How to use FILLET command

Here is a free course How to use FILLET command in AutoCAD

Use Fillet to create a new ARC object that blends between two existing LINEs or ARCs.

  • in many cases an ARC is easier to construct using Fillet than it is using the Arc command.
  • for example, it would be a challenge to create the shape shown below if you used ONLY the Arc command.

Fillet is also practical to use when LINEs meet or cross (or would meet if they were extended) in a corner to create a round corner.

You can use a Fillet Radius of zero to force LINEs & ARCs to terminate in a corner at the point of intersection.

  • for example, you can clean up corners in architectural plans if you Offset one side of a wall to create the other side.

Changing The Fillet Radius

When you invoke Fillet the current radius is reported on the command line but you can use the Radius option to change it.

– right-click in the drawing area to invoke a shortcut and pick Radius to change the current radius.

Command: FILLET

Current settings: Mode = TRIM, Radius = 0.7500

Select first object or [Polyline/Radius/Trim]: (right-click)

The Fillet command is terminated when you use the Radius option to set the new current radius.

  • the current radius is stored in the FILLETRAD system variable of the current drawing & is used automatically for the next Fillet.

you must invoke Fillet again to use the new radius.

Trim Mode

The current Trim Mode setting is also reported as one of the current 
settings on the command line when you invoke Fillet.

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if Mode = Trim the lengths of LINEs & ARCs you select for Fillet 
are adjusted to terminate at the endpoints of the new ARC.

use the Trim option of Fillet and select No Trim if you do not want to change the lengths of these selected LINEs & ARCs.

this setting is saved in the TRIMMODE system variable which is stored in your system registry (initial value is Mode = Trim )

  • You can only create one ARC in a single Fillet command.
    1. you are prompted to select two LINEs or ARCs to Fillet.
    2. to repeatedly use Fillet you can right-click in the drawing area & select Repeat Fillet to invoke this command from a shortcut.
    3. for example, the four inside corners of the gasket shown below would require four separate Fillet commands.

  • It can be important where you select objects to Fillet.

AutoCAD uses the selection point to determine what part of the LINE or ARC to keep when these objects are trimmed.

You can select parallel LINEs to Fillet.

the required radius is calculated & used automatically without

changing the radius saved in the FILLETRAD system variable.

AutoCAD changes the second LINE that you select if the LINEs must be adjusted in length.

Command: FILLET
Current settings: Mode = TRIM, Radius = 0.0000
Select first object or [Polyline/Radius/Trim]: (pick LINE near P1)
Select second object: (pick LINE near P2)

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  • You can also apply Fillet to an entire LWPOLYLINE.
  • a fillet ARC segment is inserted at each vertex of a 2D polyline where two LINE segments meet.
  • if an ARC segment separates two LINE segments AutoCAD removes the ARC segment & replaces it with the fillet ARC.

Command: FILLET
Current settings: Mode = TRIM, Radius = 0.5000
Select first object or [Polyline/Radius/Trim]: (right-click to select Polyline option)

practice with FILLET

  1. Close the drawing from the previous exercise if it is open.
  2. Open the T108_4.dwg drawing in your personal folder.
  3. Pick Modify + Fillet and right-click in the drawing area to invoke a shortcut. Select Radius and then type 1.5 as the new fillet radius. The command line history is shown.

The last time this drawing was saved the FILLETRAD system variable was 0 (TRIMMODE was set by T08.scr on page 5)

  • you just set the Radius to 1.5 for the next Fillet command.
  1. Right-click in the drawing area to invoke a shortcut and select Repeat Fillet. Then pick the LINEs near P1 and P2 to add a Fillet ARC in that corner.

  1. Use a similar technique to Fillet the other three corners.

More practice?

  1. Use Trim to modify the CIRCLEs as shown below. (Tip: press <enter> at the first prompt to use all objects as cutting edges then pick the segments that you want to delete)

  1. Use Fillet to complete the drawing (radius is still 1.5).

  1. Save the changes to this drawing and Close the file.
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