I know a polygon is not a circle but I was not sure how else to word it. Im trying to accomplish two things
1.Determine the correct diameter to use in order for make a welded chain circle be the perfect circumference to allow for an even number of links
2.Make a template to cutout another piece of sheetmetal that would fit inside of said links

Is there a way to say draw a polygon with X number of sides that are X long?
For example this was welded around a metal can and the diameter was just shy had it been a little larger I could have cut a link in half and welded it in to make a perfect circle

Can be done in Inkscape (better to do in CAD tho).

In Inkscape, you could explore using:

Creating an object the proper dimensions
Moving center of rotation
Snapping to center of rotation, center of object, snapping to guides
Tiled clones in a circle

Once you have the above, you can delete alternate links and replace with links-in-profile, to get the shape for the inner plate.



As you might imagine, some trial and error can be involved.

perhaps relevant ?

https://youtu.be/NOgSNAmEx8s

https://youtu.be/08zqdw-L0i0

For #1, there's probably some mathematical equation that can find the answer. And I'm sure that pi is involved. Oh, this just floated up from almost a half century ago. pi-R-squared. (That's not how you write it, but this editor doesn't have the right symbols.) I think R is the radius, which is half the diameter. I'm thinking pi-R-squared is the formula for the circumference. But this is really warping my old brain, lol.

Ok....so once you have the circumference, that's where the length of the links becomes important. Let's say that the length of the links is L. And circumference is C. So C divided by L needs to be an even number (no fractions left over).

So.... Ok, so start with L. Once you know L, you can figure all the rest out easily....relatively easily! If you want to give me what L is, I can try to figure it out.

I would be using the Star/Polygon tool for this (in Polygon mode).

I'm not sure if I completely understand the problem. But if I do, just finding this diameter will not tell you what diameter of can to use. Because the circumference of the can is only the inner circumference of circle of links. Because the links are so thick (and also their width matters), if you use another can to weld it around, the can will need to be a little smaller diameter than the result of the math above. That can probably be calculated as well. But probably we would need to know the thickness of the links

Tough one.

For a precise construction you need to know the parametres of a single chain link.
Radius for the rod bending, length of the link, and the diameter of the rod.
If you use a chain with different link geomety, the shape of the fitting plate would be different even with the same number of links.

Not such a big deal and no fancy math needed... follow my example and if there are gaps a fillet weld will close them.

The key is getting an accurate representation of a link.