What's the primary benefit of the adjustable 3 jaw scroll chuck?

[IamNotImportant]

Soft jaws are either aluminum or steel used for multiple parts requiring close TIR . Bore them to the finish size of your part . They are re-usable also , and can be bored for multiple set-ups . No , they will not mark parts .

just watched a nice vid about making soft jaws by Haas..

 

[Jimsehr]

These things? You make those out of round stock?

I think I'm not picturing what you have in mind... no answer needed, I'm just soaking all this in these days. I'll do some googling.

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There are more types of soft jaws. Most CNC machines use power chucks with serrated jaws. Also soft pie jaws can be the only way to hold large rings. And in a production shop it can mean profit or loss with how much time it takes to load parts. I have run tens of thousands of parts with load times of about ten SECONDS per part. And don’t forget many parts are held on the bores with soft collets that are turned to part bore size.

 

[davidpbest]

Soft jaws are not only useful to ensure tolerance from part to part, but but are often absolutely necessary to securely clamp a part that is thin walled. Example shown below where the soft jaws have been machined to perfectly fit the OD of the thin-walled part that requires additional operations. This has several benefits: 1 - increases the clamping surface area, 2 - provides a back-stop to register the part depth and flatness in the chuck, and 3 - reduce surface marring where the part is clamped in the chuck since the soft jaws are made from softer material (including plastic at times).

Here's another example using "Pie-shaped" soft jaws that have been machined to fit the part being clamped:

 

[skcncx]

Soft jaws are not only useful to ensure tolerance from part to part, but but are often absolutely necessary to securely clamp a part that is thin walled. Example shown below where the soft jaws have been machined to perfectly fit the OD of the thin-walled part that requires additional operations. This has several benefits: 1 - increases the clamping surface area, 2 - provides a back-stop to register the part depth and flatness in the chuck, and 3 - reduce surface marring where the part is clamped in the chuck since the soft jaws are made from softer material (including plastic at times).

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Here's another example using "Pie-shaped" soft jaws that have been machined to fit the part being clamped:

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It's been taking me awhile, but I'm now "getting it" as to the beneficial features to having 2 piece jaws, which means you can easily throw on soft jaws for a variety of specific scenarios. Seems to reason you can easily make your own soft jaws out of aluminum blocks... turn and bore to suite for your needs.

It took me awhile to recognize in pictures of chucks having the screw holes on the face of the jaws and what it meant... you just unscrew and screw new jaws on. Is there typically a standard hole spacing for a given chuck size?

in that pie-shape soft jaws illustration, is the clamp expanding on the part? Full faced soft jaws, pretty elaborate.

Kind of a bummer, though not a huge deal, since I am highly considering the bison combo 4 jaw chuck as my 4 jaw in my line up... hard jaws only, weight still has been concerned turning at 1000+rpm.

 

[davidpbest]

you just unscrew and screw new jaws on. Is there typically a standard hole spacing for a given chuck size?

Yes, you are now understanding how they work. And yes, there are standard hole spacing - metric and imperial. And it's not only the hole spacing that that matters here - the back of the removable jaw has alignment ways and slots. The removable jaws have tongue and groove elements that mate with the female version of same on the jaw that remains in the chuck. You can see these elements in this photo:

Here are the specs for an imperial 8" chuck with 2-piece jaws:

You can buy all kinds and shapes at a cost less than you can buy the material for at this manufacturer: monsterjaws.com

in that pie-shape soft jaws illustration, is the clamp expanding on the part? Full faced soft jaws, pretty elaborate.

Yes, absolutely. They have been machined on the lathe to precisely fit the ID of the part and also provide a back-stop registration flat to align the back of the part perpendicular to the spindle axis.

 

[Rich V]

I have an 8 inch Gator 6 jaw set true chuck on my PM 1340GT lathe. Recently I needed to bore a 0.512 hole 2.25 inches deep into D2 tool steel. My solid carbide boring bar will only go ~1.9 inches deep.


First I turned the OD of the bar true then I drilled and bored the hole to 1.9 inches deep. I then parted off the part and flipped it in the chuck. Using the set true feature I indexed the OD with a dial indicator to +/- 0.0001. That took ~90 seconds to dial in. I then bored out the remaining 0.35 inch of ID to 0.512. Finished by polishing the bore with a fine Scotch bright pad. The resulting bore would pass a 0.512 gauge pin freely but a 0.513 pin would not start.

That demonstrates what a set true chuck can do.