Cleaning Up Geometry
Trim, extend, offset, round and bevel corners, break, join, lengthen, explode, convert and reorder — the Modify tools that turn rough geometry into a finished drawing.
Draw it roughly, then clean it up. That is how most drafting actually proceeds, and this chapter covers the tools that do the cleaning.
They all follow the same rhythm as the drawing tools — see the rhythm every tool shares: start the tool by its short code or its palette button, read the context bar, press an option's letter to change how it behaves, press Enter to finish.
Prerequisites
- Some geometry to tidy up, and a nodding acquaintance with the context bar — see Drawing Basic Shapes.
Trim — T — and Extend — EX
These two are the workhorses of tidying up, and they are really one tool with two directions.
Trim
What it does. Cuts away the part of an object that sticks out past something crossing it — the overshoot where two walls meet, the bit of a line hanging past a boundary.
How: hover over the part you want gone. It shows faint and dashed — that is the preview. Click to remove it. An object that nothing crosses is removed whole. You can also drag a fence line across several parts to trim them all in one sweep. The tool keeps going until you press Enter.
Extend
What it does. The opposite: lengthens an object until it reaches the first thing in its way — the line that stops 20 short of the wall it should meet.
How: hover near the end you want extended, see the preview, click.
The trick worth knowing
Shift-click does the other one. Shift-click while trimming extends; Shift-click while extending trims.
In practice you start whichever you need more of and hold Shift for the occasional exception. You almost never switch tools.
| Option | Key | What it does |
|---|---|---|
| Edges / Boundaries | E | Pick the specific objects to cut or extend to, then Enter |
| All objects | A | Goes back to treating every object as an edge |
| Undo | U | Takes back the last change |
A whole run counts as one undo step, so a dozen trims disappear together if you change your mind.
Offset — O
What it does. Makes a parallel copy of an object at a set distance — like tracing beside it with a ruler held at a fixed width.
How: pick the object, then click the side you want the copy on; the copy follows the cursor as you choose. It keeps going until Enter.
Type a number at either step to set the distance. It is remembered between uses.
| Option | Key | What it does |
|---|---|---|
| Through | T | The copy passes through a point you click, instead of a set distance |
| Erase | E | Removes the original |
| Current layer | L | Puts the copy on the current layer rather than the original's |
Where you will use it: wall thicknesses, kerbs, rebates, setbacks — anywhere two lines run parallel at a known distance.
One behaviour to expect: offsetting a closed polyline inwards further than some of its sides can take simply leaves those sides out. That is correct, not a bug.
Fillet — F
What it does. Rounds the corner between two objects with an arc. Fillet is the engineering word for a rounded internal corner.
How: pick the first object, then the second — hovering over the second previews the result. The sides you click are the sides that are kept.
- Type a number for the radius. It is remembered.
- A radius of
0makes a sharp corner, cutting back or lengthening whatever is needed to make the two meet exactly. This is one of the most useful things in the whole program for tidying corners that nearly meet. Shift-click the second object for a sharp corner regardless of the radius setting.- Two parallel lines get a half-circle joining the ends nearer your first click.
| Option | Key | What it does |
|---|---|---|
| Trim | T | Whether the two objects are cut back to the arc. Remembered |
| Polyline | P | Rounds every corner of a polyline in one go |
| Undo | U | Takes back the last corner |
Chamfer — CH
What it does. Bevels a corner instead of rounding it — each object is cut back by its own distance, and a straight line joins the two.
How: type the first distance, then the second (Enter keeps it the same as the first), then pick the two objects exactly as with Fillet.
| Option | Key | What it does |
|---|---|---|
| Angle | A | Give a distance and an angle instead — for two lines. Remembered |
| Trim | T | Whether the objects are cut back |
| Polyline | P | Bevels every corner of a polyline |
| Undo | U | Takes back the last corner |
Break — BR
What it does. Removes the part of an object between two points — leaving a gap, or splitting it in two.
How: click the object where the break starts, then click the second point. Hovering shows what will go.
A quirk worth knowing: on a circle, the arc that survives runs counter-clockwise from the second point to the first. Click the two points in the other order and you keep the other piece.
| Option | Key | What it does |
|---|---|---|
| At point | A | Splits the object at a single point, removing nothing. Remembered |
| First point | F | Choose the first point again, this time with snaps available |
| Undo | U | Takes back the last break |
At point is the one to reach for when you want to give part of a line a different layer or linetype — split it first, then change the piece.
