Shopsmith Forums

I think this mantra comes from drill presses and drills themselves most of which are certainly not designed for handling side loads. That being said, the SS is a different beast that is designed for handling side loading operations.

Many metal lathe chucks are 3 jawed designs. It's not the chuck that takes the load, it's the bearings.

I've had very good result using the drill chuck for holding small spindles.

Would I try to hold a router bit at top speed and attempt routing operations with a drill chuck? NO. But I see no problem holding on to a 1/4" mandrel and performing lathe operations. If you are using the lathe correctly with properly sharpened tools the side loading is negligible anyways.

Like I said earlier, "We're turning a pen blank here, not a bowl."

I would certainly NOT use a drill chuck to hold a bowl blank in place, to turn it. But, like others have pointed out, we're turning a 3/4 inch pen blank, and supporting it with a tailstock.

But then, I'm using a cast iron Shopsmith, with a Jacobs brand drill chuck. YMMV.

steve

JPG40504 wrote:So has anyone determined WHY the drill chuck is unsuitable for operations involving 'side thrust', or are we citing a mantra with no forethought.

Most drill chucks attach to a drill press by a tapered interference fit. http://www.gizmology.net/tapers.htm

The problem with side loading is not that the work doesn't run true, but that it can cause the chuck to come loose from the shaft:eek:, .

When a chuck is attached to the headstock of a lathe by a Morris taper a draw bar is used to prevent it from coming loose.

With the ShopSmith drill chuck this should not be a problem as it is fixed to the shaft with a set screw.

Here is a video showing Cap'n Eddie turning a pen using a drill chuck and using a drill bit for the mandrel, 12 cent pen, so it can be done.

rpd wrote:Most drill chucks attach to a drill press by a tapered interference fit. http://www.gizmology.net/tapers.htm

The problem with side loading is not that the work doesn't run true, but that it can cause the chuck to come loose from the shaft, .

When a chuck is attached to the headstock of a lathe by a Morris taper a draw bar is used to prevent it from coming loose.

With the ShopSmith drill chuck this should not be a problem as it is fixed to the shaft with a set screw.

Here is a video showing Cap'n Eddie turning a pen using a drill chuck and using a drill bit for the mandrel, 12 cent pen, so it can be done.

Good point!!!! Also some have a taper in the chuck AND to the spindle. The taper provides axial load bearing but little side load ability.

FWIW, hand drills may also have a tapered socket in the chuck, but also have a retaining screw. Lately though threaded shafts with a center retaining screw seem the norm.

So I now see the mantra source more clearly and although still it contains some relevance, tis not the chuck entirely by itself.

So to summarize, the Morse taper chuck connection is not an issue on a Shopsmith. Neither is the spindle-bearing radial-load capability (unlike a generic drill press). Which leaves the chuck itself.

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The chuck jaws are basically wedges that are driven tight against the tool shank by a screw thread. I can see three issues that could affect the gripping stability:

1. The 120 degree spacing that JPG already mentioned, which arguably could reduce the load capability when the side load is midway between two jaws,
2. The relatively short length of the tool-gripping surface, and
3. A poor fit of the jaws to their guide slots.

Note that when routing, the force at the chuck is not a simple radial force. Instead, the router-bit shank is acting like a pry bar. This compounds the force at the jaws considerably, given the short gripping length.

But when pen turning, the other end of the workpiece is supported by the tailstock. The tailstock shares the radial load and prevents the pry-bar effect.

Thanks for the picture! Now I know what to expect when I pry my ball bearing chuck apart to replace the jaws.