Here's a tip, Be careful with your mandrel, especially if you are doing a 2 piece pen and you turn both pieces at once.
It's very easy to put too much pressure on the mandrel and have it bend every so slightly. This will cause your turned tubes to not be perfectly round.
There are ways around that, such as turning between centers, using a mandrel saver, using a collet chuck. Took me quite a while to realize that and a couple of bent mandrels.
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