Chris Schwarz's Blog

The Science of Rented Mules (aka Chisels)

Sometimes when I
write, I come to a question that paralyzes me – and I cannot continue
until I get it answered. As a newspaper journalist, I was trained to
“write my way around the problem,” which probably is one reason I don’t
work for newspapers anymore (the other reason: there aren’t any

A few days ago I was writing about chisel handles.
Blah, blah, blah. Tang, socket or Japanese. Yadda, yadda, yadda.
Ferrules, bolsters and hoops. Gabba, gabba, gabba. Best types of wood
for a handle.

And pause.

This is a good question: beech,
hornbeam, maple, white oak, hickory, something else? And what can one do
to delay a handle from splitting? Use a mallet that is softer than the
handle? A mallet that is harder than the chisel? Perhaps the mallet
doesn’t matter?

So every evening I’ve been diving deep into the
research available on the impact resistance of woods. What makes some
woods better for beating and others not so good? I have yet to turn up
much science that is really helpful to me. There is a lot of data out
there that relates to baseball bats, but most of that relates to woods
being beat on the side grain or face grain – not the end grain.

There is this article
from the Royal Society that has some interesting data, but it doesn’t
really answer the question when it comes to end grain impacts. Bruce
Hoadley’s book “Understanding Wood” deals with wood failure parallel to
the grain, but not about wood impacting wood. Where does the energy go
during the impact? What happens if the chisel handle is softer or harder
than the striking tool?

I must be missing something out there.

So if you are an impact nerd, could you drop me a line? I’d really like to get this sorted out so I can get on with my life. Thanks in advance.

— Christopher Schwarz

Resources Related to this Post
• David Charlesworth’s DVD “Chisel Techniques for Precision Joinery” is excellent. We need more information on chisels in the world.

• Here is one of the best free links ever. The Forest Product Laboratory has just released its 2010 “Wood Handbook.” You can download the whole thing for free from the U.S. Forestry Service’s web site. Go here. Bookmark it.

37 thoughts on “The Science of Rented Mules (aka Chisels)

  1. Mike

    In contrast to sweetgum, the FPL Wood Handbook lists black locust as "vedry heavy, very hard, very resistant to shock, and very strong and stiff". It was used as insulator pins (?) and wooden pegs in the construction of ships. It sounds like this wood has desirable characteristics for a handle or mallet.


    "Mark’s Standard Handbook for Mechanical Engineers" Chapter 6 Section 7 has decent discussion on the mechanical properties of different species of woods. Of particular interest would be Table 6.7.2 which has values for shear strength parallel to the wood grain. All the traditional suspects are there.

    The chisel handle failure mechanism is buckling delamination. The lecture notes on this particular area for Dr. John Hutchinson’s Fracture mechanics course at Harvard are available at: (see slide 5) if you want way too much detail.

    To roughly and poorly summarize:
    The impact of the mallet on the chisel handle imparts energy into the handle. This energy is stored in the handle in the form of strain energy. The handle gets hit, deforms (strains), and stores energy like a spring. If the strain energy stored in the handle exceeds the critical strain energy for the material then a crack will form. If a discontinuity (crack) already exists in the material then the critical strain energy for that material is lowered. Leather washers on handles absorb some of the energy from the mallet and prevent it from transferring into the handle. Hooping with metal rings would increase the critical strain energy by pre-straining the material (adding a sort of negative strain energy).

    Once a crack is formed it starts propagating through the material and the stored strain energy is released at a rate proportional to the rate of crack propagation.

    Of course the bulk of the energy should be transfered through the chisel handle to the blade, and from the blade to the work.

    (who, unfortunately, studies this sort of thing for work these days)

  3. JOS

    I am new to woodworking and so if this out to lunch forgive me.
    One aspect of the wood that I have not seen discussed in this thread is moisture content. Are we letting the wood in our hand tools dry out to much?

  4. Ryan M

    This post positively jinxed me today in the shop. I suddenly have a 5/8 mortise chisel handle on painters’-tape life-support.

