I have the Agglomeration Plate, set to recieve more than enough mana over time, it consumes the 3 items to make the Terrasteel ingot but dosent produce the ingot itself. My setup is shown below

https://puu.sh/sgcqr/4616852f31.png

That single mana spreader is not going to be able to give the plate enough mana before the items on it despawn.

Flip through the manual, it says to use Sparks.

Ok, guess i'll have to work out how to use spark then

For the Terrestrial Agglomeration Plate (and the Mana Enchanter), it's as simple as putting a spark on the plate and another spark on a nearby mana pool(s).