Dieter Schmid's Fine Tools

Grintec K2 Sharpening Guide Designed for Japanese Plane Irons

The Grintec K2 is a honing guide specially designed to sharpen traditional Japanese plane irons. In comparison to Western plane irons, Japanese irons are much shorter and thicker. They are also roughly wedge-shaped from heel to edge and the sides are also often not parallel. The name "Grintec" is a mix of the words "grind" and "technology".

For example, the iron shown in the photo to the left is made by Tsunesaburo, and the heel end is 67.6 mm wide, but it narrows to 65.2 mm at start of the bevel. The thickness changes from 9 mm at the heel of the iron to 6 mm at the beginning of the bevel. The iron is 102 mm long, measured to the beginning of the bevel. The bevel is ground at 28° and with with the narrowing of the sides including the bevel, the width of the iron at the cutting edge is 59 mm. These measurements suggest how difficult it is to design and build a honing guide that will hold the irons in place while sharpening them.

Large photos of this sharpening guide

Max. Iron thickness 10.5 mm
Min. Iron width 40 mm
Max. Iron width with adaptor 83 mm
Max. Iron width after dismounting adaptor: in theory no limit, practically speaking probably about 150 mm
Max. Iron length 120 mm
Min. Iron length 60 mm

Directions for Use

Safety Advice

Warning!

  1. During insertion and removal of plane irons from the guide, and during adjustment, sharpening and checking the edge, it is possible to drop the iron or the iron and the guide. These blades are sharp enough to cause deep cuts even from light contact, and dropping one can cause catastrophic damage to an expensive iron, honing guide, and/or one's legs or feet. Always work on a clean, orderly and stable work surface and in a work area free of other hazards and obstructions. Sturdy work clothing and security shoes are also highly recommended.
  2. Be careful not to damage the cutting edge of the tool while using the sharpening guide.
  3. Good light is very important to achieve good results with this sharpening guide.
  4. V Use and store these types of cutting tools in an area children do not have ready access to.

Advice for safe sharpening

  1. In use, the sharpening stone should be securely fixed to the work bench.
  2. Place the sharpening stone in front of you, move the iron and sharpening guide over the stone using both hands, and check the progress on the iron frequently.
  3. Be careful not to allow the guide's wheel to slide off the stone.
  4. Do not attempt to change how the Grintec K2 is put together. Do not use the tool for other applications.
  5. When using the Grintec K2, strictly follow the directions on safety and use as outlined on this page.
Diagram of the Plane Iron

Diagram of the Plane Iron

As shown in drawings B 1a and B 1b, the two sides of the iron are called the face (hasaki-men) and the back (hamoto-men). The angled part of the iron forming the edge is called the bevel (kenma-men, which translates directly as"sharpened area"). The point between the back and bevel is called (hamoto, literally translated "beginning of the cutting edge"). Then there are the sides of the iron and the unsharpened end, where you tap it with a mallet to adjust the iron, is called the head. Traditionally one uses a steel hammer to set the iron in Japan, and this creates a slight mushroom shape that we will call the "mushroom end" of the iron.

The angle between the bevel and the face of the iron is the bevel angle. The distance between the two sides of the iron is the iron's width, and the distance between the head of the iron and the cutting edge is the length.
  1. Mushroomed end of the iron's back
  2. Back
  3. Sides/edges
  4. Iron width
  5. Mushroomed end
  6. Head
  7. Bevel angle
  8. Iron length without bevel
  9. Back
  10. Bevel begin point
  11. Bevel
  12. Cutting edge
  13. Face

How to use the Grintec K2

  1. It is crucial that the bevel lies flat on the sharpening stone and that the angle between the stone and the iron remains constant. The Gintec K2 sharpening guide allows both these vital points, flat, even contact between stone and bevel, and allows that angle to be set and maintained through the sharpening process. To sharpen a plane iron maintaining the existing bevel, is called junkaku kenma in Japanese.
  2. It is important that the bevel angle on the iron is precisely formed to complement the geometry of the plane body it is to be used in. It can happen after many sharpenings that the bevel can be changed enough to hinder the function of the plane and so needs to be re-adjusted. With the Grintec K2 you can more precisely follow the existing bevel angle, and/or correct one that has become problematic. Correcting the bevel on an iron is in Japanese called hakaku shitei kenma.
  3. When honing a blade, one can do it across the entire face of the bevel, but this is really a lot of work. But the Grintec K2 allows one to change the angle slightly in order to hone just the edge of the blade, reducing the time and work required to achieve a very fine edge. This is called choshiage kenma
  4. By just raising the angle of attack between the iron and the stone, you can cut a very slight second bevel in the edge, making the edge stronger and increasing markedly the amount use the iron will tolerate between sharpenings. The Grintec K2 makes this micro-bevel easy to achieve and is called marume kenma, which literally translated "rounded off sharpening ".
On Sharpening Stones

