Last updated July 28, 2026
Filleting two lines to a sharp corner is one of the most useful things AutoCAD’s FILLET command does — set the radius to zero and it trims or extends both lines to meet at a point. The nuisance is the radius. You set it to zero, do the corners, then forget to set it back, and the next time you want an actual rounded fillet you get a sharp one instead.
This routine handles the whole cycle. It remembers your radius, sets it to zero, lets you pick the two lines, then puts your radius back — every time, without you thinking about it.
What it does in practice
Six lines of code, and every one earns its place. It reads the FILLETRAD system variable and stores it, sets FILLETRAD to zero, runs FILLET with two pauses so you can pick the two objects, then restores the stored value.
The pauses are the mechanism worth understanding if you are learning AutoLISP. A routine that calls an AutoCAD command normally has to supply every answer itself; the pause hands control back to you for one input, then resumes. That is how you wrap an interactive command without losing the interaction, and it is the reason this works at all.
Because it is FILLET underneath, everything FILLET does still applies: it trims lines back to the corner if they cross, extends them if they fall short, and works on lines, polylines and arcs alike.
Two things to know
The command is FZ. Not FILLET0, which is the name of the file and of the download. Fillet Zero, presumably. Two letters is short enough to be worth checking against your own aliases before you load it.
Cancel it and your radius stays at zero. The restore is the last line of the routine, so pressing Escape at either pick prompt exits before it runs. Your FILLETRAD is then left at zero — exactly the problem the routine exists to prevent, only now it is silent because you assume it was handled. If you cancel out of it, set FILLETRAD back yourself or run the command again and complete it.
Adding a proper error handler would fix that, and it is the obvious first improvement if you are looking for something small to practise on. The routine also stores your radius in a global variable rather than a local one, so that value stays in the drawing session afterwards.
Command reference
The file defines a single command, FZ.
How to load it
Unzip FILLET0.zip and load FILLET0.LSP with APPLOAD, or put it in the Startup Suite. This is very much a Startup Suite routine — the whole point is that it is there when you reach for it. No support files. Our AutoLISP guide covers loading.
Step-by-step usage
- Type FZ.
- Pick the first object.
- Pick the second. They meet at a sharp corner and your fillet radius is restored.
- If you escaped out partway, check FILLETRAD before your next fillet.
Worth knowing that AutoCAD’s own FILLET has a Shift-pick shortcut that forces a zero radius for one operation without changing the setting. If your release supports it, that does the same job with no routine at all — but it only applies to one corner at a time, and it is not obvious to everyone, which is why routines like this one exist.
Compatibility notes
No date in the file. It reads and writes one system variable and calls one command, none of which has changed, so there is very little here that can age.
Plain AutoLISP with no dialog boxes and no Express Tools calls, so nothing requires the full product; LT users on LT 2024 or later, the release that brought AutoLISP to LT, should be able to run it. See what runs on AutoCAD LT.
Download
| Name: | Fillet Zero Radius |
| Description: | A great lisp that fillets a 0 radius and sets the radius back to the previous radius setting. |
| Type: | AutoCAD AutoLISP Routine |
| Author: | Anon |
| File Size: | 1 Kb |
| Cost: | Free |
| Worked on: | AutoCAD |
| Download File: | FILLET0.zip |
Related routines
- Trim to Point — another wrapper around a trimming operation.
- BreakPoint — the same idea applied to BREAK.
- DOF — a double offset in one command.