Cylinder with non-planar end

hansrudolf

Oh well, when I read all these questions and answers in this forum and don't understand 99 out of 100, I feel sometimes like being in the wrong place. After this a bit pessimistic remark I want to say that Onshape is a very nice system to play a bit around with simple geometric shapes. But when it gets a bit more complicated - well then it's complicated!
So I had to learn that I can't make something like a cam. Brilliant idea - why not make just an incomplete eccentric?
That means extruding a cylinder and then cutting off a half-moon from its end. The result should be something like that:
--------
       /
     (
      \
-------

Hope that's understandable.

I then want to mate this cut-off face with the outside of a second cylinder, which I think should be possible.

Now after several hours of experimenting I found no way to generate such a form. A bit of help would be appreciated with thanks.

regards, Hansrudolf

andrew_troup

@Hansrudolf
You can extrude a surface, which uses the same tool as extruding a solid body, but selecting the surface option. The sketch from which you extrude can be any combination of arcs, lines and splines. Unlike a sketch for a solid extrusion, it does not need to enclose an area; it could be as simple as a straight line.

Then you simply extrude up to that area. I've modelled up a simple example at:

https://cad.onshape.com/documents/5bc9292bc9e9417482eace51/w/6e93f7910b86460499c6a1b8/e/746975fc1269425b98fa14e7

Open the second tab, "Extrude up to surface"

andrew_troup

@Hansrudolf
Good question. I, too, struggled to find how to hide a surface (unlike solid features or bodies, where you can simply hover the cursor arrow to their right, in the feature tree, and toggle the "eyeball" on and off) so there are likely to be others with the same question.

The trick for surfaces is to RMB on them in the display window, and choose "Hide surface"
Unlike suppressing, this allows the surface still to perform the required function in your model.

Question for Onshape: Is there a reason not to permit "Hide" functionality for surfaces via the feature tree?

andrew_troup

@Hansrudolf
You can extrude a surface, which uses the same tool as extruding a solid body, but selecting the surface option. The sketch from which you extrude can be any combination of arcs, lines and splines. Unlike a sketch for a solid extrusion, it does not need to enclose an area; it could be as simple as a straight line.

Then you simply extrude up to that area. I've modelled up a simple example at:

https://cad.onshape.com/documents/5bc9292bc9e9417482eace51/w/6e93f7910b86460499c6a1b8/e/746975fc1269425b98fa14e7

Open the second tab, "Extrude up to surface"

hansrudolf

Many thanks Andrew, that at least shows me how it could be done. I tried with your example to remove either the extruded surface, or at least the superfluous part. When I do that the cylinder also disappears, and most of the features tree gets red. Next obstacle?

Kind regards, Hansrudolf

andrew_troup

@Hansrudolf
Good question. I, too, struggled to find how to hide a surface (unlike solid features or bodies, where you can simply hover the cursor arrow to their right, in the feature tree, and toggle the "eyeball" on and off) so there are likely to be others with the same question.

The trick for surfaces is to RMB on them in the display window, and choose "Hide surface"
Unlike suppressing, this allows the surface still to perform the required function in your model.

Question for Onshape: Is there a reason not to permit "Hide" functionality for surfaces via the feature tree?

jakeramsley

Andrew_Troup said:

@Hansrudolf
Good question. I, too, struggled to find how to hide a surface (unlike solid features or bodies, where you can simply hover the cursor arrow to their right, in the feature tree, and toggle the "eyeball" on and off) so there are likely to be others with the same question.

The trick for surfaces is to RMB on them in the display window, and choose "Hide surface"
Unlike suppressing, this allows the surface still to perform the required function in your model.

Question for Onshape: Is there a reason not to permit "Hide" functionality for surfaces via the feature tree?

Hi Andrew,

Surfaces are under a specific section in the parts list that is collapsed by default.  Expanding it lists them similar to parts and allows you to hide via eye icon.

1. Expand the surface list


2. Click the eye icon to hide the desired surface

andrew_troup

Thanks a lot @Jake Ramsley; I had actually explored that, but (on a trackpad) it must be that I did not hover accurately enough to trigger expansion. It works for me now.

hansrudolf

Many thanks to you all, now my litle test mechanism is working the way I wanted!!!
It is great that on this forum even the teething troubles of a simple amateur get attention.

Kind regards, Hansrudolf

andrew_troup

@Hansrudolf Thanks for speaking up; hope you don't feel you're any bother. Seems to me almost everyone is groping around at this stage of a new paradigm, and the fundamental questions new users ask force others to better understand things they only thought they knew.
(Like me no knowing I could hide surfaces from the tree). Note to self: Use mouse more regularly, so as not to miss the finer points of the UI

BTW: when you said you learned you couldn't make a cam, were you talking real-world limitations, or perceived OnS limitations?

hansrudolf

Andrew_Troup said:

BTW: when you said you learned you couldn't make a cam, were you talking real-world limitations, or perceived OnS limitations?

Hi Andrew, thanks for your kind words.
I searched around in the forum, using words like cam or camshaft, and hit upon an entry saying that this can't be done, at least at the moment. I'm not sure if I could find that entry again... OK, possibly was this in 'designing mechanisms...':

• Kesava_Prasad_T_D Posts: 1Member ✭

  September 2014

  Any one has created a cam mechanism? There is no tangent mate in assembly.
  

   Flag  Quote ·  Vote Down  Vote Up
• Mark Biasotti Posts: 112Member ✭✭

  September 2014

  Cam mates are rare even in SW - I suspect because most real applications of a cam mate involve "contact" mate I.e. Something that goes well beyond sime constrain kinematics ( I.e. pushrods in an engine - and SW still does not have this kind of mate.) I suspect that if a cam is involved that is always in contact and providing a regular motion result, it can be better served with linkage ( or series of.) For highly irregular motion that is always in contact, then of course a contact or path mate is needed. 
  
  
  Kind regards, Hansrudolf

andrew_troup

@Hansrudolf : You can certainly model a cam as a part very nicely in OnS. What the contributors are saying above is that (at present) there is no OnS way (or at least, no intended way) to have a non-circular cam activate a follower realistically, as it spins in an assembly model of a mechanism.

In other packages (and presumably in OnS at some future date) there is a "cam mate" which allows creating a tangent mate with a path. In some cases, the path is limited to arcs and lines, in others it can be spline-based.

An option OnS might perhaps consider, if they implement a "Fit Spline" solution (which can convert chains of arcs and lines to a single spline) would be to simplify the input options to a cam mate by accepting only splines - preferably open splines, as well as closed ones. 

hansrudolf

Andrew, well what I tried to do was not a real cam like in an engine, but rather a kind of eccentric. With your help I managed to do that, and for the moment that's all I need. But it will be interesting to see what the Onshape developers bring out in the future.
Kind regards,
Hansrudolf