Truing up jaws in lathe chuck

[Harold_V]

First pic is a set of aluminum soft jaws. They have been used but once. The gripping surface is the small radius cavity you see in the picture. Jaw blanks are typically made rectangular, without the step, but the material I had on hand already had that configuration.

Notice that the jaws are somewhat symmetrical. If you make your jaws wisely, you'll be able to reverse them, using both ends for different configurations. Also, making them from steel instead of aluminum allows for welding pieces back on when you've used them up. I've done that with several sets in the past. That way you avoid making new blanks. While aluminum can be welded, it also softens the material, which is not desirable. I look at aluminum soft jaws as disposable when they're been well used, but have never discarded a steel set.

Second pic shows my 3 jaw with one of the jaws removed. It's an unusual chuck in that it has a key to register top jaws on the master jaw. American-made chucks tend to not have the key, but rely instead on a boss. It's somewhat more difficult to make the blanks with the boss than the key because of corner radius interference, but it's possible. A small end mill and an undercut works well.

Note that the slot width locates the jaws sideways. The slot and key (or boss) should always be a snug fit to prevent jaw movement under load, and also to assist in proper register when re-installing the soft jaws for future use. That helps minimize the amount of material that must be removed for a new configuration.

If you'll study the second pic, you'll notice that the cavity has two different configurations bored within. No need to completely remove the old one, just establish a generous gripping surface (and, in this case, a shoulder on which your part will locate). Because you have such large area of contact, and it conforms to the diameter of your part, the parts don't get marred, and they also tend to stay round when you grip thin walled objects.

Third pic is the spider. Nothing more than a hex nut that is drilled and tapped for, in this case, 5/16"-18 SHCS of various lengths. I've discussed the spider and reasons for its design in the earlier referenced thread, but if you don't find an answer to any questions there, feel free to inquire further.

Harold

[Metalman]

Hi Harold
Thank you for posting the photos. I understood the spider from your text description. The photos cleared up my understanding of the soft jaws very nicely and I can see the many benefits of using them. I imagine the uses could be endless. I have machined myself into a corner so to speak and couldn't remove the part without losing accuracy on my one piece three jaw chuck.

Ernie F.

[ZipSnipe]

Now let me see if I got this right, the spider will be held in the jaws of the chuck at the furthest outside edge and then you are to bore upto the spider? And is this boring operation taking place on the lathe or mill? Also what about making softjaws for one piece jaws that is lets say C-shaped and it kinda wraps around the jaw with maybe set screws on the side? Think that could work?

[Harold_V]

Now let me see if I got this right, the spider will be held in the jaws of the chuck at the furthest outside edge and then you are to bore upto the spider?

In a sense, what you said is correct, but there may or may not be an edge to which you will set the spider. I've set the spider on the master jaw, or on the soft jaw portion, depending on what I'm doing. The purpose of the spider is to load the jaws as they would be loaded holding a part you intend to machine. In order for the spider to compensate for the wear and springing most 3 jaw chucks have, the spider should be placed as far out as possible, but still allow for the jaws to be machined where the part will fit. As you get nearer and nearer the scroll, the less effective the spider becomes in tilting the jaws (less leverage), which is really what's happening, along with loading them against the scroll.

And is this boring operation taking place on the lathe or mill?

Depends. If you're turning a piece that is round, you want to do the machining with the chuck on the spindle, and not remove it for any reason until the job is finished. You bore the jaws the same way you'd bore a part. While you should be able to remove and replace a chuck, there's no guarantee that they will seat exactly the same way each time, so boring on a mill should be reserved for those occasions where the lathe won't do.

Assuming you want to chuck an irregular shaped object, using a vertical mill, you'd dial in the chuck body (looking for theoretical center) and from that machine the jaws according to the configuration at hand. It can be trying if you're not a seasoned mill hand, but with care you can establish a very well located cavity that will run each part identically, assuming they are all the same size.

Using soft jaws is something that will teach you to start holding diameters close, even when they don't have to be for other reasons. If you don't hold the parts identical to one another (± .001"), you shouldn't expect the soft jaws to run well. The extra time spent holding diameters close will be more than repaid when you second operation the parts. The more you have to handle the parts in question, the more soft jaws are to advantage.

Also what about making softjaws for one piece jaws that is lets say C-shaped and it kinda wraps around the jaw with maybe set screws on the side? Think that could work?

I would advise against that design, although it would work. What you want is something that clamps the jaw closed on the hard jaw. You'd do the same thing you're talking about, but you'd make the jaw deep enough to permit drilling a cross hole on top of the jaw, where you'd install a bolt that, when tightened, clamps the sides of the soft jaw against the hard jaw instead of spreading it.

It's important to make your jaws such that they can't be moved about once installed. If they are free to move, you're highly unlikely to be happy with the results. If you make jaws that can be moved, they'll work, no doubt, but the precision that is usually expected will be hard to come by.

Harold

[Harold_V]

Hi Harold
Thank you for posting the photos.

My pleasure! Really!

I hope to get lots of people using soft jaws. If I'm not remembered for anything else, I will be remembered for that.

There's no good reason why the home shop shouldn't be enjoying some of the methods that the commercial shops use---particularly when it's so easy and beneficial. They really are that magic bullet you need in the shop-----and can be added without spending any money in some cases.

I understood the spider from your text description. The photos cleared up my understanding of the soft jaws very nicely and I can see the many benefits of using them. I imagine the uses could be endless. I have machined myself into a corner so to speak and couldn't remove the part without losing accuracy on my one piece three jaw chuck.

Ernie F.

Your example is a good reason to use them, but they're more than that. Even when high precision isn't a requirement, because you can use them as stops, locating each part perpendicular, and they will run so nicely, even when you screw up and don't hold diameters closely, they save so much setup time that they are worth their weight just for that. When you have multiple parts to run and must handle them through several operations, they're impossible to beat. And then there's that strange part that you have a hard time setting up-----a thin object, for example. You can face off 1/16" thick "washers" or plates and hold them parallel within a few tenths, no big deal. Their uses are endless-----and limited only by one's skill and imagination.

Harold