I wanted to hold a steel part in the chuck of my ML10 lathe without damaging the carefully turned surface. I needed some 'soft jaws'. These are aluminium covers to keep the hardened chuck jaws from touching the surface of a workpiece.
This instructable shows how it was done.
My chuck is a 'standard' Pratt Burnerd 4" diameter and 2" depth (stamped 1588-10000).
The scrap of aluminium sheet I used was 0.7mm thick. Any aluminium or copper sheet of roughly similar thickness would do fine.
Step 1: Template
The template was produced using paper by trial-and-error. The final dimensions can be seen in the photograph (in mm). The PDF file has six copies of the template (only three are needed) - double-check the dimensions if you use the PDF to create your templates.
Stick three templates on to the aluminium sheet using suitable glue (a Pritt Stick is perfect - the paper is held firmly while you work, but floats off easily in water).
Step 2: Cut Out the Soft Jaws
A junior hacksaw (or fine band saw) is ideal for cutting out the aluminium sheet. Holding the tiny aluminium pieces is a real problem. A clamp and wood block helps.
The cutting needs to be fairly accurate - the 'nose' of the jaws must slide into a gap in the chuck; the 'ears' of the jaws must not be too big, or they will not fold around the chuck neatly.
The rough corners and rough edges can be tidied up using needle files.
Then the templates can be removed.
Step 3: Fold the Jaws Around the Chuck
I removed the chuck from the lathe and placed it on the bench. I then used a hexagonal nut from a plumbing fixture to hold the aluminium in place - this worked really well.
The soft jaw aluminium sheet must slide right into the chuck and be square, before bending can begin.
Flat screwdrivers helped to start the bending process - followed by a wooden 'drift'. The soft jaws fold right around the jaws of chuck.
To use them, just slide them onto the chuck jaws - they keep in place automatically.