Technical Drilling a hole in the exact center of a disc

I have some 1" plastic discs that I want to drill a hole in the exact center. Measure as I might, I can't hit the exact center. Does anyone have a "trick" on how to do this? (Something like "Bisecting an angle" when we were in 10th grade geometry class?)

 

put them in a 1 inch hole saw and drop a transfer punch down the hole for the drill bit

 

frame it , X it with string line..

 

Three jaw chuck on a lathe.
Take a caliper and set it to 1/2" and scribe from the edge in a few places. The intersection will be the center.

 

Boy, that was quick! Thanks, guys.

 

one of these:

 

center finder.

 

The way I would do it, take a piece of paper cut out to the same size circle. Fold it in half, then half the other way. Punch a small hole in the center. Then just lay it over each disc and punch the hole in the disk. Probably not the most accurate way, or most correct way, but that's what I would do. Probably why most of my holes end up being slots. haha

 

Can you use a washer as a drill guide?

Charlie Stephens

 

You just needed an excuse, right?

http://brainerd.craigslist.org/tls/5572152285.html


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Any/all of the above are good suggestions. Also, when you get ready to do the actual drilling, if you can stack them (or some of them) and still be able to clamp them it will save a lot of steps drilling multiples instead of having to mark them individually.

If you can chuck your drill bit in your tail stock you can do them perfectly on a lathe without having to do any marking.

 

draw a right triangle who's edges touch the circumference of your circle, draw it from three positions, the point where the hypotenuse from each right triangle intersect is the center.

 

Or a simple compass with a pencil. Put the point at one edge, and the pencil tip as close to center as you can. Make a mark back and forth across at center. Move it about 90 degrees and repeat. Do that for each 90 degrees, and you'll see where they all intersect, or where the opening is in the middle of the lines. You can actually make even more marks than 90 degrees, but 4 is usually enough to find the center.

 

Man, just Google and be done with it. Good luck.

http://www.todayshomeowner.com/how-to-find-the-center-of-a-circle/

 

Or stick the discs on tfeverfreds avatar ,that should centre point them.

 

What is the "exact" center? Within .01 or .0001? What are you going to use them for?

Charlie Stephens

 

Picture used for example: Draw two lines anywhere from edge to edge of the circle. Measure each of the two lines, and mark the 1/2 of the way point. At that point, draw another line perpendicular to the line; repeat with the other drawn line. Where the two perpendicularly drawn lines intersect will be the center of the circle. Hope that makes sense. Just a simple ruler/protractor is all that's needed.
I am Butch/56sedandelivery.

 

Put two nails in a board 1/2" apart. Lay the disc on the board against them. Drill a small hole in the board at the approximate center. Hold a scribe in the hole and spin the disc, creating a small circle at the center.

 

Boy, don't I wish I could!

 

I have just about everything I need to make a analog of an early Mallory "Big Brass Condenser". I need to drill a hole in the 1" plastic discs for the top terminal (and to use to turn the disc down to the proper taper). Mine won't be an exact copy; more in the vein of the faux 6 volt battery cases for Optima's. Thinking about where they mount, close will be good enough for me.

 

Won't happen, the inner drum of a 1" hole saw will be about 7/8".

If you have a lathe and a three jaw chuck, you are nearly there, you just need a center drill and the drill(s) to get to the required dimension.
If you have no lathe the techniques listed prior will work, just remember center drills are your friend. Also, the success of the job is dependant on the ridgiity of the equipment.

 

for a 1" circle, the centerfinder in reply #6 is the way to go. for theorists,



This is how to find the center of a circle:
If you have something round, you can trace around it on the paper to make your circle. You can also make a circle of any size you want using the compass.


After you have a circle on your paper, draw a line segment with your straight edge inside the circle and label it AB. The exact location and size of the line AB is not important.

Use your compass to draw two equal circles with centers on the points A and B. The radii of the circles should be at least as long as 1/2 the length of AB so that the circles intersect each other similarly to those shown.

Note that the new circles can intersect inside or outside the original circle. It works either way but they must intersect.

Draw a line segment across the intersections of the two new circles and extend it so it touches the original circle. Label the new line inside the circle as CD.




To make things a little easier to follow we removed the two red circles and part of the line. We don't need them anymore so you can erase yours if you wish.

The following is now true.....

• The line CD is perpendicular to the line AB.
• The line CD bisects the line AB.
• The line CD is a diameter of the circle.

You will now repeat to line CD what you did to line AB.
You will bisect it and draw a line perpendicular to it.
The resulting line will be another diameter of the circle.

Use your compass to draw two equal circles with centers on the points C and D. The radii of the circles should be at least as long as 1/2 the length of CD so that the circles intersect each other similarly to those shown. Note that the new circles can intersect inside or outside the original circle. It works either way but they must intersect.

Draw a line segment across the intersections of the two new circles as far as the circle. Label the new line inside the circle as EF.

Again, to make things a little easier to follow you can erase the two green circles and part of the line EF if yours extends outside the circle. You can also remove the line AB. We don't need them anymore.

The following is true ....

• The line EF is perpendicular to the line CD.
• The line EF bisects the line CD.
• The line EF is the diameter of the circle.
• The point where EF intersects CD is the center of the circle!

You now have a circle and you know exactly where the center is!!

Did you get it? Can you think of an easier way to find the center of a circle?

Further Research:
Circle calculator to calculate the area of a circle or the circumference of a circle given the radius.

This work is derived from Euclid's Elements starting at Book III Proposition 1.

Be sure to view the Introduction, and other pages, in this great work by D. E. Joyce.



from here: http://www.makeitsolar.com/science-fair-ideas/90-find-circle-center.htm

now aren't you guys mad at yourselves for slipping that issue of Hot Rod in your geometry book during study hall?

 

I think I am missing something. When you draw a circle with a compass the center is where the hole is from the compass. However, I still like using a washer approach.

Charlie Stephens

 

I knew there had to be a way! A little more complicated than bisecting an angle, but quite similar. Thank you, Southpier.

 

2 or 3x for center finder in post #6

 

I already have the pre-cut discs, with no center marked. I think you're right about the "washer approach". I'll probably be spending tomorrow in the fender washer drawer at the hardware store. If I can find the proper diameter washer, all I will have to do is match a drill bit to the hole in it.

 

I don't remember the exact process, but it involved using dryer sheets and Marvel Mystery Oil.

 

- sure

 

Now I have a headache

 

We use to raise baby hypotnuse's .