Write down which surfaces are in scope
The first criterion is a boundary. Name the parts to be cleaned: guard panels and handles, the chip conveyor and its cover, the coolant tank lid, the casting surfaces, the operator panel surround, and the base. Equally important is the exclusion list: electrical enclosures, encoder and scale positions, bearing and guideway points, hydraulic joints, and any opening or breather. An acceptance criterion that covers the whole machine is unusable, because nobody intends to clean a guideway the way they clean a guard.
Define what "clean" means for each soil type
Oil film, dried coolant residue, and compacted swarf are different problems, and a single standard of "no visible soil" hides that difference. For a guard panel, clean may mean the surface is uniform in colour and no longer tacky to a gloved finger. For a conveyor cover, it may mean no loose swarf and no mat of fines along the seam. For a coolant tank lid, it may mean the residue is removed rather than moved. Write the criterion in the terms your inspectors actually use, so two people reach the same verdict.
Set how the inspection is done
An acceptance criterion is only as good as its method. Fix the light, the angle, and whether the surface is dry when checked; residue on a wet surface and residue on a dry one look quite different. Decide whether a wipe test on a defined area is required, and whether seams, corners and fasteners count as part of the surface or as separately agreed spots. Also name who signs the sheet. A cleaning job accepted by whoever happens to be free is a criterion in name only.
Require evidence that the machine is still fit to run afterwards
Cleaning an exterior can cause the failures it was meant to prevent: water or cleaning liquor driven into a bearing, a scale or an electrical entry, residue pushed into a wiper or seal, and coolant displaced from a reservoir by run-off. Make "no ingress and no displaced services" part of acceptance, and check it concretely: covers closed and seated, sight glasses readable, filters unobstructed, no standing liquid at joints or in channels, and the machine cycling normally with its usual indications.
Where a cleaning method is being trialled for the first time, run it on one machine and let the acceptance result, not the brochure, decide whether it goes into the routine. Teams that adopt a method across a whole shop in one step usually discover the exceptions on their most sensitive machine.
Put a time and frequency limit in the criteria
An acceptance standard that takes four hours per machine will be quietly abandoned when the schedule tightens. Agree the time the cleaning is expected to take and the interval it is meant to hold, and treat those as part of the specification. If the agreed time is not achievable on a particular machine, the correct response is to change the method or the scope, not to lower the standard silently.
Choose a cleaning medium that the criteria can tolerate
Heat and pressure both help against baked-on oil, and both create their own acceptance problems through overspray. For heavy oil and cutting-fluid residue on machine exteriors, industrial steam cleaning equipment is one of the options to evaluate, because dry-steam and wet-steam modes leave very different amounts of moisture behind, and that difference changes what your ingress checks need to cover.
Whatever medium is chosen, the criteria should say what overspray is acceptable and what protection is required around the excluded areas. A method that is only safe with every bearing taped off is a method that needs its protection steps written into the same sheet.
Record the trial and keep the accepted sample
When a machine first passes, photograph the agreed surfaces and keep the images with the criteria. A reference set settles arguments far better than a paragraph of description, and it also shows a new operator what the standard looks like without training them by correction. Note the settings and the sequence used on the passing attempt so that the result can be repeated by someone other than the person who achieved it.
If your shop's requirements do not match an off-the-shelf arrangement, put the exclusion list and the acceptance method into the enquiry. On the custom equipment route those constraints become part of the specification from the start, and the supplier can say which of them they can meet and which remain the site's responsibility.
Review the criteria when the process changes
A change of coolant, a switch to a straight oil, new machine guards, or a different shift pattern all change what the exterior has to be cleaned against. Revisit the criteria on any of those changes rather than waiting for a failed audit. The point of written acceptance is not paperwork: it is that the next clean looks like the last good one, whoever does it, on every machine in the shop.
