I'm making a hollow draw bar for locking my MT4-ER40 collet chuck into my Hercus 260 spindle bore. I'm planning to use NB15 galvanised water pipe which has an OD of 21.3mm and an ID of 16.1mm. To avoid weakening the gal pipe too much I'm planning on using 1mm thread pitch. The Sketchup drawing shows what I'm planning.

The collet chuck is mounted in the 4-jaw and I've dialled it in to about 0.01mm runout at the far end. I've cleaned up the inside and outside of the short parallel section on the end. I had no problems doing that with light cuts.

Do you guys think that setup is rigid enough for single pointing the internal thread?
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