A CNC acrylic machining job is lost or won before the spindle starts. The first sign that a CNC acrylic machining service is not under control is not a scrapped part. It is a part that measures correctly on the bench and will not fit three days later, because nobody relieved the stress the cutter put into the sheet.
Acrylic machines easily and badly. Almost any router will cut it. Very few setups produce a edge that can be bonded without preparation, or a hole pattern that stays within 0.1 mm across a two metre panel.
Feeds and tooling for CNC acrylic machining
A machined acrylic part is only as good as the data behind it. Send a DXF or STEP with the sheet thickness on the layer, the grain or cast direction marked, and a datum corner identified. Add a note on which edges are cosmetic and which are trimmed.
Holes need a callout that separates clearance from interference fits. In cast acrylic, a 10 mm hole for an M8 fixing should be drawn at 8.5 to 9 mm, because the material moves with temperature far more than aluminium does. A drawing that copies metal tolerances will produce a panel that splits at the first hot day.
Tooling and feeds that leave a bondable edge
Use single-flute or double-flute solid carbide cutters designed for plastics, with a rake angle that shears rather than ploughs. Two-flute cutters at 12,000 to 18,000 rpm and 2 to 4 m per minute feed are a workable starting point for 5 to 10 mm cast sheet; thicker sections want slower feed and lighter step-down rather than a single deep pass.
Air blast beats flood coolant on acrylic. Compressed air clears the chip and cools the cutter without contaminating the edge with oil that later has to be cleaned before bonding. Where coolant is unavoidable, use a water-soluble type and wash and dry the part before any solvent cement touches it.
The three edge defects buyers see most
A frosted white edge means heat. A ribbed edge means the feed was too fast for the spindle speed. A wavy edge means the sheet was not held flat, or the vacuum table lost seal as the cutter crossed a previously cut window.
Any of the three can be removed by edge preparation, but preparation is labour, and labour is what a buyer is paying a machining service to avoid.
Stress relief is part of the process, not an extra
Machining removes material from one face and releases internal stress unevenly. On a 20 mm cast panel with a large window cut out, the released stress can bow the part by two or three millimetres over a metre. Annealing at 70 to 80 degrees Celsius, held for one hour per 3 mm of thickness and cooled at no more than 5 degrees per hour, brings the part back to a stable shape.
Ask the machining service whether annealing is included in the price or quoted as a separate line. If the answer is that acrylic does not need it, the shop has not run large parts.
Inspection that actually proves the part
A first article inspection report should list the measured window size, the diagonal, the hole positions against datum, the edge squareness and the surface condition under grazing light. Photograph the part on a surface plate with the rule in frame.
For panels that will be bonded into a assembly, add one bonded test coupon from the same batch and the same edge preparation. The coupon is cheap; discovering a contaminated edge after assembly is not.
If the part has to travel before installation, the packing specification matters as much as the machining. Our guide to acrylic and PC sheet export packing and shipping covers the crate detail that keeps a machined edge intact.
Where a machining service and a sheet supplier should meet
Buyers often source sheet from one company and machining from another, then spend weeks apportioning blame for a part that does not fit. Buying both from one supplier keeps the sheet grade, the stress history and the machining parameters in one set of records.
That is the arrangement River People prefers: cast sheet cut from the same batch, machined on our tables, annealed and inspected before it is packed.
Send the DXF, thickness, quantity and the fit that matters most to oversales@rpplexiglass.com, and we will return a machining quote with tooling assumptions and annealing stated as separate lines.
Frequently Asked Questions
What tolerance can a CNC acrylic machining service hold?
On a 1 metre part, plus or minus 0.2 mm on window size and hole position is realistic when the sheet is clamped flat and annealed after cutting. Tolerances tighter than 0.1 mm need a temperature-controlled shop and should be discussed before quoting.
Can you machine 30 mm cast acrylic?
Yes. Thick cast sheet is cut with slower feed and multiple step-downs, then annealed for around ten hours to stabilise the part. Deep pockets and narrow ribs are the limiting features, not the thickness itself.
Is laser cutting better than CNC for acrylic?
Laser gives a polished edge and no clamping force, which suits signage and thin sheet. CNC holds positional accuracy on large panels, avoids the heat-affected zone and can cut thick cast material, which is why structural and bonded parts usually go to a router.