Today's Teaser

[William Miller]

:XX This is for all you thinkers out there!
I bought some 8" (+/-) diameter cake baking pans last night which will become the backing plate for cooling my brakes.

I need to find the exact center of the pan to lay out the hole for the spindle as well as the 3 mounting bolts.

HOW DO YOU FIND THE CENTER OF A CIRCLE?

I had done this before but couldn't remember and had to resort to the WWW.
I found that there are many ways to do this.

If you can resist looking it up, how would you do it?

[Trak Ratt]

No math wiz :oops: but; accurately trace bottom outside circumference onto piece of paper. Cut out and fold into fourths. Center is point where all seams meet. Trace on pan.

[OldTee]

scribe a line from one side to the other then move 45 (or so) degrees and scribe a second line. Where they intersect is the center.
ARF

[KFJ]

I remember reading something about this once (I swear I didn't look it up). IIRC you can draw a triangle within the circle - doesn't matter the type (equilateral not necessary). Mark the middle of two legs and draw a lines from the triangle points to the middle mark. The intersection of the two lines is the center.

Forgive my crappy MS Paint skills, but you get the idea.

[HoodPin]

Another approach is try and measure the largest diameter (move ruler back and forth slightly will confirm when the measurement is largest). Then draw a line near the center. Move the ruler about 90 degrees and do it again. Where the lines intersect will be the center (intersection of 2 diameters, which should be the longest lines you can draw thru the circle).

Ok...my descriptive skill aren't so good..... But the result is the same as using the triangle in the other post.

[Jazzbass]

Amateurs. :) You use one of these. Stop by and borrow mine if you don't have one.

[Vicegrip]

Get a compass. The hinged thing with a point and a lead, not the thing with a needle that points North. Set the point on an edge and open it up to what you think is the center. Make a little scribe at that you think is center and move the outside point 90 deg and make another little scribe repeat until you have made 4 little scribes. you will find that they all cross in the center or if you are off have made a little square with concave or convex sides. This is OK. X mark the square and you have center. Ajust the compass to check you work. this is fast and makes for dead center. you can make a compass out of some coat hanger bent into a V and a pen and some tape. Snip the point end at an angle with a cutter and you have a point. Tape the pen to the other side and bend open or shut as needed.

Another that works without measuring or tools but produces good results. Take a small cut of cardboard that is slight longer than 1/2 the size of the circle. Set one edge on the disc edge and make a mark on the edge of the cardboard and the disc in the same place. Move 90 deg and check. Off? clean off the marks and tweek you guess using the info from the first time to dial it in. Repeat untill the mark on the cardboard and the mark on the disk line up with the cardboard at any point around the edge. No odd tools, no measuring, hits dead on and almost foolproof.

Yet another way. Balance the disk on a pin if you dont have a compass. Good way to start out for method #2.

[Rick V]

just buy backing plates already provisioned for cooling ducts :)
Kirk has the right "old school" answer.

[BlackTalon]

Of all these suggestions, the folded paper circle seems to be the simplest, and 2nd most accurate (Jazzbass wins that one). If you can't judge the center, how well are you going to judge moving 45 degrees? 90 degress is easier, as you can use a square as an aid. But the reality is, even the method of sliding a ruler and looking for the widest point in order to draw a diameter will probably get it close enough. And in order for the triangle method to work, two sides need to be the same length (easy to do using a ruler pivoting about the same point). But at the end of the day, the folded paper circle looks like the clear winner! :-)

I'm still waiting on DR's response... Will probably be something like "hit it with a BFH, and the maximum deflection will be at the center point!" :-)

[Trak Ratt]

DR's response... Will probably be something like "hit it with a BFH, and the maximum deflection will be at the center point!"

I considered that but thought it might make doing anything with the pan after wards somewhat moot :p

Of all these suggestions, the folded paper circle seems to be the simplest...
FUCHS WHEELS, what did you do with DoubleD (not that we want him back, just that’s he’s OK) cause the real DoubleD would never, I mean ever say something like that about one of my ideas.
I actually liked Kurt’s solution the best, can find center fast, accurately, and with the simplest of tools. I keep several coat hangers in the shop for just such undertaking. ;)

[flatsixcrazy]

I'm with Kurt's compass method. If it is 8" in diameter, open the compass to 4" and scribe the arcs from outside diameter as many times as you like (the more strikes, the more precise the center point). The point where the arcs intersect is your center. Assuming you have a compass handy and the outside diameter is 8" :-). Andy

[Dr K]

How about getting a wire brush (preferably rectangular, and at least half the diameter of the pan). Slide it along the floor while you roll the pan next to it. The center is where there's a dot in the middle of a whole lot of concentric circles. Check with the compass.

Peter

[APKhaos]

The 45 degree method that Jass showed was the way I first learned to do it, and still my fave. The compass method works just as well, but its a lot slower.

[Noah]

When I registered my Dorkiphus account, I was told there would be no math.

