Safe size of bowl blanks, given lowest speed of lathe

[Jamie Straw]

Knowing that the lowest speed of a lathe is one of the specs that dictates how big and heavy a bowl blank should be maximum, I would like to know what you recommend for a lathe with 12" swing and lower limit of 550 RPM. Friends know I'm turning, and are sending wood my way. Just want to be practical about how I plan to use it.

 

[Owen Lowe]

Knowing that the lowest speed of a lathe is one of the specs that dictates how big and heavy a bowl blank should be maximum, I would like to know what you recommend for a lathe with 12" swing and lower limit of 550 RPM. Friends know I'm turning, and are sending wood my way. Just want to be practical about how I plan to use it.

Hi Jamie.

Disclaimer: I don’t use any speed indicator on my lathe when setting the RPMs, so…

I think I’d be completely comfortable with a piece that maxes out the swing on a 12†lathe at 550 rpm — depending on how well balanced the wood is. If the lathe begins rockin’an’rollin’ then I’d investigate manually removing wood to bring the piece into better balance.

 

[hockenbery]

For a 12" lathe I like to stay with 10" bowls.

A good size blanks for cut rim bowls are are 10" diameter height of 4- 6
You might be able to turn 11" diameter and clear the banjo.

The 4" high 10 makes a nice open bowl easy to hollow.
And yields a good sized functional bowl. The 6" high produces the classic hemisphere bowl a pleasing shape to everyone.


For natural edge bowls I would look for log sections
6" in diameter cut the blanks 8" long and make that size until you are comfortably turning them out.
Then try some 10" by 6 blanks. Makes a nice appalling bowl. Bu the extra length is more difficult to work with.
After turning 6 or so smaller bowls the longer width will be easy to tackle .

These bowls have a long shallow curve

Have fun
Al

 

[Bill Boehme]

Balance is everything. If a piece is badly out of balance then 100 RPM might be too fast. If perfectly in balance then you might be able to start at 1000 RPM (although I wouldn't do it, myself). I always begin by statically balancing the wood. By doing that, vibration will be minimal if not completely eliminated.

 

[Odie]

Hi Jamie.

Disclaimer: I don’t use any speed indicator on my lathe when setting the RPMs, so…

I think I’d be completely comfortable with a piece that maxes out the swing on a 12” lathe at 550 rpm — depending on how well balanced the wood is. If the lathe begins rockin’an’rollin’ then I’d investigate manually removing wood to bring the piece into better balance.

Owen Lowe has a good response here, Jamie......

You just never know what the best speed will be, until you mount up and try it. For pieces that are out of balance, I use two things to adjust the speed......my fingers on the bedways, and a laser extension arm mounted on top of my headstock that vibrates with the lathe. These things are good to see and feel where the best rpm is going to be. As Owen says, removing some of the bulk wood will also usually alter what the best rpm is.

ko

 

[john lucas]

Good points so far. Another factor is how stable is your lathe and how big the footprint. I'm planning to add to the footprint on my lathe when I get the new shop built. That adds huge amounts of stability which lets you turn bigger blanks. Mass of the lathe is another factor. Here I'm mostly talking about out of balance pieces because 550 rpm will really make the lathe dance with an out of round piece. Al's suggestion of 10" is good. Once you've turned a bunch of 10" bowls you'll have a much better feel for how big and how fast you can turn. 8" bowls turn and sand faster. Remember if you start with 10 you'll probably end up with 9. Rarely are pieces perfectly round to begin with. Also when you cut bowl blanks it's easy to have some checks in the outer portions which also reduces the final size. Just remember a small perfectly shaped bowls is better than a larger bowl with defects or bad shapes.

