Finishing

A finish is often the last operation and the first thing the customer sees, and its faults are the ones the customer notices first. Powder coating, wet paint, anodising, plating and passivation are usually subcontracted by small sheet metal shops, so their price arrives as a supplier’s quote, and the estimator’s work is to ask for the right thing, add what the supplier does not include, and allow for what the finish does to the parts. Finishing is priced mostly by surface area, but masking, handling, colour changes, minimum charges and freight can add as much again, and a finish can change the fit of every hinge, thread and lid on the product.

This chapter prices EN-700’s powder coat from its surface area and the coater’s terms, then covers masking, coating thickness and fits, colour and lot charges, freight, and quality. The running case finds that a first figure priced only the coated area at the coater’s rate, leaving out the masking that keeps the inside faces bare and the freight to and from the coater, about A$7 per enclosure at 50 off.

Surface area

The coater prices by area, by piece or by rack, and the estimator needs the area in any case to check the price. EN-700’s external surfaces, the outside faces of the body, door, rain hood and roof, total about 1.95 m² per enclosure, half of the 3.9 m² of both faces counted in Chapter 1, because the customer’s written answer limited the coating to external surfaces.

This is an illustration. The coater’s rate, from its quote for this job, is about A$15 per square metre for a standard grey, after pre-treatment suited to galvanised steel and aluminium. External surfaces at that rate cost about A$29.26 per enclosure.

Masking

Masking keeps the finish off surfaces that must stay bare: inside faces that the customer wants galvanised, threads in self-clinching nuts, the earth stud’s contact area, gasket seats. Each masked area costs time to mask and to unmask, and plugs, caps or tape. EN-700’s coating is applied after assembly, as the general note requires, so the inside faces are masked by closing and sealing the door and cable openings, and the nut threads and earth stud are plugged.

This is an illustration. The coater quotes about A$4.00 per enclosure for masking, including the plugs for the ten nuts and the stud and the sealing of the openings. Masking is often a large share of a finishing price: here it adds about 14% to the coated area’s cost.

Figure 1Powder coating EN-700 per enclosure at 50 off, ex GST

	Basis	Cost
Coated area, external	1.95 m² at A$15	A$29.26
Masking and plugs	Inside faces sealed, 11 threads plugged	A$4.00
Freight to and from the coater	A$150 per batch ÷ 50	A$3.00
Finishing line	| A$36.26

The error: area without masking or freight

This is an illustration. The estimator’s first figure for coating was the area times the coater’s rate: about A$29.26 per enclosure. It left out the masking, because the coater’s rate sheet listed masking separately, and the freight to and from the coater, because the estimator had assumed the coater would collect and deliver.

The masking adds about A$4.00 per enclosure and the freight, a truck each way for the batch at about A$150 in total, adds about A$3.00 per enclosure at 50 off. Together they are about A$7.00 per enclosure, about 24% more than the first figure, about A$350 across 50. At 20 off, the freight alone adds A$7.50 per enclosure.

The review found it by asking the coater for a full quote for EN-700, as an assembled enclosure with its masking and delivery terms stated, rather than using the coater’s general rate sheet. The fix was a rule: finishes are priced from a supplier’s quote for the actual parts and conditions, not from a rate per square metre remembered from another job.

Figure 2Coating cost per enclosure, first figure against full cost, ex GST

Area only, first figureA$29.26

Area, masking and freight at 50 offA$36.26

Area, masking and freight at 20 offA$40.76

What to ask the coater

A coater’s quote is only as good as the request. EN-700’s request listed everything that could change the price or the result.

Figure 3Request for a powder coating quote, EN-700

• Do: PartsAssembled enclosure, drawing revision B, overall size and mass
• Do: SurfacesExternal only; inside faces masked by sealing the openings
• Do: MaskingEleven threads plugged; hinge knuckles masked; gasket seats bare
• Do: SubstratesGalvanised steel body, aluminium door; pre-treatment for both
• Do: CoatingColour, gloss and coating system as specified for outdoor use
• Do: Quantity and batching20, 50 or 200 per batch, standard grey
• Do: TestingThickness check on 1 in 10, reported
• Do: FreightWho collects and delivers, and how the enclosures are packed for transit
• Ask: Lead timeDays from receipt to return, and booth availability

Hanging points and handling marks

Every coated part hangs from something in the booth, and wherever it hangs, the coating is missing or marked. Loose parts are usually hung through a hole, and a part without a suitable hole may need one added, which is a drawing change, or a special jig. An assembled enclosure like EN-700 hangs from a fixture through its cable opening, where the mark is hidden. The hanging method should be agreed with the coater before the quote is final, because a hanging hole added to a visible face may be unacceptable to the customer, and a jig built for one job is a one-off cost.

The shop’s own handling

Sending parts to a coater is not free for the shop. They must be packed for transit, loaded, checked on return for damage and coating faults, unpacked and moved back into the flow. This is an illustration. EN-700’s handling for coating takes about 3 minutes per enclosure at the shop, about A$4.75 at A$95 an hour, which the estimate includes in its inspection and packing time rather than as a separate line, so as not to count it twice. Some shops instead add a percentage handling charge to every subcontracted cost. Either way works, provided the handling is recovered once, which is the same rule as Chapter 5’s.

