What Speed Do You Spin At?

[Paul Hannaby]

More on the centrifrugal force - an 8 inch bowl at the "optimum" speed of 750 rpm (based on that approximation that Mark doesn't like!  ) would have a force of approx 65G on it's periphery. the same bowl turning at 2000 rpm would have a force of approx 450G. It's easy to see how choosing the wrong speed could end in disaster if the piece of wood had any flaws in it.

[Graham]

More on the centrifrugal force - an 8 inch bowl at the "optimum" speed of 750 rpm (based on that approximation that Mark doesn't like!  ) would have a force of approx 65G on it's periphery. the same bowl turning at 2000 rpm would have a force of approx 450G. It's easy to see how choosing the wrong speed could end in disaster if the piece of wood had any flaws in it.

Yuk. I hadn't realised it would be anything like that.

[Bryan Milham]

I explain it slightly differently;

The circumference of a circle is calculated as πd,

So for a 2” spindle for a candlestick, rotating at 1000rpm

= π x 2 x 1000 = (approx) 6¼” x 1000 = 6250” or 525’ per minute past your tool.

And for a 8” bowl blank, rotating at 1000rpm

= π x 8 x 1000 = (approx) 25” x 1000 = 25,000” or 2100’ per minute past your tool.

Also useful for explaining why you need to cut slower as your tool moves in towards the centre of a bowl blank, the rotational speed is the same, but the speed of the wood over the tool is less.

(π = Pi, but does not show very well in this font)

[bodrighywood]

I suspect a lot of turners, experienced and new are unaware of the speeds, the forces and the velocity of a piece that breaks off. Using D'fly's calculations a bowl that breaks off at 1000 rpm will hut you at just under 30mph. Not good.

pete

[The Bowler Hatted Turner]

to complicated for me, never was any good at maths. I will stick to seat of the pants turning, start slow and wind up until I lose my nerve

[john taylor]

A few years ago when I was unable to do any turning I put together a spread sheet to work out the speed of wood on a lathe.   Belwo is a screen capture of it if anyone wants a PDF of it drop me a PM with your email and I will send you one.

Here I must insert a warning I did this for fun and not for it to be used as a guide to safe turning speeds.

john

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[edbanger]

Thanks for all the reply's to this thread it make interesting reading and the speed at which the wood could hit you should it come off the lathe call for full body armour   

Ed

[Nick Arnull]

I a uncomfortable with the table and feel the best advice is to ignore items such as this as they can be misleading,
I would personally recommend only turning sound timber and to work at a speed at which you feel comfortable and safe.
This statement was in most of the articles I wrote for GMC publications.
Nick Arnull. RPT.

[Graham]

My lathe doesn't have a digital readout of speed but it does have a chart stuck on it giving the speeds for different dial settings on each of the pulley combinations. I usually find I am turning at much slower speeds than I thought I was. 

[john taylor]

I a uncomfortable with the table and feel the best advice is to ignore items such as this as they can be misleading,
I would personally recommend only turning sound timber and to work at a speed at which you feel comfortable and safe.
This statement was in most of the articles I wrote for GMC publications.
Nick Arnull. RPT.

I agree 100% with this.

As I said it was done mainly for fun and to show the difference in speed between near the centre and the outside.

I turn at a speed that I, the lathe and the wood all feel comfortable at, which quite often varies even with blanks of the same wood and size turning the same thing.   Another important thing to mention here is to always wear a full face shield of the highest impact resistance just in case.

john

[TWiG]

All of my wood is in the form of chainsaw cut " blanks " so are invariably out of balance so I start off slow ,and gradually build as it becomes more balanced but rarely do I turn fast , except for small pieces , lids, knobs etc ,but I really have no idea what the speed is as I do not have a speed gauge on my lathe .  I have a short bed lathe and most of the time I stand at the end so am out of harms way if something comes off, which does happen on occasion ,mostly loose bark . 

[seventhdevil]

just started turning a 30"x 6" chainsaw cut walnut that weighs 70kg and started it down at the 60's. just got up to 250 near round.

[Sevilla]

The most common answer to the speed question seems to be: turn at the highest speed you feel confortable/safe. I have a problem with this because it does not rest on any logical bases. Can a subjective feeling be use for a safety issue? I do not believe so.
In my opinion the answer could be reversed. The turning speed is the lowest speed that allows a good finish. For this of course one needs a sharp tool, practice and a steady hand. Increasing the speed increases the amount of wood that touches the edge for a unit of time thus one can increase the speed of the tool travel. But the same result can be achieved with a lower lathe speed lowering the feeding rate of the tool. More difficult because it involves a better technique and probably not good for a professional for which time can be money.
There are two other points I would like to address. Radial speed is, as explained in another post, proportional to the diameter of the wood, and diminishes going from the periphery to the center (zero diameter, zero speed). But for a safe speed one must consider also the way in which the wood is hold. Spindle turning is the safest, chuck is the least safe. Also, when turning a bowl on a chuck it is important to consider the hight of the bowl since the high bowl means more overhang and stress on the tenon.
For one example I attach goblets, the tallest is exactly 17 high  (just measured) with a stem that starts at less than 3/16 inch and turned at less than 1,250 rpm.

[woodndesign]

Sergio, you've added some well founded considerations, there are so many compounding factors which we all need to know, may encounter and hopeful not within our turning life time, I consider it calls for a common bases on speed, I was given a list, read much the same in many books when I started all those years ago, it was deemed wise, let alone safe then, what has changed today, it's very much like there are speed limits on most roads/within towns .. how many still consider to drive at a greater speed ... we all have done it ... what of safety though, throw it out the window as not relevant.

The point has already been raised with the differences with lathes, vari speed/vari matic or set pulley sizes, in the latter case the given speed could well be very slow until the piece is balanced, I know only to well with both my lathes... then where you've mentioned it's not economical to the professional, as such we read as to the advocating of higher speeds, fine, yet not advisable for the novice until you've not only got more experience: but greater understanding and awareness of risk assessment.

At the end of the day each and every turner has a differing opinion on not only speeds: but most aspects of turning, ranging from the best type of tools, bevels, grinds, work holding to finishes etc.

I'll end with that's a fine display of goblets there. Thank you for your valid input.  David

[Nick Arnull]

I believe most turn at a speed that is too high and rely on the speed to provide a good finish rather than good technique.I know this is somewhat controversial but it is my opinion.
 if you have ever seen me turn I rarely run the lathe at any speed but use sharp tools technique and control to achieve the end result.
When teaching more experienced students they often  have trouble with spiral chatter on bowl work, this is caused simply by high speed and differential grain density the answer is simple, drop your speed and sharpen the tool problem solved,for Bowl turning any speed over about 1000 rpm is simply not needed in my opinion.( these comments relate to Bowl work and not other areas of turning)
Nick Arnull.