Ledd Slinger
Silver $$ Contributor
This is kind of the basis to my question.
If you're turning fire formed brass, wouldn't the inside neck diameter be a few thousandths larger than your turning mandrel, hence needing a turning mandrel of a larger diameter?
I know the turning mandrel is roughly .0005-.001 smaller than expander giving a good fit with clearance.
Or should I not worry about the extra clearance as the brass is riding the mandrel on top and held there by the cutter?
I'm using 21st century lathe setup.
You FL size then run the neck through the expander mandrel. The expander makes the brass fit the turning mandrel but also serves to straighten the inside of the neck and make it perfectly concentric with the turning mandrel. The brass is pressed between the cutter and turning mandrel as it’s being turned. That clearance will not change and thus cuts an even thickness down the entire neck. Get a neck wall thickness gauge to check if it worries you but you’ll be wasting your money if using a 21st Century neck turner because they are extremely precise cutting tools.
The Redding neck wall gauge can check thickness of the walls at any point fore and aft and is great for ensuring your cut thickness is correct for what you are trying to achieve. I will usually use a piece of cull brass to set up the turner and check my cut thickness and depth on the shoulder cut. But I quit using it for checking uniformity of cut thickness on the wall at different points once my 21st Century turners are set up because they always cut so perfectly every time.

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