when prepping for welding stipping off the old paint and rust which is better SB or FD or both

 

If your not taking the body down to bare metal all around, I'd just use a flap disc.

 

well I will be when I weld in a patch panel . so would it benefit me to start with FD then sand blast ???

 

I think it would depend on the size of the area you need to work on. A small area can easily be cleaned up using the FD. A large area may be easier and quicker to clean up by blasting. Take care as the use of sand on sheetmetal panels can cause warping and pitting.

 

yes I am aware of the warping and pitting this can cause thanks for your input __________________

 

Just my nickel's worth: A flap disk is fine for general paint prep if no rust or just very light surface rust, but if area where you intend to weld has even slight pitting from rust, then I'd sand blast that area. A flap disk will not get down and remove rust in the pits and rust will contaminate the weld. Primer and paint over minute bits of rust in the pits will not stop rust from growing eventually either out the far side or causing bubbling on painted surface.

Blasting with sand will remove all traces of rust. Blast with milder media like walnut shell or corn cob will not. If you are not going to weld within an hour or two of sandblast cover the area to be welded with weld-through primer.

 

Blasting with granular media will be able to get into inside corners, where a flap disc or wheel will be limited to flatter areas and outside corners.

 

Also, be sure the metal is good and clean, after you media blast, if you go that route. And, don't forget weld thru primer if you are over lapping anything, or will have no access to corrosion protect the back side.