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3D Modeling & CAD for Motorsport: 3D Sketching

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3D Sketching


00:00 - Now that we've taken a good look at 2D sketches, the next step is of course 3D.
00:05 All sketches in Fusion 360 are actually 3D in nature, it's just that our normal 2D sketches don't have any features in 3D.
00:14 When we sketch in 2D, we sketch on a single plane or planar surface, we refer to this as the active plane when sketching.
00:23 The basics behind 3D sketching are very similar to what we just covered in the 2D sketches module with the sketch tools, dimensions and constraints but there are some key differences, most importantly, 3D sketches are not confined to a single active plane.
00:38 These exist in 3D space and that requires a few different considerations and the use of some different CAD tools.
00:45 In a motorsport context, a common use for 3D sketches in CAD would be modelling weld mounts or welded assemblies of extruded sections.
00:54 Think something like a roll cage, a tube chassis or an exhaust system.
00:59 With each of these examples we'd expect to see solid bodies in three dimensions and likely curves or bends that don't align on a single plane.
01:07 The uses aren't limited to weld mounts though.
01:10 3D sketches are also ideal for creating surfaces with complex forms and various other features.
01:16 Heading back over to Fusion 360 and in the design workspace, let's look at an example of a really simple roll cage.
01:25 I've already created this sketch for the main hoop which runs up the B pillar and along the roof behind the driver's head.
01:31 This was done with a 2D sketch on a single plane.
01:34 As always, the file is attached below so if you'd like to follow along, pause now, download it and bring it into your Fusion 360 workspace.
01:43 The most common design for a roll cage has what's sometimes called a windscreen or A pillar bar.
01:49 This runs from the footwell, up to the dash and then up the A pillar to the roof which also move inboards towards the centre of the vehicle and then back along the roof to meet the main hoop.
02:01 It's clear that the sketch for this can't be created on a single plane so that means that a 3D sketch is ideal.
02:08 It's possible to add to the existing sketch but it's best to start a new one to keep the bars separate as they would of course be made individually before being welded together.
02:18 So let's start our new sketch on the top plane as this will be the best place to align with the existing sketch.
02:24 Although we will still be changing the active plane as we go.
02:28 Don't worry if you're a little bit confused at this point, it's all going to make more sense soon.
02:34 Let's turn on the 3D sketch preference in the sketch palate and start by making a construction line from the bottom of the main hoop to the front of the vehicle to help us place the bottom of the new bar.
02:45 We can view this from the top, add a vertical constraint and dimension the line 1500 mm.
02:51 Keep in mind that the terms vertical and horizontal are relative to our view.
02:55 Basically this constraint will just make the line parallel to whatever axis of the coordinate system it's already closest to parallel with.
03:04 OK let's deselect the construction line type as the next lines will be for the actual bar.
03:09 When we place the bottom of the next line, the important part here and specific to 3D sketches is the ability to change the active plane.
03:17 We're given the new temporary coordinate system at our current point and we want to select this new right plane as our active plane and look at the right view.
03:26 Then we can add a line straight up to the dash height without it snapping to line up with any references which we'd be able to see from a blue square at the end of the point.
03:35 Turning off the snap preference in the sketch palate can help us avoid this as the trickiest part of 3D sketching is sketch points snapping to existing features in other planes unintentionally.
03:46 So making sure there's no square, we can click to place the end point and then hit escape to finish the line.
03:53 Add a vertical constraint to the line if it isn't already there and then add a horizontal constraint between the top of the line and the centre of the curve at the corresponding height in the main hoop, which is the higher one of these two small dots.
04:06 Using the same idea again, let's look at the home iso view.
04:10 If we place the start of the next line on our last point and change the active plane to the temporary front plane, now we can look at the front view and make the new line run along the angled section of the main hoop.
04:24 Again, we need to press escape after placing the top of the line.
04:28 We don't want to constrain the line itself as we're about to move it.
04:32 Now we'll define its position which is going to make more sense in a moment.
04:36 Looking back at our home iso view, we want this line to angle back towards the rear of the vehicle following the A pillar.
04:43 To make this change, we'll use the move copy tool from under our modify tab which is quick key M on our keyboard to drag the elements of the sketch into 3D.
04:53 So let's select this point and use the arrow to drag it directly towards the rear of the vehicle by 600 mm.
05:00 The last line we need to add is for the part of the bar that goes back to meet the main hoop.
05:06 We want it to attach to the middle of the upper curve so let's make a line from the top of the A pillar to the mid point of the curve.
05:14 If we zoom in a bit, we get this triangle icon which is a mid point constraint.
05:18 This essentially sticks at a mid point between two features along a line or a curve.
05:23 We can then add a horizontal constraint to the new line and dimension it to 900 mm for example.
05:30 Finally, let's add some fillets to round these sharp corners by selecting the fillet tool, clicking on one corner and setting the dimension to 150 mm, then selecting the other corner and hitting enter to finish.
05:43 Of course the actual size of these would depend on the tooling we had available to bend the tubing.
05:48 Our sketch is still not fully defined and it can be quite tricky to get to that point with these 3D sketches.
05:54 It's worth using the fix constraint here on these lines to avoid making unintentional changes.
06:00 Now our 3D sketch for the A pillar bar is done and we could move onto sketching the remaining parts of the roll cage and of course use the sketch to create the 3D model of the roll cage, which we'll be covering in an upcoming lesson.
06:14 It's important to spend a decent amount of time experimenting with all of this and seeing what works as it can become quite tricky as the model gets more complex.
06:23 Remember, the basic create and modify sketch tools are exactly the same as they are in 2D, we just use the 3D sketch preference and the move copy tool to shift sketch elements off the active plane.
06:36 It can be best to create the initial sketch with the 3D preference deactivated so we can avoid moving points off the active plane by accident as we won't be able to see this when we're looking directly at the active plane.

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