There are many kinds of commercial parting tools provided by tool suppliers, but most of them are too large to be used on 7×10.
This is problematic because the top of the parting tool must be centered. The 7×10 interest group described many attempts (including my own), including grinding, turning, and grinding, to remove 1 / 16 “from the bottom of the carriage, but with little success. The tool holder is quite hard metal.
Even so, the gadget is tempting, because grinding a separation tool from a tool blank is painful – because so much metal has to be ground off – and the separation tool becomes dull and brittle. This tool and similar large tools use preformed tools. If you break the end, you just need to grind a new tip and continue. I haven’t done that yet, but the best solution is to use the high frequency 5 / 16 “parting tool, which may just make a custom tool holder of the right height.
This is another 1 / 2 “business separation tool. I plan to customize a knife rest for it one day.
Separation always takes place close to the chuck jaws – no more than 1 / 2 “, preferably no more than 1 / 4”. Parting cutting exerts great tangential force on the workpiece. If the cutting is too far away from the chuck claw, the workpiece may be extruded from the chuck.
For parting cutting, the top of the tool should be exactly on the center line of the lathe, or no more than 0.005 “of the center line. If the tool is a little higher, it will tend to “climb” the workpiece; if it is a little lower, it will tend to dig in. The tip of the tool should be completely perpendicular to the workpiece.
It’s a good idea to use cutting oil for a parting cut and you will find that the heat generated will most likely cause a fair amount of smoke as the cutting oil burns off. Avoid breathing this smoke cause I’m sure it’s not good for your lungs, although no proof says it has bad effect . A small fan to disperse it may be a good addition to your workbench.Chatter
Parting often causes ‘chatter’. If you have never heard this sound, you will easily recognize it when you first do. It is a pulsing, whining vibration that can shake the whole lathe and even cause it to move around on the workbench if is not bolted down. You can stop chatter quickly by backing off the pressure on the tool. The trick is to find the right speed at which to advance the tool with minimal chatter.
One limitation of parting tools is the diameter of the work that can be parted. The tool illustrated here is a little under 3/8″ long and can part off work up to 3/4″ in diameter. In the previous picture you can see that the edge of the work is rounded because it was rubbing up against the shoulder of the cutting tool. If you make the tip of the tool much longer than about 1/2″ it starts to get too limber and will easily break off. So on a small lathe like this, the largest diameter work that you can part off is probably around 1″. To cut off bigger work, you can use a small hacksaw while turning the work at low speed in the lathe. Even better, if you have a metal-cutting bandsaw, use it to cut off the work. I nearly always use the bandsaw for work larger than 1/2″ diameter.