# How to find or create bolt circle coordinates



## Metal Butcher (Feb 28, 2009)

I found this information on the internet. It enabled me to create and locate the bolt pattern on my proposed modifications to Elmers 3-cylinder radial. Without this I was totally lost. ??? 
Locating drilled or taped holes in crank cases, cylinders, and cylinder heads is no longer a mystery to me. This is very good information for those getting started in the machining hobby. 

Link: http://www.metalwebnews.com/formulas-tables/coordinates.html

RickM..


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## David Morrow (Feb 28, 2009)

Alternatively, you could cheat a little. If you have a Cad program, lay out a polar grid and enter the holes where you want them using the Snap To Grid feature. Then let the program tell you the X & Y coordinates of each point. Be sure to set the program to display at least 3 decimal points. In my program (TurboCad), it's called the Space Units; I'm not sure if that's generic terminology for Cad programs or not. 

If you can't manage either, post a message somewhere on the forum; someone who has a Cad program can do it for you pretty quickly.


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## Mike N (Feb 28, 2009)

This is a nice chart. I use AutoCad to figure out bolt circles, but the last few diagrams help to determine the diameter of a bolt circle from just 2 points. Very useful.

I converted the web page to a PDF format.

Thanks 

View attachment Bolt Circle Coordinates.pdf


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## Tin Falcon (Feb 28, 2009)

Not knocking the ling here are some other methods.
This info is also available in the Machinerys Handbook AKA the machinist bible. 
IIRC Marv Klotz has a program on his web page
 Bolt circles can be layed out with dividers 
 Many CNC programs and DRO,s will figure it out for you. 
Last but not least do the trig.
 Tin


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## mklotz (Feb 28, 2009)

The BOLTCIRC program on my page will create a printable list of coordinates for any bolt circle. If you want to lay out the circle the old-fashioned way with dividers, the CHORD program will calculate the required chord length.

If you want to derive the bolt circle radius/diameter from the chord measurement, the CSEG program will do that.


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## Jasonb (Mar 3, 2009)

Or there is the good old Zeuz tables

Jason


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