8.4 Fill Pattern & Choosing the Right Pattern Tool

8.4 Fill Pattern & Choosing the Right Pattern Tool

Quick Answer: Insert → Pattern/Mirror → Fill Pattern fills a bounded region with instances positioned by spacing and margins, not by a count you type. It is the tool for vent plates, perforated panels, and speaker grilles. SOLIDWORKS lists "linear, circular, and fill patterns" among CSWA's hands-on skills, so you need to recognize it and know when not to use it.

Sections 8.1 and 8.2 built the two patterns you will use most, and 8.3 covered Mirror. Fill Pattern is different in kind from all three, and that difference is the exam-relevant point: linear and circular patterns take an instance count from you; Fill Pattern derives the count from geometry. Confusing the two is how a perforated plate ends up with 41 holes instead of 44 and a mass answer that scores zero.

What Fill Pattern actually needs

1. A fill boundary

The boundary is the region to be populated. Valid selections:

• A planar face on the model
• A co-planar sketch (a closed sketch contour drawn on the face)
• A set of edges forming a closed loop

The boundary must enclose a closed region. A sketch with a gap will not fill. Using a sketch instead of the whole face is how you fill only part of a plate—draw the sketch outline where the vent pattern belongs, and the rest of the face stays solid.

2. Either a feature to pattern, or a seed cut

This is the option people miss. Fill Pattern gives you two routes:

The seed-cut route is faster: one feature, no pre-modeled hole. For a Circle seed you type a diameter; for Square and Diamond a dimension (with a flip between side length and vertex distance); for Polygon the number of sides plus a dimension. You also set the cut depth, which behaves like any extruded cut—if the drawing says through, do not leave a Blind depth that stops short.

3. A layout pattern

Perforation is the one to know by name. Its stagger angle offsets every other row—set 60° and you get the classic honeycomb arrangement; set 0° and you get plain aligned rows that look like a linear grid.

Margins and the derived count

Margin is the clear distance held between the pattern and the boundary edge. Raise the margin and instances near the edge drop out; the count falls. This is the mechanism behind the whole feature: spacing + margin + boundary shape ⇒ instance count.

Some layouts let you flip to instances per side or instances per loop, which hands the count back to you for that direction. Know that both modes exist, because "how is the number of instances determined?" is exactly the kind of conceptual item Drafting-style theory questions are built from.

Instances to Skip

Just like linear and circular patterns, Fill Pattern exposes Instances to Skip. Click the pink markers in the graphics area to remove individual instances—useful when the drawing shows a vent field interrupted by a mounting boss.

The decision table: which pattern tool?

This is the part worth memorizing. On a timed item you want the right tool on the first click.

Trap: Fill Pattern is seductive because it looks like it does everything. It is the wrong answer whenever the drawing dictates an exact count. 6× Ø10 EQUALLY SPACED is a Circular Pattern instruction—six instances, no ambiguity. Building it as a Fill Pattern and getting seven holes is a wrong mass and a zero, even though the plate looks right.

Mass-properties discipline for filled regions

Holes are pure material removal, so every instance the pattern creates or drops changes mass directly. A Ø6 mm hole through a 10 mm plate removes about π × 3² × 10 ≈ 283 mm³. Miss three of them on a steel plate and you are off by roughly 849 mm³ × 0.0079 g/mm³ ≈ 6.7 g—far outside a two-decimal key.

Verification ritual after any Fill Pattern:

1. Count the instances in the graphics area, or expand the feature and read the instance count in the PropertyManager.
2. Confirm the cut depth actually pierces the plate if the drawing says through.
3. Confirm no instance landed partially off the boundary edge (raise the margin if so).
4. Apply the material, then read Mass Properties.

Modification questions

A classic multi-step item reads: "Change the plate thickness from 10 mm to 14 mm and report the new mass." If your fill seed cut used a Blind 10 mm depth, the holes now leave a 4 mm plug and your mass is too high. A Through All end condition tracks the thickness change automatically. This is the same end-condition logic from 5.2 and 7.3, and it is the single most common reason a second-measurement answer goes wrong after a correct first one.

Worked exam-style scenario

Drawing: a 120 × 80 × 6 mm plate, material 1060 Alloy. A 90 × 50 mm rectangular vent field is centered on the top face and filled with Ø5 mm through perforations, staggered, 10 mm instance spacing, 5 mm margin. Report mass.

1. Units → MMGS.
2. Sketch the plate outline on Top; Extruded Boss/Base, Blind 6 mm.
3. On the plate's top face, sketch the 90 × 50 mm rectangle centered on the origin. This sketch is the fill boundary—do not extrude it.
4. Insert → Pattern/Mirror → Fill Pattern. Fill Boundary = that sketch.
5. Pattern Layout = Perforation. Instance spacing 10, stagger angle 60°, margin 5.
6. Under Features to Pattern, choose Create seed cut → Circle, diameter 5, and set the cut to Through All.
7. OK, then count the holes and confirm they all pierce.
8. Apply 1060 Alloy, then Mass Properties.

Everything the drawing gave you—field size, spacing, stagger, margin, diameter—is a Fill Pattern input. That is the signature of a genuine fill problem: the drawing specifies spacing, not a count.

Section checklist

1. Boundary must be a closed face, co-planar sketch, or edge loop.
2. Pick the layout by name: Perforation for staggered vents.
3. Use Create seed cut for plain perforations; select an existing feature only when the drawing details one.
4. Set the seed cut's end condition to Through All when the drawing says through.
5. Count the instances before trusting Mass Properties.
6. If the drawing states an exact count, you want Linear or Circular, not Fill.