When working with metal, having the right sandpaper is crucial for achieving the desired finish. Sanding metal requires abrasives that are hard enough to remove material without getting clogged up with metal dust and particles. In this article, we will discuss the important factors to consider when choosing sandpaper for metal, provide recommendations for specific grits and types of sandpaper that work best, and give tips for getting the best results when sanding metal surfaces.
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Key Factors for Choosing Sandpaper for Metal
Here are the key factors to keep in mind when selecting sandpaper for use on metal:
- Grit – The grit rating determines the roughness and cutting ability of the abrasive. For metal, start with a coarse grit in the 40 to 80 range to remove scratches and imperfections. Then smooth and polish with finer 120 to 220 grit.
- Backing material – Paper, cloth, and film are common backing types. Paper is lowest cost but tears easier. Cloth is durable for long sanding sessions. Film gives consistent scratch pattern.
- Bond – The bond determines how securely the grit is attached to the backing. Stronger bonds like resin hold up better for heavy sanding but cost more. Weaker glue bonds shed grit faster but are good for light sanding.
- Open vs closed coat – Open coat has more space between the abrasive grains, which helps clear out metal dust and particles. Closed coat gives a smoother scratch pattern.
Sandpaper Grit Guide for Metal
Here are more details on which sandpaper grits work best for specific tasks when working with metal:
40 to 80 Grit
Coarse sandpapers in this range are excellent for removing previous coatings like paint or rust and for leveling out deep scratches and pits in the metal. They aggressively remove material for stripping down to the bare metal. Use coarser grits for major surface repairs and to prep for painting.
100 to 120 Grit
Medium grits prepare metal for finishing work. They smooth out coarse scratches and create a uniform scratch pattern. Use on softer metals like aluminum or to remove file marks on harder metals. Can also be used between coats of primer or paint to roughen and level the surface.
150 to 220 Grit
Fine sandpapers provide a smooth, even finish on metal before polishing or plating. They remove small imperfections and scratch marks left by coarser grits. Use the high end of this range when the metal surface requires minimal smoothing.
240 Grit and Above
Very fine sandpapers polish metal to a satin sheen and prepare it for buffing. Grits from 240 to 600 give a smooth scratch pattern. Use wet/dry sandpaper and plenty of water when sanding at this stage to keep the surface lubricated. Finish with ultra-fine 600 to 2000 grit wet/dry sandpaper.
Best Sandpaper Materials for Metal
The material that the abrasive grit is bonded to also makes a difference for sanding metal. Here are pros and cons of common backing materials:
Aluminum Oxide
– Slightly softer and faster cutting than silicon carbide
– Best for removing heavy oxidation, paint or rust
– Leaves a deeper scratch pattern
– Used for coarse grit sandpapers
– Works on most metals including steel, cast iron, aluminum, and titanium
Silicon Carbide
– Harder and more durable than aluminum oxide
– Used in fine grit sandpapers for smoothing and finishing
– Produces a finer scratch pattern
– Works well on hard metals like stainless steel, titanium, and brass
Garnet
– Composed of natural garnet abrasive grains
– Not as hard as man-made abrasives
– Usually used in woodworking
– Occasionally used for delicate sanding on soft metals like aluminum, copper or brass
Emery Cloth
– Made from natural emery mineral containing corundum
– Slightly softer than aluminum oxide or silicon carbide
– Used for general purpose sanding on ferrous and non-ferrous metals
– Usually comes bonded to canvas or fiber paper backing
Sandpaper Backings
The backing material for sandpaper is also an important factor for metal sanding.
Paper
– Lowest cost backing material
– Less durable than cloth or film
– Tears more easily with coarse grits on hard metals
Cloth
– Cotton or polyester fabric backing
– More flexible than paper for contour sanding
– Lasts much longer than paper, especially with coarse grit
– Good for heavy duty sanding of metal
Film
– Thin paper or plastic film backing
– Very uniform surface gives consistent scratch pattern
-Firm backing works well for flat surfaces
– Resists clogging so good for soft, gummy metals like aluminum
Tips for Effectively Sanding Metal
Follow these tips to get the best results when sanding metal:
- Always sand in the direction of the grain – For example, sand lengthwise on a surface with mill marks.
- Use a sanding block for flat surfaces to ensure even pressure.
- Lubricate the surface with water, oil, or wax when sanding at higher grits to prevent loading.
- Wear eye and ear protection when dry sanding to reduce risk of injury.
- Work through progressively finer grits to remove all deep scratches before polishing.
- Clean the surface thoroughly between sanding grits to remove all dust and debris.
- Change sandpaper often to expose fresh sharp abrasive grains for faster cutting.
- Use a light touch on edges and delicate areas to prevent rounding over or gouging the surface.
Sandpaper Recommendations by Metal Type
Here are more specific sandpaper recommendations for common metal types:
Steel
– Use aluminum oxide or silicon carbide sandpaper
– Coarse grits from 36 to 80 remove rust, paint and scratches
– Medium 100 to 150 grit prepares for painting
– Fine 180 to 220 grit gives smooth finish for bluing
Stainless Steel
– Harder than normal steel so avoid coarser than 120 grit
– Silicon carbide works best from 120 to 600 grit
– Finish with 1200 to 1500 grit wet/dry sandpaper for brushed look
Aluminum
– Softer metal prone to gouging so avoid coarse grits
– Start with 120 or 150 grit to remove oxidation and smooth surface
– Use 220 to 320 grit for satin polished finish
– Can polish to mirror finish with 600 to 1500 grit
Brass
– Medium 180 to 220 grit removes tarnish and old lacquer
– Use 280 to 400 grit to polish and prepare for buffing
– For brushed look sand lengthwise with 120 to 150 grit sandpaper
Copper
– Prime grades 180 to 220 grit give smooth finish
– Final polishing with 320 to 600 grit
– To highlight copper color use 220 to 320 grit
– For muted finish use 400 to 600 grit
Cast Iron
– Start with coarse 60 to 80 grit to remove rust and flaws
– Step down to 120 to 180 grit to smooth surface
– Use 220 grit paper backed with hard block when finishing
Sandpaper Grit Chart for Metal
Here is a quick reference chart summarizing the ideal grit range for various stages of metal sanding:
| Sanding Stage | Ideal Grit Range |
|---|---|
| Removal of rust/coatings | 36 to 80 |
| Smoothing scratches | 80 to 120 |
| General purpose smoothing | 120 to 180 |
| Fine smoothing | 180 to 240 |
| Polishing | 240 and higher |
Conclusion
When selecting sandpaper for metal projects, consider the grit, backing material, and bond type. In general, start with coarse grits in the 40 to 80 range to remove damage and smooth surfaces. Then use progressively finer grits from 120 to 220 or higher for finishing and polishing, depending on the desired look. Backings like heavy cloth and open coat film work best. Ensure the abrasive bonds are rated for metal. Reference this guide to help choose the right sandpaper for your specific metal working needs.
With the proper sandpaper in hand, you can efficiently prepare metal surfaces for painting, powder coating, welding, finishing, polishing and more. Taking the time to smooth metal correctly with quality abrasives will help you achieve professional looking results.