Report: Sharpening a HSS planer blade by numbers using the SE-76

[aquataur]

I have recently sharpened the blade of a metal hand planer, which is a look-a-like of a Stanley single iron bench plane SB3 (just to make clear what I talk about). The blades are hardened (HSS), so the standard SG stone will take hours. I used a F120 corundum stone for the coarse work and a SiC stone to make it finer.

Since chisels and similar blades have a flat upper surface, the WM-200 angle tool works fine for that. The recommended grinding angles for those blades are between 20-30 dps (although there is only one side to be sharpened). The blade itself is angled at about 45° from the working surface, which leaves several degrees of relief behind the cutting edge. In my case the bevel is down.

Spoiled by sharpening by numbers, I looked if setting the angle by T-USB was feasible, which would allow for grinding and honing at a precise angle, just as it is customary todays for knives.

All associated programs ask for the jig diameter. They were obviously developed with knife sharpening in mind, so they silently assume a symmetrically round jig (at the spot where it rests on the USB at least). All past knife jigs fulfil this demand, and the diameter was chosen for simplicity and convenience.
The real value of interest however, is the distance from T-USB to the imaginary center plane that is constructed by the line through the center of the spine (of a knife) and the cutting edge (let´s call this the center plane for the lack of better words).

This is the parameter the program works with, because this distance is a crucial part in constructing the triangle that spits out the T-USB-to-stone value we are after; on a standard knife jig it comes out as 12 mm / 2 = 6 mm.
The graph here Calculations used for calculating SVM Knife Projection displays those relations quite nicely.

But note, this is a source of error: the older models of the knife jig used to have a 12 mm metal bar and thus a consistent diameter throughout. They had the potential of non-symmetric clamping, which would lead to uneven bevels. Its current successor was made symmetric, but has an inherently variable bar size due to its construction. Using it at the outmost rest will indeed yield 12 mm, but on the inner rest, for smaller knives, it will be more like 14 mm. This introduces an error probably overseen by many.

Fortunately sharpening of knives is not rocket science, a fraction of a degree up or down won´t hurt as long as the settings are consistent, repeatable and symmetric, but keep that source of error in mind particularly if you are the nit-picking type.

I used the SE-77 SE-76 square edge jig (in case this has changed over the years: I speak of the model ca. 2007) as a test candidate. The parameters needed for the program(s) are not obvious or readily measurable, so I looked into that.

The first parameter to determine is jig diameter. As mentioned before, the internally used value is the distance from T-USB to the center plane. In our case, the latter coincides with the top of the blade (there is no second blade side and there is no upper half of the jig rod). Consequently the choice for naming this parameter "jig diameter" turns out to be an unhappy one, but that´s how it evolved. Let´s call this real parameter center plane displacement for the exercise.

For the SE-77 square edge jig center plane displacement comes out as 24.5 mm 25 mm (see fig.1 "measuring center plane displacement"; measure the distance from the top of the blade to T-USB using a vernier). This is straightforward. This number is invariable and only needs to be determined once for a given jig.

According to the above explanations, this is only half of what the jig diameter parameter expects despite the fact that it internally works with exactly that number, so you have to enter double of that value, i.e. 49 mm 50mm. (Being taken for granted, this parameter accordingly does not receive particular attention in the above drawing. It is denoted by a circle around the cross-section of the USB.)

One more measurement we need is projection. Projection is defined as the distance between the point where the center plane meets the stone and a plane that is in a 90° angle to it that touches the USB bar at the stop screw (let´s call this stop screw plane, see picture). This is a bit tricky to measure. (Note that neither the jig axle's rest nor the jig stop's contact point are necessarily meeting T-USB. They are different points, but close. Refer to above mentioned graph). Thus directly measuring the distance from the USB's rear side to the cutting edge in parallel to the center plane with a vernier is not yielding the right result, since the SE-76's flanges protrude towards the operator and obstruct any direct access to the USB with the caliper's feeler fingers.

