How to create parameterizable center point arc slot that is constrained?

[nfield_auto]

I want to use center point arc slots to create a mechanism to lock a couple of tubes together, however I've found that they don't seem to follow the rules for using parameters, and I can't get the resulting sketch to be constrained. I create my named params, assign them dimensions and an angle, then create my slot. Then there are 3 problems:

1. The result is not constrained (blue lines), and I've had problems with adding constraints where it tells me things are overconstrained, but I can't figure out what hasn't been constrained.

2. When I change the params in the editor it doesn't reflect any changes in the sketch.

3. When I try to add dimensions to the resulting slot the units that it asks don't match what I entered to create it. For instance, dimensioning the arc segment for the center of the slot asks me to enter a length, but I specified an angle originally.

It seems like this type of slot is only useful if you know exactly where you want it, and aren't going to change it. Otherwise it would be more efficient to create it by hand using arc segments, half circles and the like. That I know how to be constrained and parameterizable.

I've been using fusion for a while, but I'm entirely self/youtube taught, so I'm sure there are huge and weird gaps in my knowledge. Any help would be appreciated.

[jhackney1972]

Would you please attach your model?  If you do not know how to attach your Fusion 360 model follow these easy steps. Open the model in Fusion 360, select the File menu, then Export and save as a F3D or F3Z file to your hard drive. Then use the Attachments section, of a forum post, to attach it.

[jhackney1972]

While I am waiting for your model, I create a fully parameterize center point arc that is fully constrained.  Model is attached.

[jhackney1972]

I really would love to troubleshoot your model if you would attach it.  It only takes a few minutes and the Forum has a lot of helpful people working on it all the time.

[nfield_auto]

Thanks so much for the help. I deleted my changes to the actual model because I was going crazy trying lots of things and it became a mess. But I've attached a very simple example of 3 different attempts, plus a test model I made for what I'm really trying to do (make a twist lock mechanism for a 3D printed switchable dust port system, if you have better ideas I'd be open to that too 🙂

The first component is done by entering a name=value form for each of the 3 inputs to the slot to create the parameter names automatically. The result is no parameters in the params dialog, unlike what I did with the "ICanMakeAParam" variable for the sketch line.

The second component (which I made inside the other by accident, I haven't tried figuring out how to move components around in the tree yet, I'm sure there is a way) I defined the parameter variables ahead of time ("SlotB_*"), and used those to create the slot. Then I changed the SlotB_Radius from 50 to 100 in the Parameters dialog, but the slot did not move.

The third component I tried to constrain. I thought all of them should be fully constrained on construction, since I provided their placement along the axis, and with explicit parameterized values. In the end I was able to get it fully constrained by adding construction lines and using "d" to dimension things. Note though that I had to divide my "SlotB_Width" param by 2 to get the size to be what I originally defined since that was a diameter instead of a radius. And I'm fairly sure that I could create my own slot from arc segments with about the same overall work.

Obviously I'm doing something wrong, not sure what?

Looking at the model you posted it appears that you are defining the slot by hand, and not using the Sketch->Create->Slot->Center Point Arc Slot tool. Your slot does not have rounded ends, and you have manually constrained everything. This is roughly what I was thinking I could do to define my own arc slots, but with rounded ends. It's not that I can't get the job done, it's more that I'm left scratching my head wondering what I'm doing wrong when I try to use the tool and the result doesn't seem to do anything helpful (as in parameterizable and constrainable without roughly equivalent effort to doing it by hand).

[etfrench · Accepted solution]

Adding these 3 construction lines with dimensions will give you a fully constrained slot as well as being parametric:

[etfrench]

Here's your file:

There is one warning to resolve.

[Bunga777]

I changed the data to work parametrically.

(Only the last feature was too thin-walled, so I changed it appropriately.)

I think this will work for some slot diameters and angles.

I think there are still some areas to consider, as changing the value to an extreme will cause the shape to break down.

There is no video because the work took too long, but I am attaching the data.

[nfield_auto]

The forum system is asking me to say whether anyone has answered my question, and I feel that this is the closest, in that it shows that you need to dimension 3 things.

For anyone coming after who doesn't understand, the actions are:

- Create slot

- Create 2 construction lines from slot center point to the 2 points in the slot, entering the slot arc radius you want when you create the line

- Select both of the above lines (<control>) and dimension ("d") to your desired angle

- Select one of the half-circles at the end of the slot, and dimension to your desired radius

No one addressed that slots seem to ignore input parameters when entered by hand (in terms of doing the constraints for you since I literally just typed in all 3 of the things I need to dimension in creating the slot), and that setting a parameter variable is ignored/thrown away when you create a slot. From skimming the forums it seems that the common convention is not to use named variables much, and to dimension/constrain after doing a rough placement, so maybe no one notices/cares?

Basically it seems some sketch tools allow for entering inputs by hand (at least line, angled line, circle, rectangle, extrude...), and treat them as constraints/variable declaration points, and some tools ask for inputs but if you set them by hand it acts the same as if you had just used the mouse to place them. Which are going to do which you learn through trial and error, or you just always dimension after the fact. 🙂

[laughingcreek]

I would say that the assumption that more experienced users tend to not use named/user parameters much is probably generally true.  I definitely do not.

dimensioning the slot as it is being drawn is finicky.  basicly the tool is looking for an addition mouse input after each value is entered (whether with a manual number or with a user parameter.)  if not done right it does not define a dimension for that property.  in the screen cast you can see that after a parameter is selected, there is a call out looking for an addition input, even for the slot width which is weird.-