Mortise or Tenon Main Image

Wood Bowl Mortise or Tenon – Which is Best?

Mortise or tenon, that is the question when turning or making a wood bowl. For some, there is no preference, for others, it’s either mortise or tenon, but not the other.

You’ve set up the bowl blank, begun turning and it’s now time to decide how to attach the bowl to the four jaw chuck. It’s time to make a decision. Unless, of course, you’re turning a wood bowl without a chuck. But for this article, we’re dealing with a chuck and how to attach to that chuck.

So how do you decide which to use, a mortise or tenon?

There are some factors that can be considered to come up with an answer. In this article, we will look at these factors and hopefully you will come away with a better grasp of when to best use a mortise and when to best use a tenon.

What Is A Mortise or Tenon

Before we dive too deep into this baffling question, let’s clarify what we are discussing. A mortise or tenon are two different ways to attach a wood bowl bottom to a four jaw chuck.

Usually, when turning a bowl, the bowl bottom sides and base are turned first, then the bowl is reversed, and the interior of the bowl is then cleared out and finished.

Mortise or Tenon Connection Examples
Mortise or Tenon Connection Examples

The terms mortise and tenon are traditional woodworking terms used to describe two opposite interlocking joints. The tenon is an extension of wood material, and the mortise is a recessed cavity in wood.

In woodworking joinery terms, a tenon is designed and cut to fit snuggly inside a mortise, and the two are glued or fastened together.

For our use, we only need a mortise or tenon, but not both. The bottom of the bowl, whether fitted with a mortise recessed area or a tenon extension will be attached to a four jaw wood chuck

The four jaw chuck jaws will contract to hold a tenon or expand to grasp a mortise.

Mortise or Tenon Connection Examples With Four Jaw Chuck
Mortise or Tenon Connection Examples With Four Jaw Chuck

How To Make A Mortise

The process of making a mortise or tenon starts by sizing a four jaw chuck to the bowl blank. When sizing a mortise, the chuck jaws should contract shut, and the mortise should be slightly larger to fit the chuck. With a tenon, the jaws need to contract down on the tenon but not close completely.

Mortise Labeled with Four Jaw Chuck Graphic
Mortise Labeled with Four Jaw Chuck Graphic

To make a mortise, the sized area of the bowl blank needs to be cleared out. Cutting the mortise can be done with a parting tool, bowl gouge or and combination of tools that work best for you.

With a mortise recessed area shaped, the dovetail undercut needs to be shaped along the outside edge. A skew chisel used on center works great for scraping a slightly angled undercut.

For all the details on making an excellent mortise recessed area, check out this article.

How To Make A Tenon

With the chuck size marked on the bowl blank bottom, the material around and up to the tenon is removed. I typically remove this material with my large bowl gouge.

Once I’m up to the tenon line, I will slow down and make nice clean cuts squaring up the cylinder of wood protruding from the bowl blank. I can’t stop there because a cylinder-shaped tenon will not be held well by the four jaw chuck.

Tenon Labeled with Four Jaw Chuck Graphic
Tenon Labeled with Four Jaw Chuck Graphic

I use a detail spindle gouge to turn a gently angled undercut in the bowl tenon. Starting on the tenon cylinder edge, I make a slight inward push cut until I reach the tenon shoulder. And speaking of that shoulder, it needs to be level and smooth as well for an excellent fit to the chuck.

To learn all the ins and outs of making a perfect wood bowl tenon read this full article. And whatever you do, don’t make tenons like these!

Personal Preference

Ok, so back to the question, mortise or tenon?

Why all the moralizing around the base of a bowl blank? Well, that’s a great question. I guess for some it becomes a set routine way of doing something.

We all know what happens when some people prefer one thing over another thing. For some reason, they feel compelled to defend their position at all costs.

