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sn0border88
11-22-2007, 07:30 PM
Say you have a bolt pattern that looks alot like one on a wheel, 5 bolts in a symmetrical circle. How does one find the diameter of the circle?

I have tried to transfer punch the holes to a piece of flat, then used a compass to intersect the arcs and find the center thus finding the radius. That didnt work.

My next idea is to measure the distance from center to center on 2 holes and then step that distance off 5 times to make a circle.

The piece is a pinion bearing support off a ford 9" axle, and it has protrusions on both sides so I cannot lay the holes directly on a flat surface to measure, they are a few inches above the base of it.

This is what im trying to make. http://www.pirate4x4.com/forum/showpost.php?p=6202696&postcount=2

steve45
11-22-2007, 08:02 PM
Don't know offhand how you calculate it, but I suspect there wheel manufacturers probably have a chart where you enter the distance between the studs to find the bolt circle diameter.

I've also seen a plastic ring with dozens of holes drilled in it. You rotate the ring until it slips over the studs and read the results.

Here, just found this: http://www.skulte.com/boltcircle.html

aametalmaster
11-22-2007, 08:08 PM
I can email you a drawing. I have lots of 9"s tore apart...Bob

backuproller
11-22-2007, 09:44 PM
try this http://www.filetransit.com/download.php?id=13361 it is a machinist application. but you need to know the diameter of the hole. this will allow you to get the xy to layout the blots from center like this. say you have 5 hole pattern with 8" dia, then you layout these coordinates
X4.0 Y0.0
X1.2361 Y3.8042
X-3.2361 Y2.3511
X-3.2361 Y-2.3511
X1.2361 Y-3.8042
also a machinist handbook already has the bolt patterns in it,

Mooney1el
11-22-2007, 09:56 PM
Don't know if this will be what you're are looking for, but I have found this little routine very helpful.

http://www.macamar.com/sitefiles/articles/bolt-circle-calculator/bolt-circle-calculator.xls

Richard

denrep
11-22-2007, 10:03 PM
That pinion cage probably has unevenly spaced holes, to insure correct assembly. Usually there is a seal drain and an oil trough that needs to be at the bottom.

Try transfer screws, or use a pinion cage shim, or gasket, as a pattern.

Good Luck

sn0border88
11-22-2007, 10:55 PM
Duh, why didnt I think of that. A spare shim!

Though that still leaves me with having to find the center, however it will be much easier to layout the holes accurately. I would just transfer punch the holes and weld but I want to get a cad drawing of this so I can do again for friends if needed.

Ill pm you my email address, that would be great.

Tinbasher
11-23-2007, 01:11 AM
This formula will work for 5 studs:

D= distance between 2 holes / sin 36 degrees, where D is the diameter of the bolt circle

denrep
11-23-2007, 01:35 AM
Tinbasher, You are the mathemagician! :cool: :drinkup:

If ARC theory gets too complex could we axe you for a little help, putting things in common terms?

sn0border88
11-23-2007, 05:00 PM
I tried measuring it again today using an old shim, the one hole has a 1/4" difference so its not symmetrical.

But great formula, its been saved.

William McCormick Jr
11-25-2007, 07:08 PM
I tried measuring it again today using an old shim, the one hole has a 1/4" difference so its not symmetrical.

But great formula, its been saved.

Couldn't you just use Tin Bashers formula on the holes that are in a geometric configuration?

Sincerely,

William McCormick

Roy Hodges
11-25-2007, 10:28 PM
Don't know offhand how you calculate it, but I suspect there wheel manufacturers probably have a chart where you enter the distance between the studs to find the bolt circle diameter.

I've also seen a plastic ring with dozens of holes drilled in it. You rotate the ring until it slips over the studs and read the results.

Here, just found this: http://www.skulte.com/boltcircle.html................................... .................................................. ...
America needs Americas oil ! Yeah, well, we'll get it . Once the rest of the worlds' supply runs out. Why do you think we're using up as much foreign crude FIRST ? - ( in reference to # 2 )

aczeller
11-26-2007, 12:35 AM
in order to find the center of the circle, do this...

1.) draw line between the bolt holes in order to form a rough pentagon

2.) find the mid-point between along each of the newly-created lines

3.) number each bolt hole (1 thru 5) in sequential order going in one direction (doesn't matter which way)

4.) draw a line from the center of bolt #1 to the midpoint between bolts #3 & #4.

