Have you ever thought the wood lathe speed of a bowl blank is turning too fast or too slow?
If the lathe is too fast, things can get dangerous. If the lathe is too slow, turning can become tedious.
Wood lathe speed while making wooden bowls is important for two reasons – safety and efficiency.
If the lathe is too fast the turning bowl blank can become a dangerous projectile. If the lathe is too slow, cuts become clumsy and turning a bowl can take a long time.
So what is the right wood lathe speed?
There are many factors to consider when determining lathe speed. The size of the bowl blank and the type and condition of the wood are the most critical elements to scrutinize.
In this article, I will share with you a specific way to determine lathe speed, and I will also share an easy formula and an Wood Lathe Speed Calculatation with a general guideline chart of top wood lathe speeds.
Childish Example
Turning large bowl blanks are probably the most difficult to be patient with because they need to be turned slower than small blanks.
Remember back to childhood when you and other kids played on the merry-go-round? Recall holding on for dear life as someone spun you as fast as they could?
After spinning wildly on the merry-go-round, in an instant, you were giggling in a pile on the ground because you couldn’t maintain that grip? Well, that’s what we don’t want to happen with a bowl blank on the lathe.
I’m not sure those merry-go-rounds still exist. Probably too many lawsuits nowadays.
Wood Lathe Speed Orbit
OK, this is a bit of a mind-stretching exercise.
If you have a 4” bowl blank and a 10” bowl blank on a lathe turning at 500 RPMs (revolutions per minute), which bowl’s outer edge is turning faster?
When I was first introduced to this question, I thought for sure it was a trick question. “Both bowls are traveling at the same speed, 500 RPMs.” But that is not correct.
Yes, the revolutions per minute are the same, but the outer edge speeds are different.
The outer edge of the 4” bowl has a circumference of just over 12.5 inches. While the 10” bowl has a circumference of 31.41 inches.
What this means is that in one revolution the lathe turns both bowls once, but the 10” bowl blank’s outer edge is moving almost two and a half times faster than the 4” blank in the same amount of time.
The additional rotation speed of the large bowl plays a big factor on the forces pulling the bowl outward.
In Practice
When we make a cutting pass from the rim to the bowl center, we can see this force in action. The beginning of the cut is fast and slides quickly across the surface. However, to maintain that same clean cut we must dramatically slow down the bowl gouge at the center nub of the bowl.
We must slow down the bowl gouge at the center point because we have to wait for the wood to rotate across the cutting bevel.
At the bowl rim, the material is moving much quicker than we can keep up with, but at the center, it is so slow we must be patient and wait.
Wood Lathe Speed Experiment
To illustrate this weird phenomenon try this experiment. If you can imagine it well enough in your mind, you may not need to go outside and try it, but it can be fun either way.
Find a vertical object, a tree, pole or post that is clear of obsticles all the way around.
Stand right next to the post with your hand touching the post and begin to walk slowly around the post while counting off seconds.
How long did it take to make one revolution?
Now, walk twenty paces away from that post and walk a circle around the post keeping the post in the center of your circle. Count the seconds it takes to make one rotation out there.
The post represents the center axis of the turning bowl blank, and each path represents the speed of rotation at the center of the bowl compared to the outer rim.
On the lathe, both paths, center and outer edge are completed in one rotation.
Does that illustrate how much faster the rim is turning compared to the center of the bowl?
Force and Physics
As we make larger bowls, we are adding much more speed and stress on the bowl blank. That added speed on the bowl size creates additional force that needs to be appreciated.
Don’t worry, I’m not going to get into physics. Why? Because I don’t have a clue about physics.
I do know, as wood bowl turners we need to be aware that larger bowl blanks are under much more force than smaller pieces.
That centrifugal force playing on the bowl blank will make the blank fly off the lathe if the conditions become too much for the blank to handle. Just like the kid sliding off the merry-go-round.
So why all the talk about size and rotation and physics? Because we must understand we can’t simply turn up the lathe as fast as we want without there being consequences.
Like everything in this world, there is always cause and effect.
Dangerous Habit
I started turning on a lathe with a convenient RPM digital readout. At the time it seemed cool, but that wasn’t the greatest way to learn.
Let me tell you why.