The debates are long-running and storied. Ford versus Chevy. Bud Light versus Miller Lite. Apple versus Microsoft. Coke versus Pepsi. Democrats versus Republicans. John Deere versus International. And now we will add Mortise versus Tenon. LOL

Do What Works

Now, I must say I do prefer using a tenon most of the time. I’m not a staunch “tenon only” guy, however. I will make mortises on occasion, but I prefer using tenons usually. I think you’ll see why as you continue reading.

Instead of taking a one-party ticket approach when deciding which connection to make for your bowl bottom, consider what makes the most sense for each bowl.

It’s easy to get into a routine of making only mortises or tenons and not genuinely considering the alternative. A better approach is to determine whether a mortise or tenon is best for each particular bowl you turn.

Mortise Advantages

One of the advantages of making a mortise recessed area is simplicity and speed. Turning a recessed area is relatively simple and straightforward.

Little waste material needs to be removed to create a mortise, just the mortise area itself. Make the cuts to eliminate this area with a parting tool and bowl gouge.

If a particular bowl blank is thin, a mortise works well by not wasting material around the base. Platters, especially work well with a mortise connection.

Mortises are great for beginners first learning to make a wood chuck connection to the lathe. The process to make a mortise is quick and straightforward.

Another advantage of the mortise is it is easy to remove and reattached to the chuck later. Easily reattachment can be a plus for applying finishes and not tying up the lathe for other projects.

Production work of many wood bowls can be executed more quickly utilizing mortise recesses compared to tenons. Tenons usually need to be removed later, which adds a production step.

Also, the recessed area of a mortise is a great place to hide a surprise for a wood bowl admirer. Decorative lines can be turned, patterns, colors, woodturning, or even inset items may be epoxied within the mortise area as a visual treat.

Mortise Disadvantages

The mortise, by its very nature, requires real estate inside the wall thickness of the bowl. Because of this intrusion, the final bowl thickness usually can’t be very thin.

Another big disadvantage is the mortise does not make shaping the final bowl foot easy. The large recessed area dictates the final foot design and makes alterations more complicated.

If the base of a particular bowl is narrow and the amount of wood around the mortise is thin, the wood chuck might add too much pressure to the surrounding wood. When there is not enough wood around the mortise to support the pressure of the four jaw chuck, an area of the side wall mortise will likely fail.

My big personal objection to the mortise is visibility. When a bowl with a mortise is flipped over the realization of the woodturning process is immediately evident.

I really prefer a bit of a mystery for the non-woodturner when they explore a wood bowl. It’s much more satisfying to have someone ask how a piece was made.

I guess, for me a mortise circle makes a bowl look and feel unfinished. But again, that is my preference only.

Tenon Advantages

A tenon can be turned on a bowl blank and create a secure, stable connection for almost any bowl. Narrow bowls with smaller bases do well when turned with a tenon.

Thin-walled bowls are easier to turn with tenons rather than mortises because the tenon is not interfering with the overall wall thickness. The tenon is an extension of the base rather than an intrusion.

Tenons can be initially created larger than needed to support the turning process and then reverse chucked and turned down to a much smaller profile.

Also, because of their ease of later alterations, tenons can be reshaped to match almost any design or final look needed. The portion of the tenon gripped by the wood chuck can also be included in the final base.

Mortise or Tenon Tenon Area Removed For Smaller Foot
Tenon Area Removed For Smaller Foot

A bowl tenon allows for the entire area of the bowl base to be exposed both for visualization of the final shape and turning purposes. The final foot of a bowl can be turned while still maintaining the tenon joint. Later the tenon can be cleared from the bowl foot area.

Reverse chucking and reshaping the tenon after the bowl interior is complete can be total. In other words, the entire tenon can disappear, and the area sanded revealing no clear connection between the bowl and the lathe. The mystery of the lathe connection is what I like most about using a tenon.

Mortise or Tenon Pinterest Graphic

Tenon Disadvantages

Occasionally, if wood is too dry and brittle, a tenon can break off. A tenon coming lose has only happened a couple of times to me with very dry pecan wood.

