Geared head lathes versus pulleys

[Alistair Hosie]

I am a bit confused could anyone explain to me the following.I understand that there are belt driven lathes I e the headstock has the availability to revolve at different speed according to the pulleys selected from the motor,countershaft, and spindle pulleys etc, that is not unclear.
Then there are geared head lathes which appear not to use belts . Or do they? and if they do what is their advantage.
Also the gearbox for selecting gears to alter the speeds for traversing the saddle and apron assembly and also including the screwcutting speeds etc that is also not difficult to realise what is going on.
However I have tried to read about the geared heads on lathes without much success, and it is very confusing (the little information I can find is very vague).
If you can alter the speeds on the headstock with gears why the need for a belt pulley system at all?
Or does a geared headstock do away with the need for a belt change system?
It appears from what I am reading that some lathes have both belt and geared heads and this does not make sense .I am beginning to wonder if this question makes any sense.
I hope someone can understand what I am on about and explain it or point me in the right direction with regard to where I can find out more .I have tried Google without success thanks Alistair

[John Stevenson]

Cost. Pure and simple.
It's a cheaper method to make a spindle supported on two bearings with a pulley in between than to make a closed gearbox containing again the spindle, two bearings and a minimum of 8 gears for a four speed headstock, running in an oil bath or even forced lubrication.

The fact is that both methods have provision for a range of speeds.

Main advantahges of belts are cheap, quiet and can be forgiving.

Main advantages of gears are greater power transmission.

John S.

[DR]

To add to John S's answer....

Speed changes on belt types can be a nuisance, release tension, slip belt to another position, re-tension, etc. Using back gears for low speed is even worse.

Speed changes on gear heads are almost like shifting gears in a car.

Once you've used a gear head you'll never go back.

[BC21OSH]

Alistar,

On a gearhead lathe you will have a belt drive from the motor to the gearbox however you will not need to deal with those belts until they need to be replaced. All speed changes are done with a series of levers on the front of the headstock. The guys are correct, once you have used a gearhead you may not want to go back to belt drive. Gear head lathes however are more expensive. Belt drive lathes are more forgiving. If something jams up, the belt can slip and reduce damage, the gear head will just keep going until something breaks. On the flip side, the gear head has more power transferred to the chuck and will normally take heavier cuts. Also there will be more choices of speeds in a gear head versus a belt drive. There are also the infinitly variable speed units. They either use a mechanical sheave system or electronics to vary the motor speed.

Bernard

[Dave Opincarne]

Alistair, Bernard does an excelent job of explaining the difference between the gear drive and belt drive. What may also be adding to your confusion is the difference between the spindle drive (which Bernard describes) and the various ways of transfering power from the spindel to the lead screw/power feed. This is almost allways accomplished via gears. On simpler (less expensive and/or older) machines the gears are changed out to achive various ratios between the spindle and leadscrew and thus produce differing thread pitches. The other common method available on some belt drives and all gear drives is a simpiler gear drive transfering power to a gearbox mounted low on the headstock. Screw pitch and feed rates are controled by moving leavers at this gearbox.

[lynnl]

Ok, what means the term "Engine Lathe"? That's the one that's always puzzle me.

[Dr. Rob]

Now, THAT one rang a bell. Engine lathe, or Engine Turned? Engine Turning is a form of ornamental turning, that was just recently made clear to me. Unfortunately, I don't quite remember the thing...it was described in an ebay ad for a sextuple ornamental engraving machine a while back. It was used on watches from Rolex and pens from Mont Blanc, among others I'm sure.

