Drawing tangents

Cannot find a feature to draw a line tangent to two circles that are offset from each other or having different diameters. This is a basic and absolutely necessary function when drawing eccentric mechanical shapes such as cams, belt guards, etc. I noticed that SketchUp already has the capability to draw an arc that is tangent to two lines, and it would seem to me that being able to draw a line tangent to two arcs should be doable. I realize that SketchUp uses and displays individual segments when drawing arcs or circles, but that should only be a display issue, and internally the program should always know where the respective tangent points on the circles or arcs actually are.

Have a look at TIG’s True Tangents extension, available from the SketchUcation plugin store.

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Hi Steve,
Thanks for the feedback. I had seen this info while researching but was a bit skeptical since one of the links I encountered contained a virus so I exited. However, what I cannot find is a clear and consistent set of instructions as to how to actually install a plugin or extension. The TIG True Tangents extension is not listed when searchingthrough SketchUp’ the built in extension manager and other, supposedly reputable instructions I have found on the web (i.e. How to install Plugins in SketchUp | SketchUcation), which are not applicable for my Win10 64 bit version. Particularly the path info specified is non-existent as the SketchUp folder is installed under Program Files and not Program Files (x86) as noted. There is no Plugins subfolder folder listed under the SketchUp 2017 folder. There also appears to be some inconsistencies in terminology as to what is an extension and what is a plugin. The only thing I can find that distinguishes the two is the file extension (.rbz vs .rb). I noticed that you refer to the TIG’s True Tangent plugin as an extension even though it is being called a Plugin. Can you clarify and point me to a current set of extension/plugins instructions applicable to the 64 bit Win10 version and a valid link where I can download the file? Thanks

You can download the file directly to your computer an install it via Install Extension in the Extension Manager. Or better, you can install the Sketchucation Extension Store and let it automatically install it along with others you might get from SCF. Then it’ll help you keep track when it is time to update or if you want to install the bundle when you upgrade to the next version or install on another computer.

The valid source for downloading True Tangents is Sketchucation.

If I understand right, the old name was Plugin, and a plugin had one or more Ruby files with a file extension of .rb.

As more plugins were written by more authors, naming conflicts became more common, with different plugins often using the same variable names in a common name space.

A convention became established, and from maintenance release M2 of SU v8, Extensions became the best way of distributing and installing Ruby programs for extending the capabilities of SU.

In my oversimplified view, a Plugin still can be one or more Ruby files and sub folder(s), normally copied manually into the SU Plugins folder (the location changed in different SU versions, and is different again between Windows and Mac).

An Extension is stricter. There is one Ruby loader file, installed into the Plugins folder again with a .rb extension, and a sub folder of the SU Plugins folder with (by convention) the same name as the Ruby file but without the file extension .rb.

The installation method is simpler too. The extension is compressed into one Zip file, then renamed with a .rbz or ‘ruby zipped’ extension.

This is then either installed manually through the SU GUI from the downloaded .rbz file, or automatically from the Extension Warehouse, or via the SketchUcation Plugin Store’s own plugin.

As usual @DaveR got there first, but part of my response may still clarify the evolution.


<sigh! @john_mcclenahan posted while I was writing this. Oh well, since it is already done I’ll submit it anyway. I haven’t taken the effort to assure a 100% correct timeline, so please old-timers don’t take me to task :wink:. One statement of John’s that I would correct is that namespace clashes were and can still be an issue if authors do not follow best practices in their Ruby code. Trimble’s Extension Warehouse is pretty strict about good module structure, but plugins from other sources may still be problematic.>

Dave has already addressed most of the mechanics of installing, so for your benefit and any others who might read this, I’ll write about some of your other questions.

In the early days of SketchUp, add-ons written using the Ruby API were all called “plugins” and typically consisted of a single Ruby .rb file. The user downloaded them and then installed them manually by copying the Ruby (.rb) file into the Plugins folder (which SketchUp created during installation). There were various repositories for downloading plugins, several of which are still around and active, and also some authors who provided downloads from their own sites.

Over time, several serious issues with this process became evident. Users often had trouble locating the Plugins folder to do the installation. The location was completely different for Mac vs Windows (this is still true). There could be permissions problems with trying to copy a file into the Plugins folder, as it was in a system area that ordinary users don’t have permission to write. And, as plugins became more sophisticated, many of them contained multiple files and subdirectories, all of which had to be correctly placed in Plugins. There was a constant stream of issues from people who just couldn’t get it to work. Also, particularly in corporate environments, the IT department might have policies restricting what users can and cannot download or install.

Late in the SU 8 lifetime, SketchUp started to make changes to improve the situation. They added a new manager to automate the plugin installation process, so the user wouldn’t have to know how to find the Plugins folder. They added the new .rbz file type to better handle plugins that need multiple files and/or directories (though a .rbz can perfectly legally contain a single Ruby file). A .rbz file is just a zip file containing the plugin contents, with .rbz instead of .zip as the file’s extension. The different file extension is only to help avoid someone trying to install a zip that doesn’t contain SketchUp Ruby code. The new manager knew how to unzip and install files from a .rbz and where the Plugins folder was located.

