Making Cylinder with Pillars

jsonshape18

Hi there,

I am new to Onshape, but I have spent considerable time going through the tutorials on the Parts Studio and Assembly. Nevertheless, I'm really struggling with a basic construction. I'm trying to create something that looks like the attached picture, but where the large cylinder is hollowed out. I tried to follow along in the comment from which I took the picture but it assumes that you've managed to move Derived Parts into the correct positions before using a Boolean Union, but I haven't managed to do that. I've tried to transform by mate connectors and by rotation, but it's been 3 hours (mostly I'm struggling to define a proper axis about which to do a rotation) and I think there must be a better way to snap them into place.

Here (https://cad.onshape.com/documents/948202cf383d7ac3f42ac826/w/ea7d58967adf4d752c37aaaf/e/494e00a8f1a2525adb8fbc83) is my document. I am trying to move 6 or so "Pillars" in such a way as to make the hollow cylinder stand up starting at 3.75 in above the ground. Please let me know if there's some info I'm not being clear about.

n_schoemaeker

Hi @jsonshape18 ,

welcome to OnShape :-)

I am not exactly sure what you are struggling with nor what's you intended goal. And I haven't followed the tutorial you are mentioning, so I'll try to answer with what I think is sensible.

For a starter, this is usually not a good practice to have several identical parts in a single Part Studio. You usually design the part once and then import it several times in the assembly.

One of the rare occasions when it's okay to have several identical parts is to pattern it and then do some sort of operations, like the boolean you are mentioning. But I generally try to avoid even that, as I have always find a more elegant way to do this.

So in you case, if I understand correct, you have a big central cylinder (the gray one at the top), and the 7 cylinders around it, partially overlapping. You then want to subtract so that it hollows out the central cylinder.

If that is indeed what you intend to do, I would suggest you do something like I did in Part Studio "Example 1" of this document: https://cad.onshape.com/documents/5dc98badad763540bb28cb51/w/95e8815d75175dc94927621e/e/a0e283d8875a11606f1f5d95

Basically :

• Create your central cylinder (Sketch "Central Cylinder" and Extrude "Main Part").
• On the top face of your central cylinder, create a sketch and draw your small cylinder (sketch "Small Cylinder")
• Then you have two possibilities:

1. (the one I did) : you create a circular pattern of you small cylinder inside the sketch, create, 7 instance and center on origin and then make one extrude (in Remove) of the whole sketch (thus the 7 cylinders at once).

2. : you make the extrude (in Remove) of your small cylinder sketch, and then you create a circular pattern of either the extrude feature of the extruded face

I usually prefer the former solution (pattern inside the sketch) as it leaves your feature list smaller

Anyway, in this solution (no matter if you chose 1. or 2.) you don't even need to create an additional pillar part.

If I was mistaken in the previous section, and your starting point is that you have two parts: the central gray parts and a cylinder in another Part Studio, then look at "Example 2" and "Pillar" of the same document.

Part Studio "Pillar" is just the design of your pillar, and I made it on another plane, so as to be complete.

Then what you can do is this (in "Example 2") :

• First design your central pillar like usual (sketch "Central Pillar" and Extrude "Main Part")
• Then place a point where you want the center of your pillar to be positioned, in my case I used a construction line on the Top Plane, to put it a bit outside the outer perimeter of the central gray part. (Sketch "Desired Position of Pillar")
• Then make the Derived Part to sort of "import" your pillar. It's badly positioned by default.
• Then place the pillar in one go with a second Transform, type "Transform by mate Connector".
  In "From Mate Connector", hover your pointer to the middle of the base of the pillar cylinder, you will see a Mate Connector appear on the center, then click.
  In "To Mate Connector", hover your pointer on the point you placed (in my case the extremity of the construction line) in the sketch "Desired Position of Pillar", OnShape will infer a Mate Connector on that point ; then click. You pillar is correctly positioned.
• Then you have again two ways of doing :

1. Create a circular pattern to repeat the cylinder 7 times and actually have many parts. And then Create a boolean operation to subtract. This is what I have done ("Circular Pattern" and "Subtract"). I did this because it looked like your picture, but I don't really like this.

2. Create the boolean Subtract operation right now with only one pillar, and make a circular pattern of the feature or the removed faces.

Anyway, I hope this helps

Have a good day

NeilCooke

Sounds like you’re overthinking it. Is this what you are trying to do? https://cad.onshape.com/documents/e1c5b2cfc3a4e90ad433de2b/w/d20b66b331b98e425a24daf3/e/444a3ab2d3d6d2d653b6b0bb

Also, it is best practice to use feature patterns rather than sketch patterns - they are more robust. 

jsonshape18

NeilCooke said:

Sounds like you’re overthinking it. Is this what you are trying to do? https://cad.onshape.com/documents/e1c5b2cfc3a4e90ad433de2b/w/d20b66b331b98e425a24daf3/e/444a3ab2d3d6d2d653b6b0bb

Also, it is best practice to use feature patterns rather than sketch patterns - they are more robust. 

@NeilCooke Yes, that is precisely what I am trying to make, albeit with slightly different dimensions. I tried to make it as one big part but struggled to attach the pillars "just so" like you did. I was trying to use "transform" but couldn't get mate connectors where I wanted them. Do you have any tips for doing what you did?

NeilCooke

If you make a copy of the doc you can edit each feature in turn to see how I did it.