When you’re learning any new skill, you’re basically trying to make repeatable patterns or movements to achieve an end result. As you consciously and subconsciously recall and repeat these learned movements, you form habits.
The habit of thinking a fixed RPM readout of 800, for example, is “the” ideal speed for making finishing cuts is dangerous. If all the bowls you turn are four inches, perhaps this will work. When you place an 18-inch bowl on the lathe and think 800 RPMs is the standard speed you could get in trouble.
Practical Wood Lathe Speed Application
In a moment I will share a commonly circulated wood lathe speed formula, but there is another, better way, I want to share first-human intuition.
I encourage you to put a piece of tape over an RPM readout display, if you have one, at least for a while. By blocking this information, you will not make as many assumptions, and you will probably pay more attention to the turning bowl blank.
When you pay attention to the subtle changes in sound, vibration, and the feel as you make cuts, you will be more in tune with the ideal lathe speed.
Start by attaching a bowl blank to the lathe. Always start with the lathe speed turned all the way down, then slowly increase the lathe speed.
Look, listen, and feel.
Feel the lathe, not the turning bowl blank. I just want to be clear there. LOL
If you sense any sounds or vibrations, back the speed down a bit until the rotation is smooth. This is the speed where you should begin working.
If you encounter just a subtle sound or vibration, try increasing the speed just a bit higher. Sometimes there are harmonic vibrations that occur at a particular speed, and once the speed is changed, they disappear.
There should be no odd sounds of vibrations when you turn. This can be daunting to realize, especially if you’re turning a sizeable off-balanced bowl blank.
Don’t fear, as you begin to true up the blank, you will be able to increase the speed a bit.
Wood Lathe Speed Ever-Changing
Initially, most wood bowl blanks are hardly ever perfectly balanced. Rarely will a bowl blank turn smoothly and at optimal lathe speed at first.
When you begin turning a blank bring the speed up to the point when vibration or noise starts to occur, then back the pace down a bit until smooth rotation returns.
True up the face of the bowl blank and the side as well. With these two areas smoothed, you should be able to increase the lathe speed gradually.
As you further progress in shaping the bowl, the blank will naturally become more balanced, and the lathe speed can be increased accordingly, but do not exceed safe limits for the size of bowl you are creating.
Wood Conditions
If you’ve read my other articles you know I try to not generalize. And wood is definitely a huge component in this equation that can not be generalized.
Every piece of wood you put on your lathe is different. Even if two bowl blanks were cut from the same tree or even the same log, they could be very different.
Knots, bark enclosures, rot, moisture content may be apparent or hidden at first and cause all sorts of imbalance.
If you are new to wood bowl turning, avoid turning pieces that have issues of loose bark, voids, rot, etc. There are too many variables and its best to not practice learning skills with poor quality wood.
Questionable Bowl Blanks
On the other hand, if you are more experienced, oddly shaped wood or wood with imperfections can make amazingly beautiful turned bowls. Just be aware of the hazards and take precautions.
Remove extremely loose bark or material by hand before you begin to turn. Use a screwdriver and pry out debris, so it does not become shrapnel while turning.
Once the outside of the bowl is shaped, consider taping or wrapping the exterior of the bowl with stretch packing plastic film to secure the exterior while turning the interior.
Be careful not to allow any tape or plastic to contact the headstock area.
Safety and Speed When Turning
Regardless of what type or condition of wood you are turning there are always ways to be safer on the lathe.
When turning bowls, especially larger diameter bowls do the following to increase your chances for success.
- Wear safety equipment at all times
- Wear safety glasses
- Wear a face-shield
- Stand to the side of the turning blank
- Start with the lathe speed to the lowest setting
- Do not exceed the formula guideline RPMs for a given bowl (see below)
- Avoid turning damaged or questionable wood
- If you must turn questionable wood, secure the bowl blank (see above)
- Use sharp tools
- Be patient with your progress
Wood Lathe Speed Rule of Thumb
There is a general rule of thumb for bowls and lathe speed.
However, before I share this, it’s important to note that this rule of thumb does not apply to large bowls. Large bowls MUST be turned slower.
The wood lathe speed rule of thumb is – do not to exceed 1,000 RPMs.
One thousand RPMs seems to be a magical point at which bowl blanks either go up or down if they come off the lathe.
