The bowl bottom is so critically important to wood bowl turning. In a well-made bowl, the curve flows smoothly and evenly from the side walls to the gracefully curved concave bowl bottom. When that bowl bottom isn’t smooth or flowing is when we usually take notice.
After our fingers glide across the bowl’s rim, our eyes and many times our hand moves to the inside visible wood bowl bottom surface. What’s interesting is how easy it is to overlook a well-made bowl bottom.
So many art forms, when done well, are easily overlooked, unnoticed. Many times when art or craftsmanship is done well, it is merely there and often taken for granted, almost invisible.
The wood bowl turner’s role is to take a piece of raw timber and reduce it into an elegantly shaped, pleasing bowl form. Unfortunately, an average person, with little regard for bowls, will barely register a finely turned wood bowl as anything more than a “bowl” and move on.
A good actor makes us fall into a movie. We forget they are acting and we believe the storyline they are performing. A bad actor, like a bad bowl bottom, makes us pay attention to the flaws and question the performance.
I can think of at least six bad actors that have the chance of derailing a bowl’s aesthetics. Let’s take a look at these potential bowl bottom butchers and how to counter each of them.
Bowl Bottom Shape
Nothing kills the bottom of a bowl more than form and shape. It is important to remember the initial bowl exterior formation dictates the bowl bottom interior.
Multiple levels or breaks in the flowing curve of a bowl’s walls take away from the form of a bowl. Yes, this is an opinion, and I realize there are an infinite amount of ways to shape a bowl. However, if you look at the bowls that are truly pleasing to the eye, most of them have a simple arcing curve.
There is nothing more difficult to accomplish and master in wood bowl turning than “simple.” A simple curved bowl, the one that a nonchalant observer might overlook, is usually the hardest to turn. Simplicity is our goal in wood bowl turning.
One of the worst issues with bowl bottom shape is the lack of continuity of the curve all the way across the center bottom. It is common to see bowls with side walls that curve inward toward the bottom but go flat when they reach the bowl bottom.
Why do bowls go flat in the bottom sometimes? That’s a good question. I can tell you after I blew out the bottom of a bowl once when I turned right through the side bottom of the curve (image below), I became a bit “gun shy.”
The bowl bottom needs to conform to the bowl exterior. To properly shape the bowl bottom, it is essential that there is enough material on the bowl exterior.
I quickly learned the solution is to plan. My problem was not leaving enough material in the bowl bottom combined with not measuring enough (more on that in a minute). The bowl bottom area wore thin when I was fussing with the interior bottom curve.
The solution was to leave a bit more wood on the tenon shoulder and also widen that shoulder. Not to mention, slowing down and measuring the wall thickness more often. Once I began turning with a thicker tenon shoulder, I had more leeway to make the interior bowl bottom the shape needed. That helped take away my fear and I relaxed while turning the bowl bottom to the proper curve, instead of worrying whether I was going to make another donut ring.
Take the time and feel that inside bottom curve with your hand and continue making small refining cuts until the bowl bottom has a pleasing continuous curve. You will know you’ve accomplished this when you can close your eyes and run your fingers across the bowl bottom and not feel a flat area.
One of the first visual and tactile offenses along the bowl bottom are tool marks. Like the exaggerated grooved surface of an old fashioned vinyl record, tool marks ruin the harmony of an otherwise excellent bowl.
So what makes these tool marks? The answer is simple: not riding the bowl gouge bevel. Like that old vinyl record, the bowl gouge was acting like the needle riding those grooves. When the bowl gouge is not riding bevel, there is no support for the cutting tip of the gouge, and it floats up and down making grooves or tool marks.
To make a different visual analogy, think of a snow shovel and a sidewalk with a couple of inches of snow cover. Imagine if we hold the snow shovel straight up and down with the shovel tip perpendicular to the sidewalk. As we begin walking, the shovel tip will skip, catch, hop and scratch along the walk. Imagine the pattern of snow this erratic effect will leave behind on the sidewalk.
