Members may be aware that as well as our model engineering activities, we, the Gosling Family, also rebuild ancient lorries. We always strip everything down for inspection no matter how sound it appears but unfortunately, we are sometimes caught out doing more harm to the part than good. It was one of these occasions which was the beginning of this story.

The fan drive on our 1918 Dennis lorry consists of a cast iron flange with a central boss secured to the camshaft with an eight tooth spline and a left hand thread nut. Unfortunately for me, I was caught out by the nut and only succeeded in forcing the flange more securely onto the end of the camshaft before I twigged it. Eventually, the nut came off OK but the application of a puller, a blow torch and a jemmy proved too much for the flange which snapped in two without releasing. I later cut this off but was then faced with making a replacement. The original had, of course, been in first rate condition before I broke it!

The flange is 5” diameter and was just a simple turning job. The spline, however, was a different matter and required some considerable thought. The form of the splines is square so I could grind a tool by eye to fit my keyway cutting attachment and then use that to plane them in. However, I then had the problem of accurately dividing them to match the shaft. I recalled that the George Thomas dividing attachment could be used on the bull wheel of the lathe. Now, I didn’t want to make all of that just for one job but I wondered whether a simple detent could be made to locate using the teeth of the bull wheel. Closer inspection of my Myford Super 7 showed two tapped holes in the guard exactly opposite the bull wheel which would be ideal for my purpose.

I don’t know whether they are Myford standard or were put there by a previous owner but would be quite easy for anyone to add should they so desire. First hurdle was cleared so then I counted the teeth on the bull wheel. This turned out to be 60 giving an increment between splines of seven and a half teeth! Next problem was how to get that half a tooth. Well, I made up a spring loaded detent from silver steel and mounted it in a block of aluminium such that it pointed at the centre of the spindle.
The end of the detent is machined as a wedge to lock between the gear teeth. To get the half a tooth, I cut a groove through the centre of the wedge so that I could rotate the detent through 90° and hence straddle a tooth. The groove was cut so that the tooth was gripped without backlash and this gave me 120 divisions. This is divisible by eight!
So the flange was turned, the splines were cut and I now have another attachment stored away for next time. Best of all, the new flange fitted first time. I even impressed myself!