See fig. 2 "measuring stop screw plane to rear jig offset". Place a try square flush to the top of the jig. (Left or right of the stone the jig can be flipped forward or backward and stay put in a resting position). Its one leg is in parallel to the center plane. Measure the distance from the inner edge of the other leg to the USB with the vernier.

It turns out that this offset is exactly 5.5 mm 5.3 mm. (Again, measured on my older jig). The intermediate projection value measured with the caliper was 70 mm (See fig. 3 "measuring the intermediate projection value": use your vernier to measure the distance from the cutting edge to the rear side of the jig. Aim to be in parallel to the center plane), so the correct projection is 70-5.5 70-5.3 = 64.7 mm.

I chose to grind at 27.5 dps, and the T-USB value produced by the program is 26 mm (rounded) 25.9 mm (note: this is only valid in conjunction with the current diameter of my wheel, 198 mm), which is much smaller (about factor 3) than what one may expect for knives due to the much smaller projection.

I sharpened with this value, and after sharpening I checked the edge against the angle gauge notches on the WM-200 (fig.4: "controlling the final angle"); it fits perfectly into (one half) of the 55° notch. So this is another proof that the number method works universally.

A small appliance akin to the ones existing for knives could be made to mount the planer blade at a certain projection every time, in which case one could work with the very same setting over and over until the wheel diameter has changed. Even thicker or thinner blades would not make a difference, since the jig opens towards the bottom.

I later sharpened a plain chisel with the same method. Without going into detail (since the basic procedure is well documented), the angle turns out correct.

Have fun.

Edit: I updated the jig dimension measurements above after finding a more exact method.

[cbwx34]

I have recently sharpened the blade of a metal hand planer, which is a look-a-like of a Stanley single iron bench plane SB3 (just to make clear what I talk about). The blades are hardened (HSS), so the standard SG stone will take hours. I used a F120 corundum stone for the coarse work and a SiC stone to make it finer.

Since chisels and similar blades have a flat upper surface, the WM-200 angle tool works fine for that. The recommended grinding angles for those blades are between 20-30 dps (although there is only one side to be sharpened). The blade itself is angled at about 45° from the working surface, which leaves several degrees of relief behind the cutting edge. In my case the bevel is down.

Spoiled by sharpening by numbers, I looked if setting the angle by T-USB was feasible, which would allow for grinding and honing at a precise angle, just as it is customary todays for knives.

All associated programs ask for the jig diameter. They were obviously developed with knife sharpening in mind, so they silently assume a symmetrically round jig (at the spot where it rests on the USB at least). All past knife jigs fulfil this demand, and the diameter was chosen for simplicity and convenience.
The real value of interest however, is the distance from T-USB to the imaginary center plane that is constructed by the line through the center of the spine (of a knife) and the cutting edge (let´s call this the center plane for the lack of better words).

This is the parameter the program works with, because this distance is a crucial part in constructing the triangle that spits out the T-USB-to-stone value we are after; on a standard knife jig it comes out as 12 mm / 2 = 6 mm.
The graph here Calculations used for calculating SVM Knife Projection displays those relations quite nicely.

But note, this is a source of error: the older models of the knife jig used to have a 12 mm metal bar and thus a consistent diameter throughout. They had the potential of non-symmetric clamping, which would lead to uneven bevels. Its current successor was made symmetric, but has an inherently variable bar size due to its construction. Using it at the outmost rest will indeed yield 12 mm, but on the inner rest, for smaller knives, it will be more like 14 mm. This introduces an error probably overseen by many.

Fortunately sharpening of knives is not rocket science, a fraction of a degree up or down won´t hurt as long as the settings are consistent, repeatable and symmetric, but keep that source of error in mind particularly if you are the nit-picking type.

I used the SE-77 square edge jig (in case this has changed over the years: I speak of the model ca. 2007) as a test candidate. The parameters needed for the program(s) are not obvious or readily measurable, so I looked into that.

