As a relatively new woodturner, I look at the design of many bowls that have been turned. Compared to the top opening, most bases are proportionally small. Presuming that most bowls will contain something, their base most often is so small as to induce instability with the base. From my perspective, I turn a bowl which has an equal size, or close to the size, of the diameter of the top. Do those engineers (who are members of this site), apply a mathematical rule regarding the ratio of the size of the base to the top? Is there such a rule? Do other turners have a proportional rule between the top of the bowl and its base?
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BOWL STABILITY
- Thread starter Matt Fawkner
- Start date
I usually start at 1/3 the diameter of the bowl but that also depends on the shape I decide on. I have used 1/4 the diameter and went larger than 1/3 however I average 1/3. After you turn a few bowls you can check to see how stable they are.
If you have bowls in your home take a few out and measure the diameter and the foot. If you make utilitarian bowls this would give a great starting point. Also look at the shape of any bow you may have in your kitchen and look at the curve. Many times the outside curve will help me determine the size of the foot.
If you have bowls in your home take a few out and measure the diameter and the foot. If you make utilitarian bowls this would give a great starting point. Also look at the shape of any bow you may have in your kitchen and look at the curve. Many times the outside curve will help me determine the size of the foot.
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For functional twice turned bowls I will usually do a foot that is about a 1/3 of the rim diameter
12” rim 3-4” diameter foot.
Stability is relative to some extent. I do a lot of round bottom pieces they are stable.
They rock if you bump them but the don’t fall over or go anywhere.
Many Round bottom bowls can be used functionally for salad, bread, fruit….
Once in a gallery show of mixed media where I had a few pieces, a lady backed (rule number 2 never back up in a gallery) into a pedestal with two pieces on it.
One piece fell over and rolled onto the floor my round bottom hollow form rocked back and forth never threatening to go anywhere.
12” rim 3-4” diameter foot.
Stability is relative to some extent. I do a lot of round bottom pieces they are stable.
They rock if you bump them but the don’t fall over or go anywhere.
Many Round bottom bowls can be used functionally for salad, bread, fruit….
Once in a gallery show of mixed media where I had a few pieces, a lady backed (rule number 2 never back up in a gallery) into a pedestal with two pieces on it.
One piece fell over and rolled onto the floor my round bottom hollow form rocked back and forth never threatening to go anywhere.
When you finish your foot, do you do anything to minimize surface area that will contact a table/counter/etc? If you leave the bottom of any bowl PERFECTLY flat, then most likely, the bowl won't sit reliably on any surface, it will have some rock to it.
The foot of a bowl or platter is often where some design work and embellishment goes. Generally speaking, at its simplest, you want the outer rim of the foot to contact, but the inner surface should not. A perfectly flat foot will usually have imperfections, and if the very center is higher than the rim, then you are guaranteed it won't sit flat. So the simplest solution is to turn a very slight curvature to the foot, leaving the rim lower than the center. If you expect a non-trivial amount of wood movement as the bowl continues to dry or otherwise react to humidity, you might opt to make that curvature a little more pronounced.
A foot can be more interesting than that, though. You can durn a raised rim for the foot...and it could be anywhere from 1/8" or 1/4" wide or 3/4" wide or so, with a purposefull recess in the center. Within that recess, some people like to turn circular grooves, or perhaps brand their logo, or even embed an emblem or badge. The rim will again ensure that the bowl rests on only a small, selective portion of the radius of the bottom of the bowl. The recess or depression will improve the stability of the bowl.
