Dear Ronald,
If I understand you correctly, you want to base your shipping costs only onthe weight of all products except those from cat1. The shipping cost is a fixed cost, independent from the quantity of articles or the categories (except cat1)? What if produts from cat1 are ordered? Do you not want to provide shipping at all in this case, or does is simply not influence the shipping cost, i.e. is the shipping the same whether a product from cat1 is in the cart or not? In the following, I'm using the second case (cat1 products are simply free to ship).
In this case, I would use a rule set like the following (defining a custom variable for convenience), where 42 is the ID of your cat1 (change it to your actual category ID of cat1):
Variable=AmountExCat1; Value = Amount - evaluate_for_categories(Amount, 42)
Name=Shipping under 50; AmountExCat1 < 50; Shipping=7.50
Name=Free shipping above 50; AmountExCat1 >=50; Shipping=0
The logic is as follows: As you shipping depends only on the total amount of all products minus the amount of products from cat1, we first calculate this and store it in separate variable for convenience.
In the following rules, you can then use this custom variable "AmountExCat1" just like any other variable. In these rules, you don't need any category checks any more, because the only place where the category is important is in the definition of AmountExCat1...
Best regards,
Reinhold
