Last updated July 28, 2026
TTT draws a circle tangent to three things you pick. It is the three-tangent circle construction — the one that fits a circle snugly into a corner formed by three lines, or wraps a circle around three others.
It is by Paul Standing, who also wrote the double offset and move layer routines on this site. The header describes the routine as coming “from the creative genius of Paul Standing”, which tells you something about the man’s sense of humour.
It forces the tangent snap
This is the whole mechanism, and it is worth understanding because it explains both what the routine does and what it does not do.
AutoCAD’s tangent object snap is the thing that makes this construction possible at all: it does not snap to a point you can see, it works out where the tangent point needs to be once it knows what the rest of the geometry is. The routine sets your running snap to tangent only, takes three picks, and hands them to the circle command.
So you are not picking points on the circle. You are picking the three objects the circle must touch, and AutoCAD solves for the rest.
The prompts call them “points of tangency”, which is slightly misleading — what matters is which object you click and roughly where, since that tells AutoCAD which of several possible solutions you want. Click near the side of the object the circle should touch.
AutoCAD can already do this
Worth saying plainly. The CIRCLE command has had a three-point option for a very long time, and combined with the tangent snap it produces the same result. There is also a dedicated tangent-tangent-radius option.
What this saves you is the snap management: setting the running snap to tangent, remembering to set it back, and not having to hold down a snap override three times in a row. On a drawing where you need one of these, that is minor. On a drawing where you need thirty, it adds up.
The routine captures your existing snap setting before changing it, which is the right instinct — though as with several routines of this vintage there is no error handler, so escaping partway through will leave your snaps set to tangent. Reset them if you bail out.
Command reference
The file defines a single command, TTT — tangent, tangent, tangent.
How to load it
Unzip TanTanTan.zip and load TTT.LSP with APPLOAD, or add it to the Startup Suite. No support files. Our AutoLISP guide covers loading.
Step-by-step usage
- Have the three objects the circle should touch already drawn — lines, arcs, circles or a mixture.
- Type TTT.
- At each of the three prompts, click the object the circle should touch, on the side you want it to touch.
- The circle is drawn.
If you get a circle on the wrong side of something, undo and click the other side of that object. Where you click within each object is what selects between the possible answers.
Compatibility notes
No date in the file. It sets one system variable and drives the CIRCLE command, neither of which has changed, so it stands a good chance on a current release.
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. It only adds a circle, so nothing existing is at risk.
Download
| Name: | TAN TAN TAN |
| Description: | Allows the user to draw a circle that is tangent to three points. |
| Type: | AutoCAD AutoLISP Routine |
| Author: | Paul Standing |
| File Size: | 1 Kb |
| Cost: | Free |
| Worked on: | AutoCAD |
| Download File: | TanTanTan.zip |
Related routines
- DOF — the same author’s double offset.
- MLAYER — his layer move routine.
- ATC — turn arcs back into circles.