okay, well hairy asked me to copy this out of my WIP, and so i hope it's useful to you all !
~~~
i was about to buy two of the metal ones, until i realized that i could simply make some [and so can you!]. and since somebody, somewhere needs more flamers but doesn't feel like buying bits, i'm writing a "how-to" on the flamers i make. so enjoy ! :]
on a side note: sorry about all the weird drawings in the background. i use that piece of chipboard [like cereal box material, but 5 ish times thicker] as my cutting mat. and i promise i'm not emo. i just like using the razor blade instead of x-acto/other hobby knives. more control over the cut :]
OKAY! tools/bits needed:
-hobby knife, some sort of cutting/filing tool.
-cutting mat [be safe ! don't cut your mother's table...erus is not the only one with a pointy stick]
-a friend or family member that plays IG. really, that makes the making of flamers so much easier than buying them, especially because they will have about a million extra IG flamers and nade launchers, which are the staples of these home-made flamers :]
bits:
-1 SM flamer, to check for proportions and bits sizes!
-1 bolter with a standard clip [ie, not a chaos one with a belt feed]
-1 IG flamer
-a bamboo/wood toothpick, OR a relatively fat computer wire, about 2 or 3 mm thickness, de-wired. it should be at least 1 cm long.
-1 IG 'nade launcher, or other small, cylindrical object [used as the promethium tank]
here we go !
mm. the first thing you'll need to do is separate the flamer head from the IG bit.

be careful here, because one of the pipes that run from the stock of the gun to the flamer head will be used later on.
then, carefully separate the actual head from the pipes. the bottom one on the IG flamer is the crucial one, be the most careful with that pipe because it's used later.
2
once the head is separate, you'll need to file/trim it down to normal SM flamer head length. it's usually about 1 mm, maybe 2 that you need to remove from the back of the flamer head. file it and compare with a normal SM flamer, make sure the length is correct.

then set this aside.
3
take the bolter, and you'll probably have a little thingy sticking out the side, next to where the spent casings are ejected. also remove the flash supressor, etc, from the front of the bolter. i didn't have to worry about that, because my chapter removes them anyways. hooray for big flashes and loud bangs while shooting at your enemy ! and reduced accuracy! huzzah !

trim that off, and then make a pair of cuts so that the gun stock above the hand grip is gone [but don't! cut the grip itself off, like so:]
4.
glue one of the tiny pipes into place at the business end of the now cut up bolter, centered at the top of the grip.

this one is tricky, it's such a tiny bit XD
5.
take the wire, or toothpick and trim out a section that is equal to the length of the larger pipe on a normal SM flamer. [note: remember to make sure you have a normal flamer around, to check proportions !]
cut, trim, place and glue it into place so it looks like this

then attach the flamer head
also, remove the clip, and trim what is left of where the clip went so that it is a nice, straight angle of about 30 degrees. check the pictures for clarity :]
6
take the nade launcher and carefully cut off the barrel. the 'nade casing itself won't be used, set that somewhere else.
the rest of the 'nade part is a little bit harder to explain, but the pictures should do it. i'll try my best though ! lol

trim off the tip of the barrel!

carefully cut off the squared section of the barrel, and file off the "tracking" on the top of the barrel.

and that's as far as i get with one post, keep reading for the ending :]