Start with the condition of the holding equipment, not the cleaning method
Workholding decides more of the trial result than most buyers expect, and the reason is boring and physical: heat moves things. A clamped assembly expands, a clamping force set cold is a different force when warm, and a fixture that seated cleanly on a cold table can creep once the shop has warmed up. For anyone deciding whether a cleaning method belongs on production machinery at all, the practical reading is at CNC machine cleaning equipment, where the same caution about work-holding applies in reverse: the holding device is the cheapest place to lose accuracy, so it should never be the part nobody inspected.
Before the trial, a setter or tooling engineer should walk the fixture list and write down, for each item used in the trial window, what condition it is actually in. Not "in service". Written. Which pads are worn or shiny, which locating pins have burrs or rings of hardened coolant at the base, which clamp arms have play in the pivot, which dowel holes show score marks, which rubber or polymer elements have gone soft, swollen or glazed with oil. That note becomes the trial record later, because a problem found after cleaning cannot be judged without knowing what the fixture looked like beforehand.
Decide what stays mounted and what comes off to a bench
Two different plans are in play, and mixing them is the usual cause of a wasted trial. The first is cleaning in place, with the fixture still bolted to the table. That preserves the datum and keeps the trial short, but it means every opening, port, sensor bracket and gap on both the machine and the fixture is exposed to whatever is being sprayed. The second is remove-and-clean, where the fixture, its plates and its clamps go to a separate area and the machine is dealt with on its own. That protects the machine and lets the fixture be cleaned hard, but it hands the team a reassembly problem, and every fastener, shim and locator touched becomes a question at the next setup.
The decision should be written per fixture before the trial, with a reason attached. Simple welded or cast holders with no adjustment and no electronics usually travel to the bench. A precision fixture with shims under the base, a set of height blocks, or a mounted sensor and its cable route normally stays put, or comes off only with a photographic and measured record of what was where. Grease and cutting fluid on machine exteriors is a related but separate problem, covered under machine tool steam cleaning; the fixture problem is narrower, because the deposits on a holder are thin films and hardened residue in holes, and they sit in the datum chain.
Mark the parts that carry accuracy, and write down what must not change
On every fixture in the trial, mark the faces that actually carry accuracy: the base plate as it sits on the table, the locating pins or dowels, the support pads and pads' edges, the clamping faces, any stop or anvil that sets a position, and the part-contact surfaces. Mark them physically with a stamp, witness mark or paint pen, and list them. Everything else on the fixture is structure.
Then state, in one line each, what must not change on those marked faces. Not a tolerance argument, just the requirement the shop can check with what it already owns: a pad that was scraped or blistered by a hot jet may no longer seat the same way; a hardened film removed from a pin base may let the pin sit lower than it did; a swollen seal shrunk back to size changes a clamp stroke. If the trial cannot leave a marked face untouched, then that fixture is not a candidate for in-place cleaning and the plan changes. This single list is also the most useful thing to send a supplier, because it replaces a vague request with named surfaces.
Set the measurement baseline while everything is still cold and untouched
A trial that has no before-numbers cannot prove anything about the after. So before any heat is applied, capture the baseline in the shape the shop already uses for a fixture check.
- Run indicators on the pads, locators and any datum feature used in setup, and record the read numbers, not a pass judgement.
- Make seating checks with feeler stock at the base-to-table interface and at each pad, marking where light passes.
- Clamp a test part or a dummy block and record the setup readings the way a setter would, then leave that record with the fixture.
- Photograph each fixture cold, before cleaning, from the same angles used afterwards, including pin bases, hole mouths and clamp pivots.
- Log the clamping method and the tool used to set it, because a changed clamp sequence at reassembly is a different fixture, not a dirty one.
Measure cold, measure twice, and let the same person take both the before and after readings. Temperature differences between the two sets of readings are a normal way for a trial to produce a frightening number that means nothing, and a trial that ends in a fixture being scrapped for no reason is worse than no trial at all.
Protect openings, sensors and lubrication on the fixture itself
A cleaning trial does not distinguish between a surface you want cleaned and a place you want left alone, so the staff preparing it must draw that line in advance. Write an exclusion list per fixture, then shield or seal those items physically rather than relying on operator care.
