Design into 3D: Boxes: Coopered boxes

WillAdams · March 4, 2020, 4:13am

It may be necessary to revisit this and work out different options depending on the proportions:

Next, we do something similar for the sides — here though we want to try to use stock efficiently since there are four sides — we assign half the board maxwidth to be added to the lid (one would rip a board each for the sides and front/back) — since the sides will be visible, we calculate how many boards there should be and then evenly distribute the height for a more regular appearance.

Note that we will also need to go back and revisit there being an odd number of boards for the base — probably the code could be re-used, just skip dividing at the last step — for sense it will probably be necessary to rename some variables.

WillAdams · March 5, 2020, 6:21pm

On third thought, a discrete number of boards makes more sense (and is certainly easier to program).

Trying again, (briefly considered openjscad, but it didn’t work out).

As before, we make variables:

This time, we use a module:

and we assume that the box will be wider than it is deep, and in keeping with that, we have the boards in the bottom run from front–back.

WillAdams · March 6, 2020, 4:06am

and we have the bottom portion of the box pretty much done:

WillAdams · March 7, 2020, 4:59am

and adding a sawkerf dimension allows us to have a lid base which efficiently uses two boards cut in half:

Next up is working out the math to place a board at the top of the arc for the box lid (adjusted by the board’s final width) and to determine how many boards will be necessary and at what angle(s) they will need to be cut along their edges.

WillAdams · March 7, 2020, 5:47am

Dimensions which we have:

the length of the chord of the arc (this is the box depth)
the radius of the circle

Drawing things up we have:

WillAdams · March 7, 2020, 2:17pm

2 posts were split to a new topic: Design into 3D Kickstarter Book Status

WillAdams · March 7, 2020, 3:17pm

We need a couple of variables:

arcangle — the angle at which the circle with radius r intersects the front and back of the box — determine by arcsin((boxdepth/2)/r) (see: https://www.mathportal.org/calculators/plane-geometry-calculators/right-triangle-calculator.php )
arclength — this will be the length of the arc for the chord defined by boxdepth and the circle made by r determine by 2 \pi r (arcangle/360) (see: https://www.mathopenref.com/arclength.html )

(hopefully those notes will be sufficient to let me pick up where I left off)

WillAdams · March 8, 2020, 2:31pm

Next step is making a board with the correct (and rather slight) angles:

To fill out the lid we need to ensure that the number of segments will be odd, and then rotate them into place.

WillAdams · March 9, 2020, 11:18pm

Rather than try to calculate everything about the lid we change to having multiple variables:

which are still parametric, adjusting in terms of a percentage of the box bottom height minus one:

We will iterate on numbers until we reach the point at which it can become a loop.

WillAdams · April 6, 2020, 2:16pm

This topic was automatically closed after 30 days. New replies are no longer allowed.

WillAdams · April 10, 2020, 7:53pm

Yeah, one has to model the parts in design orientation, then rotate them into place:

WillAdams · April 10, 2020, 11:44pm

A further consideration, for maximum interior volume we want the board edges to meet at the internal edges, which makes the boards which meet the lid skirt want a two-sided operation:

WillAdams · April 11, 2020, 2:01am

And it’s a house:

Next up filling in the ends: #done

then we do a 3 sided top.

WillAdams · April 12, 2020, 2:44am

Okay, the 2 sided top is pretty much just a placeholder. For the 3 faceted top, we actually want good engineering and connections, so we need to angle the parts thus: