Math question: diameter from a portion?

[rwest]

Hi,

I have a small wooden part with a curve to it and I want to replicate it on the lathe by turning a complete circle so trying to figure out how to take the measure of the slice to get the whole.

To make a simple comparison, if I had a slice from a pie and wanted to figure out the diameter of the pie from just the crust curve of one piece.

Hopefully the brain trust can steer me “straight”.

Thanks,
Rutager

[Ayles]

I think this calculator gets you what you need:
https://www.omnicalculator.com/math/sector-area

[herr_oberst]

Like this?

[stevej37]

I was about to say "I love banana cream pi"...but am afraid of where that might go.

[John Rogers]

You can do it by math or get a large enough piece or craft paper and stick a pin to act as the center and rotate your piece around it and draw a line on the outside until you get a full circle. Then measure across the circle.
John

[rwest]

Originally Posted by herr_oberst

Like this?

Perfect- great explanation and easy to follow.

Thanks!

[rwest]

Originally Posted by Ayles

I think this calculator gets you what you need:
https://www.omnicalculator.com/math/sector-area

Thanks, I found that one, but my math skills aren’t good enough to figure out where to put all the numbers!

[KFC911]

Mmmm... Cherry Pi

[sc_rufctr]

Happy Pi day

[Ayles]

Originally Posted by rwest

Thanks, I found that one, but my math skills aren’t good enough to figure out where to put all the numbers!

Ha ok! There are links to definitions of each variable so that might get you close.

What about making a compass thats big enough to accomodate the wedge?

[stevej37]

^^^ That's what she said.

[rwest]

Originally Posted by John Rogers

You can do it by math or get a large enough piece or craft paper and stick a pin to act as the center and rotate your piece around it and draw a line on the outside until you get a full circle. Then measure across the circle.
John

Hi John,

In this case, my piece doesn’t go to the center, but I bet I could run lines down each side and measure from the middle to get the empirical answer. Just tried it and apparently the diameter would be huge as the lines weren’t even close at two feet out! I may have to give up on the lathe idea.

Here’s the project- I got a bunch of hand plane bodies and I wanted to make a custom wood infill for one. The originals were Rosewood or anodized aluminum, so I do have a piece to use as a pattern, just thought it would be easier to turn a section, but my lathe won’t turn a huge diameter inboard and I’ve never tried outboard turning.

[rwest]

Apparently Byron left his camera at my place! Sorry about the blurry picture.

[cockerpunk]

this is an easily googable problem.

[stomachmonkey]

Seems infinitely simpler to use one of the pieces to trace out a template then hand shape.

[sc_rufctr]

Originally Posted by cockerpunk

this is an easily googable problem.

Yes it is but...

[rwest]

Originally Posted by stomachmonkey

Seems infinitely simpler to use one of the pieces to trace out a template then hand shape.

Yes, once I determined how huge the diameter was going to be, that’s the route I will take.

My initial thought was that since it had several facets and a compound curve that I could get a “perfect” shape if I turned it and could also make several at once and even out of different woods by doing segments on my round blank.

[Superman]

Clever.

[Amail]

You could rough-cut the shape, then attach it to a long pivoting arm and pass it over a router.

[MBAtarga]

Rutager,

If I follow your issue - why don't you cut a jig to match that diameter and just use a router with a follower bit and/or bearing?

Edit - I didn't see Amail's comment which he posted after I had opened the tab a while ago.