How to design a 4 sided fire pit

[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]

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]

I don't have any particular dimensions in mind, I am just looking to start drawing something to practice

[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]

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]

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 8.jpg (31.02 KiB) Viewed 9307 times

sketch 8.jpg (31.02 KiB) Viewed 9307 times

fire pit example.dxf

(269.19 KiB) Downloaded 92 times

fire pit example.dxf

(269.19 KiB) Downloaded 92 times

[bwmetalworks]

This is exactly what I was looking for! Really appreciate the help!!

[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]

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

[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

[adbuch]

Here is a follow-up on creating a dxf from a solid body face in Fusion 360.
David

[adbuch]

[plasmanewbie]

I typically always start with a sketch and then extrude it into a solid body so my sketch already exists to create the dxf. I had no idea this could be reversed and that you could create a sketch from a solid with no existing sketch. Pretty cool David, thanks for posting. Learning something new everyday almost!

[Joe Jones]

I made a video on this topic:

Joe

[adbuch]

I typically always start with a sketch and then extrude it into a solid body so my sketch already exists to create the dxf. I had no idea this could be reversed and that you could create a sketch from a solid with no existing sketch. Pretty cool David, thanks for posting. Learning something new everyday almost!

This can all be accomplished quickly and efficiently using Fusion 360. Then save DXF from Fusion 360 for import to SheetCam, DE, etc. for creating cut paths and g-code. No need for any other drawing programs.

David

[adbuch]

For those wanting to learn more about using Fusion 360 - either beginners or experienced users wishing to "brush up" on their Fusion 360 techniques - I strongly recommend the series of educational tutorial videos by Arnold Rowntree.



I went thru Arnold's original set of 16 tutorial lessons several years ago when I was making the transition from SolidWorks to Fusion 360. There is an accompanying drawing for each lesson - which may be downloaded and printed out to make it easy to follow along with each lesson. (link below)

https://mailchi.mp/07adc6c270fd/partoneofsixteen

Arnold also has some revised Fusion 360 tutorial lessons for those using the later versions of Fusion 360.



I did download and print the 16 drawings and went thru Arnold's tutorials several times.

Also for those thinking about getting started with 3D Printing - Fusion 360 is one of the more popular programs used to create solid models for 3D printing. I know that Tom and several other members have alternative solid modeling programs they like for their 3D printing - so there are lots of options out there.

David

[adbuch]

Langmuir Systems also has some excellent Fusion 360 tutorials geared specifically towards cnc plasma cutting. I went thru those as well - right before taking Arnold's course. Sort of a "one-two punch".

David

https://www.langmuirsystems.com/software/fusion