  5. Steve

    I think the principal reason that wood handles fracture is that wood is an inhomogeneous material. When a stress wave from an impact propagates through the material, it is going to preferentially concentrate at stress risers, which typically occur at places like the end of a crack. In hardwoods, radial ray cells are often rather loosely held in the wood matrix, and so they act like cracks (this is most obvious in oak, where you can sometimes lift a ray in quartersawn wood with your fingernail).

    The way to avoid fractures is to avoid stress risers, and the way to do that is to have the handle material as homogeneous as possible, and without any sharp corners, etc. In fact, I think the real reason the acrylic-infused handles from Blue Spruce are so tough isn’t because the acrylic is itself phenomenally strong, but rather because it homogenizes the stress/strain characteristics of the wood, so that the impact forces are uniformly absorbed throughout the handle.

  6. Ron Herman

    Chris ; In the shop ,over the years,the three woods that can take the most abuse are black locust,hophornbean(ironwood),and center cut hickory.My limited typing skills dont suit me for a long answer ,but grain acclimation is very important as well as tight growth rings.Its easier for me to show the difference than try to write it. Great topic though. Ron Herman

  7. Jerry Curry

    Just to confuse the issue some more — Lie Nielsen’s handles are actually hophornbeam (Ostrya virginiana) not hornbeam (Carpinus caroliniana). They’re both pretty hard, but if you’re looking them up, you want to get the species right.

    Jerry Curry

  8. John Walkowiak

    I am not so sure the problem is with the handle material. The most obvious issue in the photo is the flat on the top of the handles. As has been brought up, they should have a slight crown so the impact is only in the center of the handle. Antique English mortise chisels had a thick leather washer between the bolster and handle. This would absorb shock as well as even out the shock, as it would be nearly impossible to guarantee that the bolster and handle would be perfectly flat and mating exactly. I don’t see this on your chisels. The split mallet looks to be a glue joint failure. A correctly glued joint should be stronger than the wood.
    The next question is why so much force is needed? Is the workpiece secured directly on top of a bench leg, and is the bench leg sitting on a hard surface? If not, the workpiece will bounce and the mallet strike diminished and you have to strike harder to get the job done. I assume your chisels are sharp, but some woodworkers think mortise chisels don’t have to be as sharp as a bench chisel because you can just hit them harder. It should be just as sharp. The chisel bevel in the photo looks quite short, shorter than on my antique chisels. It may be too short for the amount of waste you were trying to remove, necessitating harder blows. Good luck!

  9. Christopher Schwarz

    Sometimes from the comments I can see that the original intent of my post has gone awry. Maybe I should go back to working for newspapers for a refresher in writing clearly.

    I don’t blame the chisel handle for breaking. Mortising is violent stuff. I don’t blame the mallet for breaking. It beats *all* my chisels.

    I also don’t blame myself. I take care of my tools.

    I am interested in the factors that make a good chisel handle. I’ve gotten a lot of great data off-line from this post, so I’m happy; but I don’t want people to get the impression that I hit my chisels with a framing hammer. Or I don’t sharpen them. Or I drive metal wedges with a mallet. It’s just not the case.


  10. Al Navas

    Correcting a typo…:

    On the other hand, if we don’t have sufficient *data* yet, could it be that in a few years we will learn that impregnating resins was *not* the thing to do?

    Corrected: "date" => data, and added the word "will" (…we will learn…)

  11. Al Navas

    Resin-impregnated woods in woodworking – a question:

    Has anyone reported failure of these when pounding with a mallet?

    If not, is the technology so new that we don’t have a broad enough data base to date?

    If handle breakage *is* an issue, as Schwarz’s post states, maybe the answer lies in simply applying the resin impregnation technology to *solve* the problem.

    On the other hand, if we don’t have sufficient date yet, could it be that in a few years we learn that impregnating resins was *not* the thing to do?