Foot design goes, regardless of how large your foot is. As for whether its tiny, small, large or the same diameter as the rim of the bowl, is really going to depend on the design of the bowl, how you want it to look, and maybe what its intended use is. You can get a real high curvature for some bowls, and the foot might be just 1/4 the diameter of the rim, you could aim for 1/3 to 1/2 the diameter. You lose some curvature the wider you make the foot, but it can work for some designs. A foot that is the same diameter as the rim, is usually a bowl like this:
If you want to get more fancy, you could have a bowl where the foot flares out. This would result in a constriction lower in the bowl, then the foot would flare out providing a larger area for stability:
Personally, I don't have a hard and fast rule. I'm not a long-time turner, I've been turning for a few years (started in 2020, but had a lull for a couple of years, got back into it in 2023). I experiment a lot, fail a lot, but, I do like bowls and platters of a fairly wide range of designs, so I haven't latched onto any particular "rule" for how the foot of EVERY bowl "must" be done. I usually start out with a general idea of what I want, and turn, and sometimes I might wing it as I get to the final shape as I see how things look. Most of my bowls are smaller....anywhere from a few inches to maybe 8 inches max diameter. I haven't turned anything particularly large, although I do have blanks waiting to be turned that are up to 15" in diameter or so, and some potential pieces that could be up to 20". With a good large salad bowl or something like that, I'd probably have a foot that was at least several inches in diameter...and I think that would work fine, however with a bowl 15-20" in overall size, a 4-5" foot, which IMO is quite large, would be 1/4 the diameter of the bowl. So relatively small, but there are other aspects that I think would lend to some stability as well.
The foot of a bowl or platter is often where some design work and embellishment goes. Generally speaking, at its simplest, you want the outer rim of the foot to contact, but the inner surface should not. A perfectly flat foot will usually have imperfections, and if the very center is higher than the rim, then you are guaranteed it won't sit flat. So the simplest solution is to turn a very slight curvature to the foot, leaving the rim lower than the center. If you expect a non-trivial amount of wood movement as the bowl continues to dry or otherwise react to humidity, you might opt to make that curvature a little more pronounced.
A foot can be more interesting than that, though. You can durn a raised rim for the foot...and it could be anywhere from 1/8" or 1/4" wide or 3/4" wide or so, with a purposefull recess in the center. Within that recess, some people like to turn circular grooves, or perhaps brand their logo, or even embed an emblem or badge. The rim will again ensure that the bowl rests on only a small, selective portion of the radius of the bottom of the bowl. The recess or depression will improve the stability of the bowl.
Foot design goes, regardless of how large your foot is. As for whether its tiny, small, large or the same diameter as the rim of the bowl, is really going to depend on the design of the bowl, how you want it to look, and maybe what its intended use is. You can get a real high curvature for some bowls, and the foot might be just 1/4 the diameter of the rim, you could aim for 1/3 to 1/2 the diameter. You lose some curvature the wider you make the foot, but it can work for some designs. A foot that is the same diameter as the rim, is usually a bowl like this:
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|_____________|If you want to get more fancy, you could have a bowl where the foot flares out. This would result in a constriction lower in the bowl, then the foot would flare out providing a larger area for stability:
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/_______________________\Personally, I don't have a hard and fast rule. I'm not a long-time turner, I've been turning for a few years (started in 2020, but had a lull for a couple of years, got back into it in 2023). I experiment a lot, fail a lot, but, I do like bowls and platters of a fairly wide range of designs, so I haven't latched onto any particular "rule" for how the foot of EVERY bowl "must" be done. I usually start out with a general idea of what I want, and turn, and sometimes I might wing it as I get to the final shape as I see how things look. Most of my bowls are smaller....anywhere from a few inches to maybe 8 inches max diameter. I haven't turned anything particularly large, although I do have blanks waiting to be turned that are up to 15" in diameter or so, and some potential pieces that could be up to 20". With a good large salad bowl or something like that, I'd probably have a foot that was at least several inches in diameter...and I think that would work fine, however with a bowl 15-20" in overall size, a 4-5" foot, which IMO is quite large, would be 1/4 the diameter of the bowl. So relatively small, but there are other aspects that I think would lend to some stability as well.