On Sharpening Stones

You use, depending on the condition of the plane iron, different stones with different grit sizes, coarse, medium, or fine, depending on the amount of steel you need to remove. Before starting to sharpen, make sure surface of the stone is absolutely flat. If you use a stone that has been hollowed out in use, you cannot achieve a properly-formed cutting edge, and can indeed deform the iron to the point that it will take a lot of work to set it right again. There are a number of ways to flatten a sharpening stone. You can grind it flat on a concrete slab sprinkled with abrasive, rub two different sharpening stones together, or use one of our specially-designed flattening stones. When sharpening, turning the stone often helps to reduce the hollowing effect. It is also useful, when sharpening many blades, to start with the narrower blades, and move up to the widest, using the whole surface of the stone.

B3a: flat stone surface
B3b: a stone surface ground hollow after use

Sharpening new Plane Irons

The bevel forming the edge depends on the construction and geometry of the plane's body. We recommend, before sharpening, to measure and record the precise angle on the blade. This helps a great deal if and when one must go back and correct a bevel when needed.

We often find that new plane irons are not flat across the entire bevel. In this case when starting to sharpen, the entire bevel will not be in contact with the stone. Use a coarse-grit stone to cut back the bevel until the entire bevel has been re-worked flat and contacts the stone before moving up into finer grits.
Ergonomics of Sharpening

Ergonomics of Sharpening

The Grintec K2 and the plane iron are guided with both hands during sharpening. Place, as indicated in drawing B5, your two thumbs on (L3 und R3) the back part of the sharpening guide’s housing. Your index fingers go on (L2 und R2) the forward end of the guide, and your middle fingers at (L1 und R1) on the face of the plane iron. Be careful to exert even pressure with your middle fingers on the iron’s face, and use very light thumb pressure on the back of the K2 to move the fixed-in-place iron back and forth over the face of the stone.
Be careful - the higher the pressure on the back of the K2, the faster the wheel in back will be worn down.

Finger placement

L 1: left middle finger
L 2: left index finger
L 3: left thumb

R 1: right middle finger
R 2: right index finger
R 3: right thumb
The parts of the sharpening guide - Diagram from above

The parts of the sharpening guide - Diagram from above

  1. Turning reference scale for settings, 0.0 to 0.5 mm
  2. Notch for exact centering of reference scale in (1)
  3. Fine adjustment screw for bevel angle
  4. Marking for standard angle setting (kijunsen = standard line)
  5. Thumb screw to lock in wheel setting
  6. Adjustable side assembly to accommodate various iron widths
  7. Scale to indicate iron width
  8. Side assembly locking thumb screw
  9. Thumb screw to hold plane iron in place
  10. Housing
All screws tighten by turning clockwise, and loosen by turning counterclockwise.
The parts of the sharpening guide - View from Side

The parts of the sharpening guide - View from Side

  1. Thumb screw to fix iron length
  2. Guide part for assemblies on opposite side of sharpening guide
  3. Screw-fastened axel for wheel
  4. Sharpening guide wheel
  5. Nut for thumbscrew on adjustable wheel
  6. Scale to set bevel angle
  7. Scale to set length to accept plane iron
  8. Adjustable assembly for iron-length setting
The parts of the sharpening guide - Guide for Bevel Settings

The parts of the sharpening guide - Guide for Bevel Settings

  1. Bevel angle guide scale
  2. Scale to measure iron length and width
Maintaining the current bevel angle of a plane iron

junkaku kenma - Maintaining the current bevel angle of a plane iron

This method is used for sharpening when the current bevel angle of a plane iron is judged to be correct.

The bevel angle gauge is used to measure the various features of the plane iron. The length and width of the plane iron as shown in diagrams D1a and D1b. The bevel angle is measured as shown in diagram D1c, that is the iron is placed in the various notches and the one that matches best is chosen. The plane iron in our example is 75 mm wide, 95 mm long to the beginning of the bevel, and a bevel angle of 25 degrees. If the bevel angle is out of the gauge’s measurement range, please look to. section H below.

