Using Dutchman Tables with Square-Edge Jig for Plane Irons?

[arnman]

Steve,

So if you find there are errors in my assumptions or calculations, please do elaborate.  I'll be grateful, and happy to fix it,

Kind regards,
Rich

Rich,
Thank you for responding and making that app available.  Sorry I could not recall your name when I referred to this in my post.  I was looking for your name on the website app, but did not see it.

One minor comment on the calculations you shown at the bottom of the diagram - I believe there is a typo.  It seems there is a "2" missing in equation 1, just in front of the parentheses.  I think the quick calculator is using the "2" in that equation.


Once again, I really appreciate the discussion on this topic.  There have been many more responses than I expected.  Great discussion on the effects of wheel wear.  I am hoping to dedicate some time this weekend to dive in.

Steve

[Dutchman]

...
I'm the creator of the Sharpening Handbook.
...

Rich
On your website I miss my second publication "More math for the Tormek grinder".
The following reference comes from the topic of the link in my signature.

20180702
At the request of "cbwx34" I developed mathematics for use with its robust "jig-fix" as published on https://forum.tormek.com/index.php?topic=3570.msg22912#msg22912
The new formulas can also be used to choose a different reference point for the distances than the center of the jig's stem, which is unclear and inconvenient.
As a result, the setting of the sharpening angle can be determined more accurately.
Some measurements were also made from which possible sources of error appeared.
The new document is titled "More math for the Tormek grinder"
You will find the documents in the public folder "Tormek-T7 grinder":
https://bit.ly/2lHaR3m on DropBox
https://bit.ly/2KpROFg on OneDrive
The new documents are:
    • "More math for the Tormek grinder A5 serial.pdf", serial version for tablet
    • "More math for the Tormek grinder booklet.pdf", A5 booklet to print on A4
    • "USB adjustment table.ods", spreadsheet to generate the new table

[RichColvin]

Ton,

Thank you for letting me know of the missing document.  I will add these later today. 

Kind regards,
Rich

[arnman]

Arnman, Dutchman tables do not work for the square edge jig because the geometry of this jig is substantially different from the knife jig.
...

The equations in "More math ..." can be used 

Dutchman, Thank you for your excellent work, and sharing this information.  I did not understand immediately what you meant by your comment about "More math...".   Then I realized this was a reference to an update of your original document.  I have now spent some time studying the "More math" document. 

I am pursuing the use of these concepts for chisels and plane irons, with the SE-76 square edge jig.  My question is how to establish the distance JC for this jig - which is for a single bevel blade.

Please confirm if my method is correct, or point out where I am wrong.

Distance from the jig bedding surface/bottom of blade to the bottom of USB = 23.5 mm.
Subtract 6 mm (radius of USB) from this value = 17.5 mm.
Add the full thickness of the blade (3.0 mm).
JG = 20.5 mm.

Thanks again.
Steve

[Dutchman]

...
Please confirm if my method is correct, or point out where I am wrong.

Distance from the jig bedding surface/bottom of blade to the bottom of USB = 23.5 mm.
Subtract 6 mm (radius of USB) from this value = 17.5 mm.
Add the full thickness of the blade (3.0 mm).
JG = 20.5 mm.

Thanks again.
Steve

Steve,
Please add a figure, a rough sketch is sufficient.
So as I understand now, only half the blade thickness should be added.

[Jan]

Arnman,

For SE-76 use the distance 23.7 mm.

In my understanding the square edge jig SE-76 geometry is complicated by the small raised edge in the rear part of the jig base which tilts the tool upwards by some 1.3⁰5. For sure I take this into account in my calculations. 

Jan

[cbwx34]

...
Please confirm if my method is correct, or point out where I am wrong.

Distance from the jig bedding surface/bottom of blade to the bottom of USB = 23.5 mm.
Subtract 6 mm (radius of USB) from this value = 17.5 mm.
Add the full thickness of the blade (3.0 mm).
JG = 20.5 mm.

Thanks again.
Steve

Steve,
Please add a figure, a rough sketch is sufficient.
So as I understand now, only half the blade thickness should be added.

I think he's right to use full thickness... since it's a single bevel?  (But yeah, sketch would help).

[smurfs]

Jan,

I'm just curious about the annotated angle of 91.5⁰ in your sketch as I would have just assumed it to be 90.0⁰.
Did you derive this angle mathematically or did you measure it using an AngleCube or such like?

Thanks, Andrew

[Jan]

Andrew, you are welcome! 

I got the value by measuring the height of the protruding edge (0.75 mm) and the width of the jig base (33.3 mm). The arctan of the ratio 0.75/33.3 gives the angle 1.3⁰. It is also directly measurable with a protractor. 

In both cases the accuracy is limited to some +/- 0.3⁰.

Jan

[cbwx34]

Oops  : missed Jan's sketch...  pretty much nails it! 👍🏼👍🏼

[smurfs]

Thanks for the clarification Jan.

I don't have a SE-76 but do have the SE-77 so can now determine the 'right' angle. That said if you have already done the calculation and can share it that will save me and others the effort of doing so

[arnman]

Unfortunately, I am unable to load photos small enough for the forum.

I have attached a crude sketch that shows my measurement from the bottom of USB to bedding surface.  I am interpreting Dutchman's "More math" sketches to calculate JC as shown.

It is my understanding that for a blade already ground (approximately), then the "sinking" effect could probably be neglected, and the full thickness of the (single-bevel) blade should be used for calculations, as this is the line to the tip of the blade at the grinding wheel.

If I am interpreting Dutchman's sketches correctly, the JG measurement is from the tip of blade contact with the stone to the back face of the USB as shown.  I would appreciate confirmation that I am calculating JC correctly, and interpreting the JG dimension correctly.

Jan, apparently my jig dimensions do not match yours.  Maybe I do not have an SE-76.  Also, mine does not have a notch inside to affect the bedding angle.  I guess this is why my calculations were not matching the ones you posted earlier.

More comments are welcome.  I really appreciate the discussion on this.

Steve

[Dutchman]

...
If I am interpreting Dutchman's sketches correctly, the JG measurement is from the tip of blade contact with the stone to the back face of the USB as shown.
...

It also depends on where on the arc, caused by the round stone, the grinding angle must match.
That is of academic interest, but I am not concerned about that. 

[Jan]

Thanks for the clarification Jan.

I don't have a SE-76 but do have the SE-77 so can now determine the 'right' angle. That said if you have already done the calculation and can share it that will save me and others the effort of doing so

Andrew,

I have posted only some guidance here because in my understanding Arnman intends to develop his own calculator.

I have done my calculations some three years ago, so it can take some time for me to prepare a script suitable for sharing on this forum. Evermore I am not a good Excel programmer because I have grown up with IBM FORTRAN which I still use in a DOS window. 

Jan

[cbwx34]

...
If I am interpreting Dutchman's sketches correctly, the JG measurement is from the tip of blade contact with the stone to the back face of the USB as shown.  I would appreciate confirmation that I am calculating JC correctly, and interpreting the JG dimension correctly.
...
Steve

I guess it depends on how you write your formula, but I believe JG should be from the tip of the blade to the center of the USB.