From what I have seen, the best finish youll ever get on Delrin/Acetal is from the tool (assuming youre using a good sharp pos cutter)
From there it all goes down hill.... sand it and its much worse, flaming... like said above - no go, steel wool, scotchbrite, and so on... same thing.
The closest thing to the original cut surface finish I have been able to get on Acetal after its been boogered up (sand paper etc) is some Dico polishing compound (blueish color - I got it from enco I think) and a buffing wheel on a grinder. And even still... ugh... but better than it was.
If there isnt a reason to not use some sort of chemical on the surface, you could try buffing with a little floor wax or wipe down with an oily rag...
For future reference, if there is any way to do everything on the machine, and always have your cutter push the edge its going to push up ahead of the cutter and then finally leave it in one place thats easy to debur - that will save you the most effort... but it may not be possible with your part.
I feel your pain, the acetal parts I make need the "pretty factor" because its 80% aesthetic.... and 20% function.
Wade