Table Feed CNC Processing Guide

• 1
  What table feed CNC processing actually does
• 2
  How the feed, clamp and spindle work together
• 3
  Where table feed wins and where it does not
• 4
  Material choice drives the whole setup
• 5
  Holding tolerance on a fed sheet
• 6
  How fed parts get verified before shipment
• 7
  What drives cost per part
• 8
  Table feed versus billet milling versus 5-axis

In conventional milling, one billet is clamped in a vise and the tool moves through it. Table feed CNC processing works the other way around: flat stock is indexed across a workholding table, and the spindle cuts one nested profile after another from the same plate. The feed mechanism, either a roller drive or a gantry-style gripper, advances the sheet by a programmed pitch, clamps it, then releases the cut.

The cutting head never waits for an operator to load the next blank. That is the whole point. On a machine with a Ø400 mm rotary table and a 4,000 mm maximum processing size, the same program can run straight through a full sheet of 6061 or 304 without a manual reload between parts.

Three things move at once: the sheet indexes, the clamp engages, and the spindle follows a pre-programmed path for complex 2D profiles, holes, slots and engraving. A limited Z-axis pass adds shallow pockets, countersinks or a light step. Anything deeper than about 1.5 times the tool diameter starts to behave like a milling job instead.

The table itself is not a precision surface in the metrology sense. It is a positioning surface. Accuracy comes from the servo loop, the encoder feedback and the rigidity of the clamp, not from the flatness of the bed. That distinction matters when a drawing calls for tight parallelism across a long part.

A roller feeder grips the sheet between urethane or steel rollers and pushes it forward. A gripper feeder holds the leading edge and pulls. Roller units handle thinner stock, commonly 0.5 mm to 3 mm, and tolerate surface scratches better. Gripper units reach 6 mm and above and hold position more repeatably on heavy plate.

Clamping is where most scrap is born. Vacuum chucks need a clean, flat, non-porous surface. Magnetic chucks only work on ferrous stock, so 6061 aluminium and 316 stainless are out. Mechanical toe clamps leave marks and eat into the nest. The choice of clamp determines the smallest feature you can hold and how much material you must leave as a skeleton.

Spindle speed and feed follow the same rules as any milling operation. A 6 mm carbide end mill in 6061 runs around 12,000 rpm at 2,500 mm/min. Drop to 500 mm/min in 316L and expect to change tools twice as often. Feeds and speeds do not change because the machine is sheet-fed.

Encoder feedback closes the loop. Without it, thermal growth in a long program drifts the pitch and the last parts on the sheet fall out of tolerance. This is why we monitor position on every axis rather than trusting the programmed value alone.

Table feed wins on flat parts with a consistent thickness, a nest that fills the sheet, and features that stay above roughly 1 mm. Bracket plates, heat sinks, chassis panels, gaskets, busbar and mounting plates are typical. If the same profile repeats 200 times and the tolerance sits at ±0.05 mm, feeding a sheet beats loading 200 billets.

It loses when the part needs multi-sided access. A housing with bores on four faces, a manifold with intersecting ports, or anything with a true 3D contoured surface will need 5-axis work instead. Sixteen simultaneous 5-axis machining centers handle that side of the shop; the sheet feeder does not.

Thickness variation is the quiet killer. Cold-rolled sheet holds ±0.05 mm well. Hot-rolled plate can vary 0.3 mm across a single sheet, which shifts Z-zero and ruins depth-controlled features. If your drawing has a shallow pocket at 0.4 mm depth, specify cold-rolled or expect rework.

Small batches are the other boundary. Setup, nesting and first-article checks take time. One prototype is usually better off on a 3-axis mill with a vise. The crossover sits somewhere around 20 to 50 identical parts, depending on how much of the sheet the nest uses.

Aluminium is the natural fit. 6061 and 6061-T6 cut fast, hold ±0.005 mm on well-supported features and take anodizing cleanly. 5052 and 5083 resist corrosion better but gum up tooling at high rpm. 7075 gives strength at the cost of tool life, and 2024 needs care around sharp corners.

Stainless is workable but slower. 304 and 316L work-harden if the feed rate drops, so keep the chip load up. 17-4PH in the H900 condition cuts closer to a tool steel and will shorten insert life. For thin stainless below 1 mm, expect to add a support plate or switch to a gripper feeder with edge support.

Copper and brass feed well and hold tight tolerances. C110 and C36000 are the usual picks for busbar and connector plates. Titanium, Inconel and magnesium AZ31B can be run, but heat, chip evacuation and fire risk change the setup enough that we quote them case by case.

Plastics behave differently. POM and PEEK hold dimensions. ABS and PMMA move with temperature and clamp pressure, so leave more stock and expect a slower finishing pass. Carbon fibre needs dust extraction and a diamond-coated tool.

The tolerance you get depends on three things: how the sheet is held, how far the tool reaches from the clamp, and how much heat builds up over the run. A feature cut 20 mm from the clamp holds tighter than one cut 800 mm away, because the sheet can flex and the servo has more distance to correct.

On a well-supported nest we hold ±0.005 mm on hole position and ±0.05 mm on profile edges as a working figure. Surface finish lands at Ra 0.8–1.6 μm on a standard finishing pass, and Ra 0.2–0.8 μm after a dedicated fine pass or a secondary lapping step.

Spring passes matter more than people expect. A single full-depth pass on a 3 mm aluminium plate leaves a tapered wall. Two passes at 60 percent and 100 percent depth leave a straight one. The extra 20 seconds per part is cheaper than a rejected lot.

Thermal drift shows up late in a long program. On runs above roughly 90 minutes we re-probe the sheet origin at set intervals and shift the work offset. That keeps the last parts on the sheet as true as the first.

A fed sheet hides problems well. One bad clamp point can lift a corner and shift every feature on that row. That is why inspection happens at three points rather than one: incoming material check for thickness and flatness, in-process probing during the run, and a final dimensional check on the finished parts.

First-article inspection covers every dimension on the drawing. After that, we sample critical features at a defined frequency and run 100 percent visual inspection before shipment. Inspection reports are available on request, including material certificates.

Nesting affects inspection too. Parts near the sheet edge see different clamp behavior than parts in the middle. If a feature is truly critical, say so on the drawing so it can be placed in a stable zone of the nest rather than wherever it fits.

We hold ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022. For medical and automotive work, the inspection plan follows the same documentation the customer's own quality system expects.

Four factors decide the price: material utilization, cut length, tool changes and inspection load. A nest that uses 80 percent of the sheet costs far less per part than one that uses 45 percent. Designers who leave generous spacing between parts pay for the gaps.

Cut length is the second lever. Every hole, slot and radius adds machine time. Reducing a 40-hole array to 24 holes with a larger pitch often saves more than a tool change. The cheapest hole is the one the design does not need.

Tool changes are pure lost time. A part that needs four tools and a probe cycle runs slower than one that needs two. Grouping features by tool diameter in the CAM strategy keeps the turret still and the cycle short.

Inspection load is the fourth. A drawing with 60 toleranced dimensions costs more to verify than one with 12. If a dimension does not affect fit or function, leave it as a reference rather than a hard limit.