 

[Brian Myers]

If you are just starting out , band saw your blanks round with both ends cut flat and make sure the wood is sound . Get some basic bowls under your belt then work up to blanks that are unbalanced. You should be able to turn a balanced blank that clears your bed by a 1/8" to 1/4" at that speed as long as your lathe is stable and weighted down. Like Odie said you don't know until you try but mount the first one securely to a faceplate , make sure the blank clears the lathe bed and tool rest all the way around, have the tail stock up against the blank, wear your normal safety gear , stay out of the line of fire and start it up on the lowest speed. I have a 12" lathe from the 50's and don't have a problem turning a balanced blank that just clear the bed at my lowest speed which is 630 rpms but it will depend on the mass of your lathe, how stable it is and if it is mounted to a bench , how secure it is.

 

[robo hippy]

My first lathe was a little 4 speed Atlas with a 12 inch throw. I put a 1 hp motor on it. Slow speed was about 500. I ended up with it on two gluelam beams that were 3 by 12 by 48 inches. Some chain sawn bowl blanks would have it dancing around the shop till I got things rounded out and balanced. With taking blanks from board stock, it is pretty simple to get things pretty close to a circle, and centered on a face plate or chuck, and things won't bounce around so much. Other than that, bigger is better, and variable speed is some thing that once you use it, you will never go back. If you mount a chain sawn blank, make sure to stand out of the line of fire. I do that as habit on every thing I turn. Also, I turn at what ever speed works, and have never had any type of read out. My mid range on my Beauty is about 2200 rpm. 10 to 12 inch blanks do fine at that speed for me. Most others won't use those speeds, and they are considered 'unsafe' or as I say 'Professional driver on closed track, do not attempt'.

robo hippy

 

[Jamie Straw]

Flood of info, thanks!

The detail this group is providing here is great, I really appreciate it (print, print, print). It feels like "Introduction to Bowl Turning" at a workshop😀 and I need that info! I'm careful even with spindle stock to start slow and ramp up, and hear ya about balancing the stock. The guidelines for progressing through sizes are very helpful, and will guide any cutting I do for the next few weeks especially. The Jet is still on its metal stand, but mounted to a 4x4 "mobile" base, with a little heavy stuff on the shelf, but not much. Plan this fall or winter to build a cabinet base for it to close off from shavings, and store more stuff (=weight) in it. Watched a video yesterday about turning a heart-shaped bowl (crotch wood), and for that particular project the demonstrator discussed mounting for the best shape and not necessarily balancing -- recognizing that care must be taken. Yeah, well, maybe....2016.

Reed - no worries about me running 10" blanks at 2200 rpm.😱 Do you have an armored observation booth for visitors?

 

[john lucas]

Jamie My first real lathe (other than the shopsmith) was a older delta 12" with a minumum speed of about 500rpm. I made what I thought was a fairly heavy stand out of MDF. That thing would literally dance around the room when rough turning chainsaw bowl blanks. I learned 2 things. One was I bought a really cheap electric chainsaw. That allowed me to knock off the really rough corners before starting the turning (this was before I had a bandsaw to round out blanks better) The second was instead of trying to go back and forth across the outer perimeter to try and true up the blank I would start at the bottom (making my tenon) and work my way toward the lip of the bowl. What this did was after the first few cuts I had a round area to present the gouge to. The cut would then progress up the side into the out of round area. This allowed me to start each cut on a smooth area which was less stressful and it also removed a lot of wood making the bowl lighter so it didn't bounce as much.

 

[Gerald Lawrence]

I am not in the class with most of your responders, But I will restate something. I think the one I read this from was Bill. When the piece is placed between centers in order to balance it with the lathe off give it a spin. If it stops in the same place each time it is out of balance and must be adjusted by moving center toward the lathe bed side as that is the heavy side of the mount.
This whole process is more intuitive than it sounds. Since I started doing it this way life has been simpler.

 

[Bill Boehme]

I am not in the class with most of your responders, But I will restate something. I think the one I read this from was Bill. When the piece is placed between centers in order to balance it with the lathe off give it a spin. If it stops in the same place each time it is out of balance and must be adjusted by moving center toward the lathe bed side as that is the heavy side of the mount.
This whole process is more intuitive than it sounds. Since I started doing it this way life has been simpler.