Typical entries are dowel holes and pin bores, threaded holes, the gap under a pad, sliding ways and screw actuators on an adjustable fixture, pneumatic ports and their hoses, mounted sensors and their cable glands, bearing ends, and any grease nipple or sealed-for-life bush. Where a fixture has grease or a light oil film on its own slides and screws, decide before the trial whether that film is meant to survive; if it is, the fixture goes on the remove-and-clean list or the shielded list, because a jet aimed at grime does not stop at the lubricant.
Two habits are worth declaring as rules for the trial rather than preferences. First, nothing aimed at a gap, a hole or a seal. Second, no solvent wipe on elastomer parts as a spot fix during the trial, because a changed seal is a confounding variable and the trial will not be able to tell what caused what.
Prepare storage, drying and reassembly as part of the plan
Most damage to holding equipment in a cleaning exercise is not done during cleaning. It is done afterwards, in the hour between the trial and the next setup. A fixture left standing with liquid in a hole will rust before anyone reads the results. A fixture put back on a table with a film of debris under the base will read as an accuracy failure caused by the cleaning method.
So the preparation includes the unglamorous items: a clean, level place to put the fixtures down with a soft surface under the datum faces; a route for run-off that keeps it away from electrical boxes and bearings; a drying step that reaches holes and blind bores, not just visible faces; a means of blowing or wiping pin bores clear before anything is reassembled; and a storage position that does not hang a fixture by a locating pin. Where a fixture has been removed, reassembly should be done by the person who removed it, with the photographs and the shim record in front of them, and it should end with a fresh indicator check rather than a return straight to production.
Choose one fixture for the trial and keep the others as a control
A trial needs comparison, and the cheapest comparison is an identical fixture that was never cleaned. Pick the worst realistic case for the trial: the fixture with the heaviest deposit, the most exposed holes, or the tightest seating requirement, not the easiest one. Then keep a matching fixture, made the same way and used the same length of time, untouched as a control.
Change one variable at a time and write down what it was. Judge the result with someone who did not hold the lance, using the marked faces and the recorded readings rather than an impression. If the trial covers several fixture families, then the plan has several rows in it, and a pass on one family does not transfer to another. Where a machine family has been running with the same fixture design for years, note that too: an old fixture may be doing its job through wear rather than by design, and cleaning can reveal a problem the plant already had.
Where a plant cannot decide what a supplier is actually proposing for that worst case, the written enquiry gains a lot from customized steam cleaning equipment framing: state the fixture, its marked faces, its exclusions and the readings taken, then ask for a proposal against that document instead of a brochure.
Agree the stop conditions and the hand-back before the trial starts
Write the stop conditions before the trial begins, not when someone is nervous halfway through. In plain language: the trial stops if liquid reaches an electrical enclosure, a sensor gland or a bearing; if a fixture moves or creeps on its base at any point; if a pad, seal or polymer element changes shape, colour or feel; if readings drift beyond what the plant can explain; if the run-off route fails and the floor is wet where people walk. Anyone running the trial should be allowed to call it off on those words without permission, and the run should be recorded and read afterwards, not treated as a failure.
Hand-back is equally a decision made in advance. A fixture returns to production only when the indicator check, the seating check and the setup readings are back inside the recorded before-numbers, and a named person signs that line. If they are not, the fixture goes to the tooling engineer as a repair item and the trial result is written as conditional. Nobody should be improvising that rule on the shop floor at the end of a shift.
The preparation package a supplier should receive
The point of preparing tooling and workholding before a cleaning trial is that it produces a document, and that document is what makes the trial answerable. One page per fixture, holding the items below, is enough to end the trial with a decision instead of an argument.
- The fixture identified by its shop number, with its material and any plated, coated or elastomer parts named.
- The deposit description as found, per surface, in the words the shop uses for it.
- The marked accuracy faces and the one-line requirement for each.
- The exclusion list, and the shield or seal used for each entry.
- The before readings, who took them, and the cold photographs.
- The stop conditions and the named person who signs the hand-back.
A buyer who sends that package gets a proposal that can be tested. A buyer who sends a photograph of a dirty machine gets a price. The preparation takes an afternoon, and it is the reason a cleaning trial on production machinery ends with holding equipment you can trust back on the table.
