1C: Practice Mechanisms

Exercise 8: Indexer Centering

In this exercise, you will be modeling a centering indexer for 9.5" diameter balls, similar to 1678's 2022 indexer. This mechanism features belts, chain, gear, and tube crush blocks. Be sure to pay attention to the plate sketches when modeling.

Crush Blocks

3D-printed crush blocks can be used to reinforce thin-walled tubing in assemblies where bolts pass through without a plate. Since the strength of bolts comes from their clamping force, without anything to support the thin walls, the tube can collapse before achieving proper clamping force. Crush blocks distribute the load, allowing for full clamping force while maintaining the tube’s structural integrity.

Alternatively, a "crush plate" can also be utilized to distribute the fastener force to achieve a similar effect as a crush block.

In this exercise, you will use a configurable 3D printed crush block.

Crush Blocks and Crush Plates

A 3D printed crush block (left) and crush plate (right). Crush plates tend to work well for the middle of the tubes where it may be difficult to insert a crush block.

Part Studio Instructions

Navigate to the "Exercise #8 Part Studio" tab in your copied document and refer to the solution document to complete the part studio for this exercise. The following instruction slides only provide a general outline and some key details.

1. Begin by creating the layout sketch on the top plane. Just like with the previous exercise, we define the distance between the rollers by mirroring the indexer wheel. We add 0.016" to the chain c-c to account for stretch in the chain.

2. Model the thin-wall 2x1 tubes with Extrude Individual and Tube Converter.

3. Model the top plates and bottom plates. The top plates can be modeled in the same sketch since they are on the same plane. Pay close attention to the plate constraints in the solution document.

4. Pocket the plates using the `Part Lighten` featurescript. Recall that you can select an entire sketch to automatically select all the ribs.

5. Model the #25 chain using the Belt & Chain Gen Featurescript.

8. Finish the part studio by naming your features and organizing them into folders. Assign the part materials accordingly.

Assembly Instructions

Next, navigate to the "Exercise #8 Assembly" tab in your copied document and refer to the solution document to complete the assembly for this exercise. The following instruction slides only provide a general outline and some key details.

1. Add the part studio parts to the assembly. Like before, group mate the rigid components with the Origin Cube and mate the Origin Cube to the assembly origin.

2. Insert, fasten, and replicate the 2" long, 3/8" OD plate spacers. Insert, fasten, and replicate the 1.5" long, 3/8" OD motor spacers. Copy and fasten the bottom gear plate to the 2" spacer. Insert, fasten, and replicate the 1/2" rounded hex shaft bearings.

3. Insert, fasten, and replicate the 3D printed crush blocks from the document linked at the top of this page.

4. Insert and fasten the motor, motor pulley, 48T 3D printed HTD pulley with 1/2" hex insert, 30T gears, and configurable spacer stacks fro MKCad. Fasten the belt to the pulley. Also fasten the shafts.

5. Insert and fasten the chain sprockets. Then, fasten the chain to the sprocket.

6. Insert and fasten the 6" Omni-wheels from this document and MAXHubs from MKCad.

7. Insert, configure, and fasten the Configurable Spacer Stack to fill the gap on the wheel shaft.

8. Insert, fasten, and replicate all of the required fasteners.

9. To finish the assembly, organize your components into folders and name your replicates.

Verification

Make sure to have you and/or a more experienced member/mentor of your team review your CAD! Your assembly should have 63 instances.