For a while now I’ve wanted to replace the two cap screws on the lathe gearbox cover for something a little more practical. From the factory the plastic cover over the gears is kept in place by two cap screws which requires an Allen key to undo. As many of you are aware the Allen key is never where you left it. My solution was to replace the screws with some threaded rod then make a pair of thumbscrews.
Drawings can be found at the bottom.
I began with a piece of scrap aluminium approx 25 x 100 mm. I centre drilled it and mounted it in the lathe with a revolving centre for support. The plan was to make two screws from the one bar without taking the work out of the chuck.
I began roughing out the general shape of the screws leaving 0.5mm in all dimensions for finishing.
In order to speed up the roughing process I fiddled around with the change gears.
Normally they are set up as follows;
A=20;
B=80;
C=20;
D=80
This is a ratio of 16:1, with a leadscrew which has a lead of 1.5mm. It gives 0.09375mm of travel per revolution.
By replacing the “D” gear with one with 40 teeth you get a ratio of 8:1 and therefore the leadscrew will move the saddle 0.1875mm per revolution. I found this to be perfectly satisfactory for roughing out. Ironically though the cover will not fit the gears in this configuration so it will need to be modified at a later date.
After roughing out I began the finishing cuts to bring the part to the final size.
Once I was happy with the work I knurled the thicker part of the screw and chamfered all of the edges.
I then parted the work.
I made the second part in much the same manner.
As it happens they make a good rest for the chuck key, provided there isn’t a large bar through the spindle bore.
Gareth's shed 