Firms that manufacture and/or finish large amounts of moldings have dedicated machines for sanding them. These machines often use replaceable sanding heads, each one shaped to match the profile being run. For the rest of us who need to finish automotive trim, wood moldings or fiberglass profiles, a dedicated sanding machine isn’t practical, so we need to find other solutions. The trick is to find a method that allows you to reach into the low spots of a profile without removing the details along the high spots.
If your profile is relatively simple and shallow, a good Soft Interface Pad may be all you need, but most profiles will need a more innovative solution. Fortunately, this 2Sand.com blog has offered up a number of ideas over the years. We showed an old carpenter’s trick of using a deck of cards shaped to a small profile and then clamped together with sandpaper along the edge. The cards can be reset to many different profiles. We have also explained how foam can be shaped as a custom sanding pad. We’ve even examined how body putty can be used to create a custom sanding profile.
The cards, foam, and body putty tricks are all well-suited to hand sanding. But if you have a larger batch of moldings to finish, hand work may be too slow. The foam and putty methods can be adapted to power sanding, but only with an inline stroke sander, so the sanding action only follows the line of the profile; orbital sanders just won’t work.
The one thing that all these methods require is a sanding material that can conform to the contours of the profile and still hold up in use. Cloth-backed abrasive products very durable but don't flex nearly well enough for this type of profile sanding. Paper as a backer is more flexible and will serve in many cases, but for really sharp details, nothing beats a film backed sanding product. Film is not as common a backer, but it is very flexible, resists tearing and is also generally waterproof. Many wet/dry sandpaper products are film backed. Film backers, coupled with a bit of creativity in making a profile sanding block, allow those working in metal, plastics or fiberglass to properly work whatever profiles they may need to. And the film works well with wet sanding, which can be critical to achieving the proper finish.
Choosing the best sanding supplies for your will always serve you well, and being able to take advantage of film backed sanding discs and papers is only going to make your work better.