Here is a list of quotes that will allow each person to come to his own conclusion and in the future be one of helping things in creating your own Chapters. I tried to put them in a chronological order as much as possible.
I have not quoted every single SM Codex because what is written in IA: Techmarines is just repeated time and time again with slight variation from C:SM 4th edition onwards.
Every Chapter sends a proportion of its young warriors to Mars where they are trained by the Tech-Priests of the Adeptus Mechanicus. If they prove able and studious they are inducted into the rites of the Machine Mysteries, the secret and mystical umon of man and machine, the details of which remain the most sacred mystery of the Tech-Priests. Once he has undergone his initiation the Space Marine is no longer wholly a Space Marine, he has become a Tech-Priest and a devotee of the Cuit of the Machine God. This strange duality of loyalties means that Techmarines always stand apart from other Space Marines. They are priests of the Machine God, skilled in the arcane sciences, and pertinent to the dark secrets of technology. When a Techmarine returns to his Chapter he joins his fellow Techmarines, the Chapter's corps of technicians and builders, mechanics and inventors. To their fellow Space Marines they are mysterious figures possessing disturbing skills and obscure knowledge. To undertake the manual labour of maintenance and construction, the Techmarines create cyborg Servitors, weird machine men with limbs of metal and hands formed into heavy tools.
The Iron Priest are Masters of the forge and armoury, their expertise is with technical matters and their role is akin to that of Techmarines in other Chapters. Like Techmarines they spend several years with the Tech Priests of the Adeptus Mechanicus on Mars where they learn the innermost secrets of archane mechanics. Without them to maintain the Chapter its spacecraft would soon become unspaceworthy, the Fang would crumble and the Chapter itself would die.
Iron Priest look after the many technical systems in the Fang, supervising engineering projects, building, spacecraft construction and maintenance and all the myriad of complex technical tasks that are undertaken every single day.
Whether built in the Martian weapon-forges of the Adeptus Mechanicus or the fortress monasteries of the Space Marines,...
Most Space Marine Chapters have the facilities to construct their own armoured vehicles. These Chapters maintain a large forge in which its serfs, overseen by its Techmarines, produce all the ammunition, equipment and supplies requiered by the Chapter to fulfil its obligations and objectives.
The forge will produce large numbers of Rhino chassis, a small number of which will be earmarked to provide basis for Predators, Whirlwinds and other variant patterns.
Ancient pacts sworn between the Adeptus Mechanicus and the Adeptus Astartes allow the Space Marines to send a proportion of their warriors to Mars to train with the Adeptus Mechanicus…
Within their Chapter, Techmarines are arcane engineers, maintaining and ministering to the needs of the Chapter's arms, armour and vehicles. Each Chapter has its own weapon shops, foundries and artisans. Some Chapters honour long-standing agreements with forge worlds that supply them with starships and weapons which the Techmarines subsequently modify to meet their own requirements. This practice varies from Chapter to Chapter, but few Space Marine Chapters have the facilities to build their own spacecraft, most being constructed in the shipyards of Jupiter and Mars. A notable exception to this are the Ultramarines, who maintain extensive construction yards in orbit around Calth, one of the planets within their realm of Ultramar.
The Hunter class destroyer, although based on a design long available to almost all Space Marine chapters, was pioneered primarily by the Dark Angels, whose deep distrust of other factions within the Imperial hierarchy made acquisition of vessels from shipyards and forgeworlds far more problematic than for most other chapters. As such, the Dark Angels chose the Hunter class destroyer as the most viable counterpart to the Imperial Navy’s cobra and maintain large flotillas of the vessel in all their battlefleets.
...meaning that Crusading Chapters seldom, if ever, seek the aid of other arms of the Imperium...
...Crusading Chapters often make use of equipment unique to them, designed to fulfil many of the roles which other Chapters would leave to the likes oft he Imperial Navy, the Imperial Guard or the Titan Legions.
CONSTRUCTION OF SPACE MARINE VEHICLES
Construction of most Space Marine vehicles takes place in the Chapter's forges. Each Space Marine Chapter has its own base, usually referred to as a Fortress-Monastery. Heavly defended within the Fortress-Monastery are the Chapter's Apothecarion, Chapels and Armoury.
Each Chapter has an officer responsibile for supplying the armouries with vehicles and munitions. 'Master of the Forge' is a high ranking and honourabble position amongst the Chapter Master's headquarters staff. The Master of the Forge reports directly to the Chapter master. Under the Master of the Forge are all the CHapter's Techmarines, Servitors, Techno-mats and the forge's slave workers.