At some point, they also changed the location of the Plugins folder to be in each user’s personal folders instead of the application’s folders. This eliminated the issues with permissions because a user always has permission to access their own folders. But on both Windows and Mac, the standard location of SketchUp’s user-support folders is hidden by the OS by default. The problem of users not being able to find the Plugins folder remains to this day! But, since one is now expected to use the manager instead of doing the install manually, this isn’t deemed to be the problem it once was. It it still possible to download a plugin from an arbitrary site, and if it is packaged in a .rbz, the user points SketchUp’s manager at the file to install it with minimum effort. If it is a bare .rb, the user has to deal with installing it manually.

About the same time, SketchUp added the idea of an “Extension”, which is just a plugin with a particular structure that helps SketchUp to manage it. The base .rb file of an extension contains special code that registers the extension/plugin with SketchUp. This code both identifies the extension and tells SketchUp how to load the rest of it. This information allows SketchUp to decide whether or not to load the entire extension based on user settings. In recent releases they have also added “signing” by which it is possible to verify that an extension’s contents have not been tampered with and also to set restrictions on what extensions can and cannot be loaded.

So, to reiterate, an extension is just a special kind of plugin. Today, because of their advantages, extensions are preferred over bare plugins. But there are still bare plugins available from various sources, particularly ones that the author is not actively supporting. And the two terms are often used loosely and interchangeably.

At some point (I don’t remember exactly when) SketchUcation (one of the oldest and most reputable independent SketchUp sites) created their “Plugin Store”. It is a repository in which almost anyone can place a plugin and it includes a very nice system to download, install, and manage all your extensions/plugins. There are literally thousands of plugins available from SketchUcation. Their manager is itself an extension that you download and install to start using the system. SketchUcation’s store is user-supported; it relies on its members to discuss the merits or flaws of the plugins and to report bugs to the author.

Trimble’s Extension Warehouse is conceptually similar to the SketchUcation plugin store, although Trimble reviews and approves all extensions before admitting them to the EW. This makes it somewhat less eclectic than SketchUcation’s plugin store, but also perhaps a bit safer (not to suggest that SketchUcation’s store is not safe!).

Thanks for the clarification.
I am still having difficulty locating and downloading the file for TIG’s True Tangents. The SketUcation link I found will not accept my user name/password even though I am obviously communicating with you using the same info. Any thoughts or can you steer me to a link? Thanks.

If you haven’t already registered on the SketchUcation site, it won’t know anything about your Sketchup Forum username and password.

EDIT: As DaveR says below, it has no connection with Trimble or this Community forum but is an independent entity.

Go to SketchUcation • Signup and register for a free account using the big blue button [Sign up here] at the top.

Then download the PluginStore download tool: go to Resources, Plugiin Store Download.

In SU, go to Window, Extension Manager, and Install Extension - look for it where you put the downloaded rbz file, usually Downloads.

Once that’s installed, in SU still, go to the menu Extensions: Sketchucation: ExtensionStore.

A window opens, with a search icon near bottom right.
Use that, or Advanced Search, to search for the plugin you want (that’s the generic way to find a plugin whose name or author you know).

Sketchucation is not run by SketchUp or Trimble. It is an entirely separate entity.

I did not realize that Sketchucation was a separate entity and would require a new account. I thought everything was tied together through the forum.

Not so. SketchUcation even has their own forum.

Followed your instruction for downloading and bringing up the Extension Store menu. However, I could not find a search icon nor option for Advanced search even if I manually scroll to bottom of list. See snip below:


There’s a magnifying glass icon at the bottom of the window. Drag the window to make it wider.

I believe the code defining the size of the ExtensionStore menu screen that’s displayed needs to be revised because what I showed you in my snip is a full view of the menu screen as displayed on a 25” monitor, which is why I included a portion of the Win10 taskbar in my snip. The only way I was able to view the ExtensionStore taskbar you referenced was to temporarily hide the Win10 taskbar. Shouldn’t be so and just think it’s a glitch you should be aware of. I was able to download and install the TIG’S True Tangents plugin I was looking for.

Why didn’t you just drag the edges of the window to suit the size you want? Once you’ve set it to the size you want, the dimension will re retained for the next time.

Just so you know, Dave has no connection with the SketchUcation ExtensionStore extension. Amusingly, it is actually maintained mostly by the same @TIG whose true tangents you were trying to download! I tagged him to bring your concern to his attention.

I could not get the cursor to migrate to the edges initially until I hid the task bar. Once I did that At that time, I could reduce the size of the window so that it displays your taskbar. Just wanted John to know that when first brought up, the menu size covers the full screen and your taskbar is not visible.
Since you’re the TIG guy I have a question using True Tangents. If I want to draw tangent lines between two coplanar circles of different diameters and combine them into a single surface (resulting in a beltguard shape), what is the process using common tangents? Do I first have to create two new lines superimposed on the guide lines created by common tangents, recreate the arcs, and then delete the original circles, or is there an easier way?

You evidently did not read or understand what I wrote. Dave is not TIG, he is just a Sketchup expert who is trying to help you.


Sorry Dave……my mixup