The first parameter to determine is jig diameter. As mentioned before, the internally used value is the distance from T-USB to the center plane. In our case, the latter coincides with the top of the blade (there is no second blade side and there is no upper half of the jig rod). Consequently the choice for naming this parameter "jig diameter" turns out to be an unhappy one, but that´s how it evolved. Let´s call this real parameter center plane displacement for the exercise.

For the SE-77 square edge jig center plane displacement comes out as 24.5 mm (see fig.1 "measuring center plane displacement"; measure the distance from the top of the blade to T-USB using a vernier). This is straightforward. This number is invariable and only needs to be determined once for a given jig.

According to the above explanations, this is only half of what the jig diameter parameter expects despite the fact that it internally works with exactly that number, so you have to enter double of that value, i.e. 49 mm. (Being taken for granted, this parameter accordingly does not receive particular attention in the above drawing. It is denoted by a circle around the cross-section of the USB.)

One more measurement we need is projection. Projection is defined as the distance between the point where the center plane meets the stone and a plane that is in a 90° angle to it that touches the USB bar at the stop screw (let´s call this stop screw plane, see picture). This is a bit tricky to measure. (Note that neither the jig axle's rest nor the jig stop's contact point are necessarily meeting T-USB. They are different points, but close. Refer to above mentioned graph). Thus directly measuring the distance from the USB's rear side to the cutting edge in parallel to the center plane with a vernier is not yielding the right result , since the SE-77's flanges protrude towards the operator and obstruct any direct access to the USB with the caliper's feeler fingers.

See fig. 2 "measuring stop screw plane to rear jig offset". Place a try square flush to the top of the jig. (Left or right of the stone the jig can be flipped forward or backward and stay put in a resting position). Its one leg is in parallel to the center plane. Measure the distance from the inner edge of the other leg to the USB with the vernier.

It turns out that this offset is exactly 5.5 mm. (Again, measured on my older jig). The intermediate projection value measured with the caliper was 70 mm (See fig. 3 "measuring the intermediate projection value": use your vernier to measure the distance from the cutting edge to the rear side of the jig. Aim to be in parallel to the center plane), so the correct projection is 70-5.5 = 64 mm rounded.

I chose to grind at 27.5 dps, and the T-USB value produced by the program is 26 mm (rounded) (note: this is only valid in conjunction with the current diameter of my wheel), which is much smaller (about factor 3) than what one may expect for knives due to the much smaller projection.

I sharpened with this value, and after sharpening I checked the edge against the angle gauge notches on the WM-200 (fig.4: "controlling the final angle"); it fits perfectly into (one half) of the 55° notch. So this is another proof that the number method works universally.

A small appliance akin to the ones existing for knives could be made to mount the planer blade at a certain projection every time, in which case one could work with the very same setting over and over until the wheel diameter has changed. Even thicker or thinner blades would not make a difference, since the jig opens towards the bottom.

I later sharpened a plain chisel with the same method. Without going into detail (since the basic procedure is well documented), the angle turns out correct.

Have fun.

Looks good!  There's a calculator for the SE-77 in Calcapp (under "Other Jigs/Tools") if you want to check the results.  (Projection distance is measured from the front of the jig to the edge of the chisel)...

You cannot view this attachment.

There's also a calculator in jvh's "TormekCalc" spreadsheet.

I didn't check your results... since you didn't say what the Wheel Diameter was, (or if you did I missed it), but if it's around 190mm, then we're in the ballpark. 

You may also find this thread of interest...

SE-77 & TTS-100

... in particular jvh's diagrams which (I believe) confirm your measurements.

[aquataur]

Projection distance is measured from the front of the jig to the edge of the chisel

This will lead to the same result. You will have to add a  constant offset onto the measured values if you use the stock calculator's formulae.

