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Rear parting toolpost

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Rear parting toolpost, Iím sure this must have been done to death. I personally have no problem parting from the front on my as new Raglan 5 inch, I also donít have a T slotted cross slide, ( I ordered one from John ward 3 years ago but it never came), sadly I understand John has passed. Back to the question, I have read that under dig in conditions the tool is pushed away on rear parting and dragged in on front parting. I canít see this as the mechanics in my opinion are the same in both cases. I can see that rear parting is more rigid unless you can remove the top slide and mount the parting tool holder directly on the cross slide, additionally the chips will tend to fall away from the cut at the rear but for me that is about it. Looking for a definitive explanation Phil

A rear parting tool is upside down so the force is opposite to a front parting blade .

Clearly the force is in the opposite direction, but surely the force is the same. Looking for the actual science behind the 2 options Phil

It's about the direction of the flex. A normal mounted tool is forced down the effect of the leverage from the bottom of the toolpost upward is to press the tool further into the work-piece exacerbating the bending force.

A rear mounted toolpost reversed the cutting force benring the mechanism away from the job,  so reducing the cutting force and thus regulating the cut .

This is the same mechanism that is designed into spring tools,  i.e. the cutting force is used to bend the tool away from the work.


Sorry to be unable to see this, as far as  I can see the work pushing down on the tool which is on centre height will move the tool tip down and away from the work (reduce the depth of cut) this I understand is how the sprung tool works, the rear tool post is the same in my opinion except the word down is replaced with up. Really want to understand this. Thanks for the replies Phil


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