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Making a telescope worm wheel and gear set on the mini-lathe. Part 14, Making a shaft clamp clutch for the worm wheel

Telescope worm wheels and gears on mini-lathe series index

Now you have completed your worm wheel and gear set. Well done! However, the two parts are just sitting on your work bench looking pretty. The use them, they need to be mounted. Mounting a worm wheel on your shaft requires some kind of clamp or clutch mechanism.

The worm wheel should slip nicely over your shaft and rotate freely. However, for the worm wheel to drive the shaft, you need to lock the worm to the shaft. This mechanism needs a release so that you can move the shafts independently of the worm wheel. Often you wish to move the telescope without using the motors, and it would be tiresome and risky to have to disengage the worm gear from the wheel each time.

There are a lot of complicated designs for this problem. However, because I am going to spring load my worm gear mounting (more later) I can use quite a simple clamp to hold the worm wheel on the shaft.

I make a simple collar with a set screw. This collar is bolted to the worm wheel. The set screw clamps the collar to the shaft. If we wish to release the worm wheel for free shaft movement, then the set screw merely has to be released.

The key to to make the bore in the collar concentric with the boring in the worm gear. To do this, I made the collar on the lathe with one face square to the bore. The central bore is slightly larger than the shaft. Next mark out and drill three 5.5mm holes in the worm gear and part drill these out to 9mm to accomdate the recessed heads of the hex head bolts. Then place the collar and the worm wheel together on the shaft, and using a transfer punch to mark the bolt hole positions on the collar. Make sure you use the face of the collar that is concentric to the bore!

Now drill out the holes in the collar to 4.2mm and tap with M5 tap. I made through holes in the collar just to make tapping easier. Finally bolt the collar onto the worm wheel onto the shaft. Do this slowly and carefully so that the bores are concentric.

You will need a plain shaft collar underneath the clamp to hold the whole thing on the shaft. I recommend them.

You will need to cross drill the newly made collar to take a set screw. I drilled it out 6.8mm and tapped M8. between the tip of the set screw and the shaft, put a small piece of lead or copper to prevent the stainless steel set screw marking the shaft.
the clamp clutch for the shaft
the clamp , collar and worm wheel on the shaft

Make sure you mask the part when anodising to prevent the bore getting too narrow.

The above pictures hopefully show the setup - looks quite impressive! You could make the shaft collar as well, but they are quite cheap and you should buy them.

Telescope worm wheels and gears on mini-lathe series index


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