Hi all,

Hopefully this will be a simple one, but was looking for some advice on chain drives. We have a drive system which is comprised of: 15HP variable speed DC motor -> Right angle 12:1 gear box -> 23T to 44T sprocket reduction. Total reduction of ~23:1

The issue we have is that the 12:1 gearbox is obsolete and we have the option to keep a 10:1 or 15:1 on hand as a spare. We'd like to keep the motor speed approximately the same so we need to change the driving sprocket mounted to the gearbox. My question is, what new ratio would you pick for the gearbox? If we go with the 10:1 then we have to increase the sprocket ratio and vice versa for the 15:1. We physcially have room for both, but are there any advantages/disadvantages one way or another?

Probably overthinking this, but would appreciate some advice anyway. Thanks in advance. Photo shows current setup.

hi
it's always good to have a odd number of teeth in both sprockets (but cannot always be achieved) when ever possible to help give a uniformal distbution of wear, for that reason i would go with the 15:1 gearbox and a pair of sprockets with 15 and 23 teeth (one odd) which would maintain your ~23:1

I agree, but for different reasons. I would go with the higher reduction because higher speeds will mean lower torques on internal components. Lower torques means lower transmitted forces, which I would think would also mean longer life.

I would get out the chain/sprocket and gearbox catalogs and evaluate the drive as a whole for the three cases proposed, to make sure I wasn't pushing something outside of its recommended operating envelope.

At the same time, I'd look at the structure carrying the chain pull between the sprockets.

I.e., not enough information provided to do the engineering from here.

Mike Halloran
Pembroke Pines, FL, USA

I recommend to look at the condition of the sprocket and chain first. Determine if the chain and driveN sprocket is re-usable. If in good enough condition to mix old chain and driveN sprocket with new driveR sprocket then re-use 44 tooth sprocket without de-mounting. 10:1 reducer ratio results in 2.3:1 sprocket ratio. 44/2.3 ~ 19 tooth driveR. Try to adjust center distance enough to use existing chain, or a shorter length of the existing chain. A 19 tooth sprocket is cheaper than a sprocket with more teeth and a lower ratio gearbox might be cheaper than a higher ratio gearbox. (But not having to rework your drive guard may be where the money is saved, so think about all of the items to change.) And, as stated above, there is not enough information to do the engineering from here.