Start with a 2.5KG weight
Grind the letters off the weight and find a bit of water pipe!
Turn the weight down and leave a spigot to locate the bit of water pipe which has been bored to fit the two bearings taken from my trailer at the insistence of the road safety inspection man, there is really nothing wrong with them!
Find a bit of scrap and cut a nice circular piece from it. Go to the box and get one of the salvaged washing machine shafts, stainless and very nice material!
Shorten the shaft somewhat and fit the disc on the end. I cut a short thread and stuck it on well with Loctite.
The bearings are a slide fit on the shaft. There is a short spacer (more water pipe) between the bearings.
The bearings are held in place with three screws (maybe I can find some 5mm grub screws to replace these cap screws) and the short shaft is slide into the bearings.
Four holes drilled and tapped in the top plate.
And this is where it fits, right on the cross slide.
It is off the lathe again and a 130mm round aluminium plate has been screwed on.
The shaft is in the chuck and the aluminium plate is ready to be trued up.
The edge is being trimmed.
There is a hole in the plate but it is not in the centre so I am drilling it out to a bigger size. The metal in the tool holder touches, but does not press, on the side of the drill which stops it being diverted by the off centre hole. The result is a hole quite acurately centred with respect to the lathe spindle.
It is really starting to happen now, the plate is back on the bearing and the bearing holder is on the cross slide. This is a piece of 12mm 1.75 threaded stainless which I have cut a crude tooth on to with a little grinder. I made four of these cuts around it.
Everything in position and ready to press the 'Go' button.
Just a light touch of the disc against the turning 'tap' and it begins to spin with an obvious thread pattern appearing! Spindle speed is 340 RPM.
It is whirling around but my flash can stop the action and show the thread. I am using plenty of kero and brushing the tap constantly with my nylon chip brush.
I think that is a good as I can expect!
A few minutes turning down the 'all thread' that I used for a tap and I have the completed worm and wheel set!
The wheel is 135mm diameter and has something in the region of 240 teeth, I have not counted them.
This is not the best form of worm wheel as the amount of engagement is very little, a proper worm format thread would be better and would carry a much heavier load but this is intended for moving my telescope and will be plenty strong enough.
It would be possible to use a proper tap to cut the wheel but the problem is that a big diameter wheel would foul the chuck unless the tap was in some sort of extended arbor. Quite feasible but for soft metals the cuts in 'all thread' is probably as accurate.
It is essential for an accurate wheel that the teeth are concentric with the wheel axis and this is why I made a system where the wheel could be turned to size, centre bored and teeth cut all on the one centre. The weak point in this particular exercise is the accuracy of my 3-jaw and it would be better to use a 4-jaw and to clock the shaft in properly.
Hope you enjoyed it!
