How to prevent tear out with hand planes? –The summary
- Use the plane that functions well in basic planing operations. Check the plane tuning guides for lapping the sole, mating the frog and blade, honing the cap-iron undercut and polishing the front edge, lever-cap tension and so on. The plane needs to be in tune!
- Use freshly sharpened blade/iron and sharpen immediately again when the tear out starts to reappear. Sometimes you even need to do it every few minutes!
- Make thinner shavings, aim for 0,05mm (.002”) or thinner.
- Use a higher pitch/cutting angle. 55°-60° is enough for almost any tear out. With bevel-down planes use higher angle frog or hone 5-15° back bevel. With Bevel-up planes grind the blade bevel steeper.
- Adjust the cap iron very close to the edge. According to a scientific study setting cap iron as close as 0,05-0,1mm (.001”-.002”) can significantly help to reduce the tear out.
- Hone the cap-iron leading edge to 50° or even up to 80° degrees. The study shows that the radical 80° angle is best for reducing the tear out.
- Close the mouth when using a bevel-up plane. When using the very close set cap iron with bevel-down plane keep the mouth relatively open to avoid clogging or jamming issues.
- Cutting direction – Try to always cut with the grain
- Try skewing the plane, it works sometimes with a tricky grain
- Use smaller size plane for pinpoint planing the problem areas
- Select the tight, straight-grained wood to work with
- Use card scraper, scraper plane or sanding as a last resort
What is a tear-out?
Hand plane tear-out happen when wood fibers are chipped or torn out of wood surface instead of cutting them, resulting in an uneven potholed rough surface. The tear-out occurs during the cut when the blade levers the wood fibers out in front of the cut, before actually cutting or breaking them. Wood fiber could be too strong and the chip is not breaking as it is supposed to. The tear out takes place usually when the grain changes directions during the cut(curly woods for example) or when planing against the grain. Another tricky situation is planing interlocked ribbon grain woods such as a sapele mahogany which due to its unique grain formation is prone to severe tear out.
There are many cutting variables you can adjust to change the conditions before and during the cut and thus reduce or completely eliminate the tear out during planing. Variables can be divided roughly into two groups; the tool and its set up, and the user and his or her skills to read the grain and use the tool. Let’s take a closer look at them.
How to set-up the hand plane to reduce the tear out?
The sharp blade is the most important weapon against the tear out monster
The first thing to check when planing and getting tear-out is the condition of the blade. Is it really sharp or not. Sharp blade severs fibers whereas dull blade tears and rips them. Many woodworkers test the blade sharpness by trying to cut the hair from one’s forearm, the sharp blade cuts them easily. Sharpen the blade if needed.
Use freshly sharpened blade/iron and sharpen immediately again when the tear out starts to reappear. Sometimes you even need to do it every few minutes!
The sharp blade doesn’t keep sharp forever. Sometimes when after couple square feet of planing some tricky woods perfect, you start to get tear out, then it is time to strop or hone your blade again. It could still be sharp enough for easier woods but for perfect results with gnarly woods it needs to be sharpened again. Even best quality blades dull easily with some hardwoods with high mineral content.
Reduce the depth of cut
According to the scientific study by Professor Chutaro Kato from Yamagata University, Japan, mere depth of cut change from 0,1mm (.004”) to 0,05mm (.002”) reduced the tear-out when planing against the grain. Another thing to note is that the blade in the study was without any cap iron.
Summary from the study: “If the blade is sharp and if the cutting depth is smaller than 0,05mm, then tear out will not occur even with a single blade”
So with a sharp blade and thinner shavings, you will get less or none tear-out, guaranteed. Back the blade in and start to advance it out bit by bit until you start to get very thin shavings.
The drawback with thin shavings is that you need to go over the surface more times than before.
Cap iron/chip breaker adjustment
For efficient planing strategy, we need to aim for thickest possible shaving thickness without getting tear out. Thicker the shavings, the fewer passes you need to do with the hand plane and the more productive you are. The cap iron is the key for thicker shaving without tear out.
Properly set cap iron prevents tear-out
Cap iron/chip breaker is an important part of the planes function, especially with modern thin bladed Bailey-type planes. Cap iron serves many functions. One is to support the blade and press it tightly against the frog reducing the chance to the blade chatter. Another is adjusting the cutting function of the blade by compressing and breaking the fibers of shaving right after the cut degreasing the levering action that tries to tear the fibers out in front of the blade.
