Open Time
Open time is the maximum time a single-component adhesive, coating, or contact cement film remains workable after application and before it loses tack or bond strength. In CNC/millwork shops, it is critical when laminating, edgebanding, veneering, or joining parts after machining, ensuring the adhesive remains receptive during assembly.
In millwork assembly, open time determines how many panels or edgebanding runs can be coated before press-up begins; a skin over leads to bond-line starvation. In CNC-cell workflow, open time controls the handoff between machining and assembly: parts nested-cut and edge-prepped must be glued before the adhesive loses wetting ability. Edgebanding adhesive pots and ambient temperature/airflow directly affect open time, with warmer conditions, thinner films, and porous substrates shortening it. In lamination, both faces must be assembled within the window to trap solvent properly. Open time is a process-control parameter: crews sequence machining, edge-prep, dry-fit, glue application, and clamping so bonds occur while tack remains. Supervisors manage it via batch size, spread rate, temperature, humidity, substrate porosity, and operator speed to prevent skinning and misalignment during assembly.
- Glue skins before assembly: parts sit too long after adhesive application, especially on large panels or in warm/dry air, forming a film that prevents proper wetting, causing weak lines and edge lift.
- Overrunning the batch size: too many parts are coated at once, so the last ones miss the open-time window; one corner bonds well while another peels because press-up was delayed.
- Ignoring material and shop conditions: porous MDF or dry hardwood absorb adhesive faster, while high temperature and airflow shorten the window; results are inconsistent bond quality and failures after machining.
Is open time the same as working time?
Not always. Open time is the period after application before the adhesive can no longer form a proper bond; working time is the broader period during which parts can be positioned and assembled.
Why does open time matter more in CNC/millwork than in general assembly?
Because CNC workflows often create tightly sequenced downstream tasks—edge prep, drilling, fitting, label sorting, then glue-up—so any delay can push the joint beyond the adhesive’s usable window.
What shop variables shorten open time the fastest?
Higher temperature, lower humidity, thin spread rate, porous substrates, and strong air movement typically accelerate skinning and loss of tack.