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Lathe Speed for Roughing Gouge

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Paul Hannaby:
Pete, The formula takes into account the balance and centrifugal force issues so I would suggest it is safe as long as common sense is applied regarding balance. Knots will affect the cut but not the balance to any great extent (although varying density can affect balance if there is enough of it). Also bear in mind that for a 2" blank at 3000 rpm and a 12" blank at 500 rpm the wood is going past the tool at exactly the same speed. It's a simple linear relationship.

Why do you think some small lathes such as pen lathes have upper speeds up to 5000 rpm? These lathes are designed to turn small diameter blanks. It's a simple relationship between diameter and RPM.

I just watched the video Steve suggested. A couple of points on that one - the "wobble points" Mike refers to is resonance. With variable speed lathes, even with no blank on the lathe you might find at certain speeds there are small amounts of vibration due to resonance. With these, you will find they also happen at multiples of that speed - for example if you get resonance at 200 rpm you will see it happen again at 400, 600, 800 etc. These resonances are rarely significant and you can usually increase the speed to get through them to the point where the vibration settles down. However, serious imbalance doesn't stop as you increase the speed, it just continues to get worse until the lathe shakes itself apart or throws the blank from it's mountings. You can't increase the speed through these because it won't get better.

At one point in the video, Mike is turning a 11" blank at 1400-1500 rpm. In my opinion, that is excessively fast to the point I wouldn't feel safe. You would probably get away with it with a perfectly sound blank but as I said earlier, doubling the speed beyond the safe limit will quadruple the centrifugal force and quadruple the risk of catastrophic failure.

Different people have different approaches to risk and different perceptions of danger so using a simple baseline that works the same for everyone, regardless of experience or , in my opinion reduces the risk and potential for accidents.

Twisted Trees:
All the replies are correct...

BUT in these wonderful days of variable speed rather than fixed pulley systems, when rounding off stock the less time your gouge is wobbling about in free air the better, so set the lathe off slowly turn the speed up gradually, don't let the lathe vibrate preferably at all, but if you have a small light weight lathe then not too much.

Feel the speed, don't set it to a number. once the corners are off then everything should be in balance anyway so no need for slowing down. If it's branch rather than square stock, balance can be more of an issue but the vibration will still tell you if it is too much speed, then you should concentrate on the balance before rounding the whole project..

burywoodturners:
I have just completed the AWGB Tutors Course(Let's Teach woodturning, free down load from the website) and the advice there is always start slowly and raise the speed as you feel comfortable. Finding the right speed foy you is experience, so start cautiosly and gently increase the speed.
Ron

bodrighywood:
Have to agree. When teaching, one thing I always stress is to start the lathe on a low speed. If you don't have variable speed then still start slow and move up if you want later.  I had a load of 'oak' I picked up recently, covered in dirt and old paint. All 24 x 4 x 4. Most when cleaned and blanked into spindles turned out to be spalted beech. Some was spalted heavily to one side where it had been lying on the ground for a few years and despite being square was quite off balance. If I had put that on the lathe at 3000 rpm I would have had to swithch off pretty darn quickly. Wood is far too variable to take the chance. You don't really make things any quicker at 3000 than at 1000 so why risk it. I do a lot of bobbins and other small spindle work and quite honestly I don't go much over 2000 rpm, why do I need to?

Pete

Paul Hannaby:
If you have enough time to spare, you can cut wood at the lowest speed you want to!

When I teach someone, I want them to have a basic understanding of how to arrive at a safe upper limit for speed before they go on their way because the few hours spent in a lesson doesn't really give anyone enough experience to be able to make an educated guess - which is what most of us do for the rest of the time!

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