"Pro" Guidance On Taming Sketch Dimensions

[jimmberry]

I'm a hobbyist/maker and I'm hoping to get some "pro" guidance on the best way to structure a sketch.  (I have a moderate understanding of Fusion 360.)

I almost always use variables to store key dimensions like width/length, etc.  Then I try to model my sketches so that if i change a dimension everything scales proportionally. 

The trouble is that if i don't have enough constraints, sometimes Fusion 360 changes the wrong thing on me and I get lost in a maze of trying to troubleshoot erratic adjustments.

I need an approach.

Can anyone share tips on what they do to tame their dimensions?

Specifically, I'm thinking that I should always take a key dimension (like length) and completely fix that sketch line.  Then, base everything off of that one line.   Is that a good idea or do you have a better approach?

I'm very opened minded to your likely more advanced experience.

Thanks for any tips.

[g-andresen]

Hi,

Basically I would not overload sketches but distribute them on several sketches and create their dependencies e.g. via projections.
Please share a suitable design example.

günther

[jhackney1972]

@g-andresen has given you some excellent advise.  I will add one suggestion, apply sketch constraints early and as many as you can, dimension second and you will find you have to use less.

Edit:  One last suggestion, make sure one or more of those sketch constraints uses the component or body origin.

[jimmberry]

I don't have any pending untamed sketches but have been thinking about the problems I went through on the last few designs.

For example, I had a variable for an angle.  It worked fine but when I changed the variable it would unexpectedly draw the angle in the wrong direction.  For example -28 instead of 28.   It took me awhile to realize that I needed to add constraints with construction geometry and base the angle off of that.

So you keep your sketches minimal and base a bunch of them off of projections?  (Linked projections I presume?)

As you're designing, what is going though your head to ensure that your design is going to stand up to adjustments of your key dimensions?  Especially if you're going "light" on adding dimensions?

Do you sketch in 3D?  I find it a big pain to force lines to the axis while I'm doing that.

[jimmberry]

Sounds like good advice.  I often put dimensions in first.  I will try the other way.

When you say, "make sure one or more of those sketch constraints uses the component or body origin", 

Do you mean a "Sub Sketch" that was derived from the face of a body?   I'm not too good with the nomenclature. 

[jhackney1972 · Accepted solution]

I am mainly referring to your first sketch, it should be based off of the origin normally on one of the origin planes but does not have to be.  If you are creating additional sketches using projections from other sketches and bodies, that is fine, the origin may be a secondary constraint reference.  By the way, in the Screencast, I created my Component first, so all my sketches and bodies fall under it.  This is a good practice for organizing your model.

[g-andresen]

Hi,

---

@jimmberry  schrieb:

For example, I had a variable for an angle.  It worked fine but when I changed the variable it would unexpectedly draw the angle in the wrong direction.  For example -28 instead of 28.   It took me awhile to realize that I needed to add constraints with construction geometry and base the angle off of that.

In this situation, follow the recommendations (constraints first!) of @jhackney1972 in his screencast.

So you keep your sketches minimal and base a bunch of them off of projections?  (Linked projections I presume?)

YES!

As you're designing, what is going though your head to ensure that your design is going to stand up to adjustments of your key dimensions?  Especially if you're going "light" on adding dimensions?

1. create base profiles (constrained sketch)
2. extrude profile, sweep ...
3. create sketch on these bodies using projections as reference
4. create features from 3.

Do you sketch in 3D?  I find it a big pain to force lines to the axis while I'm doing that.

No!                                                  That's why I avoid 3 D sketches where I can.                                                    

---

Günther

[jimmberry]

Wow! That's great.  

Up until now I've given the origin almost no thought.    But I can see from your video that it can be a consistent anchor point to give the design stability.

I'm going to fold this into my workflow right away!  Thanks for taking the time to narrate it.

Question:  When do you put sketches in the Root of your design and when do you put them in your component?

[jimmberry]

Awesome advice!   I'm glad to see others avoiding 3d sketching.   I found it easy to do that in sketchup but arduous in Fusion.

Thanks for the 1,2,3,4 outline.  I will be adopting this.  Up until now, I've been kinda' winging it which tends to get me messed up sometimes.

[jhackney1972]

Normally sketches belong with the component they are used to create.  I use a occasional sketch in the top level for creating independent Joints in the assembly.  An assembly requires components, so why not keep the sketches and bodies organized under them.

[laughingcreek]

---

@jimmberry wrote:...Question:  When do you put sketches in the Root of your design and when do you put them in your component?

---

any time i'm doing a top down design.  which is most of the time.

references that are shared between components should be one level up in the hierarchy. 

[davebYYPCU]

I am surprised no one has emphasised Fully Constrained.

Changing Parameters is a trigger for Unstable if not Fully Constrained.

You been told how, but the why - is only mentioned casually.

For best results, Fully Constrained is mandatory, Design dependant, but especially if changing parameters.  You have described what happens when you don’t Fully Constrain.

Depending on what colour scheme, Fully Constrained articles change colour (in the video) when implementing enough Constraint and dimensions - Dimensions are constraints.  You should not leave a sketch until Fusion changes the sketch icon to the red locked version.

Might help......

[TheCADWhisperer]

---

@jimmberry wrote:

… have been thinking about the problems I went through on the last few designs.

---

I strongly recommend that you Attach one of these completed designs here for critical analysis by one of the experts here.

I can tell you that;

1. I fully define each and every sketch element.

2. I use the BORN Technique as much as possible and practical. (The Origin center point and workplanes are single source of truth data.)

3. I generally use 2D sketches to create and control 3D sketches when 3D sketches are required.

4. I frequently start over.  I see lots of users resist starting over (…I have 3 weeks into this design - I’m not starting over…) and then waste time fighting a house of cards on a foundation of quicksand.  Start over early and start over often.  My first attempt is just to get an understanding of the geometry. I often have a second or third attempt before I achieve my Design Intent.  Sounds like a time constraint - but from my observations the highest quality is actually the fastest.

[jimmberry]

This is great info!  I will be adopting this.

It's good to know that it's a good practice to start over.   I often feel like I have to start over because of my inexperience.   I will start thinking about this differently and think of it as a way to work out issues and then do it better.   This will be a Fusion 360 life lesson for me so I tip my hat.