The Techmarines oversee the construction of new vehicle chassis'. Although each Chapter has its own traditions and rituals of contruction they follow a broadly similar pattern. Manned by Servitors, Techno-mats and slaves, the CHapter forges manufacture the required components and assemble them. The complete chassis – be it Rhino, Land Raider, Land Speeder etc, is then blessed and omen are forecast and read. Interpreting the omens indicates what type of vehicle the Machine Spirit within is, so a Rhino chassis may then be earmarked to become a Predator Annihilator, Razorback or Vindicator. The vehicle is then returned to the forges to be completed. The additional equipment required is fitted before the ceremonies of naming and awakening are performed. The naming ceremony gives each individual vehicle its unique name, examples include the Salamanders' Rhino 'Nocturne's Hammer', or the Iron Hands Land Raider 'Cestus' and 'Metallus Gravus'. Some Chapters proudly display this name, others prefer to keep it secret.
The ceremony of the awakening is the initiation of the Machine Spirit of the vehicle into the Chapter. The Machine Spirit within is awoken from its slumber. Once this ceremony is complete the vehicle has been passed fit for service and is handed to the armouries for storage until required. The Master of the Forge will allocate new vehicles to the fighting companies in need replacements, or sotre them as parts of the Chapter's central pool of heavy armour.
Not all Chapters have the facility to make every vehicle they require. For instance, the largest vehicles, such as Thunderhawk gunships, require vas manpower to construct. Some Space Marine Chapters have ties to local forge worlds. The Adeptus Mechanicus and Space Marines have sworn mutual oaths of service to the Imperium and ancient charters exist which require forge worlds to supply Space Marine Chapters where needed. In these cases, the vehicle will be constructed to order, and can only be supplied to the specific Chapter. Strict monitoring ensures than these vehicles do not fall into less trustworthy hands. Once complete, the new vehicle is delivered to the Chapter's Fortress-Monaster.
The strict security around such arrangements is required because Space Marines vehicles are amongst the most advanced technology available to the Imperium. Many of the systems within are secret, and help to give the Space Marines an edge in battle. They cannot be allowed to fall in the hands of rebels or spies who might turn them against the Imperium.
Most Chapters have ties to local forge worlds, who are responsible for training the Chapter's Techmarines. The Adeptus Mechanicus hold no power over the independent Space Marine Chapters, but souls of their machines and vehicles must be correctly tended; this is the Techmarine's task. Each serves an apprenticeship on a forge world as part of their training, some even travel to Mars to learn from the master Tech-magi. They are initiated into the ancient lore of machines and technology before returning to the Fortress-Monastery.
ADEPTUS ASTARTES CHAPTER FORGES
Separate from the entire Departmento Munitorum system of production and supply are the Adeptus Astartes Space Marine Chapters. Each Space Marine Chapter is an independent, self-sufficient force, which provides its own fighting forces and weapons of war from the Chapter forges. For the most part, these are constructed by Techmarines and servitors under the watchful eye of the Chapter's 'Master of the Forges', but for some Chapters, the larges vehicles must come from the Adeptus Mechanicus.
Some Forge Worlds, bound to supply Space Marine Chapters by ancient charters and mutual oath of service to the Imperium, do manufacture Rhinos, Land Raiders and Thunderhawk gunships, but each vehicle can only be supplied to the specific Chapter it is meant for and strict monitorin ensures they do not fall into the wrong hands. Space Marine vehicles, unlike the mass-produced behicles of the Imperial Guard, contain much classified technology and complex internal systems, making them the foremost weapons of war in the Imperium. They cannot be allowed to fall into the wrong hands.
Most Techmarines are trained by the Adeptus Mechanicus and serve an apprenticeship on a Forge World, learning the ancient lores of machines, before returning to the Chapter. They become responsible for servicing the Machine-Spirit of the Chapter's vehicles and keeping the Chapter armouries stocked with all the weapons the fighting companies will need, from bolter shells to drop pods and Thunderhawk gunships.
Many Chapter forges have the ability to manufacture the STC Codex vehicles, Rhinos, Land Raiders, and Predators. Being descendants of STC technology, these vehicles often use the same standardised parts. The Chapter forges are also capable of making one-off vehicles for special operations or environments, such as siege equipment. This is a prospect that would appal any Tech-Priest, but the Adeptus Mechanicus have no power to intervene or dictate what happens within the walls of a Chapter fortress-monastery.
Space Marines are organised into independent armies, called Chapters, of which there are roughly one thousand spread throughout the galaxy. Each Chapter has its own ships, its own heraldic uniforms and its own distinct identity and traditions. Unlike other military formations within the Imperium, a Space Marine Chapter is entirely self-sufficient, with its own forges, warships and support facilities.
Newer stuff contradics some of the old stuff but such is life. There is also one bit of information that I was not able to track down, it hails from the days of the Rogue Trader and it is that Techmarines study on Mars for 30 years, that bit of information hasn't been reprinted since then and I can't find where I read it but I distinctly remember it was 30 years because when I read it I was 10 and went like "wow that is a long time to go to school".
Have fun and use this knowledge well.