Writing VBA macros in Alphacam: where to start

The VBA inside Alphacam lets a shop write tools for its own work. It is familiar to anyone who has written an Excel macro and accessible enough that a beginner gets a first result in a few evenings. This article answers where to start and where you get stuck, from what we learned building GMacros Toolss. No programming background is assumed.

Reaching the VBA editor

The ribbon has an API tab (older releases: an API menu). From there VBA opens the Visual Basic Editor — identical to the one in Office: project tree on the left, code in the middle. Add a Module, write a Sub in it; F5 or the run button runs the macro on Alphacam's open drawing. The same tab has the Add-In Manager, which loads and unloads compiled .arb files.

Object model: App, Drawing, Path, Layer

The Alphacam API is object based. Four objects cover most of the work:

• App — the program itself: the open drawing (App.ActiveDrawing), message boxes, selection.
• Drawing — the drawing: creating geometry (CreateRectangle, CreateCircle, CreateLine…), layers, saving.
• Path — a single geometry (contour, line, circle). It has direction, start point, layer and length; Reverse flips direction, Offset offsets it.
• Layer — a layer. Found or created by name through Drawing.UserLayers; Auto Style reads that name.

The full list is in the API documentation shipped with Alphacam (Help menu or the documentation in the installation folder). Every member has parameters and an example; it is worth reading as a guide.

First macro: a button that draws a rectangle from typed dimensions

The most useful first macro takes width and height from the keyboard and draws a rectangle on the KESIM layer — half of all cabinet carcass parts are exactly that. The flow:

1. Read width and height with InputBox; convert to numbers (mind the decimal separator — Turkish Windows expects a comma in CDbl).
2. Take App.ActiveDrawing; if there is no drawing, warn and exit.
3. Find the KESIM layer, create it if missing, make it the current layer.
4. Draw with Drawing.CreateRectangle x1, y1, x2, y2.
5. Refresh with Drawing.Redraw.

These five steps are the core of the Dimensioned Rectangle Part tool in GMacros Cabinet; the extra work there is validation, multiple parts and labels. Once you combine such a macro with Auto Style, the "type dimensions → get NC" flow is complete.

Layer-name discipline: the macro's real value

The first trap every macro author falls into is drawing on the current layer. Geometry lands on whatever layer the operator happened to be on; Auto Style assigns the wrong operation or none. Rule: for every geometry it draws, the macro selects the layer by name (KESIM, DELIK, CEP, KANAL, ETIKET) and restores the operator's layer when done. Keep the layer names in one constant list; the shop's Auto Style rules use the same list.

Thinking parametrically: dimension, allowance, quantity

A good production macro does not say "draw this door"; it says "take width, height, frame allowance and number of inner offsets, and derive the door from them". The same macro then draws 300×700 and 600×1200. Taking parameters through a form (UserForm) is more comfortable: each field has a default, the last value is remembered, and a dimension list (width×height×quantity) is entered in one go. How parametric door macros are structured is detailed in How Alphacam-based parametric door and cabinet door macros work.

Compiling and distributing: .arb

When the macros are ready, the project is saved/compiled as .arb and placed in Startup; Alphacam loads it at the next start. Ribbon buttons and the tab name are defined in the project. When distributing to other computers, watch three things: Alphacam version compatibility (compiled for an older release runs on a newer one, not necessarily the reverse), 32/64-bit (recent releases are 64-bit) and Windows regional settings (decimal separator). How add-ins load is described in What is an Alphacam add-in, how is it installed and how does it work?.

Pitfalls we met in production

• Decimal separator: the text "12.5" becomes 125 with CDbl on Turkish Windows. Normalise to dot/comma first.
• Empty selection: the user presses the button with nothing selected; a loop over Selection errors. Count first; if zero, explain.
• Units: if the drawing is in inches, millimetre input is mis-scaled. Check the drawing unit.
• Direction: Path.Reverse changes climb/conventional cutting on closed contours; after nesting, directions often need bulk correction. That is why the Reverse Direction tool in GMacros exists.
• Names: avoid Turkish characters (İ, ş) in layer names; they can break posts and DXF exchange.
• Error handling: an error silently skipped with On Error Resume Next reaches the machine as a wrongly drawn part. Catch errors, tell the user.

Write it or buy it?

If the shop's job is single and specific (one part type), a macro written in an evening is enough. If the job covers doors, interior doors and carcasses in full; membrane, framed, glazed, louvred types; handle, hinge and push-to-open holes — writing and testing all of that on every Alphacam release takes months. GMacros packages exist for exactly that: Cabinet Door, Door and Cabinet macros plus GMacros Tools. For those who keep writing their own, the layer and parameter discipline in this article applies unchanged.