Harold Hall
Holder
Before they can be used on the lathe though a suitable holder will be required, typically as is illustrated in Sk. 2. See also Photograph 1. The dimensions given suit chasers 1/4” thick, and, with a small packing piece, chasers 5/32” thick, Sk.3. If you wish to use larger chasers then it will be relatively easy to increase the size of the holder. Also, if you wish to just use them hand held then the lower part can be made longer to make that possible.
Cutting the thread fully.
This will closely follow other methods of screw cutting, typically, feeding the tool in at right angle to the workpiece, or setting the top slide at half the threads internal angle, setting up the changewheels, running at a low speed, etc. For more detail on the more usual methods of screw cutting see my other pages on the subject.
However, there is one major difference when using a chaser for screw cutting and this is, how does one deal with the situation when arriving at the end of the thread being cut? Normally, a recess would be made into which the cutter would finish, at which point the lathe's half nut would be opened stopping the cutter traversing but leaving the workpiece still rotating.
This method cannot be used with a multi tooth chaser as a very wide recess would be required, something that is unlikely to be acceptable in most cases. Because of this, some other method has to be used to bring the thread to an end. I will suggest three methods.
Method one
This is, for lathes having a clutch, to use the clutch to stop the machine. With only a few dry runs (not cutting) the process is not at all difficult and works well. If this surprises the viewer, do take note that for screw cutting the lathe will be running at its slowest speed and, as a result, with so little inertia the lathes stops almost instantly.
Method two
For those who do not have a clutch just switching the drive motor off works almost as well. Whilst the motor will be running at full speed, and have a fair degree of inertia, the large gear ratio between motor and workpiece will ensure that run on of the workpiece will be very small.
Metalworking
Workshop Projects
1
The pictures can be clicked on to provide a larger view