necessary".  ;)

I'll let the person who claims "edge angle controlled with 0.1 degree accuracy" defend that one, (or maybe it doesn't apply in this case).  8)

Offline TorbenDenmark

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Re: SVM-45 optimal blade thickness?
« Reply #31 on: April 15, 2019, 11:00:59 am »
Hi all,

This is my first post in this forum. I bought a T8 a few months ago and have so far only been reading in here, learning from all the experience gathered. I must admit my expectations have not been met with this machine. Being used to sharpen knifes with water stones I expected to sharpen knives fast and precise right away. That didn't happen :). So far I am still learning but the results are getting better even though sharpening a knife still takes me forever.

The reason why I am replying to this inactive thread is that it is the newest I could find that deals with the asymmetry of the SVM-45. In this thread and another (https://www.tormek.com/forum/index.php?topic=3445.msg21408#msg21408) Lape and RickKrung measure the jig. You both measure the thickness of the flat to around 9 mm. This figure is then used to calculate the offset to the jig centerline and you both get around 1 mm and it is then concluded that a knife with a blade thickness of 2 mm will be symmetrical placed in the jig.

I have done the same measurements as you guys and I get the same numbers. However I believe that the measurement of the flat thickness (9 mm) is measured at the wrong place giving a wrong result. What I did was to place the SMV-45 bottom part on a flat surface. I measured the distance from the top of the shaft to the flat surface in each end and as it was the same, I concluded that the centerline of the jig was in parallel with the flat surface. Then I measured the distance from the flat surface to the top of the flat in the same place where you have measured it, and I also got 9 mm. However when measuring the distance from the flat surface to the top of the flat at the end of the jig where the knife is resting the distance was 9,4 mm. If you look at the plane where the knife is resting, in each side of the jig the surface is a little big higher (sorry for my bad vocabulary  :(). This is also visible on the 3rd picture in RickKrung post in before mentioned thread.

A distance of 9.4 mm leads me to conclude that the offset to center line is only 0.6 mm and that my jig (I know there are several versions) is made for a blade thickness of 1.2mm. I have checked this with control measurements with the angle master and they verify this. If I mount a knife with a blade thickness of 2 mm in the jig, I get a smaller angle on the side of the knife that rests on the bottom part of the jig relative to the other side.

As many of my knifes are around 2mm thick, this leads me to conclude that I need to take some material off the SVM-45. This seems drastic as all of you (except Wootz) are talking about inserting spacers instead. So if any of you guys still have an interest in this, please comment. Am I overseeing something? I will postpone the modification for now :).

Thank you all for sharing your knowledge in here guys. I have learned a lot from you and there is still a lot more to learn :)

PS Sorry for the orientation of the picture. I can't get it right.

Torben, Denmark     
« Last Edit: April 15, 2019, 11:08:22 am by TorbenDenmark »

Offline RichColvin

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Re: SVM-45 optimal blade thickness?
« Reply #32 on: April 15, 2019, 12:48:54 pm »
Torrent,

I like the picture you drew, and the math seems to be right.  I’m interested in what others with more knife sharpening experience have to say.

Kind regards,
Rich
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Rich Colvin
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You are born weak & frail, and you die weak & frail.  What you do between those is up to you.

Offline RickKrung

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Re: SVM-45 optimal blade thickness?
« Reply #33 on: April 15, 2019, 08:55:20 pm »
Hi all,
...snip..
As many of my knifes are around 2mm thick, this leads me to conclude that I need to take some material off the SVM-45. This seems drastic as all of you (except Wootz) are talking about inserting spacers instead. So if any of you guys still have an interest in this, please comment. Am I overseeing something? I will postpone the modification for now :).

Thank you all for sharing your knowledge in here guys. I have learned a lot from you and there is still a lot more to learn :)

PS Sorry for the orientation of the picture. I can't get it right.

Torben, Denmark   

Three things:

1) I struggled with the orientation of images for a while also.  It has to do with the orientation setting within "Properties" of your original image, as taken.  I found I have to take the photo in "landscape" in order to get it to display properly.  I tried editing that property field but that did not work.  Now what I do is take the photo in landscape, moving back far enough to get the whole object in view and then in my editor, crop the image down to include just what I want. 