D1a:
1) Measured iron width
2) Scale
Measured iron length
D1b:
Measure the length of the iron (1) not including the length of the bevel with the gauge. In this example 95 mm.
1) Plane iron
2) Measured iron length, not including bevel
Ermitteln des Fasenwinkels
Diagram D1c:
Measure the bevel angle by placing the bevel of the plane iron into the various notches until you find the one closest fit to the actual angle (2). This works best when the iron and gauge are backlit. When there is no light visible between the iron, on the bevel and the back of the blade, and the gauge, then you have found the correct angle. In this example 25 degrees. On Japanese plane irons, the face is slightly hollowed (the upper side in the plane body), this is called "Ura" in Japanese. This hollow plays no role in using this gauge. The back of the iron (bottom side in plane body) is also sometimes hollowed a bit. So do not measure the bevel angle in the middle of the blade, but rather near the edge!
1) Notch-gauges for a total of 9 angles in 0.5 mm steps from 24 - 28°
2) In this example, 25°
Setting the Side Assembly

Setting the Side Assembly

Loosen the thumbscrew (3) for the fence assembly (1) and set the scale (8) to the measured width of the iron - in this example 75 mm. The scale is read exactly at the side of of the housing. Then tighten the thumbscrew back up to lock the fence. If the iron is wider toward the back than at the bevel, use the widest measurement.
  1. Adjustable side fence to set guide to the correct iron width
  2. Housing
  3. Thumbscrew to lock side fence
  4. Thumbscrew to lock iron length/depth fence
  5. Standard line
  6. Fine adjustment thumb screw
  7. Thumbscrew to set and lock adjustable wheel
  8. Scale for iron width

Fine Adjustments

Turn the thumbscrew for fine adjustments (6) until the front notch is even with the standard line (5).
Adjusting the Depth Mechanism and the Wheel

Adjusting the Depth Mechanism and the Wheel

Loosen the locking nut on the depth mechanism (6) and for the wheel (4). Set the mechanism to accept the measured length of the iron, not including the bevel, to 95 mm and the bevel angle, 25 degrees, that you measured with the help of the scale, and then re-tighten both nuts. If the bevel angle is higher than 28 degrees or lower than 24 degrees, please have a look to H. Finally, tighten both screws back up.
  1. Scale used to adjust the mechanism for iron length
  2. Assembly that adjusts for setting the iron length
  3. The iron length and bevel angles are shown on these scales
  4. Nut for the wheel’s height adjustment screw. The angle scale is stamped on this part.
  5. Scale to set the bevel angle
  6. Thumb screw to set and lock in depth
Securing the Plane Iron in Place

Securing the Plane Iron in Place

Lay the plane iron (3) so that one, the iron touches the side- (1) and depth assembly (4) and fix it in place by tightening the thumb screw (2). The housing has a little space left to accept variously shaped heads on the plane irons. (diagram. C1c), in order to allow different heads to seat properly against the depth fence. As Japanese plane irons are repeatedly set in place with steel hammers, as is traditional, the heads will become a little bulged or mushroomed out. If the head becomes deformed to the point where it no longer seats properly and cannot be firmly secured in the Grintek sharpening guide, then you must reshape the head, using a metal file, for example.
  1. Adjustable side assembly
  2. Thumbscrew to fix in place the plane iron
  3. Plane iron
  4. Adjustable depth setting assembly
Fine Adjustment of the Sharpening Angle

Fine Adjustment of the Sharpening Angle

When you have completed the steps outlined above, the sharpening angle should match very closely the existing bevel angle on the plane iron. For an even finer and more exact match, you should, as in diagram D6 - the sharpening guide on the measuring scale and check that the bevel lies exactly on the straight edge of the sharpening guide’s scale as shown in the drawing (4). If you can see a gap at the cutting edge of the blade, then turn the fine adjustment screw (1) a little clockwise. If there is a crack or gap at the bevel, turn the fine adjustment screw a little counter-clockwise.
  1. Fine adjustment thumbscrew for setting bevel angle
  2. Wheel
  3. Plane iron
  4. Bevel must lie flat
  5. Scale
Sharpening

