On 12/05/2010 Valve made some changes to TF2's crafting system as follows:
Smelt Primary Weapons:
2 Identical primary weapons
Eg. Force-A-Nature + Force-A-Nature 1 Scrap Metal
Smelt Secondary Weapons:
2 Identical secondary weapons
Eg. Flare gun + Flare gun 1 Scrap Metal
Smelt Melee Weapons:
2 Identical melee weapons
Eg. Übersaw + Übersaw 1 Scrap Metal
Smelt Class Weapons
Any 2 weapons wielded by the same class
Eg. Ambassador + Dead Ringer (Spy Weapons) 1 Scrap Metal
Smelt Tokens
3 Tokens
Eg. Heavy Token + Demoman Token + Melee Token 1 Reclaimed Metal
Combine Scrap Metal = 1 Reclaimed Metal
3 Scrap Metal
Combine Reclaimed Metal = 1 Refined Metal
3 Reclaimed Metal
Smelt Refined Metal = 3 Reclaimed Metal
1 Refined Metal
Smelt Reclaimed Metal = 3 Scrap Metal
1 Reclaimed Metal
Source:
http://tf2wiki.net/wiki/Crafting
As you can see you only require two weapons from the same class or slot to create one scrap metal, also you can now smelt Refined and Reclaimed metal back into it's previous metals. This means with the new cost of scrap metal hats cost much less:
Random Headgear:
2 headgear or 54 weapons = 27 Scrap Metal = 9 Reclaimed Metal = 3 Refined Metal
= 27 weapons
Class-specific Headgear
75 weapons = (36 Scrap metal = 12 Reclaimed Metal = 4 Refined Metal) + 3 weapons (1 Class Token)
Also with these new changes came new weapon blueprints, with these blueprints certain items are now much easier to acquire i.e Crit-A-Cola = KritzKreig + Bonk! Atomic Punch:
Fabricate Class Weapon:
1 Class Token + 1 Slot Token + 1 Scrap Metal
Eg. Medic Token + Secondary Token + Scrap Metal 1 Class Specific Weapon
Eg. Kritzkrieg
Fabricate Crit-A-Cola = 1 Crit-A-Cola
1 Kritzkrieg + 1 Bonk! Atomic Punch
Fabricate Dalokohs Bar = 1 Dalokohs Bar
1 Sandvich + 1 Bonk! Atomic Punch
Fabricate Gunboats = 1 Gunboats
1 Chargin' Targe + 1 Razorback
Fabricate Homewrecker = 1 Homewrecker
1 Eyelander + 1 Equalizer
Fabricate Pain Train = 1 Pain Train
1 Sandman + 1 Scrap Metal
Source:
http://tf2wiki.net/wiki/Crafting