I have a cement mixer that I want to convert to a fur tumbler. In Guessing I should take out the paddles. Should I make smaller ones or will the fur and saw dust be fine with it just spinning?

Save the mixer for waxed dirt, get an old dryer for a tumbler.

X2

I use an old dryer too and they do a good job.
But to answer your question, I'd remove the paddles and just let them tumble in the media.

I know I'm late to the party but agree with an old dryer. I was able to get a free old propane one that runs on 110v so I just unplugged the blower & use the tumbler part. I use some small animal bedding pellets for my media. It's about $7 from tractor supply for a 40lb bag. It lasts a long time & imo it also helps to take out any moisture in the fur.