Cap iron needs to be set up properly for it to function well. By setting the cap iron very close ( 0,1mm (.004”) away from the edge according to Kato) to the cutting edge you can increase the cutting depth without increasing the probability to the tear out happening. The very close setting of cap iron forces the shaving to break and curl right after cutting-edge preventing the levering action that happens when cutting thick shavings without or far set cap iron.
Kato experimented with three distances from 0,3mm to 0,1mm, and when setting the cap iron farthest from the edge the resulted surface quality started to suffer in many cases. Remember that planing direction was against the grain.
The distance of the cap iron to the edge of the blade should be adjusted according to the cutting depth and the wood used. There is no “one for all” setting distance for cap iron. Tricky hardwoods need to be cut with very close set cap iron while the surface quality of softwoods will suffer if cut with it. For thicker shavings move the cap iron farther away.
Knowledge comes from experience, same is true when setting the cap iron. Exploring different settings and noting their outcome is important for best results.
The shape of the cap iron leading edge
Other major knowledge from the Kato´s study is the experimentation of the cap iron leading edge bevel angle. Kato made the test first with cap iron edge honed to 50 degrees. With that bevel, he got best results when the cap iron was set to 0,1mm away from the edge. With another cap iron honed at 80 degrees, he could move the iron back to 0,2mm and still get the good results.
The drawback for near placement of the cap iron is the increased cutting resistance. The closer it is to the edge, more resistance it creates. To counter this the leading edge of cap iron should be polished to mirror shine for shavings to glide easily.
Common knowledge states that adjusting the width of the mouth opening is the key for a tear-out free surface. I believe it to be true in some cases. With my bevel down planes, it is the only variable besides the bevel angle of the blade to set the plane for a tear-out-free cut. Bevel-up planes don’t have cap irons.
When using Bailey or Bedrock –type planes I find the close mouth problematical. If the cap iron is set very close to the cutting edge then the closed mouth setting is going to give you clogging and chip jamming issues. You need to use a very thin cut for not to jam the chips into the mouth, and the quality of cut is not improved whether or not the mouth is closed. With whispery thin shavings closely set cap iron is enough. So I advise to keep the mouth rather open and adjust the cap iron setting instead.
Pitch of the blade
The inclination of the blade to the sole, angle of attack and pitch of the blade refers to the same thing. It is one of the useful variables to adjust when needed to reduce the tear-out when planing hard or curly woods. The steeper the angle of attack, the faster the chips coming from the edge are curled up and away and broken effectively preventing the levering action to split wood uncontrollably ahead of the cut. Trade off with higher pitches is the increased cutting resistance which makes the plane harder to push compared to a normal angle.
In bevel-down planes pitch angle is determined by the frog which the blade rest on. To change the pitch, you need to replace the frog with a suitable angle. Standard frog angle in bevel-down planes is 45° degrees, called common pitch. Higher angle frogs come in 50° (York pitch) 55° (Middle pitch) and 60°(Half pitch). Most modern and vintage Bailey-type planes come only with 45° frogs and higher angle replacement frogs are not offered. Both Lie Nielsen and Veritas offers higher angle options to their planes.
One of the main selling points of the bevel-up planes is the relative ease of changing the cutting angle by mere altering the blade bevel angle. The bevel angle of the blade alters the pitch directly. In bevel-up planes the cutting angle/pitch angle = the bed-angle + bevel-angle, so you can increase the pitch by grinding and sharpening the bevel steeper by adding a suitable micro bevel. With bed angle of 12° and bevel angle of 33°, the pitch is 45°, by grinding the micro bevel to 43° you’ll get resulting cutting angle of 55° (middle pitch). For a sensible use, you should consider getting couple blades, each for every pitch.
Back bevel – bevel-up your Bailey or Bedrock plane
Now I tell you a secret called “Poor mans York pitch”. You can change the pitch of your Stanley Bailey-type bevel-down planes without changing the frog. It is as easily done as with bevel-up planes by back-beveling the blade! By adding a small micro bevel on the back of the blade you can easily increase the cutting angle of the plane and thus reduce the tear-out. The width of the back bevel needed is small, according to Ron Hock, only 0,4mm(1/64”) wide bevel is enough.
Bailey-type bench planes come always with frog angle of 45°. By adding 10° back bevel the cutting angle or pitch is increased to 55°. Good range for back bevel angle is between 5° to 15° degrees.
Tradeoffs with back bevels are the same as with higher angle frog and steeper bevel in bevel-up planes. Higher cutting angle always increases the power needed to cut.