Proper wood bowl gouge techniques are necessary to make the inside bottom of a bowl continuous, smooth and pleasing.
Now imagine placing that snow shovel down along the sidewalk surface. The large flat portion of the shovel, equivalent to the bowl gouge bevel, is almost parallel with the sidewalk and the tip glides along the walk, cleanly removing snow. Riding the bevel is the quickest way to turn the bottom of a bowl without tool marks.
Also, a round-nosed scraper can be used gently to remove any pesky tool marks inside the bowl. Be patient and use incredibly light scrapes to remove any tool marks.
These are the round nose scrapers I use and recommend. It is a heavy and sturdy tool that sits firm on the tool rest and does not add any vibration to the process. With a proper sharpening and a bit of practice, this scraper will shave off tool marks quickly and effortlessly.
Hard To Reach
Some bowls are just challenging to make good bevel contact along the bottom bowl surface. For various reasons, the bowl is not accessible enough.
There are two main reasons why the bowl bottom may be inaccessible for a traditional bevel-riding bowl gouge cut. The first reason may have to do with the depth of the bowl. Because if a bowl is too deep, it can be difficult to make a bevel supported cut across the bowl bottom.
Another reason the bowl interior may be inaccessible is that the side rim of the bowl arches inward and restricts tool access. An inward-facing rim can make it nearly impossible to gain the proper bevel angle with a traditional bowl gouge. There is a great solution for this issue: a secret bowl turning weapon called the micro bevel bowl gouge. I have another article dedicated solely to this tool. Check it out.
The micro-bevel gouge will allow an almost perpendicular bevel-supported cut along the bowl bottom. The micro-bevel gouge is an excellent solution, especially if that bowl bottom is deep or restricted by side walls.
That Pesky Bowl Bottom Nub
As pesky as that little nub can be in the bottom of the bowl, a divot is much worse. I’ll get to that in a minute. Let’s talk about that nub first. We’ve all seen nubs at the center of bowl bottoms, and we’ve all certainly made several on the center of bowl bottoms at one time or another. I know I have. It’s impossible not to make them when first turning.
The main culprit in the bowl bottom nub creation is speed. The speed at the center of the bowl is much slower than the side walls. What? You might be asking, “How can that be?” I know when I first heard this, I thought, “Um, the lathe says 850 rpm (or whatever speed). How is the center slower than the outside?“ Well, the revolutions per minute are the same for the center as the outside, but the travel distance is different.
Think of our solar system. Earth takes much less time to rotate around the sun than Pluto. If, in our example, Earth and Pluto each have the same amount of days in a year, which they don’t but just pretend, (a/k/a one rotation around the sun), Pluto being so far away from the sun would have to be moving through space much faster than Earth, covering more distance.
So how does this relate to our bowl? As you move closer to the center bowl bottom with a bowl gouge, the speed of the wood becomes slower, requiring you to slow down to make the same even cut along that surface.
If you dart toward the center with your bowl gouge in one evenly timed movement, the tool will cut less material near the middle. If the gouge is cutting less material, it rides up, and skips over wood at the last second and leaves a nub. Because of this speed difference, the center of the bowl demands slow and deliberate attention.
A slow, smooth cut across the bottom that reduces in speed at the center is the best remedy for the center bowl nub problem. Learning to slow down at the bowl center does require practice and patience.
It’s nothing for the bowl gouge to cut a beautiful smooth path over several inches in a few seconds on the outside of the bowl and then require many seconds to cut the last little tip at the center cleanly. If you look closely, while you cut toward the middle, you should see a tiny cylinder being formed at the tip right before the gouge shears it away. That is the way to a clean, smooth bowl center.
If a small nub does appear at the bowl bottom center, don’t worry. Make additional slow passes and cut off very thin layers until the nub disappears and the bowl bottom curve flows smoothly. If needed, sanding only takes a minute and will usually remove any small remaining bump.
