Turning peripheral speed

[Keithie]

So it seems like the general advice is that the bigger the item you're turning the slower the lathe speed.

Also it seems like single phase power isnt so great with low speeds.

So at first glance turning very big stuff needs slow speed (to keep peripheral speed down to 18mph ish) but a single phase machine wont like this mich.

So I looked at old lathes from the mid 20th century...like the Wadkin RS. These weigh in at several hundred kilos and can easily cope with big stuff. But their lowest speeds ... 200-240ish rpm ? If you're turning a big old bowl on that, its gonna be whipping round pretty swiftly indeed!

Go figure !

So is all this variable speed malarky just health & safety and marketing that has been developed to limit manufacturers liability for when folk half-kill themselves ...adding cost and complication to the machines ?

 

[CHJ]

....
So is all this variable speed malarky just health & safety and marketing that has been developed to limit manufacturers liability for when folk half-kill themselves ...adding cost and complication to the machines ?

Far from it, it's the advent of modern electronics enabling superior control of motor speed, be the motors Synchronus a.c , universal a.c / d.c (brushes) or permanent magnet pulse frequency/width controlled in all it's various incarnations.


Craftsmen using the bigger lathes would not have just mounted the object and switched on, they would have spent considerable time in balancing the load, ether by removing material by hand or bolting steel counter weights to the faceplate.

If you want to preserve the bearings in your lathe and minimise the risk this is something you should be doing even with home workshop machines.

Take a look at this, and note that the piece is being chewed about with an electric plane to obtain a better balance before switching on the lathe, no way would the lathe be able to hold this safely at its lowest speed.

<<<<<Clicky Link.

I could turn it unbalance on my current machine if I wanted to ignore common sense, not because it's a more robust machine but because I can turn it down to 10-15 rpm.

 

[Keithie]

Thanks ,.. I think you mentioned two of the key aspects were balance and security of fitting to the lathe when I was working on my 6x6x12 lump of wood ...and its definitely right (as I found).

At 200rpm the Wadkin RS & RU would theoretically max out at around 30" diameter ..which isnt small (but well within the ability of the lathes).

I guess by implication what you're saying is that the folk who used those types of machines with oversize pieces really knew pretty much exactly what they were doing ...(evolution by way of a bump on the head from a fast moving massive block of wood will have filtered out those who didnt!) and these days the modern electronics allow novices to protect themselves more easily and indeed take into account the fact that we might not always change the belts (speed) as we ideally should...so variable speed makes it easier & safer.

Maybe I'm just too much of a cynic ...hearing about the record lathe where the speed controller might be failing some time after the 5 year warranty ended. Old style motors with pulleys kinda dont fail in any meaningful time frame.

 

[woodfarmer]

it would help a lot to have a big heavy faceplate or similar plus a selection of gears. whilst the variable speed motors can run at various speeds they lose a lot of torque at low revs. It is very easy for me to stall my 1628 (in low gear) at its lowest speed of about 50-60 rpm. Even over 100 rpm..

However being able to stall it is bit of a safety feature so I don't really mind.

 

[Keithie]

well, flip my old boots, thats a proper stick you've got there!

I guess the concrete blocks are gonna be able to cope with any impact if it flies off!

 

[Paul Hannaby]

So it seems like the general advice is that the bigger the item you're turning the slower the lathe speed.

Yes

Also it seems like single phase power isnt so great with low speeds.

Not so - it depends on the gearing

So at first glance turning very big stuff needs slow speed (to keep peripheral speed down to 18mph ish)

That's considered the "optimum" speed for an average piece of wood.

but a single phase machine wont like this mich.

Depends on gearing...

So I looked at old lathes from the mid 20th century...like the Wadkin RS. These weigh in at several hundred kilos and can easily cope with big stuff. But their lowest speeds ... 200-240ish rpm ? If you're turning a big old bowl on that, its gonna be whipping round pretty swiftly indeed!

Not really, for the right diameter (around 25" - 30"), that's the right speed.

So is all this variable speed malarky just health & safety and marketing that has been developed to limit manufacturers liability for when folk half-kill themselves ...adding cost and complication to the machines ?

Nothing to do with health & safety at all, variable speed is a way to have better control over the speed of the machine, that's why they have become so popular. With variable speed, I can precisely match the speed of the lathe to the size and balance of what I'm turning so in my opinion, it's worth the extra cost. If the variable speed function is misused, it is still possible for turners to kill themselves if they try!

 

[woodfarmer]

well, flip my old boots, thats a proper stick you've got there!

I guess the concrete blocks are gonna be able to cope with any impact if it flies off!

Made a nice shaped bowl after marking out on the lathe I did knock the corners off with a chainsaw plus I tend to turn ugly stuff like that from the front to stay out of the firing line