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Joints, standard parts and gears

Bearings from the parts library, a block sliding along a shaft between limits, two gears turning together and a rack that turns rotation into straight motion.

8:30 · English narration, subtitles in English and Polish · Watch on YouTube

Step by step

Exactly what the narrator says, chapter by chapter. Click the time next to a chapter to jump the video there.

0:00 Introduction

  1. In this tutorial we connect parts with joints: a bearing block sliding on a linear shaft, a pair of gears and a rack with a pinion.
  2. A joint tells Foremka how two components are attached and how they may move: rigid, sliding or turning.

0:20 Standard parts

  1. The bearings come from the library of standard parts. On the Insert tab choose Standard Part.
  2. Parts are grouped by type. Each card shows the main dimensions and the source of the model with its licence.
  3. Choose SK8, a support for an 8 millimetre shaft, and insert it. It comes in at the origin as a component, already in aluminium.
  4. Right-click the component in the browser and ground it, so it stays put while other parts move.

0:50 Linear shaft

  1. Now the linear shaft: a Cylinder with a radius of 4 millimetres and a height of 200, standing next to the support.
  2. Give it the Chrome appearance, like a hardened, polished shaft: press A, search for chrome and click the swatch.
  3. Joints connect components, so right-click the body and choose Create Component from Bodies.

1:17 Rigid joint

  1. Click Joint. First point at the end of the shaft: zoom in, and the snap sits in the centre of its circular edge.
  2. Then press Fit, move the support to the middle of the view and zoom in. Point at the centre of its bore: the shaft moves into place on the same axis.
  3. The shaft only touches the face of the support. Offset Z of minus 14 millimetres, the thickness of the support, slides it through the bore.
  4. On the Motion tab the type stays Rigid: the shaft is clamped in the support. Click OK.
  5. Insert a second SK8 from the library: on the Insert tab choose Standard Part, then Shaft supports, SK8 and Insert.
  6. It also comes in at the origin, on top of the first one. Right-click it in the browser, choose Move Component and move it 260 millimetres along X.
  7. Join it to the far end of the shaft the same way. Click Joint, bring the support and the end of the shaft to the middle of the view, then point at the centre of the bore in the second support,
  8. and the end of the shaft. Offset Z of minus 14 slides the support onto the shaft.
  9. Click OK. Both supports stand on the floor, joined to the shaft.

2:48 Slider joint

  1. Next the SC8UU: an aluminium block with a linear ball bearing inside, a steel sleeve and a black ball cage.
  2. A joint again: first the centre of its bore. The middle of the shaft axis is hidden inside the shaft, so hold Ctrl over the shaft to reach it.
  3. The block lies on its side. An Angle of 90 degrees turns it around the shaft, mounting face up.
  4. On the Motion tab choose Slider and set limits that keep the block between the supports: minus 82 and 58 millimetres.
  5. Click OK and drag the block to the right. It only slides along the shaft and stops one millimetre before the support.
  6. Back to the left, and it stops at the other limit. The block can no longer hit either support.

3:50 Gear pair

  1. Revolute joints next, on a pair of gears. Hide the linear guide in the browser to make room.
  2. Create a Spur Gear with module 2, 30 teeth and an 8 millimetre hole. Place it 200 millimetres along Z, clear of the hidden guide.
  3. Turn the view so you look at the gear from above: drag across empty space.
  4. The second gear has 15 teeth and stands 45 millimetres along X: the module times the sum of teeth, halved, so the teeth mesh.
  5. Under the gears goes a plate as the frame. Create a Box: 190 millimetres long, 6 high and 160 deep.
  6. Move its corner to minus 85, minus 6 and 160: the top face of the plate lies exactly at the bottom of the gears.
  7. Select both gears and the plate in the browser, holding Ctrl, then right-click and choose Create Components from Bodies: each body becomes its own component.
  8. Ground the plate, so it stays fixed while the gears turn, then bring the gears to the middle of the view and zoom in.
  9. The gears already stand where they belong, so use an As-built Joint: it joins parts without moving them.
  10. Click the gear, then the plate, choose Revolute and point at the front edge of the hole: its centre becomes the axis of rotation.
  11. Click OK. Now the same for the small gear: As-built Joint, click the small gear, then the plate, choose Revolute and point at the edge of its hole.
  12. Click OK. Each gear now turns on its own axis, but they do not drive each other yet.
  13. Motion Link couples the two joints: choose the joint of the big gear, then the small one. One turn of the big gear is two turns of the small one: 360 and 720 degrees.
  14. Meshing gears turn in opposite directions, so tick Reverse.
  15. Animate shows the pair at work: the big gear swings half a turn each way, and the small one twice as far.
  16. Click OK and drag the big gear with the mouse. The small one follows, twice as fast and in the opposite direction.

6:23 Rack and pinion

  1. Finally a rack and pinion, which turns rotation into straight motion. First press Fit and zoom in a little, so the whole plate is in sight.
  2. Create a Rack with module 2 and 24 teeth. It starts at minus 75.4 along X, so it lies centred under the pinion, and 295 along Z, in front of the gears.
  3. The pinion is a 20-tooth gear. Its centre lies one pitch radius, 20 millimetres, behind the pitch line of the rack.
  4. Select the rack and the pinion in the browser and turn them into components with Create Components from Bodies.
  5. As-built joints again, first the pinion: As-built Joint, click the pinion, then the plate, choose Revolute and point at the edge of its hole. It turns on its own axis.
  6. Click OK. Then the rack: As-built Joint, click the rack, then the plate, and choose Slider. Point at its end face: the rack slides along the normal of that face.
  7. Click OK and open Motion Link again: the pinion joint first, then the rack. One turn of the pinion moves the rack by its pitch circumference: pi times the pitch diameter, typed as an expression.
  8. Animate, and the rack runs back and forth in step with the pinion: half a turn each way moves it about 63 millimetres.

8:06 Summary

  1. Show the linear guide again and fit the whole assembly in the view. That is all: standard parts with materials, rigid, slider and revolute joints, limits and motion links.
  2. Foremka runs in the browser at cad dot nohup dot pl. Thanks for watching.

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