Puzzled - Chuck Back Plates

B

BillWood

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Hello,

I bought a 2nd hand lathe that came complete with chucks that screw onto the 8tpi thread on the headstock.

I keep seeing references on the web and in books to chuck back plates and how to install them.

Does this mean that if I buy a new chuck then I also need to buy the appropriate backplate so that it fits my lathe ?

ie the cost of a new chuck isnt $XXX its $XXX + $YY for backplate + a couple of hours mucking around ?

I got lucky because my 2nd hand chucks already had backplates installed that screw straight onto 8tpi mandrel in headstock ?

Regards

Bill
 
You've got it right, Bill. There are a number of different ways to mount chucks to spindles other than threading them on. Thus, you purchase the chuck you want, then purchase the properly sized backplate to allow you to mount that chuck to your lathe.

Most backplates can be purchased pre-drilled to fit the chuck. If that is what you get, you first need to machine the register recess for where the chuck threads on to the spindle. The register is the cylindrical part that the backplate mates up to behind the threads on the spindle, and the register on the backplate must be machined for a nearly perfect fit on the spindle so that the backplate mounts concentric with the spindle. You do not rely on the threads to center the backplate and chuck because it will mount differently every time if you do. Once the register is machined, mount the backplate to the spindle and machine the register that will fit into the recess on the back of the chuck. This also must be machined nearly perfect for a snug fit with the chuck. Once that is done the chuck can be mounted to the backplate and checked for runout. If the job was done right, there should be very little runout, maybe only a thousandth or two, depending on the chuck.
 
Thanks Terry,

For my next lathe ..............................

Was wondering about a system where the tightening of the chuck by intermittent cuts and slitting saws becomes irrelevant .............. ie 3 studs instead of a central threaded spindle.

A quick googling found this page http://www.lathes.co.uk/latheparts/page8.html

any other good pages for learning more about pros and cons of various fitting methods ?

Bill
 
Bill,

You found the cam lock type of mounting, which is probably the most modern type. In addition to threaded spindles and cam lock, there are also some short taper and long taper types. The link that you listed above has some of the other common styles listed near the bottom of the page. Take a look at those and you will have seen all of the most common types.
 
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