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Lathe – 3 jaw chuck – construction

Most chucks are sold without the means of fitting them to the spindle of the lathe. To fit it, it is necessary to make a backplate that fits the lathe on one side and fits the chuck on the other. Looking at the back of the chuck it can be seen that there are two sets of holes. The first are for bolts that hold the chuck together. The second set are to bolt the chuck to the backplate.


fig the back of a three jaw chuck

The other key feature is the back is recessed. The backplate has to be made so that it has a protrusion that will fit this recess perfectly. This means it is impossible for the axis of the chuck cannot move at all.

If the bolts that hold the chuck together are removed it becomes possible to take the back of the chuck away from the rest of it. What will be seen on the inside of the back will be three bevel gears.


fig the three bevel gears

Each of these gears can be turned from the outside of the chuck by means of the chuck key.

If we look inside the front part of the chuck what can be seen is one large bevel gear. When the chuck is assembled this large bevel gear engages all three of the small bevel gears in the back part of the chuck.

fig the large bevel gear

If the large bevel gear is removed and turned round it will be seen that the other side of it is a single spiral.

fig the spiral

In the front part of the chuck are the jaws of the chuck. These are fitted in slots so that they can slide in and out. When the chuck is assembled these the teeth on these jaws fit in the scroll. When any of the small bevel gears are turned by using the chuck keys this turns the big bevel/scroll and as the scroll turns the jaws are moved in or out.


Three jaw chucks used in metal work are always self centering

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