I want to combine shipping "only" for items under 40 lbs.

On my OC site, my 40 Lb bags of feed are screwing us on shipping. If the person orders something else with a 40 Lb bag, 99% of the time it has to go into a seperate box. The website just adds the weights together and charges a single box rate. I need to set it up so that the 40 Lb bags of feed can't be combined with other items on the shipping total. Does anyone have any suggestions on how I would go about this? I would appreciate any help.

Take a peek via Extensions button top right at shipping extensions. One of the seasoned extension authors will likely putter by within a few hours and see your plight, too.

If you're using UPS, I believe Qphoria's UPS Deluxe extension can do this.

Beautiful. I think I will check out the UPS Deluxe. Thank you both.