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Lathe Speed for Roughing Gouge

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GeordieTurner:
As a newcomer I find lathe speeds confusing, many YouTube videos show good techniques but never mention lathe speed which I assume is important if not critical. What is the ideal lathe speed for using a roughing out gouge to turn a square spindle round? What other ‘ideal’ speeds are there for different tools or operations? Thanks for any advice

bodrighywood:
How long is a piece of string? if it just square then the best speed is the one you feel safest at. Depends if you are holding the spindle (only spindles with a roughing gouge of course)between centres or in a chuck. Also depends on the wood. Some woods like oak can chip and splinter others like beech are easier to round off. If you are roughing down a branch with bark etc then just remember that you can't always see what the wood is like and make sure you are wearing a mask as bits can fly off. In most cases it is actually safer a bit faster rather than slower as you are less likely to catch but bottom line as I said initially err on the side of caution and go at a speed that feels safe to you.

pete

seventhdevil:
pete is right and to be honest experience will answer this question for you in time.

we all start off a bit slow initially but as confidence grows you soon speed up. someone on facebook said that there was a formula for such things which is absolute tosh as it will all depend on the weight and size of your lathe and not how fast you are turning. a small late will need slower speeds but a big heavy one can safely turn large items without wobbling about.

the thing to remember is that you need to turn each piece when roughing out at least at around the fastest speed the lathe will allow for that particular bit of wood being turned.

i turn skittles for a living and turn 5 1/4" sq blocks 11" long at just under 2000rpm but a bowl blank that is a bit off center will need to be slower if the lathe starts moving around.

here is a good video on the subject.

https://www.youtube.com/watch?v=tDeo1qeV6Dg&t=737s

Paul Hannaby:
Without experience, how are people supposed to know where they should feel safe! Personally I take a more scientific approach...

The primary aim is to turn at a safe speed which isn't causing excessive vibration due to imbalance from the wood. If there is too much vibration, slow the lathe down.

Once you have taken that into account, a rough rule of thumb can be used to give the answer to how fast can be calculated by dividing the diameter of your turning blank in inches into 6000 (or into 15000 if working in centimeters). This figure is derived by starting with 26 feet/second as the "optimum" cutting speed for wood. This figure is put forward by some woodworking text books and wood cutting machines often cut at around this speed.
The figure of 6000 is arrived at by rearranging the formula for circumference and peripheral speed to give rpm as a function of diameter.

For example, for a 2" diameter blank, the rpm can be up to 3000rpm and for a 12" diameter blank, the speed would be 500rpm.

I have used this rough rule of thumb for many years and find it a simple way to estimate turning speed because all I have to remember is 6000.

I recall in one of David Ellsworth's books, he suggests dividing diameter into 6000 and 10000 to give a safe working range. There was no explanation where the numbers were derived from but they at least agreed with my rough guide at the lower end.

Remember not all types of wood are the same so as with any cutting process, you might find certain pieces of wood respond better to slightly slower / faster speeds.

It should also be remembered that any rotating object is subject to centrifrugal force and if you double the speed, you quadruple the centrifrugal force (it's an exponential relationship). Excessive speed can result in the blank tearing itself apart with potentially catastrophic results so always check your blank is sound and free of major cracks, bark inclusions etc. and wherever possible, don't stand in the line of fire when turning.

A final suggestion - if you are turning an non-circular blank (such as a square block you are roughing to a cylinder), turning too slow will lead to the tool bouncing and will make it more difficult to get a good cut. Speeding the lathe up (within the safe contraints) will reduce the bounce and will give a cleaner cut.

bodrighywood:
Basically you are saying the same thing Paul but adding numbers. I can't argue with your scentific approach but wonder how many of us actually work that way. New turners IMHO should try and get alongside a more experienced turner to start with anyway be it getting some tuition or just a mentor as however much we follow the rule of numbers it only applies in ideal circumstances. Try turning a 2" lump of oak with knots in it at 3000rpm would, I think be looking for trouble. Personally I can't remember the last time I had my lathe cranked up to that speed, certainly not when roughing out. There are far too many improbables to try and turn by a formula. OK my opinion for what it's worth. Obviously it works for you but I wouldn't personally advise it as an approach for a new turner.

Pete

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