The SUBTRACT command in AutoCAD: holes in 3D solids, PRESSPULL, and the selection order that deletes everything

Service openings through slabs, door openings in walls, pockets in beams: sooner or later a 3D model needs holes. There are two main ways. The SUBTRACT command in AutoCAD removes one solid from another, and PRESSPULL pushes a closed shape on a face down into a hole.

This article tries both on a 1000 × 1000 × 200 slab and reads the volume after every cut, checked against hand calculation. It adds two cases few tutorials mention: subtracting a solid that does not touch the slab, and picking in the wrong order. For 3D modelling taught properly, the Institute runs an AutoCAD course for construction.

Two commands, and three that do not exist

Those locations come from the 2027 acad.cuix file. Typing SU is by far the quickest route for everyday use. The web also passes around "commands" named CARVE, HOLE and DRILL for making holes. Asked directly with the getcname function, AutoCAD 2027 returns nil for all three: no such commands exist. The two real ones return _SUBTRACT and _PRESSPULL.

Holes in 3D solids with SUBTRACT, step by step

The Autodesk documentation puts it in one line: "Select the objects that you want to keep, press Enter, then select the objects that you want to subtract."

Example: a 1000 × 1000 × 200 slab with a round hole of radius 100 right through. First build a cylinder of radius 100 and height 200 exactly where the hole goes. The middle column quotes the 2027 prompts verbatim.

Run the subtract command in AutoCAD with those two selections and the slab ends up at 193 716 815. By hand: 1000 × 1000 × 200 − π × 100² × 200 = 193 716 815, exact to the unit. The cylinder is gone; it was used up making the hole.

The selection order that deletes everything

Order is what matters most: the first selection is kept, the second is subtracted. Reverse it, picking the cylinder first and the slab second, and the 2027 release reports:

Null solid created - deleted

Cylinder minus slab leaves nothing, and AutoCAD deletes both solids. The drawing is empty, slab and all. If this happens, type U straight away to undo, then pick again in the right order.

A blind hole

A hole need not go all the way through. Bolt pockets, pipe chases inside slabs and anchor holes for rebar only reach part of the depth. Use a cylinder 100 high placed from level 100 to 200, occupying only the top half of the slab. Subtract as before and the slab is 196 858 407, exactly 1000 × 1000 × 200 − π × 100² × 100. The hole is half the slab deep with a flat bottom at level 100.

The general rule: the hole takes exactly the shape of the overlap between the two solids. Make the subtracted solid as deep as the hole should be; use a box for a square pocket, rotate the tool first for an inclined one.

Many holes at once

Several holes need not be cut one by one. Build four cylinders of radius 50 through the slab, and at step 2 select all four together. The slab is 193 716 815, exactly 1000 × 1000 × 200 − 4 × π × 50² × 200. Four holes of radius 50 have the same total area as one of radius 100, so the two numbers match. Evenly spaced tools can be made with the ARRAY command first, then subtracted in one go.

PRESSPULL in AutoCAD: push a circle into a hole

PRESSPULL in AutoCAD needs no tool solid. Draw a circle of radius 100 lying on the slab's top face (level 200), run PRESSPULL, click inside the circle, then type -200 and Enter. Negative pushes in; positive pulls out.

With -200 the slab matches the SUBTRACT result exactly, and the circle stays in the drawing. With 200 the cylinder grows as part of the slab, still one solid, and the command line reports 1 extrusion(s) created. Autodesk describes the command as one that "Dynamically modifies objects by extrusion and offset."

One catch: PRESSPULL needs a mouse click. Typing a 3D coordinate at Select object or bounded area: gets 2D point or option keyword required. on the 2027 release; you must click the closed area on screen.

Subtracting a solid that does not touch the slab

This happens often when the tool sits in the wrong place, at the wrong level or on the wrong grid line. In the test below the cylinder stands at 3000,3000, well clear of the 1000 × 1000 slab, with no overlap at all, and is subtracted anyway:

AutoCAD reports no error. The slab has no hole and the cylinder has vanished, so at a glance the job looks done. After every subtraction, orbit round to check the hole, or compare volumes before and after.

Choosing SUBTRACT or PRESSPULL

Both give the same volume but suit different situations:

With PRESSPULL, the closed shape must lie on a face of the solid to push into it. With SUBTRACT, the tool must really overlap the solid, or it is simply deleted without leaving any hole. Keeping both rules in mind prevents nearly every surprise described above.

For wall openings the usual pattern is a box tool the size of the door or window, placed through the full wall thickness and subtracted; for slab penetrations a circle pushed down with PRESSPULL is quicker. Either way, check the volume afterwards if the model feeds a quantity take-off.

All results at a glance

Three things often repeated that are not true

SHELL is sometimes called a hole command too; it actually hollows a solid into a thin shell, see the SHELL command. To cut along a plane, use the SLICE command.

Frequently asked questions

Which command makes holes in 3D solids in AutoCAD?

SUBTRACT (alias SU) or PRESSPULL. There is no HOLE, DRILL or CARVE command.

Which solid do I select first in SUBTRACT?

The one to keep, then Enter, then the one to subtract. The reverse order deletes both.

How do I make a blind hole?

Build the tool only as deep as the hole should be, then subtract as usual. With PRESSPULL, typing -100 on the circle gives the same 196 858 407.

Can I cut several holes at once?

Yes. At the second selection, select all the tool solids; four cylinders of radius 50 came out exactly as the hand calculation predicted.

Why is there no hole after subtracting?

The tool did not overlap the solid. AutoCAD still deletes the tool without a word, so undo with U, move the tool into place and subtract again.

How does PRESSPULL differ from SUBTRACT?

PRESSPULL pushes a closed area on a face and needs no tool solid; the resulting volume is the same.