Assembly Services that take a machined part to a tested unit
Machining gives you parts that measure right. Assembly is where those parts have to work together, and where most of the arguments start. XS Precision builds mechanical sub-assemblies, cable terminations and complete box builds in the same building that cut the metal — so the fit, the torque and the test record belong to one supplier instead of three.
The three questions behind almost every assembly enquiry are ownership (who pays when a unit fails), evidence (what record ships with it) and revision control (which BOM revision was actually built). This page answers all three before you send us a file.
Assembly is quoted on evidence and on cycle time, not on hourly rate alone.
Three kinds of work, one build record
Assembly Services at XS Precision cover three kinds of work, and all of it happens on the same floor as the machining, which matters more than it sounds: when a housing does not fit the bearing it was machined for, the fix is a conversation across the bench, not a claim across three companies.
Torque is not clamp load. Roughly 10% of what you apply reaches the joint.
Of the torque you put on a fastener, about 40% is consumed by friction in the thread and about 50% by friction under the bolt head or nut face. Only what is left — typically around 10% — becomes the clamp load that actually holds the joint together. That split is why two assemblies built to the same torque value can have very different preload: change the lubricant, the plating or the washer material and the friction term moves.
On calibration intervals. ISO 6789-2 does not fix a mandatory period; it requires recalibration after commissioning, after any repair or suspected overload, and at a defined interval. Industry practice is 12 months for moderate use and 6 months for high-cycle stations. XS Precision logs every torque tool against its certificate, and a tool that goes out of date is pulled from the bench rather than argued about.
Seven stations between the drawing and the pallet
None of these steps is exotic. What separates a build that ships from a build that comes back is that every one of them has a written output, and the next station cannot start without it.
Turnkey, consignment or hybrid — choose by what you need to control, not by price
Assembly Services are priced on this choice more than most buyers expect, and it is worth ten minutes before the quote. Turnkey means we buy everything and you get one invoice. Consignment means you supply the material and we supply the process. Consignment is usually described as a cost tactic, which misses the point: for medical, aerospace and defence programs it is how you keep an approved vendor list, a lot genealogy and a chain of custody that an auditor will accept. Most of our customers end up on the hybrid column — they buy the long-lead and the controlled parts, we buy everything else.
Full mark = yes, open circle = partial, dash = no. The pattern to notice is that turnkey wins on overhead and accountability while consignment wins on control. If your end customer audits the supply chain, the control column usually outranks the price column — and if nobody audits it, the overhead column does. XS Precision will quote either way and will say which one we think your program actually needs.
A kit is only correct if it was picked against the BOM revision you approved
Two units built six weeks apart can behave differently without anyone making a mistake, simply because a connector was substituted or the BOM moved by one revision and the change note never reached the bench. Revision control is not paperwork for its own sake — it is the only thing that makes a second batch comparable to the first.
ISO 14644-1 is a particle ceiling, and every class step is a factor of ten
A normal machine shop is an uncontrolled space. That is fine for a bracket and meaningless for an optical assembly or an implant. The classification is a limit on airborne particles at a stated size — most specifications quote 0.5 µm — and each class down allows ten times fewer of them per cubic metre.
Two things to put in writing. First, the state: ISO 14644-1 recognises as-built, at-rest and operational, and a room that holds ISO 7 at rest will not necessarily hold it with two people working in it. Unstated, that difference is where acceptance arguments start. Second, electrostatic discharge: if the assembly carries unprotected electronics, ask for ANSI/ESD S20.20 control, where dissipative surfaces sit in the 10
Functional test, dielectric and burn-in run at 100%. Environmental, IP and vibration usually do not.
This is the section that causes the most friction after delivery, because “tested” means different coverage to the buyer and to the assembler. A 100% functional test tells you the unit worked at the station. A sampled vibration test tells you the design survives a profile — it does not tell you anything about the unit in the carton.
Three questions to settle before the fixture is cut. Who pays for the test fixture — it is a real one-off cost and it belongs to whoever paid for it. Who owns the test script, including the right to take it to a second supplier. And what the disposition is for a unit that fails: rework, use-as-is with your written approval, or scrap. Answer those three at quotation stage and the test station stops being a negotiation.
