A few pointers needed

raul_fechete

Hi,

I'm trying to learn onshape (with zero previous modelling experience) by attempting to model this obelisk:

https://static.wikia.nocookie.net/deadspace/images/3/37/LightBlackMarker.png

I made several attempts using various tools (see below), however I'm not sure I'm going about this the right way. I would really appreciate it, if someone more experienced than me could give me a few pointers what I should look into, i.e. maybe some specific tools or techniques that would be more appropriate for this design. I don't want anyone to build it for me, I just want to make sure that I'm not headed in the wrong direction.

Attempt 1: Manually defined planes (normal on a helix), manually copied / scaled / rotated sketches, loft
Result: Sort of, but there has to be a better way than doing everything manually. Also, no horizontal notches.

https://cad.onshape.com/documents/093d7bebe87f9e6a95bdfcd2/w/78a214b9b793365c161c86f9/e/4a8c46d7e87ff84d5726c368

Attempt 2: Extrude, shell, transform by path (on a helix), parameter pattern
Result: Better insofar that I don't have to do everything manually, but I cannot loft this properly, i.e. for loft I still have to select all edges individually, and the notches do not work the way I had hoped.

https://cad.onshape.com/documents/74461c4aa6696e5ca8bfea24/w/6ccc5553cbc0cf1a859000ad/e/9f24d1273f16bf02ae121afc

Attempt 3: Transform pattern, transform by path (on a helix), parameter pattern
Result: Instead of automatically creating extruded shapes (like in 2) I tried to automate copying/scaling a sketch in the hope of making lofting easier. Sketch copying is ok, but they do not scale as they should. Also, no notches.

https://cad.onshape.com/documents/4792720c2b756f7c3690fd90/w/2ec5e6c3d6db9e8fa6f99594/e/56d63df52ccab93c3cea6c8f

Any points would be highly appreciated.

Thanks a bundle!

Cheers,
Raul

MichaelPascoe

Your attempts are good, especially for first time modeling! 

There are several different ways you could do this. One of the most controlled ways would be similar to your attempt 1.

• Insert a reference image in a sketch.
• Sketch the general profile of the image. Place points where you want your sketch planes.
• Create planes on each of the desired sketch points.
• Create one sketch starting at the bottom of the obelisk. Make sure this sketch is is not constrained horizontally or vertically to anything. I made it so that it could be easily copied, pasted, and updated.
• Copy and paste the previous sketch to the next plane. If it is constrained properly, you will easily be able to constrain it to the point of rotation on the first sketch. Then, you can adjust the angle and size quickly. (Repeat this step for each plane except for the top one.)
• For the top plane all you need is a point to loft to.
• Loft the sketches and match a set of vertices.
• Transform rotate copy 180 degrees for the other half.

https://cad.onshape.com/documents/3ee44a3de4b66e6859b9b010/w/fb5d7c1f9e00bef95ce67744/e/a1b518a5cd0b4867dc038a7c

MichaelPascoe

Another useful tool for projects like this is the Final button while inside a sketch. This will allow you to see the end results, live, while editing a sketch.

raul_fechete

MichaelPascoe said: [..]

Hi Michael,

Thank you very much for your tips! That does indeed help make a few things easier.

The main problem now, however, are the notches (those [almost] horizontal cuts in the obelisk at regular intervals). 

I could try creating even more planes, copying the sketches, extruding them and then subtracting them from the main body, but that would take forever. Is there a way to somehow automate this process? Parameter pattern maybe?

Wait! How about I create the object like you did and then subtract my second attempt from it? Or is there a better way to do this?

Thanks again & cheers!