40mm is not going to fit in the spindle of a typical Model engineering / amateur / home lathe but you can still work on it using a fixed steady. You probably don't want too big a lathe for space and cost reasons if you aren't using it a lot but since stainless is a bit tough you want some strength and rigidity so don't go too small and weak. I suggest one with a 9 inch swing (4 1/2 centre height) and remember you will want a fixed steady and both 3 and 4 jaw chucks. The new far eastern ones come with these items normally but second hand (eg Boxford) may not and can add significantly to the cost. You might want to consider whether the shapes of things you want to make would dictate a milling machine as a better starting point.

Welcome!

Where abouts are you based?

Even with a lathe with 5MT spindle, you are unlikely to pass anything larger than 38mm through the mandrel.

As already suggested, grip the work in the chuck, and use a steady, but ideally you would need to pass the work into the mandrel to turn a bearing diamater that is concentric. At 40mm , unless you have a pretty large machine by Model Engineering standards, that is not possible. I would suggest, using the steady and centre drilling each end so that the work can be turned between centres.. But the stock ought to be a bit bigger than 40mm, so that it can be turned down to minimise run out, and keep it concentric with the centreline of the machine.

If you hold a short piece of material in the chuck, and turn it down to the diameter of the workpiece that you want to turn, you can then set the steady to this turned diameter, for use on the actual material.

Howard.

Your choice of lathe will depend on a number of factors. Space, Budget, work to be undertaken, availability of accessories such as chucks, steadies etc.

Since you have mentioned working on 40mm diameter material, you are likely to need a fairly big lathe, by most model engineering standards.

A Mandrel with a 5MT taper, may not accept anything larger than 38mm, based on the Chester Craftsman (which is cousin of the Warco BH600 and the ETR BL 12-24) The later geared head successors will be likely to have 5MT Mandrels.

You could buy a used machine, but : ex Industry they will be well used, or ex Tech College/School may be little used but carry battle scars. ; and may be fitted with three phase motors. No problem if you have a three phase supply available, but could mean extra expense / complication if you need to convert (Invertor or different motor) to run off a single phase supply. Availability of accessories may be a problem with second hand machines.

If you do go for a secondhand machine, try to take someone knowledgeable with you to examine / test it thoroughly. A mistake, such as a worn bed, could prove expensive.

And bear in mind the cost of moving it to your workshop, and any likely access problems. (Moving 300Kg of machine down a step and around a corner at the same time, and then lifting it up 8 or 10 inches into the shop and then into position on the bench could be difficult – I know)!

And when you install your machine, make sure that the shop is well insulated and well ventilated, to prevent rust problems. With regard to machine installation, my hobby horse is to ensure that the bed is not twisted. The tailstock can be adjusted to the centreline, but a twisted bed will result in unwanted taper turning.

Howard