For a practical use, one replacement blade with back bevel is handy which you can install if the need arises.
Learning to read the grain is a secret to tear-out free surfaces
There are many ways to examine the grain direction. Sometimes I just start planing and within first inches I know if it is a right direction or not. Planing ease, feel, and the sound of the cut tells a lot.
Another way is to give a stroke like when petting a cat. You don’t want to pet a cat against the grain, same with planing. Sometimes with certain woods, it is easy to feel which way the grain runs. Start petting you woods:)
Figures and grain lines tell the story. Learn to read the figures on the surfaces of the board. Start always by looking at the end of the board to check the orientation of the board, whether it is pith side or bark side up.
For flatsawn boards, look for V-shaped figures on the surface. With pith side up, cut into the direction of v´s, and with bark side up, cut into the v points.
Grain reversal is easy to see on flatsawn boards. Plane from both ends toward the reversal if bark side up and vice versa if pith side up.
Localized curls, swirls, and knots are easier to plane with smaller high angle smoother if available.
Working across the grain – good way to hog out lots of wood with tear-out prone boards.
Boards with severe tear out are unnerving to size along the grain. You never know how deep holes planing is going to make. And smoothing it with very thin cuts takes ages to complete.
A better way is to size and true the board working across the grain. This way the blade is not going to lift and tear the grain, instead of working across the grain simply severs the fibers. The resulting surface is not beautiful and ready for finish yet but it isn’t torn out. With smoothing plane well-tuned against tear out, you can smooth the surface within a couple passes.
One caveat when cutting across the grain is the chipping that could happen along the edges. You can avoid it by planing small bevel along the opposite edge of the board.
Skewing of the plane – My theory why it might work
Skewing the cut when planing can many times improve the cut and reduce the occurrence of tear out. Other times skewing may drastically increase the tearing, go figure. Reasons for it is sometimes hard to understand. Skewing lowers the cutting angle of the blade and reduces the width of the cut which in turn decreases the cutting resistance considerably. Also, the cutting action is more of slicing cut.
We have just learned that higher cutting angle will lessen the chance to tear out so it is really mysterious why skewing works with its reduced angle of attack?
I have developed a theory why skewing the plane works although the cutting angle is lowered by skewing action. Wood consists of adjoining fibers that are sticking and supporting each other forming a stable structure. By its nature, wood fiber orientation varies on blanks cut from the trees and many times woodworker have to plane in suboptimal direction prone to tear out.
Skewing the blade allows fibers to be cut one by one. Adjacent fibers are still on the safe zone supporting the fiber in the tear out zone. This supporting action reduces the tendency of tear-out.
Imagine the tear out zone in front of the blade. When cutting straight with no skew, all the adjacent fibers are cut at the same time. If the cut is against the grain, the tear out is happening in tear out zone and all the fibers are levered up together causing the severe tear out. Even though the fibers are attached to each other they don’t get any support against the tear out.
Skewing the plane changes the situation notably. Now the tear out zone is also skewed. The blade cuts the fibers one by one and only one fiber is in the tear out zone at a time. The fiber gets support from its neighboring fibers that are still in safe zone thus reducing the possibility for the tear out.
This hypothesis is completely my own and I welcome any discussion about the subject.
Wood – selecting the best lumber for hand planing
Preventing the tear-out starts at the lumberyard. What boards you choose and what reject determines how well they behave with the hand plane. Picking great wood really saves your time at the workbench.
Select the straight, tight grained wood. Look at the end grain first, it reveals immediately how closely spaced the growth rings are. Within same species, the tighter grained wood is almost always structurally stronger because of slower growth.
Next, check the edges of the board, grain lines should be as straight as possible. Any crooks or sudden curls in edges reveal knots and other grain reversals. Try to avoid them as much as possible. Board with grain reversals can be used if cut short lengths.
Stay away from solid wood laminated boards. They are made from thin strips of second-grade woods with the grain running any directions. Hand planing them is really a nuisance and not worth anybody’s time. They are made to be used as they are and to thickness them tear-out free is really only possible by drum or wide-belt sander.
Most precious commodity in woodworking is the time we spend at the workbench working with the wood. By choosing the woods wisely you can save a lot of time and sweat and be more productive.
Other reading about the tear-out
Review of the paper by Chutaro Kato and Yasunori Kawai, Wear of Knife Used for Hand Plane III: The influence of the cap iron
Effect of Knife Chipbreakers on Surface Finish