There is a bug report of the rack and tub not passing the quality on atm. So it may just be that and needs fixing. It appears there a few buildings with this problem atm. smelting 100q ore in my bloomery with a 100q crucible and tongs and 100 smelting I only get 95q bars. Doubt that 5% difference is a coincidence as its the exact amount the bloomery is meant to ADD to the quality result. so seems like a bug.
In regards to all this talk of the quality of a building mattering. I have a theory that you are all being a bit misled by what is meant by "quality" when refering to a building. This in part is coming from bobik being Russian and I believe that idea was a bit lost in translation. Most of these ideas about building quality mattering seem to come from his FAQ response about Quality affecting everything, and another which was more in regards to wall quality.
I think the Wiki by arrakis shows more how building quality works. Its not really the quality of the building as a result of its building materials, so much as it is the "technological quality". That's my theory about bobik is refering to, but he just lumped it all into a statement about quality affecting everything.
so for example. Blacksmiths shop > forge and anvil. In terms of "technological quality" influencing produced good.
Tools appear as a separate influence in creation, same with skill level.
check out the iron bar on the wiki and you get a feel for how I believe the quality calculation is really working.
http://lifeisfeudal.gamepedia.com/Iron_baryou notice the building is 5% influence, tools 5% and skill adding 20%.
now the wiki is far from complete (haven't done leather influences yet), and we have changed these influences a few times already.
This whole concept will be this Sunday's tests for me