“Build to IPC” is not a specification
An assembly standard only binds anyone if the purchase order names the document, the revision letter and the class. Everything else is a preference, and a preference is not something you can reject a batch against. IPC itself became the Global Electronics Association in June 2025; the document numbers did not change, but the revision letters do roughly every three years.
The habit worth forming: write “fabricate and assemble to IPC-A-610J Class 2, solder to J-STD-001J, harness to IPC/WHMA-A-620” on the order rather than “per IPC”. It costs one line and it removes the most common argument in incoming inspection.
Assembly quotes are usually decided by the fixture, not by the labor rate
Labor is the number everyone negotiates and rarely the number that matters. A functional test nest, a harness pull-test fixture and a set of foam inserts are one-off costs that dwarf a few cents an hour — and if they are missing from the first quote, they reappear later as a surprise. The ranges below are directional, based on typical programs rather than audited averages; the point is the relative size, not the exact figure.
Assembly labor itself is usually quoted per minute at the station, and the spread between a simple bolted sub-assembly and a routed harness with a test loop is roughly twenty-fold. That is why the drawing matters more than the rate: every flip of the unit mid-build adds 15–30 seconds, and every connector a technician cannot reach adds more.
Six answers that move an assembly quote more than anything else
Outsourced Assembly Services fail on missing information far more often than on capability. A quote built on assumptions is a quote you cannot hold anyone to, so these are the six answers we ask for before pricing a build.
Serial numbers, labels and packing are part of the build, not an afterthought
A unit can pass every test on the bench and still arrive with a cracked housing, because the foam insert was cut to the CAD model instead of to a real article, or because the carton was sized after the units were already packed. We cut inserts from a physical part and drop-check the first packed carton before releasing the rest.
Serialization is the other half. A serial number is only useful if it points at something: the BOM revision, the lot numbers that went in, the torque log and the test result. We keep that as one build file per serial, so a question from your customer eighteen months later is a lookup rather than an investigation.
All three are preventable at quotation stage and expensive once the material is on the bench
The six questions that come up on nearly every assembly enquiry
Every Assembly Services enquiry we field contains some of these, usually in roughly this order. The answers below are the ones we would give on a call, including the ones that cost us the job. XS Precision assembles what we machine, what you supply, and mixtures of the two.
Do you assemble parts you did not machine?
Yes, and it is about half the work. Bought-in bearings, linear rails, power supplies, connectors and boards all arrive at goods-in and get inspected against your approved vendor list before they are kitted. Machining the enclosure in-house simply removes one handoff and one argument about fit.
What is the smallest assembly order you will take?
One unit, honestly — but be aware that below roughly 50 units the documentation and fixture setup is a large share of the cost, so the unit price looks worse than it should. Between 100 and 5,000 units a year is where a proper box build setup pays for itself.
Can you hold a cleanroom class?
ISO 8 and ISO 7 in-house for assembly and packing, with gowning, sticky mats and a particle monitoring log. ISO 6 and ISO 5 are quoted through a partner facility and priced accordingly — we would rather say that up front than fail an audit later.
Who owns the test fixture and the test script?
Whoever pays for it, which is usually you, and we say so on the quote. The script is yours to take to a second supplier. If you would rather we absorb the cost into the unit price, that is possible too — it just changes what the unit price has to be.
What ships in the carton with each unit?
As standard: a certificate of conformance, the packing list, and the build file for each serial — BOM revision, lot numbers, torque log and test result. First-article reports, calibration certificates and full traceability packages are available where the end use warrants them.
What happens if I change the design mid-order?
A written change note, a re-quote for the delta, and a decision on what happens to work in progress. Units already built stay on the old revision and are labelled as such. We do not quietly mix two revisions in one shipment, and we will tell you the cost and the schedule effect before we move.
Where assembly connects to the rest of the shop
Send the assembly drawing and the BOM. We will tell you which parts we should not be buying.
Assembly Services only pay off when the supplier can be held to a number, so here is ours: we tell you what we can verify and what we cannot. Tell us what the unit has to do, what has to be tested, which parts you already own and how many you need this year. If a machined enclosure beats a molded one at your volume we will say so, and if the test you have specified cannot be run at 100% without a fixture cost you did not budget for, we will say that too — before the first kit is picked.