When turning a side-grain wood bowl, it is possible that the grain lines up cleanly with the base of the tenon which can increase the chances of separation. Again, this has only happened a couple of times with very dry wood.

To prevent a tenon from breaking off, with the bowl off the chuck, I will run a small bead of very thin CA adhesive glue around the base of the tenon. The CA helps by soaking in and bonding the wood fibers together.

If a particular piece of wood is already thin, removing waste material and forming a tenon will make it thinner. Removing around a tenon can waste a bunch of material.

Another disadvantage of the tenon is it needs to be removed. The removal process takes a bit of time, not a lot but some. There are several ways to remove a tenon, but they all take a little extra time compared to the mortise.

No-Nos

If you turn a mortise or tenon in the tender sapwood along the outside of a particular piece of timber, the connection might be compromised. Of course, this depends on other factors like species and dryness, but in general, it’s best to move away from tender, soft sapwood for a mortise or tenon.

Another thing to be aware of is end-grain turned bowls. An end-grain bowl blank should never be attached with a mortise. The outward pressure from the four jaw chuck will expand and break the blank along the grain lines and result in a loose fit a best and a flying bowl in the worst case scenario.

Mortise or Tenon Comparison Chart
Mortise or Tenon Comparison Chart

Mortise or Tenon Conclusion

Both the mortise and the tenon have their places in wood bowl turning. There is no need only exclusively to use one chuck joint over the other; both have value at different times.

Now that we’ve covered many of the advantages and disadvantages what do you think? Do you currently only use one over the other, or do you use both? Please share your wood bowl connection preference in a comment below.

Happy Turning!

Comments

  1. Just returned from a training class on bowl turning held at one of the better known wood craft supply stores. I am new to turning and have only attempted 3-4 bowls to date. We were turning walnut, wet approx. 5″-6″ dia and approx 4″ thick; not big, END GRAIN. We were instructed to cut a mortise to attach to our 4 jaw chucks. As my wall thickness became smaller, my bowl split from the bottom up the side all the way to the top edge. A few other students had their bowls fly off the lathes on more than one occasion. The moral to this story is, I wish I had read this article yesterday rather than today. Might have saved a nice bowl and several hours work. Guess that’s why they call it live and learn!

    1. Author

      Steve,

      I’m sorry to hear about your loss. And I’m a bit surprised to hear they had you make mortises in green wood. Green wood requires continued tightening of the chuck because the fibers move and compress so easily. As you keep tightening or expanding into the mortise, the chuck acts like a splitting wedge and will eventually break the mortise or the whole bowl.

      Wet wood is a perfect time to use a tenon. Unfortunately, turning a tenon requires a bit more time and practice, but it’s well worth learning and using on a regular basis.

      Probably 95% of everything I turn is mounted using a tenon. I highly recommend tenons over mortises. But it is good to turn a mortise or two so you have the experience. It sounds like you have the experience now. 😉

      Happy Turning,
      Kent

  2. Kent,

    I usually start out with a tenon. When I think I am finished, I remove it. More often than not I decide to make changes of some sort so I am left with a mortice that I can use to make the changes. It seems I am always doing this, usually because I have read something from your web site:)

  3. Wow – what an awesome website -first time I’ve visited and I am already dying to go try some new ideas… I use both – often I resort to a mortise after I cut my tenon too small 🙂

    1. Author

      Thank you Erik!

      I’m thrilled you love this site and I’m glad to help.

      Good luck with the tenons!

      Happy Turning,
      Kent

  4. I use a mortise in larger bowls and a tendon on smaller. For the first time I am going to core some large (11” to 15”) blanks. I went to my local guild to use their larger lathe. I was making a dovetail mortise and one of the mentors told me I had to use a tendon. I said I disagreed and he then refused to help me, so, I went looking for pros and cons and I will stick with mortise for bowls over 6”. I’ve been turning for 40 years but mostly bowls for about 10 years and lost count about 1,000. Thanks for a fair comparison.