If the speed is under 1,000 RPMs, then a dislodged bowl blank is supposed to fall to the floor. Speeds faster than 1,000 RPMs can send a bowl upward and at your face or torso.
Now I don’t know if the 1,000 RPM threshold can be scientifically proven or if this is an urban myth started by a shop teacher in the 1960s, but it does seem to work.
I have had a couple of bowls come off the lathe and skip across the floor, and my lathe speed was under 1,000 RPMs. By the way, those flying bowls were due to tenons that broke because of brittle, dry pecan wood, for the most part. That’s a whole other article. LOL
Wood Lathe Speed Calculation
The calculation to get a maximum ballpark speed for your bowl blank on a wood lathe is as follows.
Take the diameter (D) of the bowl divided by 9,000
9,000 / D = Maximum RPMs
For Example: 10 Inch Bowl = 9,000 / 10 = 900 RPMs Maximum
For clarity, this is the maximum speed under any conditions. Meaning, if the bowl blank is turned smooth and true and there is zero vibration still DO NOT exceed these lathe speeds based on the diameter of the bowl.
Wood Lathe Speed Guideline Chart
- 9≤ Inch Diameter Bowl and Under = 1,000 RPMs
- 10 Inch Diameter Bowl = 900 RPMs
- 11 Inch Diameter Bowl = 815 RPMs
- 12 Inch Diameter Bowl = 750 RPMs
- 13 Inch Diameter Bowl = 690 RPMs
- 14 Inch Diameter Bowl = 640 RPMs
- 15 Inch Diameter Bowl = 600 RPMs
- 16 Inch Diameter Bowl = 560 RPMs
- 17 Inch Diameter Bowl = 525 RPMs
- 18 Inch Diameter Bowl = 500 RPMs
- 19 Inch Diameter Bowl = 470 RPMs
- 20 Inch Diameter Bowl = 450 RPMs
- 21 Inch Diameter Bowl = 425 RPMs
- 22 Inch Diameter Bowl = 400 RPMs
- 23 Inch Diameter Bowl = 390 RPMs
- 24 Inch Diameter Bowl = 375 RPMs
- 25 Inch Diameter Bowl = 360 RPMs
- 26 Inch Diameter Bowl = 345 RPMs
- 27 Inch Diameter Bowl = 333 RPMs
- 28 Inch Diameter Bowl = 320 RPMs
- 29 Inch Diameter Bowl = 310 RPMs
- 30 Inch Diameter Bowl = 300 RPMs
This chart is designed to merely be a guideline of maximum speeds. Use common sense when turning any piece of wood and avoid dangerous or poor quality wood with splits, checks, or cracks.
Lathe Speed Temptation
There is often a temptation to turn faster than what is considered safe, especially when you have acquired good turning skills and the bowl blank is turned to a balanced shape.
Avoid the temptation to turn beyond what is safe. If you need to, adopt the 1,000 RPM limit “bowl goes down” rule of thumb. I use that rule, and it works for me.
Spindle Lathe Speeds
If you dabble in spindle turning too, it can be tough to slow down the lathe to make a wood bowl. Spindle turning lathe speeds can reach two, three, four thousand RPMs and higher.
Why are spindle speeds so much faster than bowl lathe speeds?
Spindle turning lathe speeds can be much faster because of the much smaller diameter of wood material and the relatively small amount of mass compared to bowl blanks.
Think back to the orbit example. A wood pen blank that is 3/4” wide can turn much much faster than any bowl.
Just remember when you venture from spindle turning to the “real world of turning” and making bowls, the speed must come down. It’s no longer play time. Ha! I’m just kidding about that…sorta.
Wood Lathe Speed Conclusion
Know the limits for the size and condition of the bowl blank you are turning. Don’t exceed those limits and all should be fine.
Use your intuition. If something seems off or odd, perhaps a subtly different sound becomes apparent, slow down the lathe a bit.
Gradually increase the lathe speed as your bowl takes shape and becomes more balanced, but don’t force the situation by ramping up the RPMs prematurely.
Use common sense, pay attention to your turning bowl blank, know the limits based on each bowl size and you can make a beautiful bowl safely and efficiently.
Original article and pictures take https://turnawoodbowl.com/safe-wood-lathe-speed-calculation/ site
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