Sheet metal + machining

How to Laser Cut My Own CNC Machine

This guide is for engineers building a router or mill frame from plate. It covers which parts should be laser cut, which should be machined after cutting, and the parameters that decide whether your gantry stays square.

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3-25 mm plate±0.1 mm cut toleranceStress relief before finishing

how to laser cut my own cnc machine frame plates

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Key takeaways

Laser cuts profiles, not fitsHoles for bearings and linear rails need a secondary boring or milling pass.

Kerf is a real dimensionA 2 mm nozzle cut removes 0.15 to 0.3 mm of material. Offset the CAD contour by half of that.

Thickness sets the processFiber laser handles 3 to 12 mm mild steel well. At 20 mm it is slow and often cheaper to waterjet.

Heat moves the partCut edges cool fast and pull the plate. Leave tabs and cut the outer contour last.

Flatness beats toleranceA laser-cut plate is accurate in XY but not flat. Machine the mounting faces if you need parallelism under 0.1 mm.

Part 1

Which CNC frame parts belong on a laser

A laser is a 2D process. It follows a contour through flat stock and leaves a clean edge. That makes it a good fit for side plates, base plates, gantry risers, motor mounts and enclosure panels, where the shape matters more than the fit.

It is a poor fit for anything with a bore. Bearing seats, linear rail mounting holes, ball screw end blocks and spindle clamps all need round holes held to a few microns. A laser leaves a slightly tapered edge and a heat-affected zone of 0.1 to 0.3 mm. You cannot hold an H7 bore that way.

The practical split is simple. Laser the outline, the lightening pockets and the clearance holes. Then send the same plate to a mill for the bores, the rail shoulders and any face that another part slides against. On a typical 750 × 1,150 × 550 mm router frame, four plates go through both processes.

One more rule. If a feature carries load in more than one direction, treat it as a machined feature even if the drawing shows a simple hole. Corners in laser-cut slots are radiused by the beam, not sharp, so a dowel pin will not seat where you drew it.

1
LaserSide plates, gussets, base plates, covers, cable trays.
2
Laser then millRail mounting faces, bearing bores, spindle plates, ball screw supports.
3
Do not laserThreads, keyways, tapered fits, anything under Ra 1.6 μm.

Part 2

Material and thickness choices for a laser-cut frame

Mild steel is the default for a rigid frame. A36 and 1018 cut cleanly from 3 to 12 mm on a fiber laser. Above 16 mm the cut speed drops sharply and the edge picks up more dross, so the cost per part climbs faster than the strength gain.

Aluminium behaves differently. It reflects more of the beam and conducts heat away fast, so 6061 and 5083 need higher power and often nitrogen assist. Cut quality is acceptable from 3 to 10 mm. Thicker aluminium plate is usually better waterjet or sawn and then machined.

Stainless 304 and 316 cut well and hold a sharp edge, which suits gantry plates on machines that see coolant. Expect more heat input than mild steel, so plan the cut sequence to keep the part cool.

The heat-affected zone is the number that matters. On 6 mm mild steel it is roughly 0.1 to 0.2 mm deep. On 10 mm stainless it can reach 0.3 mm. If a rail sits directly on a cut edge, that zone will show up as a soft spot under the bolt head. Machine the face and the problem disappears.

1
3 to 6 mmEnclosure panels, gussets, small router frames.
2
8 to 12 mmMill and router side plates, base plates, risers.
3
Over 16 mmConsider waterjet or saw plus machining instead.

Part 3

Kerf, tolerance and what the drawing must show

Kerf is the width of material the beam removes. On a 2 mm nozzle with 1.2 mm focal spot it lands between 0.15 and 0.3 mm depending on thickness and assist gas. Your CAD contour is the finished edge, so the machine offsets the path inward by half the kerf. Ask your cutter what value they use and check one test coupon before running the whole nest.

Positional tolerance on a good fiber laser is around ±0.1 mm across a 3,000 mm sheet, and ±0.05 mm on smaller plates. That is plenty for bolt clearance. It is not enough for a press fit. If your drawing shows a 20 mm bore with a plus-zero-minus-fifty-micron callout, the laser shop will either refuse it or hit it by luck.

Hole diameter has a floor. A general rule is that the smallest clean hole is about 1.2 times the material thickness. On 6 mm steel, do not draw holes under 7 mm unless you accept a rougher edge and slower cut.

Finally, mark your datums. Laser cutting gives you an accurate outline but no reference face. Add two tooling holes that the mill will use later, and keep them off the part outline so they survive the second operation.

