Bolt Circle Calculator (Free from CNCCookbook)

1 month by cncdivi

FreeBolt Circle Calculator (Free from CNCCookbook)

Yeah, I know, that “Free” on the end of that title looks a little cheezy, LOL.  What can I say, just trying to get the word out about an important new feature in our G-Wizard Calculator.  Believe it or not, it isn’t the Bolt Circle Calculator that’s important, although it’s cool.  It’s that we’re going to be offering all of the Quick Reference and Geometry applets in G-Wizard for free.  All you have to do is sign up for the 30-day trial and you can access them free, for life, including all the updates and customer service.

Pretty cool, eh?

And no, I haven’t lost my mind, the heart of G-Wizard is still Feeds and Speeds and that isn’t free (sorry!), but it pays for itself in no time through savings in time and tool life.

But what about that Bolt Circle Calculator?

It’s pretty cool too.  We’ve had a Bolt Circle Calculator for quite a while, and it does some way cool stuff:

  • You can set the start angle of the first hole, number of holes, and circle center coordinates.
  • From that, it’ll give you a scaled drawing of the bolt circle like this:

G-Wizard’s Free Bolt Circle Calculator…

Clicking the “Save” button is a new feature–it saves the coordinate table in csv format so you can load it into Excel.  Using Excel string formulas it’s easy to convert that into gcode or whatever other format you might find handy.  You could even just print it so you can take it over to your machine and dial in the bolt circle via DRO.

You can figure this all out with pencil, paper, and trig, but why bother when you can get a nifty free calculator to do the work for you?


But wait, I’d be remiss if I didn’t fill you in on some other useful tips for bolt circles:

Finding the Bolt Circle Diameter

Doing a little reverse engineering and wondering how to find the diameter of an existing bolt circle? You can figure it out by using Chord Math:

BoltCircleDiameter = HoleCenterDistance / sin( 180 / NumberOfHoles )

You can see from the screen shot above that the hole to hole centers form a circle chord.  We can set that calculation up in G-Wizard’s Chord Calculator something like this:

Bolt Circle Diameter from Hole Distance

Figuring Bolt Circle Diameter from Hole Distance…

I entered a distance between hole centers of 2″ at the top.  For the Angle, I used a trick.  I typed “360/8″ and hit <Enter>.  G-Wizard can do math in the fields and popped back with 45 degrees.  That’s all I needed to discover the radius was 2.6131”, so the diameter is twice that.

It’s nice to have all these special calculators working together for problems like this, and all for free.

Even Easier Diameter, But Only With An Even Number of Bolts

Have a look at the 8 bolt circle at the top of the article.  With an even number of bolts, pick any two holes opposite each other and the distance between them is always the diameter of the bolt circle–no Bolt Circle Calculator needed.  This only works with an even number of bolts though.

Generating Bolt Circle G-Code

G-Wizard Calculator isn’t the only software we offer, there’s also G-Wizard Editor, which includes a Conversational CNC Capability.  Making holes is probably the most common operation there is in CNC, so it should be no surprise that G-Wizard Editor includes a Hole Wizard.  You can lay out holes in circles, arcs, lines, grids, and even arbitrary coordinate lists and it will generate the gcode.  Here’s what the basic screen looks like for the Hole Wizard:

Bolt Circle GCode

Generating GCode for Bolt Circles is easy with a Conversational CNC Wizard…

If you’ve never played with G-Wizard Editor, check it out, we’ll give you a Free 30-Day Trial.


Like what you read on CNCCookbook?

Join 100,000+ CNC'ers!  Get our latest blog posts delivered straight to your email inbox once a week for free. Plus, we’ll give you access to some great CNC reference materials including:

  • Our Big List of over 200 CNC Tips and Techniques
  • Our Free GCode Programming Basics Course
  • And more!

Just enter your name and email address below:

Full Name
Email *
100% Privacy: We will never Spam you!

Rate this post

Recently updated on April 11th, 2024 at 09:13 am