FILENAMES: partingoff1.JPG partingoff2.JPG DESCRIPTION: These are diagrams showing problem and soluting to cutoff on a lathe. Posted by Graham Dowding . The following description was provided: ================================================================= Parting off: the secret to success. I used to have great difficulty with dig ins when parting steel on my 6 x 36 Taiwan lathe. I discovered the reason for this in a magazine a few years ago. I have never seen it explained anywhere else so I repeat the ideas here in the hope that someone experiences the feeling of enlightenment and relief that I had when I read about it. I couldnt understand why a dig in was not self correcting. I thought that if the tool was on centre or slightly below, when it started to dig in the cutting edge would deflect down and out of the cut, thereby self correcting the problem. However, when you think about it, for that to happen, the protruding part of the blade must flex down while no other part of the lathe moves. The pivot point about which the cutting edge deflects would be the front of the tool post or tool holder. In reality this is not what happens. In my case the blade and its holder were probably the most rigid parts involved because I had gone to a massive blade / holder to try to solve the dig in problem. This actually made the situation worse and led to the final catastrophe. What starts to flex when the dig in starts, is the tool post and cross slide. The pivot point about which the real deflection happens is somewhere well below the centre height of the lathe, and towards the front of the lathe. This means that dig ins are the opposite of self correcting; once the work grabs the cutting edge it pulls it in further. It jams deeper and deeper into the work until something gives way. In my case it was the workpiece - 1/2 inch bar bent up like a piece of wire. I also slightly damaged the scroll in the three jaw (and nearly had an underwear write off). The solution is to reverse the situation so that a dig in is self correcting. You can do this by mounting your tool behind the work but this is difficult if you don't have slots in your cross slide. The other way you can do it is by mounting the cutter upside down and running the lathe backwards. This is a problem if you have screw on chucks. I bought an upside down tool holder which is fantastic. I have not had a dig in since. Associated files are: Partingoff1.jpg - a diagram of the above. Partingoff2.jpg - a picture of the toolholder I bought. I have no association with this company except as a satisfied customer.