Maybe this is a better idea, because it uses the known method of measuring from the cutting edge to a stop with a ruler.

I never payed attention to this part of the forum so I was not aware of all that. Anyways, the pudding seems eaten and proven.

I never used TormekCalc because it does not run with alternative spreadsheet programs.
I am glad it worked out for Perra's program (Angle Calculator Lite). I like to keep things as complicated as necessary and as simple as possible.

The wheel is that diameter.

Thank you for the link.
I looked at JVH's drawings and the drawings suggests that he determines the offset in the projection plane by referencing the center of the USB, while Rich's drawing clearly references a point on the rear of the USB, which is where the "stop screw plane", as I called it meets the USB. The difference will be 6 mm. Dutchman's formulae (which I believe are the basis of all those calculators) too seem to reference the center of the USB.

I looked up Perra's spreadsheet formulae and saw that parameter "JG", which is taken for the calculation of the triangle, deducts USB/2 = 6mm from the projection value. So both are in a way correct.

I cross-checked with your online calculator, and the results are sufficiently different. What reference point did you choose for calculating the value of projection, based on the cutting-edge-to-jig-front measurement? Center of USB or rear? USB/2 is going to be deducted automatically.

 Can somebody chime in and clear this up?

[cbwx34]

This will lead to the same result. You will have to add a  constant offset onto the measured values if you use the stock calculator's formulae.

Maybe this is a better idea, because it uses the known method of measuring from the cutting edge to a stop with a ruler.

I never payed attention to this part of the forum so I was not aware of all that. Anyways, the pudding seems eaten and proven.

I never used TormekCalc because it does not run with alternative spreadsheet programs.
I am glad it worked out for Perra's program (Angle Calculator Lite). I like to keep things as complicated as necessary and as simple as possible.

The wheel is that diameter.

Thank you for the link.
I looked at JVH's drawings and the drawings suggests that he determines the offset in the projection plane by referencing the center of the USB, while Rich's drawing clearly references a point on the rear of the USB, which is where the "stop screw plane", as I called it meets the USB. The difference will be 6 mm.

Dutchman's drawing too seem to reference the center of the USB, so I guess Rich's drawing, which I used as a reference, uses a different reference point. Can somebody chime in and clear this up?

You're right about the "Constant Offset" (I use 30.1mm)

In Dutchman's original work, measurements were made to the rear of the USB.  When he wrote the "More math..." booklet, the measurements were "mathematically moved" (my phrase) to the USB center, the formula is run, then the answer is "moved" back to the rear.  Difference isn't much in most cases... just made it work better for other than its original intent.  Both booklets can be found in Dutchman's post, for those that are interested.

[aquataur]

I looked at this closely again. Ties my head in knots.

my values (plugged into Perra's program)
I measured from the cutting edge to the rear of the jig: 70mm. I determined USB to rear offset = 5.5mm, give 6. Projection thus 64mm. 5.3 mm. Projection thus 64.7 mm.

center plane displacement = 24.5mm (said to be 25) 25 mm, "jig diameter" thus 49mm 50 mm(just necessary for normal "knife" program)

wheel size = 198mm, sharpening angle 27.5dps yields T-USB = 25.7dps 25.90 dps

calcapp SE-77 values:

your projection value entered is from cutting edge to front of jig, thus 70 minus 35mm = 35
yields T-USB = 26.4 dps

So both achieve virtually the same result, which is relieving.
Those calculations rely heavily on the correct measurement of the displacements. I only had a vernier to determine them and a bit of eye-balling.

It is further relieving since I used the above described "universal" method with my "bessey" axe-jig, which worked well too.

[Ken S]

Aquataur,

I was unfamiliar with with the Stanley SB3. My bench planes are vintage (ancient) Stanley's, my grandfather's 1891 vintage Bailey #5 jack plane, and three 1909 vintage Stanley Bedrocks. Al of the irons (blades) are carbon steel and thinner than today's premium irons.

