Is there a technical reason for preferring to cut off on the rear side of the work (i.e., with a downward facing tool)?
I’m kinda confused with the question. Are you talking with a parting tool?
I know the Hardinge DSM-59/DV-59 (among others)use the parting blades upside down opposite the user, just because they are somewhat production machines.
I too am confused, there are production setups that use this, but there is no particular advantage.
Yes, I’m talking about a parting tool.
I was looking at parting tool holders for the Sherline and the Taig and both of them have rear post mount parting tool holders. Taig has only a rear mount holder. So I just wondered if there was any reason to prefer it … I couldn’t think of one.
You can set up the front and back posts at the same time. It helps for CNC.
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the only advantage I can think of would be the direction of the throw.
If mounted in the front, the direction of rotation is counter clockwise into the tool which throws the part forward. If in the back, the rotation needs to be clockwise so as to be into the tool (or the tool cold be used upside down). It will throw the part to the back. if parted well, the work piece should fall downward but accidents such as it pinching the blade happen. think of it like a kickback. cheers!
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Assume you’re referring to something like this? Seems a little odd from a rigidity standpoint however one side benefit is that the chips are thrown down and away from you but I wouldn’t think that would be a primary reason.
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That’s exactly what I’m talking about. And FWIW, that’s a photo of a Taig lathe just like mine.
I can rationalize it in a production environment but unless there’s some technical/functional reason, I couldn’t justify it in a hobbyist environment.
Nick Carter explains that with the rear parting tool the swarf doesn’t fall into and clog the cut, so there is less deflection on a thin blade.
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It also reduces the tendency of the work to “over ride” the tool and get pulled up and over the tool is even a bit below center. The rotation of the work in a rear mounted cutoff tool pushes the work away from the tool rather than into it . The makes it less likely for tool to bind. It is an issue unique to small lathes.
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