I believe it was to facilitate moisture droplets flowing out the end.
I’ve never oiled the inside of a Delrin flute, but I certainly apply some wax to the outside. Gives it a nice luster.
Great topic! Is there anyone who has tried Vicenzo di Mauro’s flutes and how do they compare to the likes of Baubet or Somers?
I have them sanded instead. It then looks more like wood, and they are easier to handle.
Who sands flutes?
If you sand Delrin with fine sandpaper, going lengthwise, it does make it look a bit more “woody”. Sort of provides a bit of grain to the surface.
Thanks. Cool!
If you try this at home, wear a dust mask. Breathing finely powdered plastic is probably ill-advised 
Not a great photo, but not all shiny/plastic.
Dave Copley’s are already sanded lengthwise, as I’d expect most to be. Look at yours carefully.
Cool thread. I’ve tried Copley, M&E, Forbes, Dixon, and Somers (R&R style) Derlin flute. This has all been some years ago, but if memory serves, I was rather impressed with the Forbes; it reminded me a bit of playing an Olwell. The Copley Delrins I played were nice, too. I wasn’t a big fan of the M&E (although I don’t remember exactly why); the Dixon was fine but rather quiet with its small dimensions. I liked the Somers Rudall, but for some reason I played rather flat on it, even with the slide pushed in. But I only played it for maybe 15 minutes, so it could have just been unfamiliarity.
Hi all, I hope nobody minds me jumping in on this thread, I’m a newcomer to the world of flute making and very happy to now be offering Delrin & wooden flutes for sale.I’m based in the UK (Midlands).The flute in the pic is my Delrin ‘Student model’ priced at £290 plus shipping.There are more details/pictures of my flutes here on my facebook page- ‘Thompson Flutes’ .Please direct any enquiries through there if possible or PM here. https://www.facebook.com/thompsonflutes/ Many Thanks, Damian.
Thanks for posting. Checked the facebook page.
Looks like lovely work throughout.