Zero Point Systems

The zero point system — the quick-change workholding system — is the coupling that lets a whole workholding setup leave the machine and return to it in seconds, in exactly the same place every time. A set of receivers is bolted to the machine table, the tombstone or the pallet, and the shop’s fixtures — the vices, the sub-plates, the modular fixtures — are fitted with matching couplings; a fixture is lowered on to the receivers, locked, machined, unlocked and lifted off, and the next fixture drops on to the same receivers and is held at the same position, without indicating, without probing and without re-setting. It is the workholding development that turns the machine’s idle time into setup time spent off the machine, and it is the reason a machining centre can run one job while the next is being set up on a plate at the bench. This entry sets out how the system works and where it earns its place.

The coupling that repeats

At the heart of a zero point system is a coupling that positions and locks at once, and its accuracy is the whole point. Each receiver holds a coupling element — a spigot, a stud or a pallet plate — and the element is pulled into a taper in the receiver, seating on a precise, repeatable surface, then locked by a mechanism within the receiver, often air- or oil-driven, sometimes mechanical. Because the element seats in the same taper the same way every time, the fixture returns to the same position relative to the machine on every change — repeatably, to a few thousandths of a millimetre, which is why the system is called zero point: the fixture always lands at the same zero. The locking is quick — a coupling engages with a click and a lock indicator — and it is positive: the taper and the lock hold the fixture firmly against the machine, as rigidly as if it were bolted down, and release it again just as quickly when the run is done.

Why the position matters

The repeatability is what makes the rest of the setup unnecessary, and it is the source of the system’s value. Because a fixture returns to the same place every time, the machine only has to know that place once: the shop sets the work offsets for the fixture the first time it runs, records them with the fixture, and every time that fixture is loaded the offsets are called up and the parts are machined in the same place — no re-probing, no re-indicating, no first-part re-setting. The fixture and its pallet are built square to the coupling, the coupling is square to the machine, and the part sits in the fixture in the position that the datum setup and the locating of the workholding group have defined; the zero point system simply delivers that position, unchanged, run after run. This is why the system suits the job that runs again and again — the fixture is stored with its offsets, and when the job returns the fixture is dropped on, the offsets are loaded, and the first part is good.

The pieces of the system

A zero point system is bought as receivers and carriers, and its pieces cover the shop’s workholding. The receiver is the part that stays on the machine — a round unit, a row of units along the table, or a pattern of receivers on a tombstone or a sub-plate — each receiver a precise socket with its own lock. The carrier is the part that goes with the workholding: a pallet plate with coupling elements on its underside, on to which the vices, the fixture or the fixture plate is bolted, so that the whole assembly is a unit that drops on to the receivers. The shop fits its existing workholding to carriers — a vice on a carrier, a modular fixture on a carrier, a tombstone’s face plate on a carrier — and keeps each carrier with its setup intact, stored off the machine. The receivers are supplied with air or oil for their locks, and the carrier is released by a lever, a foot valve or an automatic signal as the pallet changer or the loader handles it.

The workflow it enables

The system changes how a shop uses its machine time, and the change is the point of it. In the conventional setup, the machine stands idle while the operator bolts on a vice, indicates it, sets the offsets and proves the first part; in the zero point shop, that work is done off the machine — the vice or the fixture is set up on its carrier at the bench, indicated and recorded once — and the machine is loaded by dropping a finished carrier off and a fresh carrier on, a change of seconds instead of the minutes of a setup. Several fixtures can be kept ready at once, each on its carrier, so the machine moves from job to job through the day, running the batch, swapping the carrier, running the next; and because the change is quick and repeatable, the system is the natural partner of the lights-out and automated running of the shop, where the machine must change its own jobs without an operator standing by. The machine’s cutting time rises, its waiting time falls, and the operator’s skill goes into the off-machine setup where it does the most good.

When a zero point system earns its keep

The system is an investment, and it earns its keep where setups are frequent and their time is wasted. The shop that changes jobs often — the small batches, the recurring jobs, the work that comes back to the same machines — saves the setup time on every change, and the system pays for its receivers and carriers in the hours of cutting it adds to the week. The shop with a pallet changer or a robot already has the machine that can swap work; the zero point system gives that machine fixtures that swap as readily as pallets. And the shop that keeps its fixtures — the vice setups and the tombstones and the plates — stored with their offsets finds that a returning job is set up in the time it takes to drop a carrier on the receivers. For the shop that runs few jobs and never changes them, the simple bolted setup is enough; for the shop whose work changes through the week, the zero point system is the workholding that makes every change a matter of seconds — a fixture dropped on to a precise receiver, locked at the same zero point, and cutting again.