RUMCars Forum
General Category => Unusual Microcar Discussion => Topic started by: richard on September 14, 2015, 03:41:22 PM
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Is this service available anywhere , take it as fact no replacement is available
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Have you tried contacting someone like Talon who will make you one?
You can't re-cut it as the chain profile will be wrong!
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Hi Richard,
I had a lot of steering play in My All Cars Charley/ Snuggy due to wear on a big steering sprocket where it mounts to a steering shaft.
The elliptical indentures for accommodating the chain appeared to be in good shape though.
No matter where I looked, I could not find a replacement, or a center cut pattern of anywhere near similar plate thickness.
If I had, I would have had a machinist cut out centers of identical I.D. and O.D., and then had a welder attach the 2 good parts that I was interested in.
What I was forced to do instead was have the center of the bad sprocket's teeth welded in with new good metal, and then attempt the laborious and nerve racking task of trying to restore the teeth in the center of the sprocket.
First up was to drill, then final grind with a sand paper roll on a Dremel tool the exact I.D. of the center hole. No easy task for myself.
If you have a good machinist, they should at least be able to handle this part easily enough.
Next was the mission impossible task of filing the teeth without going too far and turning many hours of work into useless junk.
It started out with a traced pattern and very conservative hack sawing, and ended up with at least hundreds of trial fitments after learned intervals of filing, using machinist's blueing or magic marker applied between pattern displaying taps, which were hard to keep centered. This progressed to looking for the shiny spots on the newly filed proto- teeth that I initially filed with the slightest of taper.
Unaccountably, the clocking, or rotational alignment of the parts was seen to be important, and miraculously, perhaps a dozen hours later- I ended up with a better than new press fit.
A lot of work, and a little luck too likely at play here. So try to find a piece that you can have centers interchanged and then welded, and as a last resort, perhaps a watch maker would be more comfortable with filing new splines on a sprocket with a smaller center, as they are at least experienced at this sort of thing on a far smaller scale.
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I'm wondering if water jet cutting would be accurate enough. not expensive to have done these days. A centre boss would have to be adapted or machined however,
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It really is just a case of money... Find an engineering firm that can cut teeth and they can make you a new one. There are plenty about. Look for companies that cut teeth for motorcycles. or production lines. Motorcycle would work best probably due to the profile being the same.
Any laser or water cutting engineering firm could make them, but then need to know how to make the profile properly, sprockets are highly machined highly accurate things.
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Draw up the CAD then:-
Any toolroom with a EDM - spark eroder can easily cut perfect teeth using a copper electrode of one (indexed) or a complete set of teeth.
It is easier to machine the teeth in a copper electrode - mirror image of teeth being cut.
Better still a wire eroder - just need the CAD.
Common place in toolrooms that make press tools and mould tools.
For example:
https://www.youtube.com/watch?v=q4FinKsDfww
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I'm thinking that how the engineering firm will cut the teeth is not what Richard needs. He needs who can do it.
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Here is a starter:-
http://www.cheshirewireerosion.co.uk/
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Thank you all very much for all the informed information . All of this makes me realise why the Gordon cars were not viable once their sprockets , integral with the huge cast hub, were prematurely worn down . Luckily I do not need one cut at all but the new Gordon owner in Dorset has found that the previous owner got around this by just bolting a larger diameter sprocket OVER the worn one , unfortunately his cannot help chain alignment or speed as there must be a pile more teeth there . The enquiry was of a more general nature to see could a sprocket be recut , I think it would just not be viable hmmm
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Sprocket generation has long been used to alter bikes performance. I cannot believe that this is a hard technology to buy. What is required is a specification of what is wanted, and the likely material to be used. That becomes more of an issue when its to become part of a sub-assembly and will depend on how the part is mounted within that sub-assembly design. Yes it will cost money, but he got the car cheap from what I heard. My bud had £5k on the table, and a budget to restore the car. So from where I am its a job that has to be done if the car is to live up to that which it should be.
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This chap is pretty good, as he is used to dealing with one-offs and will be able to advise on the best process to produce what you require.
http://www.modelengineerslaser.co.uk/
Don't be put-off by the fact he does model engineering parts, he will do anything within reason.
If you want CNC machining done , then Force racing may be able to help, as again they do a lot of bespoke work.
http://www.force-racing.co.uk/
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As I said not sure if there's a job to be done but dave sent me a photo of the set up as is
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I would de rust that with the electrolytic rust removal process. Slap a bit of grease around it and probably be okay as is. How many miles is the owner likely to clock up anyway?
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Quite a few I would think , he sounds keen . But the misalignment surely will prove a problem ?
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I guess it depends how far out it is. A chain should afford you some flexibility but there are limits. Guess there is only one way to find out.
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But how is the original gear held to the assembly? Ideally that wants replacement.
The new outer one can be machine cut to a fit onto the old sprokets, as an inner. Welded in placed. No need to perpetuate a misalignment. However you retain the wrong gearing.
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Hi
What pitch chain is it and how many teeth on the original sprocket?
Sprockets of most sizes are available cheaply and will just need the centre machining then ideally heat treatment. You can probably mount it on the remains of the old one with disc brake bobbins if that's what you are trying to achieve or have it laser welded.
eg http://www.bearingboys.co.uk/?catid=3738&page=2&att1=&att2=&att3=&att4=&att5= (http://www.bearingboys.co.uk/?catid=3738&page=2&att1=&att2=&att3=&att4=&att5=)
Grommet
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The added on extra sprocket is 65 teeth - the original is 60 teeth only . What difference would this make anyone ? And can any change be offset by a change to the engine sprocket. Cheers
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65 teeth on the wheel, rather than 60, will lower the overall gearing to 60/65 of what it was - so same revs at 30 mph as it used to do at 32.5 mph.
Not a huge difference, and would help on hills, but lower top speed and economy.
Gearing would be returned to the original if the drive sprocket on the engine could be increased in similar amount. So, for example, a 20-tooth sprocket increased to 21 (still slightly lower gearing) or 22 (giving very slightly higher gearing).
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ok so you need a 60 tooth gear
Heres the sort of item that can easily be found:
http://www.ebay.co.uk/itm/Talon-Kart-Sprockets-NEW-unused-various-TKM-Rotax-Pro-kart-Cadet-60-to-78-/161826360626?var=&hash=item25ad9a4d32 (http://www.ebay.co.uk/itm/Talon-Kart-Sprockets-NEW-unused-various-TKM-Rotax-Pro-kart-Cadet-60-to-78-/161826360626?var=&hash=item25ad9a4d32)
Machine off the old gear leaving a step then machine a step in the new gear and shrink fit it. A few short welds can be used as an alternative or nut and bolt etc..
You havent said what pitch the chain is 3/8", 1/2" etc?
If you dont have access to the machinery required a local engineering shop should be able to do it for you..
Grommet
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I agree with grommet. Best method if possible.
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Many hanks for the information all - I will forward it all to Dave