5.) draw a line from the center of bolt #2 to the midpoint between bolts #4 & #5.

6.) continue this pattern around the circle. in theory, this should give you a center-point of the circle. worst case scenario, you only wasted 10-15 minutes.

hope that helps.

Later,
Andy

William McCormick Jr
11-26-2007, 04:47 PM
Say you have a bolt pattern that looks alot like one on a wheel, 5 bolts in a symmetrical circle. How does one find the diameter of the circle?

I have tried to transfer punch the holes to a piece of flat, then used a compass to intersect the arcs and find the center thus finding the radius. That didnt work.

My next idea is to measure the distance from center to center on 2 holes and then step that distance off 5 times to make a circle.

The piece is a pinion bearing support off a ford 9" axle, and it has protrusions on both sides so I cannot lay the holes directly on a flat surface to measure, they are a few inches above the base of it.

This is what im trying to make. http://www.pirate4x4.com/forum/showpost.php?p=6202696&postcount=2

If you tried it like this it should work. Unless I misunderstood something.

http://www.Rockwelder.com/geometry/CompassCenter/CompassCenter.html

Sincerely,

William McCormick

William McCormick Jr
11-27-2007, 11:49 PM
You can also use a compass set to a really large distance. To increase the accuracy of the procedure. You just need a bigger place to work.

We use a double bar compass, with two metal points. The two bars slide between a bent piece of spring steel with two slots that the two long bars that hold the pointed scribes, slide through.

When you bend the spring steel it lets you adjust the two bars either in or out to increase or decrease the radius. And then it locks the two bars when you let go. It will make a big circle.

It is great for making large circles and measuring. I had never seen one until about five years ago.

Sincerely,

William McCormick

wannabe_welder
11-28-2007, 12:59 PM
If you tried it like this it should work. Unless I misunderstood something.

http://www.Rockwelder.com/geometry/CompassCenter/CompassCenter.html

Sincerely,

William McCormick

I think what he was looking for was the bolt circle based only on having the 5 studs to work with, so he wanted to find the center and radius based from that.

William McCormick Jr
11-28-2007, 05:28 PM
I think what he was looking for was the bolt circle based only on having the 5 studs to work with, so he wanted to find the center and radius based from that.

Using a compass you should be able to find the center of the circle created by the center of the bolt holes. Then measure from the center of the circle created by the bolt holes, back to the center of the bolt hole, to find the radius.

I only used three bolt holes in that short movie.

I just drew the circle first so you could see what I was measuring. I just put a compass set to a size bigger then the radius into three bolt hole centers and drew arcs.

From that I found the center of the circle created by the four bolt holes that were in a geometric formation.

You have to set the compass to a size that works for your circle and keep it that way, or it will not find center.

Sincerely,

William McCormick

aczeller
11-28-2007, 05:44 PM
one thing that i havn't noticed anyone adress yet, is what happens if all 5 circles are not on the same radius. if you have 5 circles that are all evenly spaced apart, there is no gurantee that they are all in a perfectly circular pattern. if you draw lines from the center of one circle to the other, then measure the angles that are generated by the lines at the bolt centers, they SHOULD each be equal angles (5 bolts would be 108 degrees at each corner) if the bolts are all at the same radius from the center. if the degree at the joint is less than 108 degrees, the bolt is further from the center... likewise, if the angle is greater than 108 degrees, the bolt is closer to the center. i'm sure there is an exception to this rule, but i do not see one within the scenario at hand.

if all the bolts are at the same radius, you have no problems... you can find the center and go from there.

if they are not, you will most likely only be able to get close to the center, with a slight tolerance for error. it'd say to try it out on a sheet of paper, then cut the paper/cardboard as you plan on cutting the metal. if it works, great... if not try again.

Later,
Andy

millman52
01-27-2008, 09:10 PM
If I had a gasket or shim in hand I can make you a CAD drawing. I just don't have any 9" ford stuff (or anything automotive) around.

Donald Branscom
01-28-2008, 06:23 PM
Five holes in a circle would be 72º apart. just use a protractor and straight edge after you find the center.

TO FIND THE CENTER.

The easiest method, and there are many, is to make 3 arbitrary marks with equal spacing around the outside edge of the circle or plate.
Then open your compass to something just past the approximate middle point of the circle.

Use the compass and draw 3 circles with the CENTERS on those marks you made on the outside of the circle.
use a straight edge to draw a line thru the football shaped areas. That is the center.