[Trak Ratt]

When I registered my Dorkiphus account, I was told there would be no math.
Paper, crayon, and scissors baby ;) No math, no how :cool:

[Vicegrip]

I guess this is why its called "Pie" Get it "Pi"? ...for a pie plate. I love it, it just works on so many geeky levels.


Remember folks we have been tasked with finding center of an flattened inverted truncated cone not a neat flat circle or cylender.

[Trak Ratt]

... Get it "Pi"? ... Remember folks we have been tasked with finding center of an flattened inverted truncated cone not a neat flat circle or cylender.
I know you are talking in code, and I kind-of-sort-of remember these words being used before but it still sounds like MATH Please stop my head hurts :(

[HoodPin]

Did you hear about the Dorki who was arrested by Security at the airport when they discovered a ruler and compass in his carry-on bag?.........

He was charged with possessing weapons of math instruction. :roll:

[APKhaos]

I bought some 8" (+/-) diameter cake baking pans last night which will become the backing plate for cooling my brakes.

Kurt,
We are both potentially well out of our home ground here, but the base of a cake baking pan is round and flat, right? You're just introducing the flattened truncated cone to sow fear, uncertainty and doubt, right? :D

[William Miller]

Here is a method I'm not sure anyone mentioned.
The center can be found by drawing two cords (a line segment that touches two points on the circle, then you measure and find the center of each cord and draw a line that is perpendicular the center is where the two perpendicular lines meet. This is sort of like doing the triangles, but I think the sides don't have to be equil to base but they have to equil each other.

The second drawing shows that if you make two circles with a compass with the point on the end of the cord then a line drawn thru the points where the 2 circles meet will make a line perpendicular to the cord. I think the circles need to be big enough and the same size. (This looks like it will work, but I haven't seen it anywhere)


The second picture was the method Jazz mentioned. When I looked this up on the internet, I remembered that I had the tool with the other cool layout stuff my dad left me!
For this job it was the right tool. It's hard to put the point of a compass on the edge of the pie pan. I think all the other methods are great.
We have some talent here for sure!

What a great resource...Now.. My daughter has some homework problems that are over my head!

[William Miller]

How about getting a wire brush (preferably rectangular, and at least half the diameter of the pan). Slide it along the floor while you roll the pan next to it. The center is where there's a dot in the middle of a whole lot of concentric circles. Check with the compass.

Peter

Are these implements what you use at the office;)

[Redroc]

Have we measured the pie plate for true roundness? What is the pie plate manufacturer claiming for their percentage of error? :D I'm sure that they never figured that their simple pie plate was going to be used in such a technical fashion. Maybe Pelican should start selling them.

Mmmmm.... Key Lime Pie!!!!

[Dr K]

So now how does the pie plate help with cooling?

[KevinOyler]

Shields the rotors from hot pavement in the summer.

[William Miller]

The pie plate, along with an outlet on the back replicates the $300+ kits.
The first picture is the business end.
The second is the duct routing.
Third is my front valance. Behind the faux fog lights are intake scoops.
More air to brakes = more cooling:)

[HoodPin]

Nicely done. But I have a question. Is it necessary or helpful to use the entire backing plate? Wouldn't trimming away some of the backing plate, while leaving just enough to provide a solid mount for the duct, allow for better heat dissipation from the rotor?

[Vicegrip]

Be careful to inspect plumbed systems that fully block off the rotor vane intakes often and any time you think you might have pinched the tubing. If the intake tube gets messed up or crushed and they do from time to time the rotor will fry from less that original cooling. Some install the duct so the air is only added to the existing vane induced cooling.

EDIT Tony and I typed a post at the same time. What he said...

[Jazzbass]

Bill, I'm assuming that's your car in the 2nd pic? If so, anyone else notice some of the other goodies Bill's been secretly installing? :)

[Vicegrip]

bump steer kit and floating rotors.

[edevinney]

Bill, I'm assuming that's your car in the 2nd pic? If so, anyone else notice some of the other goodies Bill's been secretly installing? :)

Yeah, nice lift :-)

[William Miller]

All good questions.
1st... the 1st two pictures were copied from other sites. Not my car.
I'm still collecting parts for the big project.
I'm on the final planning of the 3.6 swop,
While I'm in there:
I'll be swopping the suspension over from my cab which is all almost new, slightly upgraded parts.
While I'm in there:
Makes sense to upgrade the brakes.
While I'm there it makes sense to make some provisions for cooling.

So it seems before going forward, maybe you guy's can fill in the details about your comments.
The scoop is already in place behind the fog lights. I was planning on builing the backing plate with the cake tin. I was only going to install the hose and open the fog light holes up on track days. Oh yea, the licens plate will come off too to allow more flow to the oil cooler and I have a lip that will bolt onto the bottom of the valance.
I don't know if cooling will be even necessary, but I wanted to make provisions for it while I've got everything apart.

With the current plan, the hose would be off most of the time. The backing plate only covers the center of the rotor so the faces will still be open.

Discussion....

[William Miller]

Yeah, nice lift :-)
;) Thanks again!

[William Miller]

If it's preferred, a simple backing plate like this would actually be easier.
Although I think this one probably covers the whole, hole.;)