Sharpening

Set the sharpening guide onto the stone with the wheel (3) and the iron’s bevel (2) are on the stone. Using even pressure, move the iron back and forth over the stone several times, and examine the bevel to make sure you have good even contact across the entire face of the bevel. If the edge is being ground too much, turn the fine adjustment knob a little counter-clockwise. If the top of the bevel is being ground too much, turn the knob slightly in the opposite sense. In general material should be removed evenly across the entire width of the iron. Then you move the iron back and forth as evenly as possible across the entire surface of the stone, switching it end for end occasionally to even out wear on the stone’s face until the entire bevel of the iron has been cut back to fresh metal. You then repeat these steps through progressively finer stones until the desired level of polish has been reached. It is also necessary from time to time to re-hone or flatten the back of the iron.
  1. Sharpening stone face
  2. Bevel
  3. Wheel

Resharpening

Resharpening after the first conditioning of the plane iron is relatively quick and easy, as you in general use the same settings in terms of iron length and width, but taking care to make sure the iron contacts the stone across the entire bevel each time. But after repeated sharpenings, especially if you needed to remove a lot of metal to grind out a notch in the edge, for example, you will need to re-measure and reset the Grintec guide as the dimensions of the iron change.
hakaku shitei kenma

hakaku shitei kenma - Sharpening to a prescribed bevel angle, or correcting the existing bevel angle on a plane iron

In this method the existing bevel angle on a plane iron is changed after grinding or because a different angle is needed.

We would like to clarify here that we are going to return to the example from before, an iron with a width of 75 mm and a length of 95 mm and that should be ground to a bevel angle of 25 degrees.

Setting the Side Fence

Loosen the thumbscrew of the width assembly and set the fence to 75 mm using the width scale and re-tighten the screw to fix the assembly in place.
  1. Adjustable width fence
  2. Housing
  3. Thumbscrew for width assembly adjustment
  4. Thumbscrew for depth assembly adjustment
  5. Standard line
  6. Adjustable depth assembly
  7. Fine adjustment screw for bevel angle
  8. Thumbscrew to fix wheel adjustments
  9. Scale to set iron width

Fine Adjustments

Turn the fine adjustment thumbscrew (7) so that the front notch is centered over the standard line (5), as in drawing E1.
Setting the Iron Length Assembly and the Wheel Mechanism

Setting the Iron Length Assembly and the Wheel Mechanism

Loosen the thumbscrew for the iron length assembly and the shoe with the wheel. Set the scale to the correct depth for an iron length of 95 mm and the scale on the roller shoe for a bevel angle of 25 degrees and retighten both thumbscrews to lock in the settings (fig. E3). If the desired angle is over 28 degrees or under 24 degrees have a look at table H below.
  1. Scale to set iron length (depth setting assembly)
  2. Scale mark for 95 mm and Scale mark for 25° must be set together
  3. Angle scale for roller shoe setting

Fixing Plane Iron in Place and Sharpening

Set the plane iron in place against the depth fence and the side fence and tighten the thumbscrew clockwise to lock the iron in place. Now sharpen the iron using first a coarse grit and then medium grit stone until the entire face of the bevel has been worked. Next you change to a finer honing stone or series of stones until you have reached the desired level of sharpness or polish. Then you take the iron back out of the Grintek and then if needed work the back of the iron on the appropriate stone or stones.
Honing or Polishing

choshiage kenma - Honing or Polishing

Before moving to the honing or polishing step, you must make sure the iron lies flat on the stone across the entire bevel, as shown in the diagrams D7 and E3 to the right.

Settings for Honing or Polishing

Turn the fine adjustment screw so that the notch is centered over the zero mark.
  1. Turning reference scale for settings, 0.0 to 0.5 mm
  2. Notch for exact centering of reference scale in (1)
  3. Knurled thumbscrew

Setting the Fine Adjustment Screw

Turn the fine adjustment screw clockwise until the notch is centered over 0.2. The round bevel angle scale on the side of the Grintec will show the change in the angle. The bevel angle is increased by 0.2 degrees when you turn the fine adjustment screw clockwise to 0.2.
  1. Turning reference scale for settings, 0.0 bis 0.5 mm
  2. Knurled thumbscrew
  3. Setting the notch to 0.2

Honing

If you now make 10 or 20 passes back and forth with the Grintec guide and iron over a fine honing stone, the last 0.5 mm of the bevel to the cutting edge will be honed and a wonderfully sharp and almost effortless edge will be formed. The number of passes needed to hone off that last bit depends on many factors, the fineness of the grit, the hardness of the stone, and how quickly it cuts in general. Make sure the edge is sharpened evenly across the width of the blade, and remember the number of passes it took to get a good edge. Now you can take the iron out of the Grintec and give the back a couple of passes over the stone to keep it flat and remove any burr left by the sharpening process. If you don’t need to use the sharpening guide for other irons, you can leave the settings as they are and then touching up the edge of the iron, in the course of a larger job, for instance, you can re-insert the iron and achieving the same fine edge is very quick and easy.

