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Turning on the milling machine
In the same way that it is possible to mill on a lathe by using a vertical slide it is possible to use a milling machine to turn.
The difference is that one might use the lathe to mill, not because it is done better than on a milling machine but only because the user does not have a milling machine. On the other hand turning on a milling machine enables the user to do things he might not find easy or even possible on his lathe.
One great advantage is that it is possible to turn workpieces that are of a larger diameter than his lathe might be able to manage.
The most obvious way of doing this is to fit the workpiece in the chuck which would normally hold the cutter. The cutter is a conventional lathe type cutter which is held in a toolholder mounted on the milling table. There are examples of this on YouTube.
The most convenient way of holding the workpiece is by using a milling chuck that uses ER type collets.
Usually there is no hole through a milling chuck so it is not possible to hold a long bar.If a hole is drilled through the milling chuck and a hole is drilled through the drawbar it is possible to feed a round bar through.
One possibility is that it would be possible to set up four different cutters to cut the workpiece. It would be possible to control each of these separately using the four possible stop point using the existing x and y stops on the milling table.
first method – where the workpiece has a large diameter
Using the vertical spindle the diameter of what can be held is limited. However a wide workpiece could be held on a mandrel but this would need a center at the far end to make the setup rigid enough for machining. It is quite easy to fit a center to the milling table. During “turning” the milling table would be locked in both the x and y directions.
This means the movement of the milling table cannot be used to move the cutter.It some method of moving the cutter can be arranged then this can be used for turning large diameters.
see “Turning with the Milling Machine”, Alastair Sinclair, p16 MEW no 217
first method – special case
There is one special case where this works. If the vertical spindle has an International taper and there is such a taper that needs turning then this is a convenient way to hold it. for example it can be roughly drilled on the lathe and then accurately bored on the milling machine.
In the second method the workpiece is mounted on a rotary table. The cutter is a rotating endmill.
The advantage of this is that, firstly the diameter of the workpiece can be much larger than on a similar size of lathe. Secondly it is far easier to set large workpieces up on a horizontal milling table than on a vertical faceplate on a lathe.
The example in the previous method was machining a faceplate from a large Colchester lathe to make a “faceplate” to fit the horizontal arbor on a vertical milling machine.
fig setup for turning
The fourth method is to use a dividing head to hold and rotate the workpiece. The cutter is an endmill rotating in the vertical spindle.
fig turning using a dividing head
The merit of this is that it is possible to cut very deep yet narrow slots in a turned workpiece.
The workpiece is held in some way on the milling table. The cutter is the cutter on a boring head. The boring head is fitted into the vertical spindle. As the cutter turns is cuts a round surface.