I know nothing

It's obsolete and not a training manual but this has a lot of good information:

Application and design. Like going into a shoe store and pondering the differences one finds there... ;-)

Your best bet would be to look at pictures, rather than trying to get it all described textually here. The difference between a turret lathe and a engine lathe might be comparable to a pneumatic nailer and a claw hammer. Meaningless without a mental image of both, eh?

Can you imagine the difficulties in facing a 100 lb plate on a typical lathe, as opposed to doing the same on a vertical lathe? Gravity will be your friend or foe, depending on that choice.

Kneenut? This isn't a play on TeeNut? I smell troll.

Don't you believe in reincarnation? If there is such a thing, I want to come back as a pet!

Not me , I wanna come back as a whale .

A gap-bed lathe has a section of bed ways near the headstock that is removable, for turning large discs that would hit the bed otherwise.

An engine lathe is as opposed to a bench lathe, where the bed is just bolted to the bench. The engine lathe has some sort of a pedestal as part of the machine, sometimes two completely separate pedestals at either end of the bed. Or, it may imply a geared headstock.

A turret lathe has a tool turret on the carriage/cross slide, and generally has no tailstock, as the turret is often tall and wide enough to block material from passing over it. There is usually some system like a turret stop on each axis as well. It is used for production work on relatively short parts.

A knee mill would refer to machines like the classic Bridgeport. It has a "knee" that elevates the entire X-Y table and the work. The Bridgeport is called a "turret mill" by the maker, due to the swivel arrangement at the top of the main base casting. That swivel is not used much at all in most cases, but can get you out of a jam on a huge workpiece. So, the turret there is totally different than the turret on a lathe.

Some other machines elevate the head by a variety of means to compensate for fixture and workpiece height, and tool length. There are benchtop knee mills, like the one of the Burkes, I think. Many benchtop mills elevate the head to adjust height.

Jon

Well ... knee only applies to mills. The X-Y table is on a knee which is raised by a jackscrew to move the work closer to or farther from the spindle.

As for the lathe names you used:

1) gap -- the bed of most lathes continues right up to (and under) the headstock.

A gap-bed lathe has a section of the bed which can be removed near the headstock to allow you to turn workpieces of a diameter which would otherwise hit the bed. (Think making a flywheel or a model locomotive wheel.)

The disadvantage is that once you remove the gap plug, is is highly unlikely that you will get it back in precisely enough to restore the originally accuracy. The plug is fitted, and the ways are ground with it in place, and the factory never touches it again, so it is up to you to make the tradeoff between workpiece capacity and accuracy.

2) Engine -- pretty much any lathe with gear fed threading motions for the carriage. (This then eliminates wood lathes, chucker lathes and CNC lathes.

Some say that it is simply a lathe with its own motor instead of being driven by overhead shafts and belts -- a really old way of supplying power from a single big electric motor or steam engine to many tools).

3) Turret (not turrent) -- instead of the tooling all being mounted, one at a time, on the cross-slide, it has a moving and rotating object which holds multiple tools (six in my machine), and automatically rotates to bring the next tool into position as the current one finishes its task and is withdrawn. These do not have a tailstock and are designed to work on fairly short workpieces on the end of bar stock fed through the spindle. Finish one workpiece, part it off, and advance the bar through the spindle to bring up stock for the next workpiece.

This is very good for small scale production. It takes some work and knowledge to set it up for a specific job, while the typical toolroom lathe has interchangeable tools on the carriage, and a tailstock for supporting long workpieces. This is a lot easier to use for one-off projects, but a bit slower at production runs of identical parts.

Enjoy, DoN.