Improved threading banjo
The banjo that carries the change gears for threading on the standard lathe is quite difficult ot use as the space around it is cramped and setting up a new gear ratio is tedious. Richard Hagenbuch designed a new banjo that was simple to make and use. His version is made from thick aluminium plate which is bored , milled and slotted to give more or less the same shape as shown above. When I was considering making Richards style of banjo I had no suitable plate so I improvised my version from 3 mm x 50 mm hot rolled steel strip. The design has one advantage over Richard's original version in that the position of the banjo can be fixed on the lead screw pillow block extension. The clamping concept of the new banjo is based on the design of clamps used to join exhaust systems on motor cars together.
The banjo is made by first folding a strip of 3 mm x 50 mm hot rolled strip over on itself as shown in this photo.
After folding the strip is shaped, bored and slotted as shown here.
The bottom of the banjo is then cut through with a slitting saw. Cut outs are made on the fold for the special clamp nut and washer.
This photo shows the special nut and washer for the clamp bolt. These were made from 10 mm round steel. The projecting lug fits between the two halves of the fold. This stops them from rotating when the clamp bolt is tightened.
This shows the sliding stub axle. This is drilled out and tapped M5. This fits into the slot of the banjo and is secured with a M5 hex head bolt and washer
This shows how the banjo fixes to the leadscrew pillow block.
This photo shows the banjo in position and set up for the normal 20/80,20/80 fine feed gearing but with the last 80 tooth gear removed so that the banjo can be seen. All the bolts to adjust the banjo are readily accessible.
This is the banjo locating ring. It is bored out 20 mm to fit the pillow block extension and it slides between the two halves of the folded metal. The grub screw then retains the ring on the pillow block extension.
This shows the locating ring in position and clamped to the pillow block extension. The ring prevents the banjo moving along the extension ensuring that the correct meshing of the gears is maintained during a gear change.