Join — J
What it does. The opposite of Break. Takes selected objects that meet end to end, or overlap along the same line or circle, and makes them one object.
There are no steps: select, run it, and a message tells you how many objects became how many. Lines, arcs and polylines that meet end to end become a polyline.
To join a spline to a line or an arc, use Polyline Edit instead.
Lengthen — LE
What it does. Changes how long an object is, at one end.
How: hover near an end to see it previewed at its new length, then click. Type a number to change the value in the prompt.
| Option | Key | Changes the length |
|---|---|---|
| Delta | D | By an amount |
| Percent | P | To a percentage of what it is now |
| Total | T | To an exact length |
| Drag | G | Click the end, then its new position |
All four are remembered. An elliptical arc extends around its ellipse; a spline can only be shortened. U takes back the last change.
This is the tool for "make that line exactly 2400". The Properties panel will show you a line's length but will not let you type into it, because length is a derived value — see the Properties panel.
Explode — X
What it does. Breaks objects apart into the simpler pieces they are made of. It works on everything selected at once.
| Object | Becomes |
|---|---|
| A polyline | Its separate lines and arcs |
| A block reference | The block's objects, back on their own layers |
| A text | The outlines of its letters |
| A hatch | Its individual lines |
| A dimension or leader | Its separate parts |
Viewports are left alone.
Explode is a one-way door
An exploded dimension is just lines and text. It will not follow the geometry any more, and it will not update when something moves. The same goes for a hatch.
Ctrl+Zis the only way back, so explode deliberately.
Convert to Spline and Convert to Polyline
Convert to Spline turns selected lines, arcs, circles, polylines and ellipses into splines of the same shape.
Convert to Polyline turns splines and ellipses into polylines made of short straight segments. You type the tolerance — how far the straight segments may stray from the true curve (Enter keeps the current value).
Why you would. Some other programs, and many machines, will not accept splines at all. Converting to a polyline gives them something they can read, at an accuracy you choose.
Polyline Edit — PE
What it does. Changes a polyline one segment or one corner at a time.
How: pick a polyline — a plain line or arc is turned into one first. Then click a segment or a vertex to change it, or press an option letter. Hovering shows what a click would take. Enter steps back out a level.
| What you have picked | Options |
|---|---|
| The whole polyline | Close (C) or Open (O), Join (J), Width (W), Reverse (R), Straighten (S), Undo (U) |
| One segment | Width (W) at its start and end, Straighten (S), Curve (A) through a point, Insert vertex (I) |
| One vertex | Move (M), Remove (D) |
(A vertex is a corner point of the polyline.)
Align — AL
What it does. Moves and turns objects so that two of their points land on two other points — a move, a rotate and (optionally) a scale, in one command.
How: give the first source point and where it should go, then the second pair. Pressing Enter at the second source moves the objects without rotating them.
Scale to fit (S) also scales them, so the second source point lands exactly on the second destination. Remembered.
Where you will use it: dropping a detail into position against two known points, without measuring the angle or working out a scale factor.
Draw Order
What it does. Decides which objects are drawn over which — which matters as soon as you have hatches, wipeouts or solid fills.
How: select the objects (or pick them and press Enter), then choose where they go.
| Option | Key | Puts them |
|---|---|---|
| Front | F | Over everything |
| Back | B | Under everything |
| Above an object | A | Over one you pick |
| Under an object | U | Under one you pick |
Enter repeats the last choice. The objects keep their order relative to each other.
Reach for this when a hatch or a wipeout is covering something it should not.
Match Properties — MP
What it does. Copies the look of one object onto others — its layer, colour, linetype, lineweight and transparency.
How: pick the source object, then pick the objects to change — clicks or boxes, each applied immediately — until Enter.
| Option | Key | Carries across |
|---|---|---|
| Layer | L | The layer |
| Colour | C | The colour |
| Linetype | T | The linetype |
| Lineweight | W | The lineweight |
| Transparency | R | The transparency |
| Style | S | A text's or dimension's style, or a hatch's pattern |
All remembered. Match Properties is also on the toolbar, next to the Layers button.
Why it beats changing things by hand: one pick gets everything right at once, including the layer — which is the thing people most often forget to change.
Next Steps
Next: Working with Text
Transforming Geometry
Move, Copy, Rotate, Scale, Mirror, Stretch and Array — reposition, duplicate and resize what you have already drawn, and build grids, rings and runs of copies.
Working with Text
Put notes on a drawing with the Text tool — height, justification, rotation and style, wrapping to a box, symbols and fields, and how to edit a note afterwards.