Another very helpful edit is to reduce the image size to 640x480 pixels so it displays the whole image in the browser, to eliminated the unnecessary action of scrolling oversized images. 

2) There is a raised "Tormek" logo on the back of my jigs, which could cause the difference in readings you report.  If the raised logo is present on your jig, it will NOT be resting parallel with your reference base.  I think you may need to rest the jig on some precision parallels to get it level before you take the measurements. 

3) I HAVE modified some of my jigs, as Wootz has, to enable the use of shims for getting blades more centered.  I have four SVM-45s.  Two are unmodified.  One is modified by removing 0.5mm, another by removing 1.0mm.  I also shortened a set of feeler gauges so they are only slightly longer than the SVM-45 jig is wide.  This really helps when blades are narrow and/or short enough that full sized feel gauges interfere with getting the bevels to the grindstone. 

For the time being, using these modified jigs and shims has somewhat alleviated my need for a true self-centering jig, although I am still pursuing such a jig. 

Rick
If you want nice clean, fresh oats, you must pay a fair price. However, if you can be satisfied with oats that have already been through the horse, that comes at a lower price.

Offline RickKrung

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Re: SVM-45 optimal blade thickness?
« Reply #34 on: April 15, 2019, 09:44:09 pm »
Hi all,
...snip...
However when measuring the distance from the flat surface to the top of the flat at the end of the jig where the knife is resting the distance was 9,4 mm. If you look at the plane where the knife is resting, in each side of the jig the surface is a little big higher (sorry for my bad vocabulary  :(). This is also visible on the 3rd picture in RickKrung post in before mentioned thread.

A distance of 9.4 mm leads me to conclude that the offset to center line is only 0.6 mm and that my jig (I know there are several versions) is made for a blade thickness of 1.2mm.
...snip...
Torben, Denmark   
...snip...
2) There is a raised "Tormek" logo on the back of my jigs, which could cause the difference in readings you report.  If the raised logo is present on your jig, it will NOT be resting parallel with your reference base.  I think you may need to rest the jig on some precision parallels to get it level before you take the measurements. 
...snip...
Rick

I drafted this out in my CAD program.

The distance from the bottom rear of the fixed jaw to the close side of the raised logo is 39.63mm (1.560") (I did this in inches and rounded the mm's so there may be some slight discrepancies in the mm numbers).  The distance from the bottom rear to the front of the jaws is 84.84mm (3.340"). 

I drew a parallel line at length 39.63mm and then another offset 0.18mm (0.007") which is the height of the raised logo.  I then drew a line from the bottom rear point to the raised logo height point.  And THEN projected that angled line to 84.84mm to represent the front jaw height.  The offset of that front jaw point from the parallel line was 0.38mm, which if rounded yields 0.4mm. 

0.4mm is exactly the number you got with your measurements. 

Rick
If you want nice clean, fresh oats, you must pay a fair price. However, if you can be satisfied with oats that have already been through the horse, that comes at a lower price.

Offline Jan

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Re: SVM-45 optimal blade thickness?
« Reply #35 on: April 16, 2019, 10:06:17 am »
The uncertainty in the offset estimation lead me to estimate the value by a deductive way.

I have assumed that the Small Knife Holder works symmetrically with respect to flip. Because the steel guide bar (1) of the Small Knife Holder has a thickness of 2.5 mm, I have deduced that the jig offset is 1.25 mm.
https://www.tormek.com/forum/index.php?topic=2577.msg15232#msg15232

Jan
« Last Edit: April 16, 2019, 10:11:06 am by Jan »

Offline TorbenDenmark

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Re: SVM-45 optimal blade thickness?
« Reply #36 on: April 16, 2019, 10:59:39 am »
cbwx34 and Rick thank you for your messages and effort to investigate my observation. I will post a reply here soon...

Jan thank you for your input. I have seen your post before about this. I respect your way as I have also realized that this is more complex than I first thought it would be :). But... 1.25 mm seems like a lot to me. When I mount my 2 mm thick kitchen knife in the SVM-45 jig and I compare the angles on each side of the blade with the anglemaster, the anglemaster tells me that the side of the blade in contact with the bottom part of the jig is sharpened at a slightly smaller angle than the other side. This is, according to my understanding, caused by the center of the knife blade being above the centerline of the jig, meaning that the knife is too thick for this jig. Your estimation says that the jig should sharpen a 2.5 mm thick knife symetrically. I do not own a 2.5 mm thick knife but I expect the asymmetry would be significant. Does this work for you? And if yes, can our jigs vary that much? I saw a picture in here of a SVM-45 where the shaft was not straight at all.   

