Trim and knit surfaces in Solidworks - Step-by-Step Guide

Introduction

This feature helps you cut away parts of surfaces and then join the remaining pieces into one smooth surface. It solves the problem of messy or overlapping surfaces in your 3D model.

When you want to remove unwanted parts of a surface to fit a design shape.

When you have multiple surfaces that need to be joined into one seamless surface.

When you want to clean up a model before creating a solid body.

When you need to prepare surfaces for further modeling or analysis.

When you want to fix gaps or overlaps between surfaces.

Steps

Step 1: Click

- Surfaces tab > Trim Surface tool

The Trim Surface property manager opens on the right side

💡 Choose the trimming type carefully based on your cutting needs

Step 2: Select

- Surface or plane to use as the cutting tool

The selected surface or plane highlights in the graphics area

Step 3: Choose

- Trimming type options (e.g., 'Trim away', 'Keep selections', 'Mutual trim')

The preview updates to show which parts will be kept or removed

Step 4: Click

- OK button in the Trim Surface property manager

The surface trims according to your selections

Step 5: Click

- Surfaces tab > Knit Surface tool

The Knit Surface property manager opens

Step 6: Select

- All surfaces you want to join

Selected surfaces highlight in the graphics area

Step 7: Check

- 'Try to form solid' option if you want a solid body

Option enables solid creation if surfaces fully enclose a volume

Step 8: Click

- OK button in the Knit Surface property manager

Surfaces knit together into one surface or solid

Before vs After

Before

Multiple overlapping surfaces with unwanted parts and gaps

After

Clean trimmed surfaces joined smoothly into one surface or solid

Settings Reference

Trimming Type

📍 Trim Surface property manager

Defines which parts of the surface to remove or keep

Default: Trim away

Try to form solid

📍 Knit Surface property manager

Attempts to create a solid body if surfaces enclose a volume

Default: Unchecked

Gap Control

📍 Knit Surface property manager

Controls maximum gap allowed between surfaces to knit

Default: 0.01 mm

Common Mistakes

Not selecting the correct trimming type

Leads to removing wrong parts or keeping unwanted areas

Review trimming options and preview carefully before applying

Trying to knit surfaces with large gaps

Surfaces will not join properly and knitting fails

Use gap control settings or fix surfaces before knitting

Expecting a solid without fully enclosed surfaces

Knit will not create a solid if surfaces do not form a closed volume

Ensure surfaces fully enclose a volume or uncheck 'Try to form solid'

Summary

Trim surfaces to remove unwanted parts using a cutting tool.

Knit surfaces to join them into one smooth surface or solid.

Check trimming type and gap settings to get correct results.

Practice

1.

What is the main purpose of the Trim tool in SolidWorks surface modeling?

easy

A. To cut surfaces to a desired shape

B. To join multiple surfaces into one

C. To create new solid bodies directly

D. To add thickness to surfaces

Solution

1. Step 1: Understand the function of Trim

   The Trim tool is used to cut or remove parts of surfaces to get the shape you want.

2. Step 2: Differentiate from other tools

   Knit joins surfaces, and adding thickness is done by other features, so Trim specifically cuts surfaces.

3. Final Answer:

   To cut surfaces to a desired shape -> Option A

4. Quick Check:

   Trim = Cutting surfaces [OK]

Hint: Trim cuts surfaces; think of scissors cutting paper [OK]

Common Mistakes:

• Confusing Trim with Knit which joins surfaces
• Thinking Trim creates solids directly
• Assuming Trim adds thickness

2.

Which of the following is the correct sequence to create a solid from multiple surfaces in SolidWorks?

1. Knit surfaces
2. Trim surfaces
3. Use Knit with 'Create solid' option

easy

A. Trim surfaces, then Knit surfaces with 'Create solid' option

B. Knit surfaces, then Trim surfaces, then create solid

C. Create solid first, then Trim and Knit surfaces

D. Use Knit surfaces with 'Create solid' option after trimming

Solution

1. Step 1: Trim surfaces to desired shape

   First, use Trim to cut surfaces to the correct shape.

