Dose anyone know what kinds of funerary rights the mechanicus would have, especially the Mechanicus of the Lathes?

Would they scorn any kind of funerary rights for their sentimentality and strip the body for anything recyclable or entomb fellow priests with all their true flesh intact? Would they hook the minds up to some odd cogitation machine that dose nothing but beep as a way (if only symbolic) of being closer to the omnisiah now that they no longer are confined by the flesh or pass their true flesh on to a new younger tech-priest as an odd kind of reincarnation of sorts?

The novel Crossfire has the skulls of particularly revered servants of the Omnissiah converted into a special type of servo-skulls (lumiants), allowing their service to extend beyond organic death. An exceptional privilage, especially given the multiple tasks they can perform and their potency when forced into combat. This is hardly new information, being turned into a servo skulls after death being a common reward for the favoured of the Machine Cult.

The common forge worker gets nothing besides reduction into nutrient paste, I'd imagine. Perhaps their passing would be recorded, but with the teeming billions of men and women on a forge world it would take too much time to have some form of ceremony for each one. Perhaps there would be some short ceremony when however many thousand corpses are placed into the machine that will break their organic forms down and make use of the materials (the Mechanicus equivalent of a mass grave?). As for the less than exceptional tech-priest, I can not say what would happen when they pass on.

I do not have any source-based knowledge, but expect (as already mentioned) any "furnery rite" of the Mechanicus to involve "processing".

Skull turned into Servoskull
Remain used for buildung of Servitor
Used as "spare parts" for other constructs
Bionics salvaged for later use in other Tech-Priests.

Those "minors" who have no/not much bionics are simply turned into servitor, servitor parts or food...

I've not got any source based stuff, but my guess would be:

Menials would have their Augmetics taken from them for re-use. Their body would be ground into Nutri-paste or something, anything of worth would be extracted for re-use. So a skull, a brain possibly...

Higher ups may be entomed or something. There's pictures in the corebooks of beings attached to walls with cables and mechandrites etc, I'd imagine they'd be programmed as guards, or simply statues that spout (de)motivating quotes.

Ie; walking past a forge one of the statues would log your passing and feebly croak;
"Repent today, for tomorrow you may be dead!"

Servitorisation is considered to be a punishment for Tech Adepts, usually such practices are either done to hereteks or the most lowly and unimportant menials when, for some reason vat-grown organic parts are unavailable...

i figure they do like in CA with the large data tombs they store the MIU's data inside a cogitator to be "one with the machine" their parts are used again unless they are corrupt and the biological parts are probably used by magos biologi for study

If I remember correctly, in one of the IG novels (which I won't name to avoid spoilers but you'll probably get it anyways), three senior AdMecs find a Magos that was trapped on an Ork infested planet for some 35 years and even with all of his fleshy parts reduced to nothing, his mind still existed inside a small HD like device that they pulled from his head and booted him up through one of their own to talk to him.

The way I take it, if they reach such high levels (i.e. the rank of Magos) maybe their minds can be perserved that way so that they can continue their services in the name of the Omnissah and anyone below that would either:

1. just be recycled for their parts

2. Turned into a Servitor (if they were bad in life)

3. Gain virtual immortality in the way I described above should they have died within easy reach of their fellow Tech-Priest and are lavished with the honor of such.

Thanks so far, guys!

So far, it's about what i expected it to be though i was hopping there was a bit of something somewhere that would make my eyelids flap.

Another question to add to the first, though. What is the mechanicus' view on the afterlife? Do they have one or are they strictly materialists? They believe in machine spirits, dose this translate to the souls of Tech-Priests as well and, if so, what becomes of those souls upon death? And what of machine spirits, what happens to a machine spirit upon the destruction of the machine?

Another question to add to the first, though. What is the mechanicus' view on the afterlife? Do they have one or are they strictly materialists? They believe in machine spirits, dose this translate to the souls of Tech-Priests as well and, if so, what becomes of those souls upon death?

That's probably dependant on the techpriest and his specific sect in question - just as the Ministorum, the AdMech isn't too unified in matters of faith beyond the very central ones. Some might believe in nothing happening after death, some in reincarnation into machine spirits and some in unification with the Omnissiah.

And what of machine spirits, what happens to a machine spirit upon the destruction of the machine?

If last rites are administered properly, it reunites with the Omnissiah.