    Al Navas

  12. Ken

    Just as another data point, the Japanese Woodworker catalog lists chisels with handles turned from oak branches so that the rings are concentric around the axis of the handle to increase durability. This intuitively seems to make sense and I have made a few handles from magnolia, sycamore, and oak using this technique, but haven’t noticed any particular difference in impact resistance. The obvious answer to handle breakage is the Stanley Everlast (or later incarnation No. 60) chisels with solid steel from the striking end to the cutting edge. Personally, I just don’t like the way they feel or sound when being whacked.

  13. Devin

    I agree with George, no matter what the task is, if I find myself either working too hard or breaking tools its time to re-evaluate how I am performing the task. Is there an easier way? John mentioned it as a safety valve I think thats a good way of thinking of it. When a tool breaks it is either do to excessive force just prior to its breaking, or excessive force accumulated over time until it fractured.

  14. George Walker

    A couple of thoughts. Burl was commonly used for traditional mallets. It’s not uncommon to find them worn to an hour glass shape from millions of blows, but seldom split. Is there a point where it makes sense to use a drill to horse out material rather than a chisel? I use a chisel for most work, but turn to a drill when the work is deep or wide. Unless the handle was defective, I’d guess you are pushing it (and yourself)too far. Most of the time when I break a tool, it’s me not the tool.


  15. John Snyder

    At a certain point we need to recognize the value of wood splitting. It’s an important "safety valve" mechanism that protects the steel. I’m a woodworker, not a blacksmith…I can repair handles.

    John Snyder

  16. Sean

    – the seating of the tang (i.e., if the fit is too tight, you have a internal wedge issue)
    – the the fortuity of the grain of the handle (as with plane totes and saw handles, it matters a ton as far as duarability)
    – the presence of any cushion at the bolster (soem have leather washers which I always assumed was to keep the wood from impacting the steel bolster as hard)
    – the type of mallet used (i.e., a wood is good urethane mallet is not as likely to break a handle as a hickory one)
    – how the chisel is being used (i.e., trying to take too large bites in too hard a wood by beating the living crap out of the chisel – multiply if the chisel is dull)

  17. Al Navas


    Your question is important from a life-cycle standpoint. I wonder if the development of using resins to impregnate wood, such as used by Czeck Edge and Blue Spruce, might be a long-term solution?

    Maybe these wood-polymer composites are the answer to durability of the chisel handles.

    Table 19-5, page 442 of the PDF file provided by Forest Products Laboratory shows increased wood strength and hardness.


    gonçalo alves wood, my choose
    what about to attach a side grain piece of wood to the end grain of the handles ?

  19. Floss

    Get some Sweetgum(Red Gum).

    When I lived in Columbus McNally lumber used to have it, one of the last great local lumber yards. A lot of older homes had gum trim as well.

    Air dried is best if you can get it. I had some for firewood and it is one of the more hateful species to try and split with a maul. It also eats wedges.


  20. Justin Ashley

    Not to put a pin in everyone’s balloon, but exactly just how hard must you hit a chisel to bust a well made hardwood handle and shear a laminated mallet head? The picture of a monkey hitting a rock with a club comes to mind… Now, which is the better question? What’s the best wood for the monkeys club? Or rather, what the hell is the monkey trying to do? Either way you’re still a monkey…

  21. JC

    Don’t neglect the issue of shape. A handle with a rounded end gets impacted towards the center, and thus the outer layers of wood help prevent splitting. Those flat ended handles in your photo just beg to be chipped and split…

  22. Jones largent

    The best wood is not just wood, but the combo of wood that has been infused with acrylic to fill every cell a la "Blue spruce". I’ve been hitting mine with a hammer, and still no dent or crack.

    Jones & Co.

  23. Eric R

    I read you comment twice and still can’t figure out what you said exactly.
    But man, I bet you did good in school !

  24. Ryan M

    I feel as though shape and grain are more important variables in the lifespan of a mortise chisel handle.