Coating thickness and fits

Powder coat adds a film, typically tens of micrometres thick, to every coated surface, and the film affects fits. A hinge’s knuckles may bind; a lid that fitted bare may not close coated; a screw may not enter a nut whose thread has collected powder; a gasket may not seat on a coated flange as it did on bare metal. Coating after assembly, as EN-700 is, avoids some of these by coating the assembled product, but it can coat over joints and fasteners that should stay bare. Each fit that the finish could affect should be checked on a coated prototype, and its masking or clearance specified. EN-700’s prototype, coated after assembly, showed that the door’s hinge needed its knuckles masked to keep it free, which the coater added to the masking at no extra charge because it was raised before the quote was final.

Pre-treatment and the substrate

A powder coat’s durability depends on the surface beneath it. Galvanised steel and aluminium need pre-treatments suited to them, and a coater who treats them like bare steel may produce a coating that peels. The coater’s quote should name the pre-treatment, and for outdoor products the customer may specify a coating system for its environment, which is the coater’s area of expertise. The estimator’s role is to make sure the quote asked for the system the customer specified, and that the coater’s price covers it.

Colour, lot and minimum charges

Coaters often charge for colour changes, set a minimum charge per batch, or price standard colours lower than special ones. A batch of 20 enclosures in a standard grey may cost less per square metre than a batch of 20 in a special colour, because the special colour needs the coater’s booth cleaned before and after. Small batches are particularly exposed to minimum charges: a coater’s minimum of, say, A$300 per batch would exceed the area cost of a very small job, so a quote for a handful of enclosures must check it. EN-700’s standard grey and its batches of 20 or more stay above any minimum in this illustration.

Coating before or after assembly

The customer’s note said “after assembly”, which settled EN-700’s case, but the choice is often open, and it changes the price. Coating parts before assembly coats every face, including faces that will be hidden, but lets each part hang freely in the booth and avoids masking openings. Coating after assembly coats only the outside, but needs the assembly masked and hung as a whole, and coats over any joints, rivet heads and seams. Sheet Metal Joints by the Numbers discusses the effect on the joints: riveting after coating can crack the coating at each head, and coating after riveting traps the rivets under the coat. Where the choice is open, both routes can be priced, and the quote can offer the one that suits the product.

Quality and rework

Coating faults, runs, thin patches, contamination, poor adhesion, are found at inspection after the parts return, and fixing them means stripping and recoating or touching up. The coater normally reworks its own faults, but the shop bears the delay and the extra freight. A quote can include a small allowance for coating rework, or fold it into the risk line of Chapter 9; a quote that depends on a fixed delivery date should allow time for a possible recoat. EN-700’s specification asks for a coating thickness check on one enclosure in ten, which the coater performs and reports. The shop keeps those reports with the job, so that a coating complaint months later can be traced to a batch and its measured thickness rather than argued about from memory, and so that a coater whose results drift can be raised with the coater before the next batch.

The finisher’s lead time

A subcontracted finish adds its own time to the job, and often its own queue. This is an illustration. EN-700’s coater quotes five working days from receipt to return for a batch of 50, plus a day each way for freight: about a week and a half of the six-week lead time promised in Chapter 1, during which the shop can do nothing more to the enclosures. Coaters’ queues lengthen in busy seasons, and a coater that is quick in one month may be slow in the next. The quote’s lead time should use the coater’s current figure, and a job with a hard delivery date may justify asking the coater to reserve a slot when the order is placed.

The finishing line in summary

For EN-700 at 50 off, finishing costs about A$36.26 per enclosure: A$29.26 of coated area, A$4.00 of masking and A$3.00 of freight. At 20 off it is about A$40.76 and at 200 off about A$34.01, the difference being the freight per batch. It is the third-largest line in the quote after the material and the assembly, and its price depends more than any other on asking the supplier the right questions, because so much of it lies in the conditions rather than the area.

Finishing and regulation

Finishing processes involve chemicals, fumes and waste, and finishers operate under environmental and work health and safety regulation that the shop does not have to manage when it subcontracts. That is one reason small shops subcontract finishing, and one reason finishers’ prices are what they are. A shop considering bringing finishing in-house to save the subcontract margin should price not only the equipment and labour but the licences, waste handling, ventilation and compliance that come with it.

Other finishes

Other finishes follow the same pattern. Anodising aluminium is priced by area or by rack, with jig marks where parts hang. Zinc plating small parts is priced by mass or by barrel load. Passivation of stainless is priced by area or by batch. Wet painting is priced by area and coats, with masking. For each, the estimator asks the finisher, ideally two finishers for comparison, for a quote for the actual parts, with masking, quantities, freight and minimum charges stated, and checks it against the area, so that a price far from the expected rate per square metre prompts a question before it goes into the quote.

Exercise: coating before assembly

Suppose the customer agrees that EN-700’s parts may be coated before assembly, all faces, at the coater’s rate of A$15 per square metre, with no masking of inside faces but with the eleven threads still plugged at about A$0.30 each, and with the same A$150 freight per batch. What is the finishing cost per enclosure at 50 off, and how does it compare with coating after assembly?

Worked answer. All faces total about 3.9 m², costing about 3.9 × A$15 = A$58.52. The plugs add 11 × A$0.30 = A$3.30, and the freight adds A$3.00 at 50 off. The finishing line becomes about A$64.82 per enclosure, against A$36.26 for coating after assembly.

Coating before assembly costs about A$28.56 more per enclosure, mostly because it coats the inside faces too. It would be worth considering only if the customer wanted the inside coated anyway, or if coating the assembled enclosure caused problems that coating parts avoided. It would also coat the seams’ flanges before clinching, which the joints’ tooling and tests would need to confirm. On the numbers alone, the customer’s original instruction is the cheaper route.