Sanding with a Flap Wheel Head

Jacob Malherbe of supplies a brief explanation of how flap-wheel sander heads work, with tips on getting the best from your machine. May 4, 2010

By Jacob Malherbe of

Imagine you have taken a great deal of time and care to create an intricate profile for a special project, either by hand, manual router, CNC machine or molder. The next step is sanding this profile without destroying the detail.

I know of only one tool that works well - the flap wheel head. Flap wheel heads are designed to be flexible, conforming to the shape being sanded. This has the unique benefit of requiring very few changes in machine or head settings to accommodate different profiles.

Raw Wood Sanding
1) Flap wheel sanding de-nibs the small fibers that pop up when sanded with any other tool, or when a chemical or water is applied to the material. These fibers, if not removed, set in a dried position, causing a rough primer or stain and seal coat, and requiring additional sanding between coats to achieve a smooth topcoat. Use of a flap wheel head results in much less sanding time between coats. In some cases, less finish material is required because there is less fiber to cover.

2) Flap wheel heads ensure uniform pore openings in the material, resulting in uniform color across the surface.

3) Sharp edges are slightly softened, so that stain, sealer, or paint adheres to corners better. This radius eliminates the weak area in a finish. It also makes sealer or primer sanding much easier, because you are less likely to sand through the finish in these areas.

Sealer or Primer Sanding
1) A more thorough and uniform scuff of the sealer or primer coat is achieved, ensuring a superior bond between seal or primer coat and topcoat.

2) If the material was properly sanded in the raw, flap wheel sanding the sealer or primer coat does not burn through or white-line the product.

3) A more uniform and overall higher quality finish is achieved.

Finally, what's the biggest benefit in raw and sealer or primer sanding? You increase quality while decreasing labor!

Setting up a Flap Wheel Head after the Molder

If you start with sharp, well-balanced tooling; never overdrive feed speeds; and produce a clean molding cut, flap wheel sanding will finish sand your product to the point of applying stain or primer. Good tooling is critical because a flap wheel head only removes a small amount of material, so a limited amount of tooling marks is removed.

The alternative to a flap wheel head for sanding moldings is a shaped wheel (similar to a grinding wheel) that matches the profile of your product. A shaped wheel can remove a fair amount of material along with tooling marks, but will not de-nib your surface or balance color. In addition, you need a head to match each profile you create.

With a flap wheel head, which flexes and conforms to your profile, your end result will be a better finish that requires less sanding between coats and less chemicals.

Building a flap wheel head attachment on the out-feed end of the molder is a good option for some. Easy availability of inexpensive motors and controllers helps make this viable.

In most cases, mounting a motor or two with heads on the out-feed end of a molder is not difficult to do. Make sure the heads can be adjusted up and down to accommodate materials of different thickness. The ability to tilt the head can also be useful when running a profile that is considerably thicker along one edge than the other.

Keep in mind that more heads are needed as feed rates increase. It will take approximately two heads for up to 20-foot-per-minute feed rates. Using four heads will get you up to approximately 60- to 70-foot-per-minute feed rates and still give good quality sanding. Also, make sure the heads are counter rotating. Counter rotation ensures that one direction of spin will lift the fibers while the other direction removes the fibers.

By Jacob Malherbe of