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

[arnman]

I found the excellent threads discussing the Kenjig and Dutchman tables.  It seems the discussions and Dutchman's tables were developed for the knife jig.

I would like to develop some quick-set jigs for plane irons and chisels.  I have the old-style square jig, if that matters.

I don't see any reason why I could not use Dutchman's equations to develop settings for my purpose, but I thought I would throw this out to more experienced users first.

Thanks.
Steve

[Ken S]

Excellent question, Steve.

I don't see why Dutchman's tables would not work. In my case, I started what would evolve iinto the kenjig sharpening my chisels and plane blades. This was before Dutchman posted his tables. My goal at the time was to avoid having to measure each blade using the Anglemaster. By keeping the Distance and Projection constant, I could sharpen chisels and plane blades all day without having to remeasure.

I used the two holes in the TTS-100 to set a constant Distance. With this Distance set, I used the Anglemaster to set the appropriate Projection. I then marked this projection (from the front of the square edge jig) on a piece of blank label tape placed in one of the three slots of the TTS-100. I made a mark at the end of the blade in the slot and labeled it (eg. "25 degrees"). Adjusting the Projection instead of the Distance is a bit clumsy, however, I only needed to do it once.

You might have to compensate to use Dutchman's tables with the square edge jig. I have not tried this, however, I don't think it would be omplicated. Hopefully Dutchman will post. He is the authority on this. I will email him.

Ken

[arnman]

Thanks Ken.

I thought about using some trial and error to set the projection (and make a jig), using a fixed support distance from the wheel surface.  However, I know that over time this relationship would change.  Of course, I don't know how long that will take.

My thought was possibly to develop a spreadsheet using Dutchman's equations, specifically for use with the square grind jig.  As you know, there would be a different range of "S" and "A" values with the square grind jig vs the knife jig.  Also, I thought I may as well use the spreadsheet for the range of wheel diameter I will be working in for the realistic future (which is 230 mm to 240 mm).  I could run the spreadsheet for each 1 mm change in wheel diameter.  At this time, I don't know how sensitive cutting bevel is to a slight change in wheel diameter.  But for the level of sharp we all like to chase, I suppose it would be sensitive.  I guess if I get it really close with the set-up, I can do a slight adjustment using the sharpie method before grinding.

I have a lot of ideas floating through my mind right now about how to implement this.  One of them would be to develop an adjustable projection jig, which would allow the projection to be set to the spreadsheet projection values - which would ALL be established for the SAME distance between the support and wheel surface "S).  I could use a spacer block to set the support bar.

I hope that makes sense.  I have to think through the details a bit more. 

I don't have much experience with the machine, so I could be chasing a bad idea.

Steve

[Ken S]

Steve,

I think you are overthinking this. Most bench chisels are sharpened with a 25° bevel. Paring chisels normally get 20°. If you happen to use mortise chisels, they get 35°. Plane blades normally get 25°.

One of the reasons I used the TTS-100 is that the two small wheels are Tormek's patented means to auto correct for wheel diameter changes. (The 250mm T8 wheels and the 200mm T4 wheels use the same TTS-100 with no adjustments.) A plane blade or chisel back is a large enough surface to work well with the Anglemaster. Either the tape mark in the slot or wooden stop blocks work well to set the Protraction.

You have good creative instincts. I just think another project would be better for them.

Keep thinking!

Ken

[Jan]

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

Nevertheless you can use the Dutchman's approach and equations to calculate tables for square edge jig. I have a simple calculator for it, so I can verify your results. Let me know.
 
Jan

P.S. Important guidance resulting from recently closed discussion on this forum: the set up does not depend on the chisel thickness!

[arnman]

Thanks Jan.  I understand Dutchman's tables are outside the range of the square edge jig.

I developed a calculator for use with the square edge jig.  Here is my input:
Wheel diameter = 237.0 mm
Surface of wheel to center of support bar = 19.0 mm
Grinding bevel angle = 25.0 degrees

Here is my output:
Back of support bar to wheel surface = 41.78 mm

The blade projection from the front of jig will have to be determined after I get a good measurement directly from the jig.

As I said earlier, I would hope that I can make a sliding jig that will allow a changing blade projection setting as the wheel diameter changes.  I have a simple prototype in mind that is just a couple of wood blocks with slots and a screw to tighten.  Of course, I don't know how quickly the wheel diameter will change, as I am expecting the original wheel to last many more years.

