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speed

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I have seen numerous recommendations as to safe and effective speeds for turning, from the decal on my old General lathe that prescribes speeds for large pieces lower than the original Reeves drive was capable of to "diameter in inches x rpm should equal 6000-9000" to "If the lathe isn't shaking and you aren't shaking everything is cool" to Stuart Batty talking about a rim speed of 40 mph (which is in the range of diameter x rpms =13,500 if my arithmetic is correct).

Obviously when roughing out one can't cut effectively with more than a little vibration. High speed is good for smooth cutting but potentially hazardous if anything launches. Subjective assessment of the soundness of the workpiece has to be a factor. How do all you folks approach this topic?
 
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hockenbery

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I try to balance cutting effectiveness with cutting smoothness.

Higher vibration less cutting smoothness
Higher speed to a point more cutting effectiveness.

each turner will have a comfort zone with each piece. You will find your comfort zones.
Bad things happen faster at higher speeds.

I strive to match feed rate of the tool to speed of the wood so that my cuts are a continuous spiral around the form.
Like we peel Apples to get one long continuous peel.
In demos I show cuts rotating the piece by hand and it Is darn difficult to cut that continuous spiral at 3 rpm.

Most of my bowls and hollow forms are turned from half logs partially rounded on the bandsaw.

I start between centers and shift the tailstock to balance for weight by letting the heavy side rotate to the bottom then move the tail center toward the heavy side. Then spin the piece slowly by hand and find the heavy side and shift again. After 2-3 the piece will spin slowly by hand with no side being so heavy as to force that side downward.

i then find the highest cutting speed by increasing the speed until a get a noticeable vibration. Then I test higher speed to see if I get less vibration (most of the time the is one) at a higher speed. Then I rough at the speed. Once the cut begins the vibration is reduced by the heavy roughing cuts.

Then before I turn into the desired form, I move the tailstock to balance the grain ore the rims. I will fine tune this as the form gets close to outside shape. Each time the center is moved the piece will be out of balance so I search for the best speed above the first noticeable vibration. As the piec is turned into round I will increase the speed to get cleaner cut.

you can see exactly how I do this in the the working with green wood thread and the natural edge
https://www.aawforum.org/community/index.php?threads/working-with-green-wood.11626/
https://www.aawforum.org/community/index.php?threads/naural-edge-bowl-from-a-crotch.11058/
 
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Turned a half a log today to round and a tenon for finishing later. I made sure it was balanced per Lyle Jameison's video. As it became a round piece, I would turn on some more speed until I was at max RPMs. I had a piece come off the chuck, bounce off the wall and, by Murphy's Law, scrape my arm. Still have faint scars as a reminder.
 
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Randy Anderson

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I've often wondered if I turn too slow. Like others I spin a rough blank up to the point it shakes the lathe a bit then back off and start. As I get it rounded off I crank it up a bit and start again. Multiple times as it gets more balanced. That said, I almost never turn a bowl above 800-900 rpm. I see folks online turning well above 1,000 for good sized bowls and I get that speed impacts cut quality and wonder if I need to crank it up a bit. I do very little spindle turning and when I do I really try to turn much faster since it makes a very noticeable difference in the turning. Like a lot of things with turning there are multiple right answers but I think I need to "test" going faster to see if I get better cuts.
 

john lucas

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Speed only affects cut quality if you push the tool too hard. I have done experiments where I purposely turned the lathe way down, like 200 rpm and made a pass and then cranked it up to 1500 or so and made a pass. There wasn't a difference in the quality of the cut. I did have to move the gauge way slower across the work at 200 rpm and when turning a large curve it takes a lot more skill to achieve a clean smooth curve than if you can move the gouge at faster pace. Now a small spindle traveling at 3000 rpm requires about the same cut a larger bowl rotating at 500 or 800 rpm.
 
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I believe the speed equation is primarily a safety concern. If you stay inside the rule of Diameter x RPM = 6 x 9000 (someone correct me if this is incorrect) then if bowl breaks or comes off lathe then more than likely it will fall to floor. If you turn too much faster it will go airborne and hit something. If you have watched Jimmy Clewes demonstrate, he uses as much speed as possible and typically a very small tenon and for him (so far) has worked. Personally, while I love watching him and loved the class taken from him, his turning speed skares me remember the equation for centrifugal force is Force = mass x radius x angular velocity squared. So for a given weight and diameter increasing rpms increases force by the square of the velocity increase. So does not take a great deal of rpm increase to produce safety concerns. Just my 2 cents.
 
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Someone please explain to me this rule of thumb, something doesn't equate too me at all here.
As quoted the above formula;
Diameter x RPM = 6 x 9000 or
10" dia X 800 rpms = 6 X 9000 or
8000 = 54000
What is this formula supposed to be telling me.
 
