Author Topic: Sprocket on EW and later drums  (Read 4841 times)

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Offline Ian

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Sprocket on EW and later drums
« on: 29 Sep 2006 at 07:18 »
Folks, I am having a problem with the final fitting of the splined drum style hubs to my OC - the sprocket that is attached to the drum is too far towards the centre of the wheel. What I want to do is remove it and turn it round so it lines up nicely with the gearbox. All picture of the OC I have seen have the sprocket near the edge of the drum. I can see no sign that this is welded to the drum so I am assuming some kind of solder ? Any suggestions as to how to go about this ?

Offline Ian

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Re: Sprocket on EW and later drums
« Reply #1 on: 31 Oct 2006 at 21:56 »
Can anyone help me with this ? I am hoping it is soldered but need to do something soon.

Offline Doug

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Re: Sprocket on EW and later drums
« Reply #2 on: 02 Nov 2006 at 03:01 »
Douglas used a number of different ways to attach the sprocket to the brake drum.

At least some of the EW models have the sprocket soft soldered to the brake drum. This is on the lightweight wheels, where the brake drum is also the left hand spoke flange. The fillet of solder is very small, and can be mistaken for a fillet of paint (or road grunge.)

I am not sure if the did this on the 600EW as well when it was first introduced. I have a F28 (1928 600EW) and there they did something a little different. Rather than a simple plate sprocket as on the EW, the sprocket has a spigot through which it is riveted to the brake drum. See illustration.


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My SW has this same type attachment, though I am not entirely certain it is the original arrangement for this model as my SW was converted from DT specs back in the 1950s.

Around about 1930 Douglas started using something a little different. These are plate sprockets on pressed metal drums, with no readily visible means of an attachment. But if you look closely, you will see small blisters spaced about every two inches around the root of the sprocket. I am pretty sure this is the result of a spot welding process. It is not a tack weld, as you can see a crack between the sprocket and drum.


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I have seen these on the S6 models, and on the A31. The picture above is from a discarded A31 sprocket. There is no evidence of the spot weld on the inside of the drum surface, so I can only assume it was removed when the drum was machined. If you have one of these drums, I do not think you are going to be able to remove the sprocket without destroying it.

By the mid-thirties Douglas had switched to cast iron for the rear brake drum (the front had changed to cast iron several years previously) and this called for a different method of attachment. The sprocket is slightly T shaped in section to give the base slightly more contact area. The drum was knurled where the sprocket sat, and further had small keys silver soldered every few inches; the sprocket being notched to suit. Then the sprocket was expanded with heat and dropped over the drum and allowed to cool to a shrink fit. Personally I do not think they needed to knurl the drum, as I have taken one of these sprockets off and saw no evidence of the knurls ‘biting’ into the sprocket.



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-Doug