CIRCLE CENTER FINDER

**Toolmaker51** · Dec 24, 2017, 11:09 AM

Originally Posted by mklotz

The intended application suggests you don't need tenths (or even thousandths) accuracy in locating the center so perhaps a device based on my math post above might work.
On a metal bar, mount two identical pins about six inches apart on the centerline of the bar. Draw a line on the bar midway between the two pin locations. This is your "chord generator".
Push it against the circumference of the disk until the pins touch. Lay a machinist square on the top of the bar, align with the center mark and draw the bisector on the disk. Repeat. The center is the point where the two lines cross.
It's just a gedanken-design but it might inspire you in your build.

I like that "chord generator". Akin what tool gunsmiths use to mark centerline of shotgun ribs for beads, woodworkers use a larger version to bisect material. Both are identical to your example; with a hole mid-point twixt the dowels, sized for transfer punch of choice.

Math and geometry are fine, and I use them regularly. Plates too rusty to scribe with nice old M&W dividers.
But constructing a center finder, I can do wearing gloves and cold weather gear.
It's 21F degrees outside and a couple colder in the building; Wednesday 17F. In the spring I anticipate 375K BTU boiler to arrive and plumb iron radiators I've collected. Several tons of machinery make excellent heat batteries. Next year I'll be working down there any time I dang well please!

**mklotz** · Dec 24, 2017, 11:37 AM

Make your "chord bar" with lots of holes and several pin sizes and you've got a dual purpose tool, e.g.,

http://www.homemadetools.net/forum/l...r-finder-27455

In that thread, Paul Jones asked the purpose of the brass bar along the edge of the tool and I remarked that I had forgotten why I put it there.

This thread has reminded my aging brain why I did that. Of course, it marks the perpendicular bisector of the chord when the bar is used as described in my last post to find the center of circles.

In deference to your sensibilities I won't report the temperature here in LA. Let's just say the only white we'll have for Xmas will be the surf at the beach. See for yourself...

https://eatgoodstuff.com/resources/strandcam/

**Toolmaker51** · Dec 24, 2017, 12:39 PM

Originally Posted by mklotz

In deference to your sensibilities I won't report the temperature here in LA. Let's just say the only white we'll have for Xmas will be the surf at the beach. See for yourself...

That dodge won't work. Dad and two sisters live there...They've already called to gloat.
My sensibility is shored up by one thing; only place with an affordable right-sized building. And a nice old [1902] home across town for Ms. Toolmaker. Sounds like two, a package counts as one IMHO.