The cut is where an extrusion stops being a section and starts being a part. Most drawings we receive spend pages on the profile and one line on the length, and that line reads “L = 1,200 mm”. Then the end caps arrive without clearance, or a carton holds three lengths that look alike and get mixed on the assembly line.
Custom cut LED optical manufacturing is decided before the saw runs: which method cuts the profile, what the length band is measured against, and how the pieces are bundled. Get those three right and the cut is boring. Boring is the target.
What the cut actually controls
Fit at the end cap. A profile that runs 0.8 mm long will not seat against a gasket designed for contact. One that runs 2 mm short leaves a shadow line across the fixture. Neither shows up in a photo of a sample, and both show up on the line.
Material yield. Offcut from a 6 m length cut into 1,150 mm pieces is money on the floor. A supplier who plans the nest against the delivery length loses less than one who cuts and discards the remainder. That is why we price custom cut to length work from a cut list rather than a single nominal length.
Packing density. Length decides the carton, the carton decides the pallet, the pallet decides freight cost per piece.
The four cutting methods
| Method | What sets length accuracy | End condition | Use it when |
|---|---|---|---|
| Flying saw, on the line | Encoder resolution and saw carriage response. Drifts when line speed changes | Square, light burr, needs deburring | Long runs at one or two lengths |
| Fixed stop saw, off the line | Stop repeatability, and how squarely the bundle is loaded | Square, burr on the exit face | Mixed cut lists, short runs |
| CNC or milled ends | Fixture and program, piece by piece | Cleanest. Chamfer and radius possible | Visible ends, first articles |
| Shear or guillotine | Blade condition and clamp pressure | Distorted on hollow sections, stress marks | Nothing where the end is seen or mates |
Ask which method will run your part, and what the band will be measured on. A supplier who answers “our standard tolerance” has answered neither question.
Where length error comes from
Measuring a warm part. A profile cut at the end of the cooling tank is still above room temperature and shrinks as it stabilises. A piece that measured 1,200.0 mm at the saw can measure 1,199.4 mm the next morning. If the drawing says nothing, the measurement happens whenever someone picks up a caliper.
Stop and encoder drift. A fixed stop wears, a bundle loaded at an angle reads long on one edge and short on the other, and a flying saw lags when the line accelerates. None of this shows in a single sample. It shows across a run. That is why a drawing needs two bands: one per piece, one across 20 consecutive pieces.
Handling after the cut. A 2.4 m linear diffuser profile with a thin wall, supported at both ends, will bow under its own weight in a stack. Measured flat it passes. Measured as it sits in the carton it does not.
What to put on the drawing
| Item | What most drawings say | What to write instead |
|---|---|---|
| Nominal length | L = 1,200 mm | L = 1,200 mm with a stated band, measured on the cooled part |
| Tolerance basis | As per standard | One band per piece, plus one band across 20 consecutive pieces |
| Measurement condition | Nothing | Hours after cutting, ambient temperature, flat reference |
| End squareness | Nothing | Deviation over the profile width, and whether the end stays visible |
| Mating condition | Nothing | Named gasket compression, or a named clearance at one end |
| Bundle definition | Nothing | Pieces per bundle, one length per bundle, count on the label |
Two lines do most of the work. The measurement condition removes the argument about who measured wrong. The mating condition turns a number into a function, which is what the end cap actually needs. The section itself, width, wall and straightness, is a separate question and has to be settled first.
Thermal movement and the length you install
PC and PMMA move far more than the aluminium or steel housing they sit in. Over a 2.4 m piece, the gap between a 15 °C warehouse and a 45 °C ceiling is enough to close a clearance you left at assembly, or open one you had closed.
So cut to a mating condition, not a bare length. Fixed at both ends means the profile needs clearance, and the clearance needs a temperature attached. Floating at one end with a gasket means the cut length is set by gasket compression, not by the housing print.
Packing changes once the lengths are fixed
With continuous profile, the bundle is a way to move material. With pre-cut pieces, the bundle is the delivery unit and the label is the cut list.
One length per bundle. Mixed bundles are how 1,150 mm pieces end up in a 1,200 mm box. Print the length and the piece count on both label and carton.
Protect both ends. A chipped cut end on a snap-in profile cannot enter the housing, so the last piece of every length is lost. Foam blocks or end caps at both ends, not just the bottom.
Size the carton to the longest piece. A carton long enough for the longest length with slack lets short pieces telescope and rub. More than three lengths in one carton usually costs more in sorting than a second carton costs to ship. The rest of the transit routine is in the export packaging guide. Cut lengths add one failure mode to that list, which is mix-up rather than damage.
Checking a delivery in ten minutes
Take the bundle from the bottom layer of the pallet. That is where compression shows first, and it is the bundle nobody opens.
Measure five consecutive pieces, not one. One piece says the saw can hit the number. Five say whether it holds it. Sight along each piece on a flat surface, and check one end against a machinist square for a burr that would sit under a gasket.
Then count the bundle against the label. A count error is not a quality defect, but it is the one that stops a production line, and it is free to catch here.
What we run
Baoming Optical has extruded optical profile since 2008, on 20 or more extrusion lines, at a daily output above 10,000 pieces. Profiles run from 10 to 2,000 g/m, prismatic covers from 23 to 195 mm wide, beam angles at 35, 45, 60, 85, 95, 100 and 105 degrees, and transmittance from 0 to 97% depending on material and surface. Minimum order is 500 pieces, for custom sections and cut lengths alike.
Quality management is certified to ISO 9001:2015 under CQC certificate 00124Q34175R1S/3300, valid to 16 May 2027. UL yellow cards E242424 and E300275 cover the materials at Component Plastics level, which is a material recognition and not a listing of any finished luminaire. Where a market requires EN 60598, IEC 60695 or UL 94 performance, the profile has to be specified to meet that requirement for the application.
Send a cut list with the drawing and the quote comes back against your lengths. Typical custom diffuser lead time runs from drawing review through tooling, first articles and a pilot batch, and the cut plan is confirmed at the pilot stage. If the lengths are still moving, say so and request a quote with a range rather than a fixed number.
Frequently asked questions
What cut length tolerance can you hold?
The band is agreed per drawing, because a 300 mm piece and a 2.4 m piece are not the same promise. We quote the band we can hold on the method that will run the part, measured on the cooled profile at the condition written on the drawing. Ask for both numbers: per piece, and across a run.
Can one drawing be cut into several lengths?
Yes, and it is common. A linear profile often ships as two or three fixture lengths from the same die. Each length needs its own band and its own bundle definition, and each should be packed separately so the receiving line does not sort them.
Do you cut after extrusion or before packing?
Both, on the same flow. The profile is cut as it leaves the line or on a fixed stop afterwards, then bundled by length and packed. The sequence matters because a piece cut warm and packed immediately is measured before it stabilises, so the inspection point sits after cooling, not at the saw.
What is the minimum order for a cut length?
500 pieces, the same as for a custom section. Below that the setup and the packing dominate the price, and a stock profile cut to length is usually the better answer.