Thanks for your help.  I can attach my Excel file if you would like.

Steve

[Jan]

Arnman,

For D=237 mm, chisel/plain iron protrusion 50 mm and target angle 25⁰ the distance between USB centre and stone surface should be 27.8 mm. The spacer block USB/stone would be by 6 mm shorter i.e. 21.8 mm.

Jan

[arnman]

Jan,
Can you please clarify what you mean by "protrusion"?

Is that the distance from the back of the USB to the stone, or the distance from FRONT of square jig to stone?

Thanks.

[Jan]

Arnman, the protrusion is measured from the front of the square edge jig to the stone surface. My calculations are for the SE-76 jig. I hope it will work for the jig SE-77 also, but cannot guarantee it because I do not have it.

The angle 25⁰ is at the tip of the plane iron. If you measure it with protractor you get slightly larger angle because you measure chord angle between the back, tip and the heel. For  plane iron which is 4 mm thick the chord angle is some 27⁰ in this case.

Jan

[Dutchman]

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 

[Jan]

Arnman,

the attached graph can answer some of your questions concerning stone wear. Chisels and plane irons are handled in the same way.

Jan

[Ken S]

Jan's graph says a lot. When I designed the kenjig, I decided to leave the Projection constant (at 139mm, although the 140mm used by others is just as valid). I wanted to incorporate the self correcting double wheels of the TTS-100. Although Tormek only uses this patented feature for turning tools, it can just as easily be used for woodworking tools and knives.

Jan's graph, like Dutchman's tables, uses diameter changes of ten millimeters. I constructed the kenjig using the 15° line on Dutchman's 250mm diameter chart. Going across to 139mm Projection, I went up to 80mm Distance. At first I debated between making a set of kenjigs for ten millimeter diameter wear reduction or dedicating the kenjig to that particular grinding wheel and modifying the jig as needed for wear. Kenjigs cost almost nothing to make, and they are  quickly made. Either option would work. A professional sharpener might prefer to make a set.

At the risk of sounding like a heretic, I do not believe that home shop sharpeners, the majority of us, need to be concerned about wheel wear. Wheel wear of ten millimeters (diameter) will change the bevel angle by about one degree. (2° with the double bevel). I can see where that amount of change might make some of us nervous. If so, it's time for a new kenjig. I make the wooden kenjigs using my table saw and bandsaw. The set up is what takes the time. I think it is wise to make up several spare blanks. With a diameter change of one millimeter, a change of 1/10° will happen. Yes, this is noticeable with the math. Can we accurately measure this change, or, more importantly, can we detect a difference in cutting?

How long will it take the average home sharpener to wear off ten millimeters from his wheel diameter? How many longtime Tormek users are still using their original grinding wheels. For most of us, wheel wear is glacial.

As constant diameter diamond and CBN wheels become more commonly used, I see wheel wear becoming increasingly less important.

Several years ago, I was particularly impressed with the comment Jan made pointing out the error in my kenjig. Jan is enough of a highly skilled mathematician to notice the error and a practical and honest enough sharpener to also note that the error was not significant.

We need both skilled mathematicians and practical sharpeners.

Ken

[Jan]

Ken, I think that the protrusion 53 mm used in the graph above and below resulted from some discussion with you. But because it is already some three years ago I have forgotten what was the reason for this unusual dimension. Nevertheless the graph is still useful.

I am attaching another graph which shows the situation for 30⁰ edge angle used for chiselling in hard wood.

Jan

[arnman]

Thanks for this discussion.  I hope to have time to review some of your comments this weekend.

One thing I did notice - I made my own spreadsheet based on Dutchman's calculations and assumptions, and I match the numbers in his tables exactly.

I found another website app (from one of the Tormek site members) called Sharpening Handbook.  The math is basically the same as Dutchman's, but there are some slightly different assumptions involved - such as the distance from the top of the USB to the center of jig.

I found that these differences result in minor changes in the results.  I don't really mind the slight difference - I am more concerned with jig settings for repeatability.

Steve

[RichColvin]

Steve,

I'm the creator of the Sharpening Handbook.  I truly believe I will never be the font of all wisdom (though I've had plenty of learning mistakes), and this tool can only get better with others' help.  And since most of the information came from others, it will stay free to use. 

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