Introduction: Mechanical Assembly

In the previous lesson, we created a base model for the bottle lock. We used tools like Loft, Revolve, and Extrude in conjunction with Sketches to make a base model with a mechanical assembly.

In this lesson, we'll continue to work on the base model. We'll add a hinge pin with proper tolerances, and smooth out the edges of the model so it's more ergonomic so that it's ready to print.

Create Hasp Features

I’ve measured the hook part of the padlock, so now I need to draw the profile of the hasp so I can create that feature.

Create a Sketch on the Mid-Plane for the Lock

I create a sketch in the mid-plane and draw circles that represent the inside and outside diameters of the loop at the end of the padlock hook.

I draw lines that represent the straight cut at the back of the hasp, then offset the circles by .5mm so that the lock can easily slide in and out of the hasp.

Extrude the Sketch (Direction: Symmetric) to Cut Out the Shape

With the profile finished, I extrude it to create the hasp cuts in both halves of the bottle lock. I hit the down arrow when I hover over the part I want to extrude until the profile is highlighted. I extrude the profile using the diameter of the padlock hook and add .25mm (remember the tolerance we decided on in the Fit Tests lesson?), giving me a cutout with a little play when I use the symmetric direction.

Offset the Hinge Arc on the Two Parts for a .25mm Clearance

Extrude the Profile for Clearance (Top)

Extrude the Profile for Clearance (Bottom)

Next, I need to create a small gap between the hinge parts on each of the clamp halves. I create profiles on the top and bottom faces, then offset the inside arc by .25mm, then extrude this new profile to the midpoint of the model.

Hinge Pin & Part Refinement

Human hands don’t like sharp edges. Sharp edges also tend to split and chip with a lot of use on almost any material, including 3D printed plastic. To refine our parts, we're going to use the Fillet tool.

Modify > Fillet (5mm for hasp cutout)

I start by selecting the Fillet tool in the Modify menu, then selecting the edges of the flat part of the hasp cutout. I want these to have a generous radius of 5mm, mostly for aesthetic reasons.

Modify > Fillet (1mm for all outside edges)

Next, I hide one of the halves so I can see what I’m doing. I select Fillet again, then select all of the model’s edges except for the ridges on the inside where the clamp contacts the bottle. I give everything a 1mm fillet, which seems to look good on every edge.

Sketch: Offset Outside Arc 2mm, Create Circle

Now that I’ve got my fillets, I can make the pin feature on the hinge and make sure it doesn’t conflict with any of the other geometry. I create a sketch on the bottom of the part where the hinge will be located, then offset a circle by 2mm from the outside. This gives me another 1mm on the inside of the filleted edge which will allow me to have a fully rounded opening for the female part of the hinge.

Create > Extrude (hinge pin)

Modify > Fillet (1mm for hinge pin end)

I extrude the circle I just made so that it meets the bottom of the part, then I fillet this edge by 1mm as well. When I make rules for myself, like the radii of filleted edges, I try to stay consistent with them wherever possible.

Sketch > Project (hinge pin profile)

Sketch > Offset (.25mm from hinge pin profile)

I create another sketch on the bottom plane of the other part, then project the profile of the hinge pin I made previously. I offset this by .25mm to give me the proper amount of play in the hinge.

Create > Extrude (hinge pin hole in lower part)

I extrude this profile through to the top of the feature.

Modify > Fillet (1mm for all outside edges on lower part)


Now that my part’s geometry is complete, I use the fillet tool again to smooth out all the edges. My Bottle Lock design is now finished!

    "id": "quiz-1",
    "question": "What does the fillet tool do?",
    "answers": [
            "title": "Turns one edge into two with a flat plane inbetween.",
            "correct": false
            "title": "Makes a rounded profile along the selected edge of a given radius.",
            "correct": true
    "correctNotice": "You got it!",
    "incorrectNotice": "Nope! That's what the Chamfer tool does."

Contact Sets & Appearance

If you want to see the extent of your part movements in Fusion, you can use Contact Sets. I go to Assemble > Enable All Contact. This will keep your components from crossing into each other when they move.

With All Contact enabled, I can see that my lock will stop at 174º at its widest point. This becomes very useful when assemblies are more complex.

When assemblies have multiple parts, it’s also a good idea to change their appearance so you can distinguish between parts. I right click and select Appearance from the popup menu, then just click and drag the material swatches onto my components.

Now it's time to use the Slicing and Printing skills we learned in the stamp lesson to print out the parts!

Apply Your Skills

In this lesson, we went further down the rabbit hole and learned some useful new skills.

We used the extrude tool to create the hasp feature and to increase the tolerance at the hinge feature.

We created interlocking pin and hole features to allow our parts to have a hinge action.

We used contact sets to test the range of motion of our parts, and we used appearance to make it easier to visualize the design.

Finally, the fillet tool allowed us to smooth out edges and create smooth transitions between features:

In future projects, remember that the fillet tool is a good way to create arcs to soften the corners between surfaces. It's also useful for rounding off sharp edges to make things easier on the eyes and easier on the hands. This tutorial from the Fusion 360 Youtube channel has some good examples of how to use fillets.

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