Years ago I was in Ohio after my first wife's dad died and we had to take care of his house and belongings. While there I got in touch with Roger Rothhaarr and have yet to meet a more gracious man. I spent two days with him and he showed me how to sharpen snuffers. He started with a large mill bastard file and stroked two blades at a time rotating the blade after each stroke. He did this 30 times so each blade got 10 swipes of the file. Then he checked the edge of each blade to be sure there was a burr on each one for its full length. If he wasn't happy at that point he repeated the process, as he would on each step along the way. Then he used the back of the file, which gets the least amount of use and is therefore sharper than the front end and he would lay that part of the file on two blade and using it like a butcher's steel he would very lightly, using just the weight of the file, to stroke two blades at a time for another count of 30, doing two different blades on each stroke. The purpose of this step is to remove the burr. At that stage he claimed that they are "hunting sharp"...the edges are not polished to a razor edge but they can take off hair and can kill cleanly. To get a razor edge he would use an artificial diamond stone and do two blades at a time, pulling back to front for a count of 30, rotating two blades on each stroke. He would then strop the heads on a hard maple block but said that leather or cardboard would do fine.
What I have found, using the method he taught me, was that the most crucial part was the first two steps with the file. Get a burr, then gently remove it. After that you can polish the edges to get the razor edge or you could stop right there and hunt with confidence. If you don't get that burr and successfully remove it correctly you will spend a lot of time getting nowhere. I have found the to be true on all three blade heads that i have tried to sharpen.
On heads that have harder steel I do what Westbrook does and I find that a well used belt on a belt sander gets the burr up quickly. It is also is a fast way to deal with those heads that have been used for practice or have been shot into the ground and need more work than one might want to attempt with just the file. The file just takes a bit longer.