What kind of equipment do you have available?

The short answer

What a machine list should tell you

When a buyer asks what equipment a supplier has, the useful answer is not a list of model numbers. Machines are tools with capability envelopes, and the same model number can sit in a well-maintained shop that holds a tight tolerance and in a neglected one that does not. What matters is which classes are present, what tolerance each class can hold on a sustained basis, what size and shape envelope the shop can reach, and what equipment exists to prove the result. A list of a hundred machines says nothing about any of those things, while a short list matched to the tolerances and shapes your parts need says everything.

It also helps to know why the classes exist rather than treating them as interchangeable. A three-axis mill is the workhorse for prismatic parts. A four-axis machine indexes the part around one rotary axis so that features on four sides can be cut without a second fixture. A five-axis machine adds a second rotary axis so the tool can approach from any angle, which is what makes contoured surfaces and multi-face parts possible in one setup. Turning machines do the opposite of milling: the workpiece spins and a single-point tool cuts, which is the natural route for anything built around an axis. Grinding and EDM exist for what cutting tools cannot reach or cannot hold. Inspection equipment exists to prove that any of it worked.

Milling machines: three, four and five axes

The three-axis mill moves the tool in X, Y and Z and covers the majority of prismatic work: plates, brackets, housings, pockets, flats, holes and slots. It is the least expensive class per hour and the easiest to program, and for a part whose features are all reachable from one direction it is the correct answer rather than a compromise. Its limitation is that additional faces require repositioning, and each re-clamp introduces a datum shift in the region of 0.02 to 0.05 mm that accumulates across the part.

The four-axis machine adds a rotary table, so a part can be indexed to four sides in a single fixture. That improves positioning accuracy between faces and cuts the handling time, and it suits cams, gear blanks and cylindrical housings with features around the circumference. It does not solve undercuts or compound angles, which need a second rotary axis.

The five-axis machine adds that second rotary axis, and its value is not simply a tighter number. It is that a part which would need five three-axis setups can be completed in one or two, and every eliminated setup removes both a handling step and a tolerance stack-up. Published comparisons put a well-fixtured five-axis mill at 0.01 mm where a long-reach three-axis setup holds 0.02 mm, and describe thermal warm-up protocols on the rotary axes reducing first-article variation substantially. The counterweight is cost: a five-axis machine bills at roughly one and a half to two and a half times the three-axis rate, so on a part that only has features on one face it buys nothing but a higher rate.

Turning machines and Swiss-type lathes

A CNC turning centre rotates the workpiece against a stationary single-point tool, which makes it the natural and cheapest route for any body of revolution. It produces shafts, pins, bushings, sleeves, threaded parts and fittings with excellent concentricity, and the strength of the process is precisely the set of dimensions that follow the rotation: diameter, roundness, cylindricity and runout. A conventional turning centre normally handles parts up to a few hundred millimetres in diameter, and with live tooling it can also mill a flat, drill a cross hole or cut a keyway without releasing the part from the chuck.

A Swiss-type lathe is a fundamentally different machine rather than a smaller one. The bar stock feeds through a guide bushing set a millimetre or two behind the cutting edge, so the unsupported span never grows and the effective overhang stays constant whatever the part length. That is what lets it hold tight roundness on slender work at length-to-diameter ratios that a chucking lathe cannot manage, and it is why bone screws, micro-valves, contact pins and similar small precise parts are made that way. The class tops out at a small bar diameter, so it is not a substitute for a conventional lathe on larger work; the two are complementary.

Grinding, EDM and secondary processes

Some features lie outside what a cutting tool can hold, and the machines that reach them are the finishing classes. Grinding uses an abrasive wheel to remove material in very small increments, achieving sub-micron roundness and finishes below Ra 0.2 micrometres on hardened steel. It is slow and expensive per cubic millimetre, so it is almost always a finishing operation rather than a roughing one, and it is reserved for bearing journals, seal faces, gauge blocks and similar features where the drawing calls for a tolerance or a finish that milling cannot deliver.

Electrical discharge machining erodes conductive material with controlled sparks through a dielectric fluid, so hardness is irrelevant: a wire EDM machine cuts a hardened tool steel as readily as an annealed one. Wire EDM cuts two-dimensional profiles through a full plate thickness with no cutting force at all, which suits thin walls and sharp internal corners, while sinker EDM burns cavities and undercuts with a shaped electrode. Both are slow, so they belong on features that cannot be produced any other way rather than on general work. Deburring, polishing, heat treatment and coating are secondary operations that usually run outside the machining cell, and each is a separate queue rather than a station on the machine.

Inspection equipment: how the numbers are proved

The equipment that decides whether a capability claim is real is the metrology, not the machining. A coordinate measuring machine performs full three-dimensional dimensional verification of complex geometry and is the instrument that settles a first article; a two-dimensional vision system handles fast inspection of small precision parts in batch; a surface roughness and hardness tester confirms the finish and the material condition that the function depends on. A final check before packaging, and a traceable inspection record against your drawing, are what turn a claimed tolerance into a demonstrated one.

This is the part of the equipment list a buyer should read most carefully. A shop that promises a tight figure without a CMM or equivalent metrology is selling a number rather than a capability, and the gap only becomes visible when the second lot arrives and nobody can show what changed. The right question is not which machines are on the floor but which measurements are made on your features, with what instrument, and against what calibration record.

What to ask instead of "what machines do you have"

Six questions extract more than any asset list, and each one has a useful answer and a weak one.

• Which class would you route my part to, and why? A strong answer names a machine class, a setup count and the reason; a weak one names a model number.
• What tolerance do you hold on that class across a batch, not on a sample? Watch for a capability figure with a batch size behind it rather than a best-case number.
• What is your size and shape envelope? Ask for the machine travels in the axes that matter, because a part outside the envelope is a different quote or a different supplier.
• How do you prove the tolerance? The answer should name the instrument, the feature, and the report you will receive.
• Is the same equipment used for the prototype and the series? If the process changes between the sample you approve and the run you receive, the approval means less than it appears.
• What is the calibration and maintenance routine? A worn spindle is not fixed by slowing the feed, and the routine is what keeps a machine inside its specification.

Where a long equipment list misleads a buyer

A long asset list can be actively misleading in four ways. First, more machines do not mean more relevant capability; a floor of a hundred three-axis mills cannot hold a five-axis tolerance or reach a five-axis shape. Second, a machine class that is present but rarely used for your tolerance adds nothing, because capability is a function of routine rather than of ownership. Third, the envelope matters as much as the class: a shop that advertises five-axis work but whose travels are half your part size will quote it as a two-operation job, which changes both price and tolerance stack-up. Fourth, and most often missed, the equipment list describes the machining side and stays silent on the measurement and finishing sides, which is where most delivery surprises originate.

The limits of this answer are worth stating plainly. The tolerance figures above are published capability ranges for each machine class and not a specification for any particular shop, and the same class can differ by a factor of two between a well-maintained machine and a tired one. The right way to use an equipment list is as a first filter for class and envelope, followed by a conversation about which specific machines would run your specific features and how the result would be measured.

Send the STEP model and a toleranced drawing, the material grade and condition, the quantity with an annual forecast, the finish per surface, the size and weight limits your assembly imposes, and a note naming which features are functional. Those items let a supplier route the part to a machine class and tell you whether it needs one operation or three, which is a more useful answer than a floor tour. See CNC machining for how the classes compare in practice, surface finishing for the operations that follow the machine, and become our partners for how a supplier's equipment is reviewed before it enters our network.