What Is a Perpendicularity Gauge? A Guide to Measuring Bottle Verticality and Ovality
A perpendicularity gauge measures how far the neck of a bottle or a preform leans away from its vertical axis. This deviation, also called verticality or lean, affects how the bottle runs on the filling and capping line, how the cap sits on the finish and how the container looks on the shelf. Perpendicularity gauges are standard equipment for glass and PET bottle manufacturers, preform producers and bottlers.
How does a perpendicularity gauge work?
The bottle stands on a reference base and is held in a clamp that lets it turn about its vertical axis. An indicator touches the outside of the finish. As the bottle turns through 360°, a vertical and perfectly round finish stays at the same distance from the indicator, while a leaning finish moves closer and further away, and the reading changes.
Total reading: the difference between the highest and the lowest reading during one turn.
Verticality: for glass bottles, ISO 9008 defines verticality as half the diameter of the circle described by the center of the finish as the bottle turns, which corresponds to half the total reading.
On the AT2E UBPT-1, the digital indicator sends its readings to an optional automatic calculator, which displays the MAX, MIN and SAD values (the sum of absolute difference between MAX and MIN). Preforms are measured on the same principle: the AT2E PPG-D holds preforms of different sizes in a high-accuracy three-jaw chuck.
Main applications
Glass bottles: verticality of the finish after forming.
PET bottles: perpendicularity after blow molding, which depends on the preform and on the blowing process.
Preforms: perpendicularity of the preform before blowing.
Wine and spirits bottles: roundness of the bottleneck, where the cork seals.
Blown bottle bases: centering of the injection point of the preform in the base of the bottle.
Key concepts: perpendicularity, ovality and gate centering
Perpendicularity: the offset of the finish from the vertical axis of the bottle. Depending on the industry and the standard, it is also called verticality or lean.
Ovality: the difference between the largest and the smallest diameter of a part that should be round. The AT2E IBMS-1 measures the internal diameter of the bottleneck at several angles, from 0° to 90°, and at any depth from 0 to 55 mm (0 to 2.2 in) below the finish, which shows the roundness of the neck along its length.
Gate centering: the injection point of a preform, or gate, ends up in the base of the blown bottle. The AT2E GCG gate center gauge gives a quick and easy check of whether it is centered.
Accuracy and repeatability: the digital indicator of the UBPT-1 has a resolution of 0.01 mm and an accuracy of ±0.01 mm, while the repeatability of the perpendicularity result is 0.1 mm (0.004 in): the complete measurement, including how the bottle sits on its base, varies more than the indicator alone.
A wobbling bicycle wheel
Spin a bicycle wheel and watch the rim pass the brake pad: if the rim moves sideways, the wheel is out of true. A bike mechanic measures that wobble on a truing stand, turning the wheel slowly against a fixed gauge. A perpendicularity gauge does the same with a bottle: the bottle turns, the indicator stays still, and any lean of the neck shows up as a movement of the reading.
The comparison also shows why the base matters. A wheel mounted badly on the stand wobbles even if its rim is true. In the same way, a dirty base plate or a bottle that does not sit flat adds an error that has nothing to do with the bottle itself.
Calibration of a perpendicularity gauge
A perpendicularity gauge is checked with a reference part of known geometry:
Install a verification column, a reference cylinder of known perpendicularity, in place of the bottle.
Turn it through 360° and check that the reading stays within the expected value.
Check the indicator itself against gauge blocks, record the deviations, and adjust if they exceed the acceptable limit.
A verification column is available as an option for the UBPT and the PPG. Keeping the base plate and the clamp clean is part of the method.
AT2E perpendicularity and ovality gauges
AT2E gauges cover bottles, preforms and bottlenecks:
UBPT: universal bottle perpendicularity gauge for PET and glass bottles 50 to 120 mm in diameter and 110 to 380 mm high, measuring range 0 to 10 mm; versions with 2 or 3 measuring heads also measure mouth clearance and height, and a custom 4-head version also measures roundness.
PPG-A / PPG-D: preform perpendicularity gauge with analog or digital indicator and three-jaw chuck, for preforms up to 39 mm in finish outer diameter and 250 mm high, resolution 0.01 mm (PPG-D).
GCG: gate center gauge for a quick check of the injection point of blown bottles up to 85 mm in diameter.
IBMS-1: internal bottleneck measuring system, internal diameter 10 to 30 mm at several angles and depths, accuracy ±0.05 mm.
PBMS-AUTO: fully automatic preform and bottle measuring system that also measures perpendicularity and finish inner diameter.
Conclusion
A neck that leans by a fraction of a millimeter is invisible to the eye, but filling valves and capping heads are not so forgiving. Measuring perpendicularity and ovality on a clean base, with a calibrated indicator and the same method every time, gives forming and blowing teams a clear signal to adjust their process before the problem reaches the line.
Request a quote
AT2E is an ISO 9001 certified company (AFNOR Certification).
Request a quote: info@at2e.com
Comments