4.4: Sanding and Finishing

4.4 Sanding and Finishing

Sanding is not simply the last thing you do before applying finish.

It is the final stage of shaping and surface preparation.

Good sanding preserves the form you worked to create. Poor sanding can flatten curves, round over details unintentionally, or leave scratches that become more visible after finish is applied.

Learning Outcomes

After completing this section, you should be able to:

• Select an appropriate sanding sequence.
• Sand faces, edges, and interior curves without changing the intended shape.
• Recognize when scratches from a previous grit remain.
• Prepare the cutting board through 320 grit.
• Apply a food-safe oil finish.

Sanding Does Not Fix Poor Shaping

Before beginning fine sanding, the overall form should already be correct.

Use cutting and shaping tools to establish:

• curves;
• transitions;
• edges; and
• the handle opening.

Use sandpaper to refine the surface, not to redesign the project.

Work Through the Grits

Abrasives are identified by grit number.

Lower grit numbers are coarser and remove material more quickly.

Higher grit numbers are finer and remove smaller scratches.

Your exact starting grit depends on the condition of the surface.

A possible progression might include:

80 → 100 → 120 → 150 → 180 → 220 → 320

You may not need every grit in every situation.

What matters is that each grit removes the scratches left by the previous one.

The finished cutting board must be sanded through 320 grit.

Do Not Skip Too Far

Moving from a very coarse abrasive directly to a very fine abrasive can leave deep scratches behind.

The fine abrasive may polish the surface without removing them.

When finish is applied, those scratches may become much easier to see.

Before moving to the next grit:

1. Inspect the surface under good light.
2. Look across the grain as well as with it.
3. Feel the surface.
4. Make sure the scratches from the previous grit are gone.

Sand With the Grain

For final hand sanding on a face, sand in the direction of the grain.

Cross-grain scratches are especially visible after finish is applied.

Curves and interior openings may require different hand motions, but the final surface should be free of obvious scratches.

Preserve the Shape

Be careful around:

• outside curves;
• transitions;
• the handle;
• thin areas; and
• corners.

Do not allow sanding to flatten a flowing curve or make one side noticeably different from the other unless that difference is intentional.

Break Sharp Edges

A perfectly sharp machined edge is uncomfortable to handle and easily damaged.

Lightly soften exposed edges.

The goal is generally not to create a large roundover unless your design calls for one. A few controlled passes with fine abrasive may be enough to make the edge comfortable.

Inspect Before Finishing

Finish makes many surface defects more visible.

Before applying oil:

• remove sanding dust;
• inspect both faces;
• inspect the entire perimeter;
• check the handle opening;
• look for scratches;
• feel for rough areas; and
• make sure you are satisfied with the form.

Do not apply finish simply because you are tired of sanding.

Food-Safe Oil Finish

The cutting board is finished with an oil appropriate for food-contact use.

Mineral oil is one suitable option for this project.

Your instructor will provide the finish used in class and demonstrate the application process.

In general:

1. Make sure the surface is clean and free of sanding dust.
2. Apply the oil evenly to the faces, edges, and interior opening.
3. Allow the wood to absorb the finish.
4. Remove excess finish as directed.
5. Apply additional coats when appropriate.

Oil will deepen the color of the wood and make the grain and figure more visible.

A Cutting Board Will Be Used

A cutting board is a functional object.

It may eventually develop:

• knife marks;
• stains;
• dents;
• and other evidence of use.

That is normal.

The goal of the project is not to create an object too precious to use. The goal is to make a well-designed, carefully crafted object that works.

Project Complete

Before considering the project finished, confirm that:

• the board is made from one piece of hardwood;
• the dimensions meet the project requirements;
• the handle opening is complete;
• the form is intentional and comfortable;
• all surfaces are sanded through 320 grit;
• the board is clean and free of visible sanding scratches; and
• the food-safe oil finish has been applied properly.

Then use it.

Check Yourself

1. Why should the final form be established before fine sanding begins?
2. What should each abrasive grit remove?
3. Why are cross-grain scratches a problem?
4. Why should sharp edges be softened slightly?
5. What should you inspect before applying finish?
6. What is one appropriate finish for this project?