What You Need to Know About Finished Bore Sprockets

The main thing to know about finished bore sprockets is that they come with the keyway already machined into the bore, and with the set screw to secure the sprocket to the shaft. But is there anything you need to know about the keyway?

Shafts and sprockets work together via a keyed joint. The key is a piece of steel or other metal on the part of the shaft that passes through the sprocket.

Finished Bore Roller Chain SprocketThe sprocket, then, has a notch – the keyway – for the key, all machined to ANSI tolerances. Even with the close fit, at least one set screw connects the key to the keyway.

This not only assists torque transmission between the shaft and the sprocket, but also prevents axial displacement of the shaft along the keyway. One set screw is always “top down” from the keyway into the key. If there’s a second set screw, it is oriented 90 degrees away, securing the keyed joint from the side. An important advantage of a second set screw is that it reduces the amount of stress the shaft experiences at the junction. Keyed joints introduce a stress point on the shaft, first due to machining the hole and then because of the rotational force applied to that hole. While a second set screw puts another notch in the shaft, the lower stress at any one point minimizes the detriment to the shaft.

The keyway and set screw tolerances are based on the diameter of the shaft. For a given range of shaft diameter, the width and depth of the key seat and the diameter of the set screw(s) are available from ANSI specs.

Finished bore sprockets are ready out of the box, whereas plain bore sprockets need to be “finished” with a keyway. This makes finish bore sprockets ideal for standardized applications. However, they can still be machined further for a custom application – they’re not truly finished until they are right for your process!

MDS has hundreds of finished bore sprockets for roller chain pitches starting at 1/2″ (#40 and up) and bore sizes from 1/2 – 2″. Get in touch with any questions or specific needs for sprockets, roller chain or any other power transmission equipment.

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