4-Jaw Chucks

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4-Jaw Chucks

3inch_4jaw_y.jpg (11175 bytes) 3-inch 4-jaw chuck from J&L

A 4-jaw chuck is a great, almost essential, accessory for any serious lathe worker. While it lacks the self-centering convenience of the the 3-jaw chuck, it has other capabilities. Some things you can do with the 4-jaw are...

Here's a nice summary of 3-jaw versus 4-jaw features posted by Bruce Simpson:

Benefits of a 3-jaw:
1. self-centering
2. can hold hex bar-stock
3. quick and easy to use.

Disadvantages of a 3-jaw:
1. can't hold square bar-stock
2. run-out/off-center can't be easily fixed
3. can't hold irregularly shaped work
4. can't turn off-center

Advantages of a 4-jaw:
1. work can be centered to high precision
2. can handle square/rectangular bar
3. can turn work off-center
4. slightly more grip on round stock

Disadvantages of a 4-jaw:
1. slower/fiddlier to mount work (dial-indicator required)
2. can't hold hex-stock

The standard HF SKU 33684 mini-lathe as well as the Grizzly 7x12 have six mounting holes in the spindle plate that mate directly with the J&L 3" 4-jaw chuck. Note that these mounting holes are not found on the HF SKU 39916 mini-lathe or on the Grizzly Outlet 7x10.  Due to its excellent quality, reasonable price and ease of mounting, I highly recommend this chuck.

Spindle_y.jpg (30772 bytes)


Centering Cylindrical Stock

There are a number of ways to center stock in the 4-jaw chuck; the technique I will describe here uses a dial indicator. The basic procedure is as follows...

DI_centering_bolt_y.jpg (14915 bytes)

These steps get us ready. Next we follow these steps...

Here's how it works: When the DI needle is at its maximum counterclockwise movement, the top surface of the workpiece is at its lowest point. We loosen the topmost jaw to make room to move the workpiece upwards, then rotate the chuck to bring the opposite jaw on top (or any position where you can easily tighten it) and then tighten that jaw to move the workpiece more on center.

Initially, you will make relatively large movements of the workpiece, but as it becomes more nearly centered you will need to make smaller adjustments or you may overshoot and move it off center in the other direction. When you get very close to center - the DI needle is moving just a few thousandths - you can make the final centering adjustment by tightening the opposite jaw without first loosening the topmost jaw. This will ensure that the workpiece is tightly clamped and will help to avoid overshooting when only a very small adjustment is needed.

Like any new skill, this procedure takes a little practice at first, but after you do it a few times you will find that is is almost second-nature and can be done in a minute or so.


Forming Non-cylindrical Objects

Due to its inherent rotational nature, a lathe is ideal for turning radially symetrical shapes: cylinders, that is; so it sometimes surprises beginning lathe workers to discover that you can use a lathe to form cubes and other six-sided rectangular objects. This is done through a sequence of facing operations using a 4-jaw chuck. The following photos  show the transformation of a cylinder into a rectangular shape (technically, a rectangular parallelepiped). Once you grasp this potential of the lathe, it opens up a whole new class of things that you can make.

cube1_y.jpg (17779 bytes) Cube2_y.jpg (17101 bytes) Cube3_y.jpg (20379 bytes) Cube6_y.jpg (19567 bytes) Cube7_y.jpg (22103 bytes) Cube8_y.jpg (17682 bytes) Cube9_y.jpg (16108 bytes) Cube10_y.jpg (15087 bytes)

No effort was made on this workpiece to protect the surface from being marred by the chuck jaws, so jaw marks are plainly visible on the finished surface.


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Mini-lathe:  Accessories   Adjustments   Capabilities    Chucks    Dial Indicators   Features   Getting Started   Glossary     Introduction   Materials    Modifications   My Shop   Operation    Reviews    Sieg Factory    Tool Grinding    Troubleshooting   Tuning     Versions