How to design a 4 sided fire pit

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bwmetalworks
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How to design a 4 sided fire pit

Post by bwmetalworks »

I am wanting to design a fire pit in fusion 360 with a square center section and 4 trapezoid sides. For the life of me I cannot remember what the math is that I need to do to calculate the angle and dimensions of each side so that when I put each side in place and lift them up to my desired "Depth" that they all fit evenly.
adbuch
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Re: How to design a 4 sided fire pit

Post by adbuch »

If you draw your bottom and top, then you can loft it to create the sides. What are the dimensions of the top, bottom and distance between the top and bottom?

David
bwmetalworks
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Re: How to design a 4 sided fire pit

Post by bwmetalworks »

I don't have any particular dimensions in mind, I am just looking to start drawing something to practice
adbuch
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Re: How to design a 4 sided fire pit

Post by adbuch »

I'll be back later this evening to elaborate. Are you after a solid model or just the flat pieces to cut?
David
bwmetalworks
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Re: How to design a 4 sided fire pit

Post by bwmetalworks »

I put in some random measurments and was able to create the loft, now how do I "break" apart the loft so that i just have the individual sides?
adbuch
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Re: How to design a 4 sided fire pit

Post by adbuch »

I don't know of any way to "break apart" the solid model from the loft. But here is one way to come up with the sides. In this case the model was created from 2 squares of different sizes. Bottom square is 27" x 27", and top square is 36" x 36". The loft distance is 15". Construct a new sketch on one of the side faces duplicating the dimensions of the face. Then either export the sketched face as dxf or extrude to material thickness (1/4"), switch to Manufacture mode, and create cut path and post process to create G-code file to cut part. Your process will depend on which programs you have available to use.

There was a slightly more elegant method posted a while back by one of the other members where he projected the face of the solid model onto a newly constructed plane and then exported the dxf from that sketch. Unfortunately it wasn't posted in the Autodesk AutoCAD & Fusion 360 section of the forum, so I don't remember exactly where the thread is located.

David
sketch 1.jpg
sketch 2.jpg
sketch 3.jpg
sketch 4.jpg
sketch 5.jpg
sketch 6.jpg
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sketch 8.jpg
sketch 8.jpg (31.02 KiB) Viewed 2225 times
fire pit example.dxf
(269.19 KiB) Downloaded 64 times
Last edited by adbuch on Thu Feb 02, 2023 1:38 am, edited 1 time in total.
bwmetalworks
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Re: How to design a 4 sided fire pit

Post by bwmetalworks »

This is exactly what I was looking for! Really appreciate the help!!
BMCF
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Re: How to design a 4 sided fire pit

Post by BMCF »

You dont need math to figure out the angles. If I want to make a firepit that flares out at the top, I make the top 4" longer than the bottom measurement 2" per side) usually comes out to 15 degrees. Or you can just pick an angle you want the side to flare out. Then make the top measurement to fit that angle.
adbuch
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Re: How to design a 4 sided fire pit

Post by adbuch »

There was no math involved in the method I described above. In fact, I don't even know what the angles were - although they are easy enough to measure. The angles were automatically determined by specifying the bottom and top sizes, and then the distance between the top and bottom. Fusion 360 did the rest. In your example with the top 4 inches longer that the bottom, the angles will be dictated by the distance between the top and bottom. If a specific angle was required, then either the sizes of the top and bottom and/or the distance between then could be adjusted to create the specified angle. In any case, I certainly agree that there is usually more than one way to skin a cat - as they say.

David
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Re: How to design a 4 sided fire pit

Post by adbuch »

I just checked the dxf file and it turns out that for this particular fire pit drawing the angle is 16 degrees. So pretty close to your 15 degree typical measurement.

David
fire pit angle.jpg
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