    I have the best success with handles made from riven blanks, but the crucial thing seems to be always maintaining a rounding or wide chamfer as the heel is deformed over time from use. My hunch has been that a beefy handle rarely splits from shock, but more often from a blow that grabs an arris and imparts its force off-center.


    This is an overly simplistic answer, but maybe the answer is not to obsess so much about the wood durability (since we generally know what wears well) but to figure out how hard you should be hitting the chisel in the first place. Durable woods will absorb a good amount of shock when smacked together, but you’ll destroy anything if you hit it too hard.

    I’ve noticed that, when mortising, there’s a point where I’m not really chopping into the wood so much anymore, but rather, just sort of sending the shock of the blow everywhere beside the cutting edge of the chisel. That’s because a significant amount of the blade is now tightly contacting the wood. At that point, it seems like it’s time to do some waste-levering.

    One time (long since blogged) I went way too far past that point with an old pigsticker and broke my mallet. I glued it back together and have since tried to keep myself from hitting so hard.

  26. Michael

    Well, I am an engineer and my employer is in the business of impact wear parts and grinding consumables used in the hard rock mining business. I don’t see how any of this applies to a wood chisel handle. Either make the thing out of a tough, no-splitable wood, like black gum, or any of a number of synthetic materials that would be better suited for the task. By the way, a metal button type striking cap on the impact end is not a bad idea either.

  27. Doug F.

    Essentially, you are talking about energy transference. In traditional archery there is an argument about what wood is best for arrows. A heavy wood, like ash, is slower to reach the target, but, because of its mass, it penetrates deeper. A light wood, like sitka spruce, moves faster to the target but penetrates less. Which do you want when hunting is the point of contention.

    The same thing, I think, applies to chisels. The mallet is the bowstring while the arrow is the chisel. Not all of the energy is transferred to the chisel edge, though, so the handle has to be able to absorb some punishment. Therefore, I would like the heaviest, densest material I could find for my chisel handles. Persimmon or lignum vitae, perhaps? Same thing for my mallets. Locally, that’s hickory or osage orange.

    Now, if you are trying to find ways to avoid splitting your handle, putting leather pads on your handles helps, but something like horn might be better. Again, density and mass. Some of the war bows used by the English during the Hundred Years War had draw weights in excess of 150lbs. Basically your putting the energy of a 150lb weight into the end of an arrow that is only about 3/8" in diameter. To prevent arrows from splitting when being shot they inserted splines made of horn into the ends. Denser woods than the arrow material works, too, but horn was the preference.

  28. neinfill

    Sounds like really 2 related problems.

    Fracture caused by strictly a strength of materials/forces involved (Free body diagram anyone?)
    Input force vs the weakest link in the following string:
    User (complex tendons etc.)
    Mallet Handle (Shear)
    Mallet Head (Compression)
    Chisel Handle (Compression)
    Chisel Body (Compression & buckling)
    Edge (should be sharpened to infinity and not exist)
    Chip (Shear/wedging & Acceleration)
    Workpiece (Shear/wedging)
    Vise? (Friction)
    Bench (Compression)
    Ground (Compression)
    Which ever member is weakest is the one that gives. Taking too big of a bite means you are likely to damage an undesired piece of the equation (not the chip)

    Then comes the fatigue: so long as the forces in the members stay below the elastic limit they’ll all last forever, (collectors tools input forces are extremely low so that can explain the life of many tools) the problem is that our materials aren’t perfectly homogeneous (most notably the wood) and have minute cracks. These cracks will propagate with each impact if the force required to open them is exceeded. Once the crack’s grown sufficiently to make that member the weakest link – Goodbye.

    This would seem to imply that chisels handles and mallets should be:
    -Not struck to provide enough force to cause shear fracture (good idea)
    -Not struck to provide enough force to cause crack propagation and fatigue (might be too weak to get any work done)
    -Should be made of a material with high crack opening forces (interlocking grain vs red oak)
    -Should be prestressed (hooped) such that the crack propagation forces will not exceed the the compressive forces from the hoop and allow the crack to open.

