I have a question about clockmaker lathes. I have just purchased an 8mm lathe and need to purchase collets or a universal 3 jaw chuck

What is the advantage or disadvantage of using an adjustable chuck such as the ¼” Jacobs type you see on eBay over the collets and needing many sizes on hand to cover clock repairs?

I see these chucks for as little as 30-50 dollars each. And collets sell for 15 dollars apiece new? Money wise it seem that one should buy the 3 jaw chuck. But there must be a reason collets win over the 3 jaw type. I guess that the collets might hold the material better and turning might be more accurate than the universal type.

Also what is the purpose of the indexing pin? I have no clue?

It's all about the accuracy Bob.You could never achieve the level of accuracy with a three or four jaw chuck that you would get with a collet.The tolerances are much tighter with a collet.
As far as an index plate goes such as the type you normally see on the headstock of your lathe.Well it is normally used to provide equal spacing around the periphery of a chucked pc. being that all those neat little holes are all spaced equally around the circumference of the plate proper.For example,lets say you wanted to take an arbor and file a new end for your clock key.You would start at one of the twin holes in the index plate,these are usually every 90 degrees and file one flat on your arbor.You would then rotate your spindle or pulley to the next 90 degree twin hole and so on.This will give you four equally spaced 90 degree flats.That is basically how an index plate works.
Respectfully,Bob Fullerton

Bob thanks for the reply. I kind of got the feeling that collets were far more accurate over the adjustable chucks. I am new at working with the lathe. I just picked up a Elson lathe on ebay from IHC-185 member Deena. I am currently waiting on gravers to arrive and I also ordered a couple of collets today to start buildind a collection of collets. I am not sure how far a collet can vary +/- beyond its size without damaging it?

As for the indexing pin I now see the use for it. Thanks for the information. I do have a lot to learn.
Bob