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Reader Question: We have not yet invested in a zero-point workholding system. They look handy, but we are stuck on how we would implement this fully day to day and justify the cost. What is your advice?

The reason it is hard to picture is that the catalog sells these as fast-change fixtures, and faster setups alone are a tough way to justify the cost. That is not where the value is. The value is that your machine stops being tied to your setups, and once you see it that way the day-to-day uses are easy to find.

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Take a normal interruption first, since you already deal with these. A job is running and another one must jump the queue. Today, that means stopping the current job, tearing down its fixture, indicating in the new one, then later rebuilding the first fixture and re-indicating it to get back to where you were. You pay for setup twice and you hope the first job returns to the same zero. With a zero-point system you lift the running job off the machine with the part still clamped in its fixture and set the whole thing on a bench. The second job drops onto the same locating points, runs and when it clears the first fixture goes back down against the same locators it left. Same zero, no indicating on either end. The interruption costs you the run time of the job that jumped in and very little else.

Spindle Time

That same capability changes how setups relate to spindle time even when nothing is jumping the queue. On a conventional job, building and indicating the fixture happens on the machine, and the machine is not cutting while you do it. A zero-point system lets you build and verify the next fixture on a bench while the current job runs, so the changeover becomes a drop-in that takes minutes. The work did not disappear; it moved off the spindle. That is the number to hold against the price. The hours a machine spends not cutting while someone sets it are hours you have already paid for, and on high-mix work they pile up faster than most shops bother to track. A zero-point system turns a real share of that idle setup time back into cutting time, and that recovered capacity, not the speed of any single change, is what pays for the system. Squaring moves off the spindle too. Instead of truing up a vise or a fixture every time you set a job, you tram the base once when it is installed and every fixture that seats on it inherits that alignment. A recurring task on every setup becomes a one-time event.

Work in Progress

It also lets you start a job before you have finished planning it. You do not always have the finishing strategy settled when material arrives, and sometimes a tool you need is still on order. Normally the part waits and the machine waits with it. Instead, you can rough the part now, pull it off still clamped, and set it aside while the spindle goes back to other work. A few hours or a day later, when the tool shows up or you have the finish passes worked out, the part drops back onto its locators, and you carry on. You have taken material removal off the critical path and started making chips before the process was fully figured out.

Quality/Rework

There is a quality angle to the same idea. Because the part comes back to the same place every time, you are not forced to release it the moment the cycle ends. You can do some of your checking with the part still against the locators, and if something needs another pass you put it back exactly where it was and take it. The option to rescue a part instead of scrapping it is worth real money on anything with hours of cut time already in it, and you only have that option if you can return the part to a known position.

The Caveat

I want to be straight about what makes the difference between a system that pays and an expensive fixture that does not, because shops get burned here. All this rests on the offset standard holding across the shop. Everyone must reference the same points the same way, and the discipline must survive the first busy week. A zero-point base used like an ordinary fixture, with one-off setups and indicated zeros layered back on top, gives you none of what I just described. The hardware does not create the discipline. It pays back the discipline you already run.

Running as a System

If you do run it as a system, there is a payoff worth pointing out, because you asked about day to day and this one shows up later. Look at what those uses have in common. Setup happens off the machine. Parts return to a known position on their own. Jobs interweave instead of requiring they run front to back. Work gets verified before it is released. That list is also a fair description of what a machine needs to run without a person standing at it. Every one of those is a pre-requisite for automation, so a shop running zero point well is not getting ready to automate or still thinking about it. It has already started.

That is the part I would weigh most heavily if you were on the fence. Standardizing your processes is the true first step toward automation and no fixture changes that. But of the physical gear on the floor, nothing moves you in that direction faster or for less than a zero-point system. The same receivers that locate your fixtures will locate a pallet, so a robot or a pallet pool drops parts onto the points the machine already knows. The bridge turns out to be hardware you bought for reasons that paid off the day it went in.

Do you have a machining question? Ask the expert. John Miller leans on more than a decade of industry experience to answer machining questions from MMS readers. Submit your question online at mmsonline.com/MillersEdge.