You read in Chapter 11 (Working with Roller Chain and Sprockets) about how roller chain and sprockets can be used to transfer power between rotating shafts. In this project, you'll do exactly that for the project robot. First, you'll make and install the tensioner blocks. Then, you'll size the chain and install it. Finally, you'll add any spacers, if necessary, to tweak the chain tension. Note: It's likely that the chains will be super oily, so you may want to get some latex gloves from the hardware store, or have lots of clean rags handy.
|Caution: Eye protection is required for all of these operations. Review all of the general power-tool safety protocols described in Chapter 5 of Kickin' Bot, as well as the sections that correspond to the specific tools used below.|
In this operation, you'll make four plates from scrap 3/16" aluminum that will be inserted below the tensioner blocks to push them up to a height that gives correct chain tension.
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|Begin by marking a 1" wide strip at least 7" long on a scrap of 3/16" aluminum from the base. Use the bandsaw to cut the strip, using the techniques described in Chapter 6 (Cutting Metal).|
|Clean up the strip on the disc sander, being careful to stay on the side of the disc that rotates down, as described in Chapter 6 (Shaping and Finishing Metal). You will have to flip the piece over to sand the entire length of the strip. In this photo, I've drawn a center "do not cross" line on the disc sander table.|
|Finish the edge on the deburring wheel.|
|Mark four 1-3/4" plates on the strip. The kerf of the bandsaw blade is relatively small, and the length of these plates isn't that critical, so you can mark them all at once. This picture demonstrates use of the miter gauge to help guide the work in a straight cut. For the best results, make sure to hold the workpiece firmly to the gauge with your right hand, as shown. Cut the strips and clean them up on the disc sander and deburring wheel.|
|Nest, you'll drill the plates. You can save time by clamping all four plates together as shown and drilling all of the 1/4" holes at once. Use spray adhesive to apply the hole pattern to the top plate, and mark the hole positions with an automatic center punch before drilling.|
|Here are four completed plates. By clamping them all together in a stack, I was able to make all 8 holes by drilling just two holes.|
|Install the plates and check the chain tension. You should be able to move the chain at least 1/8", but not so much that the upper part of the chain comes in contact with the lower part. Correct tension should appear as shown. You can also use washers to tweak the height of the block. [Note: Don't be surprised if over time, your chains begin to stretch and sag. It's natural, and an example of why it's a good idea to have a tensioner in the system. You may have to make another set of spacer blocks in the future, using the technique above to maintain tension.]|