Cutting Internal Keyways

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Cutting Internal Keyways

Post  kenneth on Tue Nov 27, 2012 12:26 am

Hello Everyone,

Recently I have come across 2 methods of cutting keyways without using a broach.

Background on keyways:

"Keyways" are used to transmit torque (a turning force) between things that are supposed to rotate together. More can be found about them here

Previously, the team has cut internal keyways using the milling machine, creating a semicircular profile. This worked fine, however bits would occasionally break due to too much side loading. Milling machine bits happen to be expensive, so breaking the isn't good.

Other methods of transmitting torque used by the team include "split pins" and setscrews.

Split pins (roll pins/spring pins) are pressed into a hole drilled perpendicular to the rotational axis of the shafts. They are relatively difficult to remove and they have sheered in the past. They have been used to secure the shooter wheels to the shaft on the 2012 robot.

Setscrews allen (internal hexagon) head bolts, where the size of the allen key used is smaller than the diameter of the bolt. They transmit torque by clamping a hub to a shaft through a threaded hole, perpendicular to the axis of rotation of the shaft. When they are not used with a flattened portion of shaft, or a small hole, they can slip and also vibrate loose. Setscrews were used on the steering sprockets of the 2011 robot.

Cutting Keyways:

One of them involves using a lathe as illustrated in this video:

The other method involves stacking hacksaw blades in a hacksaw to gain the desired width, then feeding the stack of saws through a hole to key it. Most hacksaw blades are around 1/2" tall, so a stack of them will not fit through 1/2" hole without some grinding. In order to keep the keyway centred, a bushing similar to those used in broaching could be used to guide the blades, shown below.


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