[Alistair Hosie]

Thanks Dave no I am quite familiar an happy with the power getting to the saddle area and the spindle speed.That is I understand that the speed relationship between the headstock and traversing of the saddle and therefore slide with tool are intermarried matematically and Mechanically through a gearbox or at least a gear ratio using change wheels if no gearbox is present.What I am having difficulty in undestanding (perhaps because I have misread it) is how the motor speed effects the spindle speed in this arrangement,I am full coversent with the normal pulley arangements through a countershaft etc that is fine but I cannot understand why a lathe would need a full pulley arrangement, and a gearbox as one would cancel out the other surely wouldn't it?.Or perhaps in a geared head this arrangement of pulleys is superfluous and I have read it incorrectly regards and thank you for your replies to dat guys Alistair

[Dave Opincarne]

Ok Alistair, sorry I wasn't sure wear your confusion lay. Bernard's response is still a very acurate description between the two. Both use a belt and pulley but the "belt drives" use mulltiple pulleys to provide speed changes while geared heads use a simple pulley and a gear box to provide speed changes.

It just occured to me what may be causing some confusion. I was about to say that belt drive units don't incorperate gears but I realise that's inncorect. Belt drives frequently incorperate a simple back gear to provide a reduction in spindle speeds. So here's a grossley oversimplified way to think about it: excluding frequency drives and simpler setups, all lathes are belt driven with a back gear. "Belt drives" have multiple Pulleys and a simple back gear to provide a high/low range. "Gear drives" use a simple pully and a complex "back gear" to control speed.

Hope I haven't made this more confusing.

-Dave

[Alistair Hosie]

Dave no that's fine I was a bit confused as one article said that geared heads did not use belts and another implied that the geared head did use belts. Now I see that the belt is ony a simple set (single pullied) up to provide direct drive in this case to the gearbox main spimdle,and all subsequent speed are then taken over by the gearbox in the head through a levers system which is filled with oil to provide constant lubrication.Thanks Dave Alistair

[Dave Opincarne]

Forgot to add a bit about engine lathes. The term engine lathe is a holdover from the early days of powered lathes to distinguish between human powered machines and steam powered machines. Today the term seems to refer to medium to large general purpouse lathes.

[BC21OSH]

Dr. Rob,

You are correct that engine turning is a form of ornametal work commonly used on high end metal items. To engine turn they simply apply the end of an abrasive in the form of a small round spinning device to the surface of the metal to be decorated and overlap these small circular patterns in precise well defined rows. It is strictly ornamental in nature.

Bernard

[Randy]

Just from obsevation it seems to me that the distinction between engine lathes and bench lathes is this: An engine lathe has an integral stand, usually enclosing the motor and part of the drive train. A bench lathe is mounted an a workbench or other stand, and has the motor hanging off the back. Also, as Dave mentioned, engine lathes are usually larger, more than 12" swing or so, bench lathes are usually 12" or smaller. Rather soft definitions, and not quite true to the roots that Dave mentions, but reasonably accurate.

[darryl]

Adding my quarter's worth- I think the term 'engine lathe' came about when lathe's were actually driven by engines, steam or otherwise. The term is technically incorrect for any machine driven by an electric motor, those should correctly be called 'motor lathes'. Ornamental turning has nothing intrinsic to do with engines, as any method of drive, be it engine, motor, or treadle, can be used to spin the spindle. Is my lathe a bench lathe, or what? I could have mounted it on a bench, or a stand, or a pair of sawhorses. Would that make it a 'sawhorse' lathe? Whatever. Hope y'all had a nice weekend.

[wierdscience]

The term "engine lathe"came about because in the early days lathes didn't have leadscrews and change gears for threading.This work was accomplished either by laying out and cutting by hand or with the help of special chasers.The term "engine" was added to several machines of various types and is used to describe a machine that can accomplish a complex task trough the use of its own gearing.If you read some of the industry publications of the time when the leadscrew was first added it became a qauntum leap in production.Similar action happened when thread rolling first came into the bolt industry overnight prices began to fall as production got cheaper.Another machine to use the term"engine"is the clockmakers gear cutting engine.I also recall the term first was used in England,this would make sense because I believe it was Edward Muadsley who first came up with the idea of a leadscrew on a lathe.

[This message has been edited by wierdscience (edited 03-16-2003).]