A lot will depend on the rear wheel construction, some you can use the casting as supplied, some need the casting machined others use a built up rim that does not need to go on the lathe. If you don't need to machine the rims then the final drive gear is the largest part that needs to be turned.

1" You would need minimum of 5" swing or 6" if the wheels need machining.

2" Minimum 9" swing or 12" if wheels need machining

Edited By JasonB on 24/04/2018 07:09:34

5" = 127mm

6" = 152.4mm

9" = 228.6mm

12" = 304.8mm

I'd suggest you brush up on how to convert one to the other and vice versa before you start building your TE

I meant the difference between imperial and metric.

As Jason says, much model engineering stuff out there is still dimensioned in imperial – apologies from the mother country!

This issue is being approached from the wrong direction. For any given scale the size of the engine will vary considerably depending upon it's type. For instance a ploughing engine will be far bigger than a small road engine for the same scale.

So first decide which engine to make, and then look at the largest diameters to be turned, which will determine the size of lathe needed. On my engines the flywheel is rather bigger than the final drive gears, and is the biggest part that needs turning, albeit it can be done in the gap.

Andrew

This is an important factor not to be overlooked. A 3.5" lathe can swing much bigger than 7" diameter if it has a gap in the bed, as Myfords and Drummonds do. Just make sure the gap is wide enough to accommodate the job in hand. Myfords will swing up to a 10" diameter faceplate so that is a rough guide.

If you find doing metric conversion that difficult, have you really looked at the complexity and hundreds, maybe thousands, of hours of work required to build a traction engine? The kind of effort and initiative required is in another league. Perhaps you should look at a simpler project to begin with?