I am aware that the way I mount the knife and tighten the jig can also influence the angle but I pay attention to this and I do it as advised in this forum.   

Torben

Offline Jan

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Re: SVM-45 optimal blade thickness?
« Reply #37 on: April 16, 2019, 05:05:59 pm »
Torben, from your reply I see you understand that really in depth!  :)

Your estimation, that your jig works symmetrically for blade thickness of 1.2 mm riddles me. I consider this value for anomalous one.

Since I have accepted the value 2.5 mm, I use standard SVM-45 knife jig for all blades with thicknesses from 2.0 to 3.0 mm. With a naked eye I am not able to see any asymmetry in the edge width. I was not diligent enough to study the edge width under the microscope.

For thicker blades I use now my prototype of a self-centring knife jig.

Jan

Offline TorbenDenmark

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Re: SVM-45 optimal blade thickness?
« Reply #38 on: April 17, 2019, 10:25:21 am »
Torben, from your reply I see you understand that really in depth!  :)

And then clearly not :). cbwx34 has been so nice to inform me that I got it backwards. So to save some honour I hereby state that I have not got it backwards, I just wrote the opposite of what I mean  :). What I meant was...

I put a 2 mm thick blade in the SVM-45 jig. The angle master tells me that bottom side of the blade (in touch with the bottom part of the jig) is sharpened at a higher angle than the top side. This leads me to conclude that the blade center line is above the jig center line and hence the knife is too thick for the jig.

Hope I got it right this time.

Jan just like you, my (little) experience with this machine also tells me that I will not be able to see these small difference with a naked eye. But I find it quite funny analysing and maybe optimizing these small things. It makes me feel I'm in control of the sharpening process. I hope it is ok to enter nerd mode once in a while. I can see I am not the only one doing it in here :)

Torben
« Last Edit: April 17, 2019, 01:48:22 pm by TorbenDenmark »

Offline TorbenDenmark

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Re: SVM-45 optimal blade thickness?
« Reply #39 on: April 17, 2019, 02:17:03 pm »
I drafted this out in my CAD program.

The distance from the bottom rear of the fixed jaw to the close side of the raised logo is 39.63mm (1.560") (I did this in inches and rounded the mm's so there may be some slight discrepancies in the mm numbers).  The distance from the bottom rear to the front of the jaws is 84.84mm (3.340"). 

I drew a parallel line at length 39.63mm and then another offset 0.18mm (0.007") which is the height of the raised logo.  I then drew a line from the bottom rear point to the raised logo height point.  And THEN projected that angled line to 84.84mm to represent the front jaw height.  The offset of that front jaw point from the parallel line was 0.38mm, which if rounded yields 0.4mm. 

0.4mm is exactly the number you got with your measurements. 

I see your point about the TORMEK logo on the back side of the jig Rick and the fact that you are able to derive the same 0.4 mm difference as I measure, verifies that the difference is caused by the raised logo.

I was aware of the logo when I did the measurements. However as you have now derived that the raised logo lifts the end of the jig where the knife rests by 0.4 mm, I would also expect the other end of the jig (the shaft) to drop. I measured the distance from the ground surface to the top of the shaft - in each end of the shaft (see attached picture), and found the distance the same in both ends. So I concluded that the shaft was in parallel with the ground plane and hereby the centerline of the jig too. This I still don't understand.

After reading your post I have remeasured the shaft and also measured on the jig when I push the raised logo just outside the surface that the jig rests on, with the purpose of cancelling the effect of the logo. I have measured many times but I must unfortunetaly conclude that I am not able to achieve consistens accurate results. I do not posses the proper measuring equipment and maybe also the skills to do this. So I have to stop here. It bothers me to leave this without fully understanding, but without being able to make accurate measurements I will not get any further.   

Thank you for your effort and response cbwx34 and Rick.

Torben
« Last Edit: April 17, 2019, 02:21:33 pm by TorbenDenmark »