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The rule of thumb as I have seen it is "Diameter in inches x rpm should equal 6000-9000", not 6 x 9000. i abbreviated the 6000 figure in my initial question, sorry for the confusion.The 6-9000 figures are relative to the rim speed of the object being turned and give an idea of the forces involved. If the number is 9000, the rim of the turning is moving at around 27 mph. If a piece comes off, that's how fast it will be going if it hits you in the face.
 
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Plenty of variables in this question, what kind of cutting tool, what species of wood, green wood, dry wood, shape of billet, weight of billet, what type of support for the billet,
balance of the billet, out of round billet, square billet, spindle billet. tailstock support. Each variable dictates a proper speed to do the work, experience and common sense usually guides the wood turner to the correct speed. Start slow and work your way up to faster speeds when your knowledge, experience and skill sets will guide you..
 

odie

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Plenty of variables in this question, what kind of cutting tool, what species of wood, green wood, dry wood, shape of billet, weight of billet, what type of support for the billet,
balance of the billet, out of round billet, square billet, spindle billet. tailstock support. Each variable dictates a proper speed to do the work, experience and common sense usually guides the wood turner to the correct speed. Start slow and work your way up to faster speeds when your knowledge, experience and skill sets will guide you..

Mike has a great post here......You just can't have a "formula" to determine the best speed. Each piece of wood is an individual. Each lathe has it's own characteristics. Each turner has his own skill set, which are a result of his own experiences. I know how I come to the best speed for me, and I'm sure Mike has his, which are probably not the same as mine.:D

I used to run overall higher rpm's than I do now. I have evolved, you have evolved, you and I will continue to evolve! o_O

-----odie-----
 
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I would never be able to work by formula.... After years of turning, I do it by feel. Mostly I pay attention to how the wood is cutting. When roughing, I just want waste out of the way. Finish cuts are a different thing...

robo hippy
 
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Yeah I'm with you there, I would need a calculator next to the lathe for that to work... Not going to happen.
I'll continue to turn it up until unbalanced then back off.
 
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It has been so long since I have done anything other than standard math, I don't think I could do algebra with a calculator. If I could even figure out how to use the calculator....

robo hippy
 
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Every cutting process I perform starts at zero rpm, and I turn the speed dial up to the point where my inner safety consultant says to stop there, cut some, review the conditions, and then adjust if warranted. Heck, I don't even know which step pulley I'm on anymore to know the number of its top rpm.

I learned that equation in the '90s and promptly forgot it, or rather dismissed it. Prudence and experience guide the speed knob. But it probably had more usefulness in the days of wood lathes being mainly step pulley machines. But, lathes have been around a lot longer than that theoretical rpm equation. Imagine trying to run a bow lathe or treadle lathe according to that equation.

Come to think of it, I doubt I've ever run any lathe higher than the low 2000rpm area. I've never deemed it necessary, nor do I want to take to effort to change pulley positions. I think I'm working on the 1800rpm range of my lathe nearly all the time.
 
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I turn as fast as I'm comfortable with, just as most responses indicate. There's a bit of a problem with that - there is not a standardized "risk meter" that all humans adhere to. Some are comfortable doing things that others would never attempt. When I started turning I researched turning speeds from dozens of sources, including wood cutting manufacturing sources. The "rule of thumb" dia x rpm = 6000-9000, presented in several different ways, was the prevailing speed range for roughing and finishing. It has proven to be a good rule of thumb from my 5-6 years of experience.

As mentioned, lathe vibration plays a role, but "vibration" is alone is not a satisfactory description. With larger out of balance work the lathe could be hopping off the floor, at the hi speed end it can refer to a hi frequency hum, and anything in-between. At the low end, each person's "risk meter" comes into play, as well as the particular lathe and setup. It really comes down to how much movement of the lathe/tool rest is a person comfortable with. With time and experience I have become more comfortable with with the lathe moving around while I get a piece balanced. I like to get a piece up to at least 300 rpm for initial roughing. If that speed causes too much movement for me, I get out the 4" handheld grinder with chain wheel to get better balance. It would be helpful to have a "standard" for this. I'm going to investigate smart phone vibration apps. Might provide a cheap method to have a more standardized value, amplitude and frequency, "g's", etc. At the hi speed end, A hum while cutting can be tuned out with speed, tool selection, depth of cut, dust under the tail or headstock - a lot of variables and typically not a safety concern but quality of cut. My lathe goes to 5000 rpm, but the only time I've had it that high was to check out the lathe when new. Don't think I've actually cut at more than 2500 rpm, even with small xmas ornament spindles.