Thanks for explaining how to do it. Once you have done it, it is easy to understand.

Something that I have done to speed up the process when the piece isn't exactly round (as in sort of octagonal chain sawn) is to deliberately mount the piece off center and then use a Sharpie to mark the plumb line (vertical line). Then I repeat this process with the piece rotated about 90°. Where the two lines cross should be fairly close to being balanced. Using cup centers (remove the points) will enable you to make minor tweaks without the point causing it to creep back.

If you put a live center in both the headstock spindle and tailstock then you can crank in a bit more pressure needed when balancing really heavy pieces. I have managed to wrestle pieces up to about 75 pounds, but on those really heavy ones I'll settle for "good enough" as being good enough.

A balanced piece is a joy to turn because you don't have to contend with all of the vibration. I have done this with crooked mesquite logs (is there any other kind) as large as about 14" diameter and 22" long. No problems other than the bug juice. 🙄

 

[Owen Lowe]

I learned 2 things. One was I bought a really cheap electric chainsaw. That allowed me to knock off the really rough corners before starting the turning (this was before I had a bandsaw to round out blanks better)

Ditto ^^^. An electric saw keeps the neighbors happy at 11PM as well as doesn’t poison the family with exhaust coming from the basement turnery.

The second was instead of trying to go back and forth across the outer perimeter to try and true up the blank I would start at the bottom (making my tenon) and work my way toward the lip of the bowl. What this did was after the first few cuts I had a round area to present the gouge to. The cut would then progress up the side into the out of round area. This allowed me to start each cut on a smooth area which was less stressful and it also removed a lot of wood making the bowl lighter so it didn't bounce as much.

John’s roughing method ^^^ is spot on. I’ve seen so many tutorial videos on YouTube where the turner starts by bringing the circumference into round. It can be a physically exhausting process and can lead to horrible catches. Begin on the face side at the live center or drive center area and work it outwards - much more controllable and less physically punishing.

 

[Steve Worcester]

Speed is so relative to the situation. The balance of weight on the piece, the stability of the lathe in both it's construction and how it is planted on the ground. I started out on a Delta and 550 RPM was it's lower limit, and my naiveté allowed me to work with it. Now that I am more experienced, I would say for many pieces in the 10"-12" diameter , that isn't anywhere near slow enough. Even after being rounded by chisel or bandsaw, the same holds true. Use good judgement, no piece of wood is worth death.

 

[Jamie Straw]

I am not in the class with most of your responders, But I will restate something. I think the one I read this from was Bill. When the piece is placed between centers in order to balance it with the lathe off give it a spin. If it stops in the same place each time it is out of balance and must be adjusted by moving center toward the lathe bed side as that is the heavy side of the mount.
This whole process is more intuitive than it sounds. Since I started doing it this way life has been simpler.

It makes total sense! Reminds me of balancing the grinder wheels. Not sure how to get it to spin, though, as the belt provides resistance. Perhaps this involves a different head-stock center than what I'm using for spindle stock?

 

[Bill Boehme]

It makes total sense! Reminds me of balancing the grinder wheels. Not sure how to get it to spin, though, as the belt provides resistance. Perhaps this involves a different head-stock center than what I'm using for spindle stock?

There are three ways:

• Usually you can use just light tail stock pressure so that only the points touch
• when you need more tailstock pressure, you can put a live center in the headstock.
• If you don't have two live centers, you can loosen the belt. This is quick and easy on many lathes.

When you have really heavy pieces, back driving the motor is not a problem.

 

[hockenbery]

It makes total sense! Reminds me of balancing the grinder wheels. Not sure how to get it to spin, though, as the belt provides resistance. Perhaps this involves a different head-stock center than what I'm using for spindle stock?

