# Thread: geometric solution for circular bolt hole

1. Member
Join Date
Apr 2005
Posts
53

## geometric solution for circular bolt hole

I just came across this geometric solution to laying out bolt hole patterns on a circle. For any diameter circle AD divide the diameter into as many equal part as bolt holes needed. Then draw an arc intersection that has a radius of the diameter of the circle from A and D and labial this E. A,D,E form an equal lateral triangle with A,D as diameter of circle. Now draw a line from E throw the second equal point from A on the diameter to intersect with the far side of arc of the circle and labial this F. Now take dividers and set to length A,F. Use this length to work around circle to divide the circle evenly.

2. Senior Member
Join Date
May 2002
Location
SE Texas
Posts
11,239
Before looking for a mathmatical proof of this, I tried a few examples with my CAD program. It works for 3, 4, and 6 divisions but not for 5, or 12. It appears to be an approximation that is limited to some low count divisions.

3. Senior Member
Join Date
May 2003
Location
Riddells Creek, Australia
Posts
256
Why not just use TRIG, it's spot on for any number of holes, or refer to Machinery's Handbook.

4. Senior Member
Join Date
Aug 2006
Location
Taylorsville Ky
Posts
6,041
Yep, Machinery handbook, Everede bolt circle slide rule or DRO. Works perfect everytime.

BUT, if you have to lay out the bolt circle by hand, then using cordinates don't work. I use the guess work method and keep trying untill all the holes fit evenly on the circumference.

5. Senior Member
Join Date
Dec 2005
Posts
4,448
Marvin Klotz posted a program to do this in dos,

I posted one that does polar holes locations in visual basic.. runs in windows.. It is archived on the www.metalillness.com site in documents section.

6. Member
Join Date
Apr 2005
Posts
53
Paul
It does work for 5 divisions. I jest ran it on my CAD program. It is not approximate I expect you set your cad program to round to only 3 digits set to 6 or more it is dead nut on.
Luthor
Can you measure 100 thousands I cant you can use jest parallels and scribe and careful layout to do it.
Carld, David
Yes DRO and dividing head will do it. I have seen posts of Newbes asking how to make dividing plates this will work with jest careful layout.

7. Senior Member
Join Date
May 2003
Location
Riddells Creek, Australia
Posts
256
[QUOTE=New chips]Paul
Luthor
Can you measure 100 thousands I cant you can use jest parallels and scribe and careful layout to do it.

Huh????????

8. Senior Member
Join Date
Dec 2005
Posts
4,448
I've done it with graph paper, caliper and a punch too.

You can lay it out on cad, print it 1:1 and punch right through the paper.. I used to do printed circuits like this too.. drill right through the paper.

Stubborn as heck.. You have to be when you are poor.

9. Senior Member
Join Date
Dec 2007
Location
South Wales
Posts
6,375
buy youself a chord rule and a dividers, it works, flanges that fit arent that difficult with a little practice and a lot of faith

10. Senior Member
Join Date
May 2002
Location
SE Texas
Posts
11,239
Originally Posted by New chips
Paul
It does work for 5 divisions. I jest ran it on my CAD program. It is not approximate I expect you set your cad program to round to only 3 digits set to 6 or more it is dead nut on.
Luthor
Can you measure 100 thousands I cant you can use jest parallels and scribe and careful layout to do it.
Carld, David
Yes DRO and dividing head will do it. I have seen posts of Newbes asking how to make dividing plates this will work with jest careful layout.
My CAD is "set" to more than 6 digits. Five inch circle divided into five and it was off by about 0.002" per hole: total error at the end was about 0.010". Eight inch circle divided into eight and each hole is off by 0.013": total error about 0.104". Six inch circle divided into 12 and each hole was off by almost 0.025": total error about 0.300". I don't know.

Have you seen any proper mathematical proof of this method? Are you sure you did it properly in the CAD program? There are so many other ways that I wouldn't risk using this.

Page 1 of 3 123 Last

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•