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Things tip when the center of gravity is no longer over the support, the foot in case of a bowl. The center of gravity of most bowls is pretty low and in the middle so 1/3ish of the diameter usually works. If you put things in the bowl they tend to collect in the middle and so doesn’t change much. Maybe if the bowl is full of something substantial (not popcorn) AND it’s piled up toward one side of the bowl you will see some instability.
These days for me its all about aesthetics , small feet and openings, no real formula. What I do ,do is increase the bottom of the vessel to give it stability, somewhere around the last 25%. Most of what I do now is intentional by that I mean the vessel is complete in my minds eye, rarely do just put a chunk on the lathe and wing it.
Where you can really go wrong is to make the base so big that it looks like a dog bowl. Stable, but ugly.
Do you mean that you increase the wall thickness down low?
Be careful with varying wall or bottom thickness. That can quickly crack a bowl that has some drying to do yet because of different drying rates in the bowl.
No. I see some bowls which have such a small base, and are so tall that they appear unstable.
No. Some bowls have a small base that they appear to me to be potentially unstable.
No. I am asking if there is an accepted ratio between the rim of the bowl and its base.
yes, sometimes depending on what it is it can be 2-3 times the upper portion
very rare for me as most of what I use has been drying for many years. In fact I havent turned any green wood in maybe 10-15 years
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There maybe, but I havent really heard of it and most likely wouldn't adhere to it. The only rule that I look at is the rule of thirds. But even then due to the amount of time I have spent in Asia and its influence on me often causes some degree of variation in the rule.
Thanks for the guidance.
I'm a firm believer when you want design ideas to look in the kitchen cabinets for ideas on size and design. We have a set of pottery type salad bowls that are 6" diameter at rim, 2 1/8" at base, and 3 1/2" tall. Looking at the bowl you would think it's not going to be stable but it is stable, even when cutting up your lettuce. It does meet the 1/3 rule for base to rim but it looks too tall to be stable.
Roger Wiegand
Beta Tester
Look at bowls you like and at bowls you use and think work well and measure the ratios on them. For many people that results in the suggested 1/3 ratio. The more interesting cases are often the ones that break the "rule" but still look good.
Flat bottom bowls need a larger foot, but are generally less desirable. If you do a flowing rounded profile, you can have a much smaller foot, because partially full, the center of gravity will naturally be more centered.
I more of less follow that 1/3" rule, kinda/sorta. Interestingly enough, some world-class turners like David Ellsworth have very tiny feet relative to the height of a piece, and his work is in galleries and museums! (Though, to be fair, he has done far more of the hollow forms he is known for than bowls, judging by his book and the extensive gallery of his works in his home, which I had the fortune to admire and study while taking his class a couple of summers ago!).
I have always gone with about 1/3 the diameter of the rim for the base. I never measure it. Some times I might go a bit bigger, mostly because I want to use my bigger chuck. If I go 1/4 or so the rim diameter, I am one of those people who just steps into the room, and it will fall over and break. For platters, I generally go half or more the diameter of the rim.
robo hippy
robo hippy
Thanks Ross.
Thank you.
Thanks Ron.
Thank you Aaron.
Thanks.
Thanks Aaron.
Thank you.
Thanks.
Thanks.
Thank you.
Thanks.
Thanks.
My bowls are mostly utilitarian by design, and open form in style. As such, the weight of the contents is typically concentrated in the middle/bottom of the form. I favor a footed bowl with a diameter of about 1/4 the largest diameter. This does two things - it provides adequate stability when using, and it allows the fingers to rest at the edge of the foot, or at the center of the foot when holding or carrying - it gives a very secure hold at least with my mid-sized hands.
I find bowls in particular to be very tactile items. They’re used to present and serve food - an act of giving and welcome. With the thumb hooked over the rim, the fingers at or on the foot provide a secure hold. It feels good in the hand.
I find bowls in particular to be very tactile items. They’re used to present and serve food - an act of giving and welcome. With the thumb hooked over the rim, the fingers at or on the foot provide a secure hold. It feels good in the hand.