You HAVE to make sure the bridge is lined up or rotated with the opening on the cart.
I am not sure how familiar you are with the 510, but you do not have to line up the cart with the atty on any that I have had to prevent melting. I have used a dozen different attys with 30+ carts and never had this problem until I received this one atty that was just a tad out of spec. I just trashed the one I had and never looked back.