Woodturning Class and Speed

[Ed Brekke]

I had the great pleasure last week to take a one week class in woodturning at the JC Campbell Folk School in Brasstown, North Carolina. First of all what a great place. There are dedicated studios for every craft. Maximum class sizes are 10. The Woodturning studio has 11 Powermatics with each station set up with a work bench and tool rack with all the tools and chucks you may need. (You can bring your own tools if you prefer.) A lot of emphasis was given to tool sharpening, tool selection and specifically how to ride the bevel and use the bevel to achieve a surface without tear out.
We also spent time discussing turning speed. A subject on which there are so many different opinions. Basically our instructor summarized it this way: low speed for sanding higher speeds for turning. And by higher speeds he defined it as turning at a speed you are comfortable with. He did the majority of his turning at speeds between 1200 and 1700 rpm’s. His work was beautiful! As someone who typically turned between 800 - 1000 rpm this was a revelation to me. A second key learning was his preference for mortises over tenons. And his mortises varied from 3/16 - 5/16 max. This made finishing a bowl with a completed bottom so easy. I had always been digging out mortises as deep as the jaws would go. And I used tenons much more frequently than mortises because they seemed easier to me. Here are some photos of work I completed in the class.

 

[Kevin Jenness]

Sounds like a great class.

On the subject of speed, rpms have to be considered relative to diameter. There is a rule of thumb stating that rpms x diameter in inches should be 6000-9000. It's not written in stone, but it's a useful reference. At the upper end (rpms x D = 9000) the rim speed is about 27 miles per hour. The more mass and the higher the rim speed, the more energy is embodied in the spinning wood and the more damage it can do if something breaks loose.

You probably know all this, and everyone can make their own judgments about shop safety. My tolerance for getting hit by speeding objects is pretty low. I tend to regulate the speed by perceptible vibration and adjust my tool feed rate to match.

I was showing my friend how to use his McNaughton coring system on a 8.5" walnut bowl blank last Monday. It looked quite sound to me. He called me later that day to say he had blown the piece up at 1700 rpm, about 2/3 faster than I would have spun it. He's getting to be a good turner, but he's only been doing it for a year, usually wears only safety glasses, and had never heard of my rule of thumb. I worry that he is going to get beaned one day.

 

[Lennart Delin]

I usually go as fast as seems comfortable to me. If I get vibrations, giving undulating surface I reduce a little. I like small feet, so mostly a tenon, but on large bowls, say 30 cm and above, I often use mortice. I always finish the outside completely, including sanding, before turning the inside. I never go back to return the foot. These are typical tenons and mortice I use for turning the inside. I also strive for a uniform wall thickness and bottom thickness.

 

[robo hippy]

I don't think I have ever used a tenon on a bowl. Not positive though. I do use a NRS for the inside of the recess, and it gives a nice protected place for my signature. Mine are at most maybe 1/8 inch. The trick is to make sure you have enough shoulder on the recess to support the turning loads. I think Mike Mahoney on his platters, generally turned from dry or drier wood, goes 1/16 inch deep on his. When our club first formed, there was a discussion about which to use for bowls. I was pretty new at turning back then, and every problem the others mentioned with their recesses, I had solved, so I didn't have those problems.

robo hippy

 

[Alan Weinberg]

after a couple classes with Jimmy Clewes, who was constantly saying, “faster, faster, faster.” I have turned up the rpm a bit. I’ve alternated between tenon and recess, depends on the wood. That adequate shoulder on a recess is definitely needed.

 

[Ed Brekke]

Sounds like a great class.

On the subject of speed, rpms have to be considered relative to diameter. There is a rule of thumb stating that rpms x diameter in inches should be 6000-9000. It's not written in stone, but it's a useful reference. At the upper end (rpms x D = 9000) the rim speed is about 27 miles per hour. The more mass and the higher the rim speed, the more energy is embodied in the spinning wood and the more damage it can do if something breaks loose.

You probably know all this, and everyone can make their own judgments about shop safety. My tolerance for getting hit by speeding objects is pretty low. I tend to regulate the speed by perceptible vibration and adjust my tool feed rate to match.

I was showing my friend how to use his McNaughton coring system on a 8.5" walnut bowl blank last Monday. It looked quite sound to me. He called me later that day to say he had blown the piece up at 1700 rpm, about 2/3 faster than I would have spun it. He's getting to be a good turner, but he's only been doing it for a year, usually wears only safety glasses, and had never heard of my rule of thumb. I worry that he is going to get beaned one day.

I have read about that rule of thumb in the past but having struggled with 9th an 10th grade algebra, it does not make sense to me. Basically, the formula goes: RPM X Diameter = Speed But the "speed" on my lathe is a measure of RPM's. So the rule of thumb equation would look like this: RPM X Diameter = RPM which is an unsolvable equation. Unless, of course, the RPM's on my machine is a measure of the motor RPM, not the spindle speed.

Like most of you have said: It depends. Are you turning a bowl or a spindle? What type of wood are you turning? I think the "formula" I like best is: "The proper speed is a balance between safety and turning quality" and what you are comfortable with.

 

[Ed Brekke]

I usually go as fast as seems comfortable to me. If I get vibrations, giving undulating surface I reduce a little. I like small feet, so mostly a tenon, but on large bowls, say 30 cm and above, I often use mortice. I always finish the outside completely, including sanding, before turning the inside. I never go back to return the foot. These are typical tenons and mortice I use for turning the inside. I also strive for a uniform wall thickness and bottom thickness.
View attachment 75183

I am feeling very comfortable now that I have started using the mortise like in your live edge piece. By the way, I take note that your diagram is in Swedish. Personally, I prefer Utvendig grip.

 

[Ed Brekke]

I don't think I have ever used a tenon on a bowl. Not positive though. I do use a NRS for the inside of the recess, and it gives a nice protected place for my signature. Mine are at most maybe 1/8 inch. The trick is to make sure you have enough shoulder on the recess to support the turning loads. I think Mike Mahoney on his platters, generally turned from dry or drier wood, goes 1/16 inch deep on his. When our club first formed, there was a discussion about which to use for bowls. I was pretty new at turning back then, and every problem the others mentioned with their recesses, I had solved, so I didn't have those problems.

robo hippy

Mike Mahoney is a legend here in San Diego. I missed him last time he visited our local association here but his videos are awesome.