anyone know what accuracy kart sprockets are made to?

[daveyjones97]

ive got time to research and ponder things while i try and save up again for my ebike mid build. I realised if i use a kart 105t to a 7t drive sprocket on a 219 chain then i dont need a second set of sprockets for further gear reduction. The problem is i cant find anything like a 7t for 219 chain. Whatabout adapting a 12t? Looks feasable assuming the tolerances arent to 5 decimal places. Anyone know how precise the tolerances should be?

 

[bobc]

a 7 tooth sprocket? Personally I wouldn't go below 12 if you can help it. Doing 15:1 in one stage is a bit ambitious & I'd expect noise, inefficiency, rapid chain wear and very rapid 7 tooth sprocket wear.....
regarding accuracy I find laser cutting to be fine for chain sprockets right down to 1/4", the place I use seem to be good to around a thou
Bob
PS I've also seen homemade sprockets done with a drill & a file that looked rather ropey but "allegedly" worked OK....for how long I wonder... non-concentricity causes flap and inaccuracy accelerates wear

 

[daveyjones97]

i have a pillar drill and some engineering experience but im not sure the .1mm i could probably achieve is enough. Where did you get sprockets made? Im in the uk. I would get it hardened after i made it. Would 8t make much improvement in noise and wear? if its made accurately enough it wouldnt be too bad for noise and wear would it? Hmm why is nothing worth doing easy?

 

[Hillhater]

8T 219 sprockets are available, but rare. 9T and up are common. Low teeth counts are avoided if possible for karts due to the horrific wear rates when driving 30bhp at 15k rpm.....but may not be such an issue with lower power and speeds.
however, i dont recall ever seeing a kart 219 sprocket of more than 98T ( because the diameter is then greater than the standard kart tyre !)..so i assume that 105t is a "special" ?.

 

[bobc]

I just use the laser cutting shop on the industrial estate where I work. They will do EN8 or even EN24 (I think....) if you specify it. There must be thousands of these places all over the country..... I drop a dxf file off at lunchtime & pick up the goods a few days later - dead easy!

 

[daveyjones97]

thanks bobc roughly how much £, thats the deciding factor.
Hillhater, the sprocket size extremes vary with the different chains; 35 219 or other. The 219 has a finer roller pitch hence higher tooth count for a given diameter. Cant post a link atm as on my fone. I think youre right that the wear on a 3hp ebike would be acceptable if i make the 7t accurate enough, just the noise is a worry. Stealth is wealth

 

[bobc]

this size stuff tends to be a tenner per thing for one-offs , half that for multiples.

 

[daveyjones97]

Thanks bobc i think il get one made and see. Its so much neater than a second pair of sprockets and a shaft. Unfortunately the build is going to have to wait a few months yet after a bad few months financially but at least i have almost everything planned now.

 

[Hillhater]

the sprocket size extremes vary with the different chains; 35 219 or other. The 219 has a finer roller pitch hence higher tooth count for a given diameter.

Yep, but a 98T, 219 sprocket touches the ground when used with a 11.1" dia kart tyre ( standard race tyre)
hence why there is no market for larger 219 sprockets for karts, but you may find a larger size in use on something else.
And remember it's not the tooth count that is important, but the diameter ratios between the sprockets !