Scroll chuck jaws.

[Honest John]

I was changing the jaws on a chuck today when a thought got struck me! I have three scroll chucks, a super Nova 2, a Sorby Patriot, and a Record Power SC4. The jaws on these chucks are interchangable seemingly without problem. I noticed the SC4 jaw set that I was fitting to the Super Nova body were all numbered, as are the SuperNova jaws. The Sorby jaws are not numbered, and have made much of this on past advertising, that their jaws are so accurate that they don't need to number them and can be fitted in any position.
Now am I missing the point of this? Surely each jaw is identical or I couldn't interchange them with the Sorby fitments. I have never noticed any inaccuracies when interchanging any combination of body and jaw set. It is very possible that I am being rather obtuse and completely missing the understanding of why they need to be numbered, but if someone could explained n this to me I would appreciate it.

 

[Paul Hannaby]

The jaws are made in one piece as a single disc, which is then cut into four quadrants. On this basis, it would be very unlikely that any of the four jaws would be different. The bit that does differ is the jaw carrier. Each one of those has the grooves to match the scroll in a different position so when they are mounted on the spiral scroll, they are all the same difference from the centre.

Looking at this logically, I think the only reason for the numbering on the jaws is to make it easier to identify the right carrier so it can be put in the right slot once they are attached to the jaws.

 

[Honest John]

Thanks for the reply Paul. I can see how the carriers will be different otherwise they couldn't engage in the scroll, and would only engage in a circle..... And then of course the chuck wouldn't work. The jaws locate in a groove which is essentially concentric to the centre of the chuck, and it therefore follows that each jaw quadrant must be identical. The carriers on my chucks do not "wind out" as on some chucks but stay attached to the scroll until the chuck is disassembled. The carrier to scroll relationship is important and I can see why the carriers should be numbered to assist you ln reassembly, but I still can't see why identical jaw quadrants need to be identified with a number?

 

[CHJ]

..I still can't see why identical jaw quadrants need to be identified with a number?

In the past not all jaw carriers carried an easily viewable number when accessory jaws were fitted (not on the periphery as is more common now)