I found this listing for the Stanley SB3:

https://toolservices.co.za/products/stanley-sb3-bench-plane-iron

The listing states that the Stanley irons are chrome carbon steel. I do not know the steel used in your iron. Most irons are carbon steel. My bench planes are ancient Stanley's (1891 and 1909 vintage). The irons are thinner carbon steel and can be resharpened in just a few minutes with the SG-250.

I am the odd duck on this forum. I use the TTS-100, described in the thread mentioned earlier by CB. I have nothing against any of the set up programs; I have just found them unnecessary for chisels and plane irons.

Ken

[aquataur]

Ken,

it is not strictly a Stanley, which is why I said "akin". Funnily, most people here used to be able to relate to a "stanley planer". It´s actually a now pretty old "Witte Plano" planer.
It has "HSS" stamped on the blade. They were also commonly referred to as "Resopal planers".

I agree that it is not strictly necessary to use a program for simple things like that. That said, devices like the TTS-100 or so may not work too well on surfaces like leather or felt for honing purposes. If we transfer Vadim's knowledge onto chisels and planer blades then honing angles are critical with respect to the grinding angle. The grinding angle by itself is deemed less critical.

I have heared of professionals that do everything by hand and produce razor sharp edges, but those sources seldomly mention the years and years of practise. A "method" that is repeatable and executable by a novice with only a little practise will lead to acceptable results without dedicating a lifetime to the subject.

Curtis, program (parts) like the one you did for the square edge jig are useful, but bear a trap.
The jig may change and all assumptions about its dimensions are up the swanee, or somebody else may have a knock-off that is slightly different.

So providing the basic idea behind it let's people adapt things to their needs. As a famous ancestor of ours said analogously: "I rather teach people to catch fish than providing food for them" ;-)

May I suggest that you add the information to your program how you measure the projection. It is not obvious.

[cbwx34]

I looked at this closely again. Ties my head in knots.

my values (plugged into Perra's program)
I measured from the cutting edge to the rear of the jig: 70mm. I determined USB to rear offset = 5.5mm, give 6. Projection thus 64mm.

center plane displacement = 24.5mm (said to be 25), "jig diameter" thus 49mm (just necessary for normal program)

wheel size = 198mm, sharpening angle 27.5dps yields T-USB = 25.7dps

calcapp SE-77 values:

your projection value entered is from cutting edge to front of jig, thus 70 minus 35mm = 35
yields T-USB = 26.4 dps

So both achieve virtually the same result, which is relieving.
Those calculations rely heavily on the correct measurement of the displacements. I only had a vernier to determine them and a bit of eye-balling.

It is further relieving since I used the above described "universal" method with my "bessey" axe-jig, which worked well too.

Ah... I misunderstood your earlier post.  Yes, to measure the Projection Distance in order to enter it into a "knife" calculator, you'd do just what you did... from the back of the USB to the edge of the blade.  Calcapp just makes the measurement easier, the "30.1mm" puts it to the back of the USB.  And the difference is negligible... if you "rounded down" to 5 instead of up to 6... the answers match... in other words, no big deal.

[aquataur]

Thats great. We just described an alternative way that lets people do some number crunching for virtually any jig to come.

Cheers! ;-)

-Helmut

[aquataur]

Small update. My jig is a SE-76, obviously a predecessor. The dimensions are very slightly different.

Calcapp just makes the measurement easier, the "30.1mm" puts it to the back of the USB.

I found this number on the SE-76 to be 29.4mm, so if I interpolate the values it comes out practically the same.
This is besides the fact that this all is not rocket science, to quote myself.

Note that I updated the jig dimension measurements above after finding a more exact method.

A note for Ken:
I was not in vain that I invested the work to describe the planes and what to look for.
The "bessey" method I described somewhere here for sharpening an axe uses exactly the same principles. You cannot use any of the angle jigs to set up the grinding angle on an axe that has curved surfaces all over it.