2. Step 2: Knit trimmed surfaces with 'Create solid'

   Then, knit the trimmed surfaces and select the 'Create solid' option to form a solid body.

3. Final Answer:

   Use Knit surfaces with 'Create solid' option after trimming -> Option D

4. Quick Check:

   Trim then Knit with solid option = C [OK]

Hint: Trim first, then Knit with 'Create solid' checked [OK]

Common Mistakes:

• Trying to create solid before trimming
• Knitting before trimming without solid option
• Trimming after knitting

3.

Given three overlapping surfaces, you trim one surface to remove the overlap, then knit all three surfaces with the 'Create solid' option checked. What is the expected result?

medium

A. A single solid body formed from the knit surfaces

B. Separate surfaces remain, no solid created

C. An error message about overlapping surfaces

D. Only the trimmed surface becomes a solid

Solution

1. Step 1: Trim removes overlapping parts

   Trimming one surface removes overlap, so surfaces fit together cleanly.

2. Step 2: Knit with 'Create solid' joins surfaces into solid

   Knitting all surfaces with the solid option creates one solid body from the joined surfaces.

3. Final Answer:

   A single solid body formed from the knit surfaces -> Option A

4. Quick Check:

   Trim + Knit solid = one solid body [OK]

Hint: Trim overlaps first, then knit with solid option for one solid [OK]

Common Mistakes:

• Expecting separate surfaces after knitting
• Ignoring overlap causing knit failure
• Assuming only trimmed surface becomes solid

4.

You tried to knit several surfaces but got an error saying the surfaces do not form a closed volume. What is the most likely cause?

medium

A. The Knit tool was used before trimming surfaces

B. Some surfaces overlap and were not trimmed properly

C. The 'Create solid' option was not selected

D. The surfaces are already solids

Solution

1. Step 1: Understand knit error cause

   The error about not forming a closed volume usually means surfaces overlap or gaps exist.

2. Step 2: Check trimming of surfaces

   If surfaces overlap and are not trimmed, they cannot form a closed volume when knitted.

3. Final Answer:

   Some surfaces overlap and were not trimmed properly -> Option B

4. Quick Check:

   Overlap without trimming causes knit error [OK]

Hint: Trim overlaps before knitting to avoid closed volume errors [OK]

Common Mistakes:

• Assuming 'Create solid' option fixes volume errors
• Knitting before trimming is always wrong
• Thinking surfaces already solids cause knit errors

5.

You have a complex model with multiple intersecting surfaces. You want to create a single solid body. Which sequence of actions is best?

1. Trim intersecting surfaces to remove overlaps
2. Knit all trimmed surfaces with 'Create solid' option
3. Check for gaps and fill if needed before knitting

hard

A. Fill gaps first, then trim and knit surfaces without solid option

B. Knit surfaces first, then trim overlaps and fill gaps

C. Trim surfaces, fill gaps, then knit with 'Create solid' option

D. Create solid first, then trim and knit surfaces

Solution

1. Step 1: Trim intersecting surfaces

   Remove overlaps by trimming so surfaces fit together cleanly.

2. Step 2: Fill any gaps between trimmed surfaces

   Check and fill gaps to ensure surfaces form a closed volume.

3. Step 3: Knit all surfaces with 'Create solid' option

   Join surfaces into one solid body after trimming and gap filling.

4. Final Answer:

   Trim surfaces, fill gaps, then knit with 'Create solid' option -> Option C

5. Quick Check:

   Trim + fill gaps + knit solid = solid body [OK]

Hint: Trim, fill gaps, then knit with solid option for best results [OK]

Common Mistakes:

• Knitting before trimming or filling gaps
• Ignoring gaps causing knit failure
• Trying to create solid before cleaning surfaces