I'm reading about Trade and nowhere does it mention blueprints. Is it by purpose to simplify, by knowing the trade you know all that you need to fabricate an object of the trade? Or is it a blunder?

In a world where tecnology is mystic and a sacred secret it seems plausible that no one makes anything remotly technical without manual, technical description and blueprints.

In the same time it states in IH that Trade (Armourer) is " ..One of the most commonly used Skills and potentally most useful in everyday application, Trade (Armourer) grants you unparalelled creativity in costomising your kit."

Somehow I sense that the author did not envision the acolyte bogged down by finding enviously guarded blueprints from high security data-crypt on forge worlds.

So, how do you do it in your game?

Bear in mind that one 'feature' of Imperial technology is that it all integrates together really well. The whole point of STC technology is that pretty much any pattern of lasgun (for example) will accept any pattern of gunsight or power cell.

Trade (Armourer) wouldn't let you build a gunsight or shot selector from scratch, but it would let you strip down a kantrael pattern lasgun into its component parts (like you would to clean a rifle) and then (because it's all STC) you can slot in a triplex-pattern focussing array instead before building it back up.

Obviously you'll have to get the triplex bits from somewhere, but once you're done, you've got a lasgun with a power selector switch on the side.

What you are refering to is modifying which is, in my opinion, coverd by the rules. It states that if you wish to install a weapon uppgrade you make a trade (Armourer) test.

What I'm intressted in is how to create for exampel weapons. In the rules it states that you can creat, modify and repair wepons, but not how, more then that you need parts and the skill.

This was expanded upon in the Inquisitors Handbook, which also gives some examples.

Personally I think this part of the system is a mess, and have tried to categorize and structure these and related skills in my House Rules (Appendix A).

I run Rogue Trader, but with an Explorator and and Arch-Heretek Rogue Trader this has come up multiple times. I assume that if you have Tech-Use you can read a schematic and put components together. This allows you to use an STC schematic to build MOST things (Very Rare or lower for Rogue Trader), but at a cost one step below the final item. This represents buying the various components and assembling and tuning it yourself. If you have the Trade Skill, then you can assemble simple items (Scarce or lower availability) that you would reasonably know how to make without a schematic. Anything more complex or rare requires you have the STC. If you use Trade, however, you pay a cost two steps lower. This represents buying more basic parts and modifying/adapting them as you craft the item. For time and skill checks, I use the rules from Inquisitor's Handbook with some minor modifications.