This page is a continuation of the previous laser-cutting project where we will be tweaking our design and laser-cutting out of a new material.

 

Improving Design:

Extending Rack:

From the previous design, it was realized that the rack-to-pinion gear teeth ratio could be larger to better display the translation of motion between the two gears. This choice was made because the pinion gear could not completely rotate on the previous design. Instead of completely redoing the design, we will be modifying the rack so that the entire design can be scaled down for the desired size gears. We will also be adding a hole to the pinion so that a bolt can be screwed into it to serve as a handle. This is done by doing the following:

• Edit the rectangular pattern that was used to make the rack teeth double the quantity it previously was
• Next, edit the sketch of the rack base so the top corners are coincident with the corners of the new outside teeth. This can be easily done by projecting the points at the corners of the outside teeth into the sketch and making the top corners of the box coincident with the appropriate corner.

• Create a sketch of a hole on the pinion gear and extrude-cut it from the body.

Now that the rack is larger both it and the pinion can be cut out at half the scale they previously were for the same rack length as before but now with a smaller pinion.

Sizing hardware holes and Backing: 

Before doing this we will need to go to the hardware store to get some hardware to hold all the acrylic pieces together. Since I am using 3mm acrylic, I bought 3 bolts that were 1/4″-20 and 3/4″ long, 1 bolt that was 1/4″-20 and 1.25″ long, and a 1/4″ID 1″ long spacer. The longer bolt and spacer will be used to make a handle on the gear to turn it and the other 3 bolts will be used to hold the rack and the pinion.

In order to find the right hole size to cut into the acrylic so that the bolts are able to screw into it, I cut holes varying in size from 0.19″ to 0.26″ and tested screwing the bolts into them. From this, I found that 0.23″ diameter holes work best for threading into and 0.25″ works best for holes things rotate around or slide in. Based on this, I can now size the pinion holes, rack slot, and backing holes accordingly. This is done by:

• Dimensioning “threaded” holes (such as the pinion handle hole and backing holes) to be 0.23″ when scaled to cut size
• Dimensioning “slider” holes (such as the pinion center hole and rack slot) to be 0.25″ when scaled to cut size

Now that those holes are to size, measure the distance from the pinion center hole to the top of the rack slot so that dimension can be adjusted on the previous backing for the correct gear fit. My measurement was 7.6″ but since my rack and pinion design is 4x the size of what I am going to laser-cut, I spaced the holes 1.9″ apart on the backing sketch, which is the correct size.

 

Prepping files and laser-cutting:

Creating DXF files and importing to Ruby:

• Create a new sketch for each part you have to laser-cut and project the geometry of the part into the new sketch, then save that sketch as a dxf.
• Import the dxf files into Ruby as new designs, scale them to the appropriate size, and assign a single color to all the cut lines

Adding Graphics: 

In order to better illustrate the motion of the mechanism, we will be adding arrows showing how the parts move and text on the backing that says what the mechanism is. To do this:

• Find an image online with a blank background and save it to your computer
• Open the design you want to add the image to
• “Add image to design” to import the image
• Resize and move the image as needed
• Set the image(s) to a different color than was used for the cut lines

To add the text:

• Select the “A” in the toolbar to add text
• Type text and change font and size as desired
• Reposition as needed
• Set to the same color as the images

Create Job for Laser-cutter:

Once all your designs are prepped it is time to add them to a job to queue to the laser-cutter. I have 2 pieces of acrylic that are different colors so I will be making 2 jobs: one for the rack and pinion gears and one for the backing they will be mounted to

• “Create job” from an open design or “add new job” (+ symbol) from the jobs tab
• Drag in all the needed designs from the menu on the left
• Arrange them nicely to waste the least amount of material
• Make sure the arrangement will be cutting on your material by creating a box the size of your material and ensuring all designs are inside of it
• On the right, select the material you are using
• Click on the colors to assign them to the appropriate action
• Queue when ready

Laser-cut and Assemble:

• Turn on the laser-cutter and follow the startup steps
• Place your material where your job was positioned to cut (easiest aligned with the corner)
• Pull up your queued job and start when ready
• Remove and repeat if needed
• Screw hardware into appropriate holes to assemble
• Admire your work

 

Files:

Link to files.

*Note: “PinionProfile” and “RackProfile” are 4x the size of “BackingProfile” so either they must be scaled down to 25% size or the backing must be scaled up to 400% to fit together