Parts, materials and finishes
Remove milling marks without going to the polisher
A small machined part comes out with tool marks. Polishing is not always necessary: sometimes a uniform surface is enough. For that, microblasting is the quickest option there is.
You take a part out of the machine and it is right: dimensions, geometry and function. Yet the tool marks show. The passes, the change of direction, the point where the cutter entered.
Many people then take the long route — sanding, polishing, ever-finer finishing passes — when the real goal is often not shine.
The goal is uniformity.
That distinction saves hours. A homogeneous matte surface reads as finished. A shiny surface with a mark across it does not. The eye does not seek shine: it seeks continuity.
Why microblasting rather than something else
Abrasive blasting does not remove significant material: it evens the surface. Pressurised particles impact it and leave a homogeneous texture that removes the difference between areas the cutter left well and those it left less well.
For small parts it has three advantages over sanding or polishing:
- It reaches where a hand cannot. Corners, recesses, internal radii, the bottom of a pocket. Sandpaper cannot get there; abrasive can.
- It does not round edges if pressure and distance are controlled. Hand-sanding a small part almost always wears away the edges.
- It is extremely fast. Seconds per face, not minutes.
For parts measuring 50 × 50 × 10 mm, a large cabinet is unnecessary. A microblasting pencil with its own reservoir is enough, takes up little space and uses little air.
Two abrasives, two different results
Corundum (aluminium oxide). Angular and cutting. It leaves a matte surface with bite and removes deep marks. Choose it before painting or coating, because that roughness anchors the coating.
Glass beads. Spherical, so they do not cut: they impact. They leave a satin finish, more closed and slightly lighter, without removing material. Choose them when the finish is the final result and there will be no paint.
If using both, the order is corundum first and beads afterwards: one removes marks, the other evens the surface.
Particle size: where everyone gets stuck
Here is the practical detail almost nobody mentions, and the one that costs you an afternoon.
A microblasting pencil has a very fine nozzle, which limits the grain size that can pass through. With a nozzle just over a millimetre, abrasive intended for a large cabinet simply does not flow well.
The specific case: 50/70 mesh glass beads — roughly 210 to 300 microns — are perfectly normal for a cabinet and too coarse for a pencil.
What works in the pencil is 100 mesh glass beads, around 150 microns. They flow without trouble, leave a uniform satin finish and become the working abrasive.
Buy abrasive without checking this and you end up with a perfectly good sack you cannot use with your equipment. Keep it for when you have a cabinet and buy finer media separately.
Air: the part nobody checks until it fails
Microblasting needs air, and compressor air carries moisture.
A small receiver compressor easily supplies a pencil — consumption is low — but moisture condenses inside the tank and travels with the air. When it reaches the abrasive, it clumps. The pencil spits in bursts, blocks, and you end up thinking the abrasive is bad or the nozzle worn.
A filter-regulator removes liquid water and is the minimum. Fine work needs proper drying, with a dryer or at least an additional separation stage.
And a habit that takes ten seconds and avoids half the problems: drain the receiver after each use and leave it empty. Water that does not accumulate cannot cause trouble.
The sequence that works
- Deburr first. Blasting evens the surface; it does not remove burrs. A burr going in comes out as a satin-finished burr.
- Degrease. Abrasive bounces off grease instead of working, and contaminates the media for subsequent parts.
- Blast with continuous movement, never dwelling at one point. Consistent distance and angle create uniformity.
- Blow off and clean. Abrasive remains lodged in corners and holes. If coating follows, that guarantees a defect.
- Do not touch with your fingers if a coating is planned. Hand grease shows afterwards.
When this is not the answer
If you need a mirror surface, blasting will not get you there. It takes you in the opposite direction.
If roughness is functional — a sealing area, a sliding fit, a datum face — do not blast it. You are changing a surface someone specified.
And for a large part, the pencil is too small and a cabinet is needed. But for short runs of small parts, where milling marks hurt most, it is hard to find anything more efficient.
At 7Axis Industrial we manufacture parts and short runs with finish included in the job. A functional part that is also properly finished does not cost much more, and the difference shows everywhere else.