Segmented bowls rings: Make two driven dimensions equal?

[robertmarteau]

Hi,

I'm quite new to Fusion, and I'm trying to create a parametric design to help me define dimensions of segments when creating a segmented bowl.

[sidenote:] In woodturning, a segmented bowl is a bowl "machined" out of a stack of rings made up of trapezoidal segments glued together.

Depending on the curvature of the bowl (which is usually designed revolving a spline), defining a good number of segment and segment length and width can be quite tricky.

Here is how I created my sketch (in attach)

- Design a trapeze

- Constrain the 2 parallel lines to be... parallel and space them using user parameter segment_width

- Set the angles of the trapeze to 22,5° (originally, I intended only to create an 8 segments ring..), then in an attempt to make it work, set these angles to driven dimensions

- Draw a construction centerline in the trapeze and set its dimension to user parameter revolve_radius

- Select the 4 lines of my trapeze and create a circular pattern (8 segments originally)

- Make the sides of the trapezes colinear.

This worked quite fine with 8 segments, but I'd like to add a user parameter for that number (segments_number) and have the design adapt to that number. This is the point where things get ugly, with my trapezes getting different angles on each side

I tried to have the angles (which I set to driven dimensions, since their value will change depending on the segments number) equal, but it doesn't seem to be possible to do that.

I suspect there's another way to do that (that doesn't involve any equal driven dimensions...) but I'm stuck there for hours, so if anyone can help, it'll be very appreciated.

[davebYYPCU]

Do not use sketch patterns where the exact same pattern works for you in the Modelling area.

In your second picture it shows the short line not related to the long line.

Many ways to do it I would constrain both mid points to be vertical.

Set the side angles to be 360 degrees divided by the segment count as a parameter.

Something has to be flexible, bowl diameter, line length or count.

Edit:  I don’t have access to the file while travelling, and just studied the first sketch to see how you got the second one to distort.

Ah, why is a Revolve model sketch not using the origin for the centre of rotation?

Changing Parameters in a fully defined sketch works well, but

that can’t be said for sketches not fully defined.  Why so many driven dimensions?

The OMG moment was that only the long line might be using the origin, but I doubt that too.

Might help....

[davebYYPCU]

That said let’s do it from scratch.

Start with a 400 circle on the origin.

Draw a vertical centre line down at 230

Draw a horizontal line in white space near the bottom of the centre line.

Using Mid point Constraint, click the new blue line, then click the centre line end point.

Draw a line from the end of the horizontal line to the centre point, repeat for the other side.

Dimension these two lines to (360 / count)

Draw another horizontal line inside and connected to the angle lines. Dimension to the other horizontal line.  

If every thing is done right, Changing the count value in the angle line dimension should not break the sketch.  Test it.

Extrude the Block and pattern the block, in the modelling area.

Combine Join, the Bodies.

Now Edit the sketch, make driven dimension between an angled line and your first horizontal line. (To set the docking saw angle)

Might help.....

[robertmarteau]

Hi Dave,

Thanks very much for your input. I don't have the computer I'm designing on with me right now, but I'll definitely try it "your way". To be honest, I never used the "modelling area" (only design and render so far...), but by the time I get home to try, I'll make sure to get more info on that 😉

[davebYYPCU]

Modelling area, same as Design, 

solid modelling normal interface, sketches are a necessary branch of the Design.

Might help.....

[robertmarteau]

Hi,

Sorry it took me so long to get back to this... It's actually part of another project, and I had to focus on other aspects of it, so I left this on the side.

I tried your method, and I have to say it's WAY better than mine... it works flawlessly, thank you very much. "My" (well, Dave's) sketch is in attach, for anyone interested in using it.

Now...

Now is the time to get greedy... I wonder if it would be possible to improve the design and use it to define (and optimize) aspects of a bowl.

The construction of this kind of elements is based on 5 elements:

3 parameters already used:

- revolve_radius

- segment_width

- segment_count

1 additional parameter in the other dimension:

- segment_thickness.

1 form consisting of 2 spline connected at both end that defines the form of the bowl

- Bowl_curvature

The volume defined by the revolved splines has to be fully inside the volume formed by the extruded segments (otherwise, parts of your bowl wall will be... void).

There are some values there that are dictated by the project itself (I.E. the shape and dimensions of the bowl you want to turn) and some that can be adjusted

- Segment width and thickness : Since this is made out of wood, you should be able to define maximum values for that (the stock your'e working with has a defined section, so 1 segment cannot exceed those...)

- Segment count is a bit "up to you", since it's a balance between

- the quantity of wood you're willing to waste (the more segments you add, the closer you get to the actual shape)

- The time you're willing to spend gluing lots of tiny pieces together

- The number of joints you're willing to have in your final bowl.

--> Do you think there's a way to give Fusion the following:

- Bowl radius or diameter

- Bowl shape (the splines)

- Maximum width and thickness of the segments

- Segments count

And have it adjust segment width (without exceeding the maximum value) and thickness to match the form?

Anyway... that's way above my competence with fusion360, but I would be interested to at least know if it's possible, so that I can come back to it in the future, when I'm more proficient with the software...

[TrippyLighting]

I would start with designing the finished product and then derive the proper segment dimensions from that.

I don't see any splines in your design.
I see two sketches with sketch pattens. Sketch patterns are not encouraged. 

[robertmarteau]

Well, the file I sent was about creating a sketch in which I can input values (radius, count, diameter, width) and get the length  of the segments I have to cut. 

The splines are visible in the screenshot I added to my last post (section analysis of a bowl).

That image is mainly there so people can better understand what I'm talking about...

[davebYYPCU]

I deleted the clutter, to keep what we do need.

Your model pic did not come from this file, there is no bowl shape (Required)

Nothing in parameters tells me the block thickness.  (I got 80 x ??? so far.)  

(Required for next step - make first block).

There will be a sketch like this for each level of (12) blocks.

(Bowl height / stock thickness,) will tell how many rings.

Lower down the stock has to be wider than the top, which will be longer than the bottom pieces with same count, but

will it be the same count per ring?

Might help....

[Neil_Relph-Olivewoodturning]

Do you know that there are plenty of segment calculators freely available on the web? I'm not sure what the requirements are. for what you're trying to do, but look here for one example of a calculator. Segment Calculator