1947 A7 belt driven dynamo Home brew

[allanwinks]

Has anyone out there made their own toothed belt dynamo drive?

[muskrat]

G'day Allan.
Why would you bother?
I have the old 10mm SRM type in both my A's. If I were to need another I'd get the 15mm
https://dynamoregulators.com/wide/drive-belt-kit.php
Cheers

[allanwinks]

Good for you!
I would bother because I can, unlike others I don’t have endless cash but have the ability to use a lathe and so making these would give me greater pleasure than just buying them in!

[RDfella]

Has anyone out there made their own toothed belt dynamo drive?

Yes. Piece of cake. Needed if for my first vee as the drive was exposed so a chain wasn't appropriate.

[berger]

allanwinks why ask then just get on with it!

[allanwinks]

For info on the taper and ratios chosen.

[berger]

tapers are  on the shafts

[chaterlea25]

Hi All,
The magneto tapers are 1 in 10 taper, I wonder if the dynamos are the same?
It  shouldn't be difficult to measure the dimensions on the sprockets and work out the angle?
 can you mount the dynamo armature in the lathe and use a dial gauge to adjust the  compound slide ?

John

[RichardL]

Good for you!
I would bother because I can, unlike others I don’t have endless cash but have the ability to use a lathe and so making these would give me greater pleasure than just buying them in!

I would love to see your machine shop. Way-back-when, we had a thread where members were asked to share pictures of their machine tools. You’ve certainly raised the group curiosity for how you will get this all done. For me, it’s the teeth and the flanges. I’m sure it can be explained, but you know the old saying, “A picture is worth…’”

Richard L.

[Swarfcut]

These days toothed belts can be unexpectedly found in many consumer durables, cordless hedge trimmers and vacuum cleaners to name a couple of examples. GTec here in the UK have a known failure rate due to the small motors used and heavy loads some folks impose on the appliance. These all have rather nice die cast toothed pulleys, as do some electric lawnmowers. It's a case of searching these toothed pulleys out in unexpected places.

  So the trick is not to scrap worn sprockets but turn them into the tapered centre part of a Frankenstein pulley. The toothed belt is the least of your worries, something suitable in terms of lengths, widths and pitches are out there from the usual bearing and transmission  factors.

  Swarfy.

[Rex]

Some years back I made up a toothed belt drive on my Indian, as these bike's Achilles Heel is the dynamo.
Having access to a wide range of toothed pulleys at work helped, but the area which was problematic was the drive belts. As the engine kicks backwards under compression as it comes to a stop, the inertia of the armature really affects the longevity of the teeth under the shock load of rotational reversal.
Belts didn't last long, and even when steel-banded polyurethane belts were used the teeth were short-lived.
I eventually gave up and returned to a Vee belt, as fitted by the factory. The kick-back is irrelevant to a vee belt.
Presumably the kits sold by SRM etc have solved the problems of teeth-shedding belts by now though.
As I recall RS (and others) do a wide range of sizes of the toothed pulleys.

[muskrat]

Good for you!
I would bother because I can, unlike others I don’t have endless cash but have the ability to use a lathe and so making these would give me greater pleasure than just buying them in!

G'day Allan.
I have a lathe (I'm a machinist by trade) but I don't have a mill and cutters or a dividing head to cut the teeth. I could jerry rig a Dremel with a carbide burr in the tool post and a way of indexing the headstock. The time involved would outweigh the cost of a bought set.
Please keep us posted (with a few pics) of your progress.
Cheers

[Joolstacho]

A machine I came across years ago is my Taper Grinder. I used it for rough-shaping guitar necks. It's basically set up for external taper grinding but I guess it could be adapted to do internal tapers too. Weird looking thing... weighs TONS!!!

[Swarfcut]

  Maybe to state the obvious.... But the drive on a toothed belt is transmitted by the tension in the belt, not the strength of the teeth. When cambelts replaced chains, sheared off teeth were a prelude to disaster, all because the belt was set up with insufficient tension. The teeth serve solely to locate the relationship between the crank and cam.

 So whatever the application the belt needs to be tight.

 Swarfy.

[Rex]

Yes and no. Setting the tension "by the book" requires a tensometer, but the rule of thumb for tensioning is the ability to turn the longest run of the belt through 90', and it's usually as good as identical to the tensometer setting.
Obviously this was done as an initial setting on my bike.
I rather doubt that the shear strength of the material for any given belt is made from alters greatly over the range of tensions, if that were even possible.
Clearly the belt can't be run over or under tensioned. There's an optimum tension for the belt to operate under, and this won't be compromised in efforts to make the belt/teeth somehow last longer.
There's light load drive belts (as used in desktop printers, for instance) and high load belts as used in industrial applications, and clearly the specs can be very different.