protecting material in lathe chuck

robbor · Mar 7, 2008

Im sure this has come up on a regular basis but did not find much in search.
What are the prefered methods of chucking up an item on the lathe and protecting the surface. I use collets at school on the lathes but only have a 3 and 4 jaw for my lathe at home. I prefer the accuracy of the 4 jaw but always kill the surface of the material im working with. On the collets at school i cant get less than .001 run out which is ok for most stuff but that is the best i can get by switching between collets, collet chucks and different lathes. I saw a mention of using paper but theres got to be a better way.

pipeclay · Mar 7, 2008

You can try using pieces of aluminium or copper strip between the jaws and workpiece.

JunkyardJ · Mar 7, 2008

Brass shim stock???

I've always just wrrapped it in some thin brass shim stock. I've also used a pop can cut into strips, paper, copper tubing, cardboard, plastic, and whatever happens to be handy at the time! I saw a guy that made a set of brass jaw shields out of some thin brass sheet (thicker than shim stock). They kinda folded onto the gripping edge of the jaws with a couple tabs around the outside. They just slid off the ends. I dunno, I've seen chucks that have replacable aluminum jaws you carve up to the proper diameter. I personally like brass shim stock, because it's a consistant thickness, which helps to hold it straight.

Forrest Addy · Mar 7, 2008

I use #6 copper wire annealed and rolled into a ring that catches all 4 jaws in a serration. You have to pick a wire gage that suits the serration on your jaws and #610 suits mine.

You can also use square or flattened magnet wire from the remnent spools at your local motor rewind shop.

Or hunks of aluminum, heavy plant fiber gasket material, tabs torn from single oayer cardboard boxes, etc. The softer the work the softer the padding has to be. You'll soon accumulate a collection of paassing stuff in a box that lives on the headstock.

There's no need to scar up finishes when padding is available. At first inserting padding between the jaws and heavy work pieces can be a real juggling session but you soon learn the tricks.

Old Bill · Mar 7, 2008

I cut a piece of sheet aluminum and roll it into a ring. It is easier to handle than 4 seperate pieces.It helps that we have one of those little hand crank things with the 3 rolls.
Old Bill

stuball48 · Mar 7, 2008

Piece of emery cloth--with grit facing chuck jaws and smooth side on material.

Mike72 · Mar 7, 2008

When I worked in the gasket business, I would collect many of the slugs from different head gasket dies. Some were the perfect shape and size for use when chucking in a 4 jaw. I found head gasket material to be about the best thing for this purpose. If you can find some old unused head gaskets you can cut out your own. The gasket material with the metal core really holds up well and can be reused many times.

deltaenterprizes · Mar 7, 2008

Pennies are cheap and readily available!

Carl Darnell · Mar 7, 2008

I have a coffee can full of brass, copper and aluminum rings I have bent into different diameters. They also vary in width and thickness. I also use pieces of aluminum sheet from 1/16" to 1/8" thick to use.

When using the rectangular pieces I tape them to the jaw with masking tape to keep them in place.

I also have several pieces of different width and thickness of banding material and that works real good on big heavy stuff that aluminum and copper don't work good with.

I've kind of been using banding material more lately for everything.

daryl bane · Mar 7, 2008

Plastic shim stock, especially in the thicker sizes, accurate and tough.

standish · Mar 7, 2008

I have a little box with a bunch of strips made by cutting up business cards sitting on the headstock for the purpose. I also keep a few various size sections of PVC pipe with a slit up one side to use when the pipe ID is close to the ID of the workpiece.

gwilson · Mar 8, 2008

Never try to use masking tape,or any tape with sticky adhesive on it. The glue gets very slippery when under pressure,and will let the part slip.

PixMan · Mar 8, 2008

I have strips of copper about 1/32" thick, cut to the length and width of the jaw faces that I use with my 4-jaw chuck. Orient the chuck with jaws at 12, 3, 6 and 9 o'clock. Lay one at 6 o'clock, set the workpiece on it. Lay another under the 12'0'clock jaw, snug it up a bit.

Hold one at the 3 o'clock jaw, bring it up to touch. Hold the last one at the 9 o'clock jaw, bring up to snug. Indicate workpiece into true.

Done.

I got good enough at it that I could get a piece chucked within .015" without the indicator in less then 45 seconds, true up in a couple of minutes. Copper displaces far less than plastic or card stock, I could take some pretty heavy cuts without the workpiece budging a bit.

Carl Darnell · Mar 8, 2008

Everyone in the shop used masking tape to hold the shims in place and we never had a part slip during machining.

As a matter of fact when you pull the part out of the chuck the tape is gone where the part was in contact with the shim and it is bare metal.

These are parts that weight from 100 lb to about 1000 lb and are in a 4 jaw chuck held on the step of the jaw that is about 3/4" wide. All the time I worked there we never had a trunnion jump out of the chuck.

Old Bill · Mar 16, 2008

One thing I have learned to avoid is using plastic to protect a finish. The plastic will compress or "take a set" and result with reduced holding pressure.
Old Bill

The real Leigh · Mar 16, 2008

Carl Darnell said:
[W]hen you pull the part out of the chuck the tape is gone where the part was in contact with the shim and it is bare metal.

This rather defeats the purpose of using the shim to protect the surface, yes/no???

Troup · Mar 16, 2008

I think you misunderstand - as I understand it, Carl is using masking tape to hold the protective shim in place. The purpose of the tape is not protection but retention

Carl Darnell · Mar 16, 2008

Leigh, actually no because the shim is still between the jaw and the work. The tape was only to hold the shim while putting the part in the chuck. It don't mater which shim stock you use they are hard to keep in place and I sure don't want my hand under a 500 or 1000 lb chunk of steel trying to hold a shim in place. I have even bent them into a U shape that fits tight on the jaw. I also have 4 shims with a coil spring that I can strech over the back of the jaw to hold them in place.

The banding material works the best of anything I have tried so far unless the work material is soft such as aluminum, plastic, etc. then you have to get creative.

Bernoulli · Mar 16, 2008

I use aluminum shims cut out of stock (about .09") to fit jaws. I hold the shims in place with grease while I'm setting up. Kind of like replacing needle bearings in a transmission.

Cuda · Mar 16, 2008

Carl Darnell said:
I also have several pieces of different width and thickness of banding material and that works real good on big heavy stuff that aluminum and copper don't work good with.

I've kind of been using banding material more lately for everything.

Dito, I use different width steel banding material a lot, just cut it to length and make sure it's deburred and it works great, I also use thin aluminum scrap when I need to chuck on something like a casting, the aluminum will deform to the shape of the casting and give better grip than a hard steel jaw.

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