Your father says TAKE IT OFF, then take it off.
If you want them back on, you can move out, and live in YOUR OWN home. You are 18, and if you live in the USA, you should have saved enough money, finished HS, and able to find work, and live on your own.
This is HIS HOUSE, and you either SHAPE UP or ship out! Is there someway, you can soften him up?
My father what he says, goes! No, he wouldn't let me have that, but there's a lot I have to fight for that belongs to me, my hair for instance. He wants it short, I want it long, but it is MY HAIR! I brought in good grades, and it wasn't affecting my grades, plus the Blessed Virgin Mary had long hair, etc. Or wearing mini-skirts, and I did anyway, since I made THEM, and bought them with my own money. He knew, I needed clothes for school, and I made enough for the whole school year. Sometimes, he needs to come into his senses.
When my BF gave me a dog to bring home, as my pet, he wouldn't allow it. I didn't understand why, since we have dogs, chickens, pigs back home in Asia, but, I didn't know about being a responsible dog-owner. It made me sad for awhile, "if he goes, then, I go', but I came to my senses! So, we kept it (my BF - kept him). My dad, dog-sit him, during our honeymoon, and he didn't complain about that, but he got used to him.
Once you become a parent, YOU'LL NEVER understand where his mind & common sense is, but your dad wants it gone, and he's very upset. You need to come into sense, too, that until you become a parent will you really know WHY. Because he loves you, and protect you, and care about YOU.