    Interesting topic, Each member would also act as a spring as well, deforming elastically along the way. I’m guessing some other engineering types will pipe in here to correct erroneous statements I’ve made here.

  29. Jon

    I can’t approach this question with any particular Materials Science expertise, but I’ll hazard a guess. I think that woods that are difficult to rive or split (irrespective of their hardness) would make good chisel handles. I don’t know if resistance to splitting is due to interlocking grain or differences in early and latewood in ring-pourous woods or something else entirely. Maybe a good rule of thumb would be, if you would dread chopping it as firewood (ie elm), it would probably make a good chisel handle.

    Here is a paragraph from "The Wood Handbook: Wood as an engineering material" about the choice of hickory for handles and spokes that may address your question:

    The work or shock-resisting ability is greatest in wide-ringed wood that has from 5 to 14 rings per inch (rings 1.8-5 mm thick), is fairly constant from 14 to 38 rings per inch (rings 0.7-1.8 mm thick), and decreases rapidly from 38 to 47 rings per inch (rings 0.5-0.7 mm thick). The strength at maximum load is not so great with the most rapid-growing wood; it is maximum with from 14 to 20 rings per inch (rings 1.3-1.8 mm thick), and again becomes less as the wood becomes more closely ringed. The natural deduction is that wood of first-class mechanical value shows from 5 to 20 rings per inch (rings 1.3-5 mm thick) and that slower growth yields poorer stock. Thus the inspector or buyer of hickory should discriminate against timber that has more than 20 rings per inch (rings less than 1.3 mm thick). Exceptions exist, however, in the case of normal growth upon dry situations, in which the slow-growing material may be strong and tough.

  30. Chris Schwarz

    This post is not about any brand of chisel. I’ve broken handles on Lie-Nielsen, Swan, Hirsch, Marples, geese you name it chisels. Handles break — if you use them.

    I love my Ray Iles chisels and would buy them again. Same with the Back Channel mallet. I love it. Mallets break — if you use them. This a post about something far more important than brands. …..

  31. David

    Chris – The probability of failure (fracture) of any solid is based on the material’s properties (duh…), but more imporantly, on the acceleration/deceleration from the impact and over what area it is spread.

    One way to think about this is from the physics of car crashes. Hitting a brick wall at 80 miles per hour is going to have a very different effect than hitting a foam pit at the same velocity.

    Similarly, you’re a heck of a lot more likely to fracture a chisel handle if you’re attempting to chisel granite than you are jello.

    So while one could obsess over the "best wood" for a chisel handle, how you use it and what you’re trying to chisel is much more likely to affect the length of the handle’s life than a nuanced choice of dry hickory vs. white oak.

  32. jeff stafford

    this may require statistical analysis. (aka sending chris pix of your tired & beaten) or pouring over ebay pix to see what the common "sad bastards" are.

  33. Michael Brady

    None other than Frank Klaus at WIA expounded that it was impossible to fracture the handle of a pigsticker-style chisel. Your photos must be some sort of PhotoShop trickery. I

    Also the the cutaway of the DeLegno mallet to show the tapered tenon construction is brilliant.

    What are you doing with your tools to manifest such havoc?…..Using them?

  34. Damien

    I sidestepped the impact resistance problem by stating that a soft rubber mallet gives the highest energy transmission (lower peak but a longer contact time), but I am still searching a way to test this with real wood and chisels.

  35. Guy Rivest

    You almost had me burst into tears there. The reason being that I just bought 4 Ray Iles mortise chisels from Tools for Working Wood and that same Back Channel mallet from Di Legno Woodshop Supply that is shown in your photo and now I’m starting to regret it. Did I make the wrong choices?

  36. SteveD

    Are there additional variables at work to those you already mentioned? Is there effect from the work stock hardness and density, the orientation of the cutting edge to grain, quality of the edge, angle of the edge, aggressiveness of the cut?

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