A Simple Jig for Straight Brush Marks on an Aluminum Sample

A straight brushed finish becomes difficult to repeat when every stroke starts in a different place or curls at the end. A simple bench guide can make those movements easier to control. Use the guide to establish direction and travel; use a cleaned sample to judge the finish. The guide cannot make an unsuitable abrasive produce the texture you want.

Start with a flat, bare, nonstructural aluminum offcut. This is a sample-making method, not permission to sand a mast, spar, aircraft component, or anodized part. Work on an actual structural component requires its manufacturer's applicable maintenance instructions.

Give the stroke somewhere to start and finish

Choose an offcut longer than the area whose appearance you want to compare. Mark an inspection window on tape beside the sample, leaving generous unused length at both ends. Those ends are the run-in and run-out areas: the block settles before entering the window and leaves it before you lift.

For example, a 400 mm-long offcut could have a central 200 mm inspection window. A block with a 70 mm contact length can remain fully supported in each 100 mm end area. These are layout dimensions for a practice setup, not a required stroke length or a recipe for a particular surface roughness.

Secure the sample flat to a stable base, keeping clamps outside the block's path. Clamp a smooth, straight fence alongside it so the side of the block can register against the fence without the fence touching the abrasive face. Check that the block slides freely and does not rock or lift. Recess or move any hardware that could touch the paper or sample.

Put a reference mark on top of the block and mark its start and finish positions beside the fence. Rehearse the movement with no abrasive contact. The marks should place the whole block on the sample at the start and end, with its contact face completely outside the inspection window. Use visible marks rather than a hard stop that encourages you to bang the block into place.

Choose the texture on a spare area

Fit a fresh piece of abrasive tightly to a flat block. Start with the sample's intended finishing grade, not a coarse grit chosen merely to make lines visible. If you have an accepted finish sample, compare against it under the same light.

For a small trial of a 320-grit sheet texture, eQualle 320-grit sheets in a 10-pack can be cut to fit the block. The same 10-sheet option supplies replacements for repeated practice. Choosing 320 here defines one trial; it does not establish a standard “brushed aluminum” finish.

Sheet abrasive and a nonwoven finishing pad can produce different appearances. Norton lists nonwoven abrasives for decorative and satin metal finishing, including aluminum. If the target was made with a pad, test that abrasive construction rather than assuming a paper grit number will match it.

For wet practice, use waterproof paper, a water-tolerant bare sample and base, and a tray to collect residue. Keep the wet or dry method the same throughout the comparison. Clean the paper and sample when residue obscures the contact or inspection; replace damaged or persistently loaded paper.

Make one repeatable lane first

Lower the block flat in the start area. Move forward alongside the fence in one steady stroke, maintaining light contact without pressing sideways into the guide. Pass fully through the inspection window, reach the finish mark, then lift. Return above the surface so the return movement cannot add a second pattern.

Repeat only long enough to establish a readable pattern, then clean and dry the sample. Inspect from more than one light direction. Straight marks through the window, without curved ends or conspicuous start bands, indicate that the travel is behaving as intended. They do not measure scratch depth or material removal.

If you see hooks, check where you lifted and whether your wrist turned while the abrasive was still in contact. If one end looks different, move the inspection window farther from the settling or lifting area and repeat on fresh scrap. A single deep line calls for inspecting the abrasive, block and surface for debris before another stroke.

Extend the setup without losing the reference

For a wider sample, move the fence to a marked parallel position after completing a lane. Set the spacing slightly smaller than the abrasive's working width so lanes overlap, and record that spacing. Keep the same stroke boundaries for every lane.

Inspect the overlaps as well as the middle of each lane. A visible stripe may need a different overlap or more even contact. Change one of those variables on another practice sample instead of rubbing locally at the stripe. Local correction can introduce a different direction or texture into the field you are trying to make consistent.

Keep the accepted sample with its abrasive identity, block size, fence spacing, start/end marks and wet/dry method. That gives the next operator an appearance to match and a setup they can reconstruct.

Short aluminum scratch-refinement tip