I have students do their first bowl from a band sawn disc hole drilled in the middle mounted on the screw in the chuck,
Already round and balanced. With minimal or no interrupted cuts students can concentrate on the bevel riding cuts.
Some turners use this method on almost all the bowls they ever turn.
If you don't care about lining up the grain beyond what you can do with the saw this is the method to stick with.

Once students get experience with the basic cuts, making a tenon, shaping and surface I move them to a between centers mount.
I try to cut the student blanks from symmetrical log sections and round them on the band saw so they will be close to in balance when put in the lathe.

Between centers the spur drive I drive into the center of the future opening of the bowl with a wooden mallet. I align the Spurs 45 degrees to the grain so they drive in evenly. This center can be moved but I plan on not doing so unless something bad shows up in the wood. The tail center side of the blank must have a fairly flat area of solid wood the the center to hold. I first balance for weight Gerald gave a great description.
I turn away the high spots only crudely working toward a bowl shape and leave an area about 3" in diameter where the chuck will be uncut so k can move the center and still have 2" of wood for my tenon. Once the blank is running somewhat smoothly I reposition the tail center to line up the grain. Lining up the grain is how to get the hyperbola grain patterns centered around the center of the bowl bottom. This is one element that sets a hand turned bowl apart from the masse produced bowls.
Once the center is repositioned to line up the grain, the lathe speed is turned down the bowl will again be unbalanced but not as much as when first mounted.
The shape a notion of the rim, a notion of the foot and tenon connect the foot to the rim with a pleasing curve.

I encourage you to get some experience with turning blanks as close to discs as possible. It you have a big band saw this is easy.
With a chain saw I cut two parallel faces for the top and bottom maybe 5" thick. Find the center of the opening - center of the log works best for the grain.
Make a 10" circle and a 11.5" circle. With the chain saw cut all the bigger circle away and leave all the small circle. This is usually easier cutting opposite sides which become opposite corners off.

I mount almost all my bowls and hollow forms between centers. I pick my center point with a lot of thought because it will determine how I can show the grains.

Have fun
Work safely

Al

 

[Jamie Straw]

There are three ways:

• Usually you can use just light tail stock pressure so that only the points touch
• when you need more tailstock pressure, you can put a live center in the headstock.
• If you don't have two live centers, you can loosen the belt. This is quick and easy on many lathes.

When you have really heavy pieces, back driving the motor is not a problem.

Thanks, Bill, the first two are my best options. What is "back driving"?😕

 

[Jamie Straw]

Thanks, Al!

I have students do their first bowl from a band sawn disc hole drilled in the middle mounted on the screw in the chuck,[snip]
Have fun
Work safely

Al

Lots of detail there for me, thanks Al. I will probably have questions when the bowl blanks head to the lathe. I've found 8 or 9 small bowls that I turned green 5 years ago before the hiatus, some very small, biggest one 6"D x 3"H including base. And one round bowl blank, 2.5"H x 4+ D estimate. I noticed that the bowls I turned on my own tended to be deep relative to their diameter, the ones that someone helped me with were shallower, which was probably more difficult. I think I'll see if the local AAW mentor would help me go through those bowls to choose the ones that are still safe to turn, and take them close to finished size. A couple are pretty grungy, probably need to be bleached. Two are natural edge, and are ones I did solo -- small D and pretty deep. As someone who has quite a bit of teaching in her background, I appreciate the progressive nature of your instruction.

PS: Yes, I have a band saw -- 14". Big enough for now.

 

[Bill Boehme]

Thanks, Bill, he first two are my best options, thanks. What is "back driving"?😕

That's when somebody in the back seat ... No wait ... That's a different sort of back driving. 😀

Back driving simply means that the unbalanced load is able to rotate the whole drive train ... spindle, pulleys, belts, and motor (with the power off, of course). Basically, the load is driving the motor. This would be the case if a really heavy piece of wood that was badly out of balance were mounted on the lathe. When a heavy piece gets close to being balanced it is best to loosen the drive belt so that fine tuning will be more accurate.