Re-honing

If the settings for iron length and width are exactly maintained, when the iron begins to dull, it can be reinserted into the guide at the same setting and the edge can be renewed in a few seconds on the stone. This system works only up to a point however. The process will take longer and longer, and as metal is removed from the edge, the secondary bevel angle will gradually widen and the angle will change to the point where you must go back and reform the entire bevel to recover the correct angle.
Micro-Bevel

Micro-Bevel (literally, rounding the cutting edge) - to Increase the Working Life of the Cutting Edge

Set the Grintec with iron on the stone as demonstrated in drawings D7, E3 or F4.

Micro-Bevel

In this process by moving the iron back and forth over the stone while varying the angle, you make an even smaller micro-bevel in the edge. When moving forward, the Grintec and iron are moved normally over the stone as in drawing G1 with both the roller and iron in contact, but in drawing the iron backward on the stone, you lift up the back of the iron until it forms an angle of approximately 45 degrees, as in drawing G2. If you repeat this process 5 or 10 times a third tiny micro bevel will be formed, making the cutting edge noticeably stronger and longer-lasting.

Advice on this Micro-Bevel

1. Always use a very fine stone for this step
2. If the blade is moved forward over the stone at an increased angle, the edge will be be damaged
3. Do not use this method for more than 10 passes over the stone.
Bevel Angles Outside those marked on the Grintec Scale
Bevel Angles Outside those marked on the Grintec Scale

Bevel Angles Outside those marked on the Grintec Scale

With the Grintec scale, you can measure plane iron bevel angles between 24 and 28 degrees. The scale for setting the bevel on the housing also shows this range. If the bevel angle you need is more than 28 degrees or less than 24, you can achieve these angles using the following method to set the sharpening guide.
  1. Plane iron back
  2. Degree scale
  3. Bevel

Using the Bevel-Angle Calculator Graph

With the measured length of the iron, from head to the beginning of the bevel angle on the back of the iron, and the bevel angle that exists on the iron or the one you would like to cut, you can use the iron length setting to reach the desired settings. To do this, you use the graph in illustration H2. (You can see an enlarged version at H4). The vertical axis is marked with an arrow at the measured length of 93 mm. Take from here a line at a right angle over to the measured bevel angle, in this case 31 degrees, and from that point a line straight down to the horizontal axis gives a value of 103.7 mm. The baseline bevel angle setting on the sharpening guide is always set at 26 degrees when doing these calculations.
Setting the Depth and Wheel Assemblies

Setting the Depth and Wheel Assemblies

As in diagram H3 shows, the bevel angle is set to 26 degrees and the depth adjustment to 103.7 and locked in place with the thumb screws. With the calculator table you can calculate the necessary depth settings for various other bevels in the same manner. The wheel depth scale is always set at 26 degrees regardless of the angle desired.

H: Scale for setting iron length
R: Scale for setting the bevel angle
26 x 103.7: The markings for 103.7 mm and 26° must align exactly.

The calculator graphic is shown in an enlarged version below to allow the iron length and angle figures to be read more easily. If you print out the calculator graph, you can use a ruler and pencil to mark the page and calculate the settings necessary for your plane iron, exactly as we did in drawing H2.

calculator graphic

Maintenance

When you, after a lot of use, have worn the wheel down, you must change it. It should not be allowed to get smaller than 19 mm before replacement. To change it, loosen the screw on the axel and take off the wheel.

Make sure that all the moving parts of the sharpening guide move easily and freely. Remember that oil can damage a water stone so avoid using it on the Grintek.

Make sure the thumbscrews thread securely into their fittings. If they become loose, the iron cannot be properly secured and there is a real danger that it might fall out of the guide in use.

Wash the Grintec in water as needed and then carefully dry is with a cloth towel. If it is allowed to stay wet, rust can set in, potentially damaging the tool.

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