Help! I'm losing my mind

[PBERLAN]

As if teaching isn't hard enough it seems I've been challenged with what seems to be a medial task. I have a student that wants to build an octagon firepit. The bottom 32". Problem is I would be good with that but he wants the sides to taper to a 36" top. I have drawn it 1,000 times but I'm scared those trapezoids aren't going to fit. Anyone know of a way, or willing to walk me through away to get this done. Wanting to do it out of 10 ga to start. Any help would be greatly appreciated. Thanks.

[manac]

How tall?
Are the dimensions to the points or flats?

[TJS]

Need to know the angle of the layback trapezoids as well. I made one a while back. Needed some math to do it.

[manac]

Here is a online calculator that will calculate the sides.

https://rechneronline.de/pi/octagon.php

[adbuch]

As if teaching isn't hard enough it seems I've been challenged with what seems to be a medial task. I have a student that wants to build an octagon firepit. The bottom 32". Problem is I would be good with that but he wants the sides to taper to a 36" top. I have drawn it 1,000 times but I'm scared those trapezoids aren't going to fit. Anyone know of a way, or willing to walk me through away to get this done. Wanting to do it out of 10 ga to start. Any help would be greatly appreciated. Thanks.

This seems very simple if we know the overall height. What do you mean "those trapezoids aren't going to fit"? Please provide the dimensions of the top, bottom, and overall height and I will provide you with the dimensions you seek.
David

[TJS]

Here is the one I made for someone. I can post my SVGs if you want.

trapezoid2.jpg (92.11 KiB) Viewed 901 times

trapezoid2.jpg (92.11 KiB) Viewed 901 times

trapezoid.jpg (66.64 KiB) Viewed 901 times

trapezoid.jpg (66.64 KiB) Viewed 901 times

[manac]

Here you go.

Inputs
N= number of segments
R_U = Radius of polygon upper (center to point) for your octagon of 36" would be 18"
R_l = Radius of polygon lower (center to point) for your octagon of 32" would be 16"
H = Vertical height of pit

Outputs
Side_U = upper width of trapezoid
Side_L = lower width of trapezoid
H_m = height of trapezoid
alpha = lean over (if there is such a thing
beta = layback

FirePit.xls

FirePit Polygon Calculator

(30 KiB) Downloaded 52 times

FirePit.xls

FirePit Polygon Calculator

(30 KiB) Downloaded 52 times

[PBERLAN]

How tall?
Are the dimensions to the points or flats?

Looking to make it 16" tall. The dimensions would be to the points.

[PBERLAN]

We are looking to build it 16" tall. The only reason I said 32" bottom and a 36" top is to let you guys that there would be a "kick out", "taper or "obtuse" angle like the one posted in this thread. I don't really know what angles I just know we want it to not be at 90 with the base of the fire pit.

[PBERLAN]

Just getting home for the day and will definitely be working on this tonight and hopefully cut by the end of the week. I really appreciate all of the links and files shared. This is going to make life much easier. Im sure it's easier than I am making it out to be, but then again, probably not lol.

[adbuch]

Here is a very simple method to calculate the dimensions of the sides. I am assuming that the 32" and 36" dimensions are across the flats. The difference between the base (32") and the top (36") will result in an overhang of 2". Your specified height is 16", so a simple right triangle with sides of 16" and 2" and the length of the hypotenuse calculated using the Pythagorean Theorem. The lengths of the sides of the octagons can be derived from first principles, measured from a CAD drawing, or found using one of the online calculators.
David

Firepit.zip

(300.76 KiB) Downloaded 52 times

Firepit.zip

(300.76 KiB) Downloaded 52 times

[PBERLAN]

Sorry, Just getting time to sit and see exactly how you are figuring this out. I see now. Its really simple when you lay it out like that. Thank you so much!

[adbuch]

Sorry, Just getting time to sit and see exactly how you are figuring this out. I see now. Its really simple when you lay it out like that. Thank you so much!

You're welcome! Happy to help.
David