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Milling Prototype PC Boards With The Roland EGX-350

We take Roland's EGX-350 CNC milling machine on a test run making fast prototype PC boards. We found it surprisingly good ? it can route, drill and cut out a complete PC board quickly, without using chemicals. It lets you move from concept to working prototype in a matter of hours.

Review by Mauro Grassi

Specifications at a glance:

Table (work) size: 305(W) x 230(D) mm

XYZ-axes travels: 305(X) x 230(Y) x 40(Z) mm

XYZ-axes drive system: Stepping motor – 3-axis simultaneous control

Operating speed:

X and Y axes: 0.1 to 60mm/second

Z axis: 0.1 to 30mm/second

Software resolution: 0.01mm/step or 0.025 mm/step

Mechanical resolution:

X and Y axes: 0.0025 mm/step

Z axis: 0.00125 mm/step

Spindle motor: Brushless DC motor - maximum 50W

Spindle speed: 5000 to 20000 RPM

Dimensions: 616(W) x 591(D) x 393(H) mm

Weight: 34kg

Click for larger image

There are several options when it comes to making prototype PC boards, whether at professional designer level or in a school, college – or even an advanced hobbyist.

One is to send the artwork to a specialist PC board prototyping house and pay for it to be done. While relatively expensive, for many that’s a completely viable option (and one we’ve used here at SILICON CHIP), even though the turnaround will normally be at least 3-5 days.

A big advantage of this method is that the board will (usually) be returned to you with all holes drilled, perhaps with a “conformal” protective coating on the copper and solder mask; sometimes even with a silk-screen component overlay.

Another option is to etch your own PC boards, using perhaps a photo-resist pre-sensitised board and a UV light exposure box.

The results can be good but you have to use chemicals and drill the holes manually, neither of which is particularly pleasant. The chemicals are somewhat hazardous and must be disposed of properly. However, the quickest, most hassle free method, is to use a CNC (Computer Numerically Controlled) milling machine.

A CNC machine’s head can be controlled precisely using a computer. It functions very much like a plotter but has a spinning head containing either a milling (or engraving) “bit” or a drill.

How does it do it?

Blank PC board consists of a non-conductive base layer, usually of fibreglass or a resin-bonded paper, onto which is laminated a very thin sheet of copper.

In the normal “etched” board, the pads and tracks are protected by “resist” while the areas between them are chemically dissolved away, leaving the tracks electrically isolated from each other.

Milling a PC board achieves a similar result but instead of etching, the areas between the tracks are mechanically milled or engraved away, down to the base layer, under the control of a computer. In fact, the software used to create the PC board pattern is usually able to produce the file which can control the CNC milling machine.

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