Another solution to remove the bottom center nub is to use the heavy round nose scraper. Position the tool rest so the cutting edge of the scraper is exactly center and level. Turn the lathe speed up to a fast, vibration-free speed. Check out this article all about lathe vibration as well.
This technique will nibble that nub away. Raise the scraper handle and then gently lower the handle until the scraper edge comes up and just barely contacts the nub. Once the scraper is perfectly level in the center of the nub, rotate the scraper to the left then disengage the scraper tip.
Return to the center position, raise the handle (which lowers the cutting edge) and slowly scrape up and then left, again. Continue making very small passes until the bowl center is nicely blended into the surrounding area and the nub is gone.
The round nose scraper can do amazing things, including cut a smooth finished surface. Read this article to learn a ton more about the round nose scraper.
The Bowl Bottom Dreaded Divot
The one problem that is much more difficult in a bowl bottom is a gouge or divot in the bowl center.
Divots in the wood can occur when the bowl gouge tip is pointed downward, off bevel, and moves too quickly across the bowl center. A divot is when wood grain is dug out or torn rather than cut away from the bowl surface. Torn wood or divots usually pull fibers from underneath and leave a small hole or pit.
Fast, deep, and aggressive cuts with a bowl gouge usually make divots. To remedy this, make the cut depth shallow, just shaving off a little bit with each pass and slow down.
Repairing a bowl divot requires removing all the material around the divot by making slow, even passes until the surface is smooth, again.
If there isn’t enough material in the bowl bottom to remove around the divot, you may need to treat the divot like a bowl crack and repair it.
Blending Side to Bowl Bottom
Continuous bowl wall thickness plays a critical role in making a great bowl. Uneven walls can easily be detected as soon as anyone touches the bowl. Making even bowl walls takes patience and lots of practice.
It is important to pay attention to “deadman’s corner,” as they call it—-the area of the bowl interior where the walls angle inward and merge with the bowl bottom.
When doing the interior of a bowl, remember it costs nothing to stop and check the wall thickness. I’ve found I get in trouble when I’m excited to see the finished bowl and work too quickly. Slow down and check the thickness again and again.
Use wall thickness calipers to measure the wall thickness, if the bowl is large and your fingers won’t reach beyond a certain distance. Your fingers and your brain can feel wall thickness issues very well. Trust your fingers and the calipers.
Try to get in the habit of looking down on the turning bowl, instead of bending over and looking into the bowl. Looking down on the wood will help develop an intuitive sense of where the gouge is within the bowl. Even if you can’t see the tip of the bowl gouge, you will be able to sense its position based on the handle angle, tool rest position, speed and even sound. It’s impossible to gauge if you’re veering into the sidewall if you’re looking in the open end of the turning bowl.
The excessive measuring of the bowl wall thickness is to prevent going too thin or thick in a given area. A wall that is too thick can be worked a bit more; however, a wall that is too thin cannot.
A common bowl wall issue is a wall that starts nice and even, then continues without curving and veers into the side too much. It’s possible to turn right through the bowl wall if the wall thinness isn’t detected soon enough.
The solution for a smooth transition from side walls to bowl bottom is to measure. Measure, measure, measure wall thickness to make a nice continuous wall thickness throughout the bowl.
There you have it: six misfits that can bring unwanted attention to an inside bowl bottom. Hopefully, this article has given you some new insight that you can use on your next bowl bottom.
The goal is to avoid sparking unwanted attention or questions from a casual observer and possibly to impress a fellow woodturner that knows a good performance when they see one!
– Check out the equipment mentioned in this article. See my Recommended Equipment Guide.
Finishing the Bowl Bottom is important, so are these topics:
• WOOD BOWL EXTERIOR-CRITICAL DESIGN MOMENT
• WALL THICKNESS WOES – BOWL TURNING TECHNIQUES
• 13 WAYS TO RUIN A WOODTURNED BOWL
• 14 WAYS TO AVOID GRAIN TEAR OUT WITH WOOD BOWL
• 10 BOWL TURNING BASICS – IMPORTANT FAQS ANSWERED
Thanks and Happy Turning,