    1. Author

      Jim,

      Thanks for the comment. Yes, it’s really a personal preference unless there isn’t enough wall for a mortise or if its an end grain turning. It’s sad that some people get so set on something being one way or another.

      I think it all goes back to how they are trained. My mentor really doesn’t like oak, so I’ve avoided oak without question. I just came across some Holm Oak, and OMG it is amazing. We have to have open minds!

      Thanks again and Happy Turning,
      Kent

  5. Just found your site. Nice.
    I use a recess most of the time but also use tenons. Mine are almost always practical bowls so I follow the 1/3 or golden rule for the base.
    If you remember your pi r squared.. even deleting the center area there is 3X the amount of wood to break away with a 2″ recess surrounded with 1″ compared to a 2″ tenon. Never had a recess shear off like a tenon.
    In the “No Removal Required” I would rate them the same.
    In the “No attachment Evidence” I would also rate them the same.
    You can leave both or remove both. Not a problem with either.

  6. Reverse chucking remains a challenge for me with removing or shaping tenons. What method for reverse chucking do you recommend?

    1. Author

      I mostly use a simple scrap wood jam chuck with a piece of carpet padding to prevent scuffing the bowl interior. The tailstock is pulled up and the bowl gets centered on the tailstock. I will use pull cuts to remove the tenon and make the final bowl bottom shape. In this configuration, I will also power-sand the newly shaped area to match the rest of the bowl exterior sanding. I carefully recess and shape the area inside the bowl foot until there is just a small cone connecting the bowl to the tailstock. I will then remove the bowl from the lathe, chisel off the cone nub and carefully sand the inside foot area, usually with a 2″ sanding disk.

      Another great way to approach this is to use the vacuum chuck. Everything is the same as above, except when you get to the little remaining nub, you remove the tailstock and cleanly turn away the inside bottom foot area while the vacuum chuck holds the bowl in place. I hope this helps. Happy Turning!

  7. Hi Kent- an excellent description and critique of the tenon and mortise. I teach woodturning and cannot emphasise enough of how important it is to make a “perfect”tenon. I also recommend that the face (ie where the faces of the chuck jaws meet the wood)of the tenon is slightly undercut- this also helps with a square fit. A poor fit of the tenon/jaws results in having to reshape the outside of the bowl- a lot of wasted time, particularly if sanding has been performed as well!
    My choice is the tenon most of the time as it allows a variety of foot designs and if making articles with small diameter bases the tenon wood can be used as well as you point out.

    1. Author

      Brian, Thank for sharing your comment. Yes, the tenon is the critical foundation to a quality turned bowl. And it offers so many options for final appearance. Thanks again!

  8. I would consider myself to be a beginner turner with my training being watching many episodes of Tim Yoder. I’ve had my lathe for just over a year. I have mostly used the mortise method because it creates a foot on the small bowls I’ve turned. I will be more conscious of selecting my mounting method now after reading this post. Thank you.

  9. My teacher is one who does both but always uses the ” X ” pattern when mounting.. ” X ” referring to grain orientation. Spreading the expansion / compression of the jaws as equal as possible and always uses the tail stock for safety / support ..

    1. Author

      Sounds interesting. Can you explain the “X” pattern in more detail?

      1. Look at the chuck jaw… 10 — 2 — 4 — 8 position… Now orient the grain in a X 10 … 4 2 ….. 8 a X .. spreads the force equally.. either in expansion or compression

          1. My teacher uses a box of soda straws glued together to form a log.. the straws the grain of the wood.. and it shows expansion / compressor very well as a teaching tool

  10. I use Both, After learning by Trial with Flying Bowls, I am Much more inclined to pay a lot of attention to the Wood I’m turning. I prefer a Tenon, But, I have had more occasions of Losness, or having to re-tighten the jaws using a tenon. I Use a Mortise quite Often now on Bowls, and do some embellishment, and sign the project in this area. K-ray

  11. Very good info. It verifies everything I learned yesterday at a “hands On Demo/class at our AAW sponsored event.

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