I keep the attached speed chart posted at the lathe and refer to it often. The red line is "6000", the green line is "9000", and the light blue line is Stuart Batty's "40 mph". The dark blue is a min speed to make a decent cut. BTW Stuart's big point about "40 mph" is the work will still fall down at that speed - above that speed it will get airborne. The provides me with a good reference point for target speeds.. Big pieces always start at 100 rpm, my min speed. Up to 4-5 inch dia I'll start at 500 rpm (a speed preset).Lathe Speed Pic.jpg
 
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Speaking of bowls, plates, etc has anyone confirmed that above 1500 rpm they will fly off the lathe and below they fall to the floor if they escape the chuck?
 
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I turn as fast as I'm comfortable with, just as most responses indicate. There's a bit of a problem with that - there is not a standardized "risk meter" that all humans adhere to.
Our local high school woodshop teacher is very big on speed and the formula when he starts the students out on turning. Doug, would you mind if I share your chart with him? Is it possible to get it in a bigger format than the thumbnail?

My experience with novice turners has been something of a surprise. I expected the students to fire things up way too fast. Perhaps the teacher's safety talks explain it, but I have never been fearful of the speed the students think feels 'safe and sane'. Setting speed by the feel, they are often too slow and I find myself turning up their speed so they can make better cuts. These are the guys who duct tape skis to their BMX bikes in the winter and try them on those giant skateboard half pipes. I figured they'd bring their risk enthusiasm into the shop.
 

hockenbery

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My experience with novice turners has been something of a surprise. I expected the students to fire things up way too fast

My experience is similar.

If I suggest lathe speed change it probably runs 5 to faster for every one I suggest slower.
If the students are getting efficient cuts and a smooth surface I don’t mess with their speed unless I am uncomfortable with the speed.

I do check every lathe before class to see that they are on the low pulley and that they run.
 
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Our local high school woodshop teacher is very big on speed and the formula when he starts the students out on turning. Doug, would you mind if I share your chart with him? Is it possible to get it in a bigger format than the thumbnail?

I posted it to share with anyone that wants to use it. I’m a bit confused about picture posting, ie I thought the thumbnail showed small in the post but the full size pic was available if clicked on. Can someone link me to a sticky that explains pic posting, in posts and the gallery?
 
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Reviewing this thread. I recall a demonstrator starting a piece of wood at maximum speed on a Powermatic and using a skew to turn to round. He is an experience turner but I'm a bit leery of that. I start at a slow speed and increase as the piece shape progresses.
 

hockenbery

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Reviewing this thread. I recall a demonstrator starting a piece of wood at maximum speed on a Powermatic and using a skew to turn to round. He is an experience turner but I'm a bit leery of that. I start at a slow speed and increase as the piece shape progresses.

Both Diameter of wood and weight balance affect what safe speeds are for the piece being turned

most spindles are very well weight balanced and diameters are usually less than 6”

It is quite safe to rough many spindles at high speed if youdon’t get catches.
 

hockenbery

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BTW, this was a square block, if I recall. Chips flying everywhere!
If centered, square stock stock will be well balanced.
Higher speed produces a louder propeller noise but little vibration.

it is much easier to rough turn square stock at 1500-3000 rpm than at 50 rpm.
Max speed on Powermatic is a bit over 3000.
The ONEWAY 1018 tops out around 4000 rpm a dream machine for small,spindle roughing.

Most turners want to spend as long as it takes to get the detail work right and as little time as they have to to get the roughing done.
 
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40 mph surface speed is not very useful as a guide for safe turning. Perhaps this table that i calculated may be more relatable and helpful:

40 miles/hour surface speed equivalents
Bowl Diameter vs Max RPM
4" 3361
6" 2240
8" 1680
10" 1344
12" 1120
15" 896
20" 672

Derivation: First I converted Batty's surface speed of 40mph to inches/minute. 1 mph=1056 in/min (by multiplying 5280 ft/mile by 12inches/foot and dividing 60 min/hour)
40mph = 40x1056 = 42,240 inches/minute

The circumference of a circle or pi times diameter or 3.14 times diameter( inches ) is the distance(surface area) the bowl travels for 1 rpm.
The table was generated by individually substituting the above bowl diameters and dividing it into 42,240 and dividing the result by PI. Alternatively, You could divide 42,240 by PI which gives you 13445. You can then divide it by any diameter that i didn't calculate to get the Batty Recommended lathe RPM.


Hope this may help someone. I still follow the gut-o-meter to determine speed. Usually slower. I agree with the others that say you never know where a piece will end up if it flies off the lathe. I wouldn't depend on this table to predict the path of an airborne piece that flew off the lathe. There are so many other variables involved,
 
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Then there is Jimmy Clewes...... Talk about a propeller that is loud...

Part of speed problems is being able to know when you are going too fast. That, and maybe making sure you turn the speed down to 0 before turning on the lathe, unless you are production turning a bunch of the same things...

robo hippy
 
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