1
Kerf offsetHalf of kerf, applied by the cutter, not by you.
2
Minimum holeAbout 1.2 × thickness for a clean edge.
3
DatumsTwo tooling holes, reused for the milling setup.

Step by step

Step by step: from CAD to a squared frame

Follow the order. Skipping the coupon or the stress relief is where most home-built frames go out of square.

1
Model the frame in 3DBuild the assembly, not just the plates. Check that the rail spacing, the ball screw center height and the motor mount bolt circle all resolve before you cut metal. Export a 2D DXF per plate with the outline on one layer and the tooling holes on another.
2
Choose material and thicknessFor a router up to 1,200 mm travel, 10 to 12 mm mild steel side plates are a sensible starting point. For a small mill, 16 mm steel risers are common. Confirm the plate is flat to within 0.5 mm per meter before cutting.
3
Set the cut parameters6 mm mild steel: about 1.5 to 2 kW, 3 to 4 m/min, oxygen assist. 6 mm 6061 aluminium: 2.5 to 3 kW, 2 to 3 m/min, nitrogen at 12 to 15 bar. 6 mm 304 stainless: 2.5 to 3 kW, 2.5 to 3.5 m/min, nitrogen. Treat these as starting points and dial in on the coupon.
4
Cut a test coupon firstTake a 100 × 100 mm offcut of the same heat and thickness. Cut a 10 mm hole, a 6 mm hole and a straight 200 mm edge. Measure the hole with a pin gauge and the edge with a micrometer. This tells you the real kerf and the real hole undersize on your material.
5
Nest with tabs and a cut orderPlace the outer contour last so the plate stays stiff while the inner pockets are cut. Leave 3 to 5 mm tabs every 150 to 200 mm on the outer contour. Tabs stop the part from tipping into the slats and getting a gouged edge.
6
Stress relieve before machiningLaser cutting puts local heat into the plate. Even a 0.2 mm heat-affected zone can pull a long plate out of flat. Have the plates normalized or at least let them sit 24 hours, then measure flatness again before the milling setup.
7
Machine the critical facesSet the plate on the tooling holes. Face both rail mounting surfaces in one setup so they are parallel. Bore the bearing seats to the drawing fit and drill and tap the rail holes. Keep the laser edge as the cosmetic outline, not as a datum.
8
Assemble and check squareBolt the frame together loose, then measure the diagonal across the gantry. Adjust until both diagonals match within 0.1 mm, then torque in a star pattern. Recheck after 24 hours, because bolted joints settle.

Process check

Laser cutting compared with the alternatives

Numbers are typical for a 6 mm plate. Your shop may differ.

Process	Edge quality	Best thickness	Use it for
Fiber laser	Clean, small HAZ	3 to 12 mm steel	Outlines, pockets, covers
Waterjet	No heat input	Up to 50 mm	Thick plate, heat-sensitive alloys
Plasma	Rough, wide HAZ	Over 12 mm	Rough blanks for later machining
CNC mill from solid	Ra 1.6 μm or better	Any	Bores, rail faces, tight fits

FAQs

Questions engineers ask before cutting

Can a laser cut the bearing bores directly?

No, not to a press fit. A laser leaves a slightly tapered edge and a heat-affected zone, so an H7 bore is out of reach.

Cut the hole undersize and bore it on a mill. Leave 0.5 to 1 mm of stock, and set the tooling holes as your datum.

What is the largest frame plate I can laser cut?

Most fiber laser beds take 3,000 × 1,500 mm sheets, and some handle 4,000 mm in one axis. That covers almost every router frame in one piece.

If your plate is longer, split it at a natural joint and add a bolted splice. A splice is easier to keep square than a welded seam.

Does laser cutting leave the plate warped?

It can. The heat-affected zone is shallow, but a long thin plate with a lot of cut length will curl.

Reduce it by cutting the outer contour last, leaving tabs, and letting the plate cool flat. For critical frames, stress relieve after cutting and machine the faces afterwards.

Should I weld the frame or bolt it?

For a first build, bolt it. Bolted joints let you shim and re-square without rework.

Weld only when you have a fixture and a plan for post-weld machining. Welding moves a frame far more than laser cutting does.

How tight can the laser hold hole position?

Around ±0.1 mm across a full sheet on a well-maintained machine, and tighter on small plates.

That is fine for M6 and M8 clearance holes. For rail mounting holes, drill them in the milling setup instead of relying on the laser position.

What finish should the frame get after cutting?

Bare laser edges rust quickly in a shop with coolant mist. A light oil or a black oxide pass protects them.

If the machine sits in a clean room or a medical build, bead blasting followed by anodizing or powder coating gives a better result. Keep coated faces out of the rail mounting surfaces.