Finishing
Four ways to finish an acrylic edge, and how to tell them apart
Two identical panels with different edge finishes look like different products at different prices. This is the specification most often left vague and most often visible.
Finishing
Two identical panels with different edge finishes look like different products at different prices. This is the specification most often left vague and most often visible.
An acrylic edge is where the material shows what was done to it. A sawn edge is matte grey-green, a flame-polished edge is glossy but slightly rounded, a diamond-polished edge is water-clear and transmits light along the panel like a fibre optic. The labour difference between the first and the last is substantial, and so is the visual difference.
| Finish | Appearance | Relative cost | Use it for |
|---|---|---|---|
| Sawn / as-cut | Matte, slightly rough, visible tool marks | Included in cutting | Hidden edges, parts that will be bonded, internal structure |
| Sanded | Uniform matte, no tool marks | Low | A deliberate satin look, or preparation before polishing |
| Flame polished | Glossy, slightly rounded edge, faint ripple possible | Low–medium | High volume, low-cost display work, edges not viewed closely |
| Diamond polished | Water-clear, sharp, transmits light | High — a skilled hand operation | Anything judged at close range: displays, awards, vitrines, premium fixtures |
| Router with polished finish pass | Near-polished, very consistent | Medium | Straight edges in volume where a diamond polish is not justified |
A saw leaves a matte edge with fine parallel marks. A router leaves a cleaner, more uniform matte edge, and if run with a finishing cutter at the right feed it can be close to polished. Neither transmits light along the panel, so a sawn edge on a display piece reads as a dull grey line.
A hydrogen-oxygen flame is passed quickly along the edge, melting a thin surface layer so it flows and solidifies glossy. It is fast and cheap, but it rounds the edge slightly and can introduce stress, which matters if the part will later be solvent bonded or exposed to chemicals. It also cannot produce the optical clarity of a mechanical polish — the edge looks glossy, not clear.
The edge is machined flat, then worked through a sequence of abrasive and diamond compounds on a wheel until it is optically flat and clear. It is hand work, it is slow, and it is the only finish that makes an acrylic edge look like glass. On a thick edge the effect is dramatic: light entering the polished edge travels through the panel and glows out of the opposite edge or a machined detail.
"Polished edge" on a drawing means whatever the shop does by default. If the appearance matters, specify the process and attach a photograph of an accepted sample. This is the single most effective way to make two suppliers produce the same part.
Diamond polishing is priced per metre of edge and it dominates the cost of small thick parts. A 100 mm acrylic cube has 1.2 m of edge to polish; a 600 mm panel has 2.4 m. On a thin flat panel the polishing can cost more than the material and the cutting combined.
Three ways to control the cost without losing the look:
Any machining on a polished face — a hole, a slot, an engraved line — leaves a matte area that must be re-polished if it is visible. This is why a design that puts a lot of holes in a visible face costs more than one that does not, and why we ask which faces are seen before quoting.
Annealing after machining relieves stress but can slightly dull a polished surface, so the sequence matters: machine, anneal, then finish. A part polished before annealing will need polishing again.
No. Flame polishing gives a glossy but slightly hazy edge with a rounded profile, and it introduces stress. Diamond polishing gives a clear, sharp edge. The visual difference is obvious on any part viewed closely.
Yes, in a workshop. A local polish restores the edge, though the match at the boundary depends on the skill of the operator. On a bonded assembly the part usually has to come back to the factory.
That is the natural body colour of cast PMMA, which is only visible along a long light path. Optical grades reduce it. If the edge looks green on a thin panel, it is probably not polished — a matte edge diffuses the light and reads grey-green rather than clear.
A polish removes micro-cracks from the edge, which slightly improves fatigue resistance, but it also thins the edge very slightly. The effect is negligible compared with the fixing detail, which is what actually decides whether a part cracks.
Name the process, name the edges and attach a sample. For example: "Diamond polish edges A and B to match approved sample. Edges C and D as routed." An adjective alone will not survive a change of supplier.
Tell us which faces and edges are visible and which are hidden, and we will quote the minimum polishing that gives the finish you need.