Custom Part Manufacturing Guide
Calculating Kinematics of a CTR
Graph Paper In-Plane Bending Experiment
Out-of-Plane Rotation Experiment
The exact instructions for laser cutting and 3D printing your custom parts will depend on the machines that you are using. This page will include some general tips for both processes.
Make sure to follow all training guides and instructions for your specific laser cutter.
Each laser cutter is going to have different settings. Some models will ask you to input your material type (”acrylic”) and the material thickness (either “1/2 in.” or “1/4 in.”), and then it will do all of the math for you. Other laser cutters will have you tune the settings more manually. This involves changing the power (typically a percentage) and the passes (number of times the laser passes over the material). When tolerances are important, you should always use low power with many passes.
Many, but not all, laser cutters have a feature called a pilot laser. A pilot laser projects a very low power beam onto your part so you can see precisely where the laser will cut. This allows you to make sure that your acrylic piece is placed correctly.
After the laser has stopped moving, do NOT move any of the parts until you have verified that the laser cut all the way through the part. Once you move the acrylic, you may never perfectly line the piece up again. If the laser did not cut all the way through, simply run the program again. This will be equivalent to running more passes of the laser. Do not increase the power unless the laser is still struggling to cut through after 10 or so passes.
Before laser-cutting any of the below components, use the sample part linked below to verify tolerances and tune your passes and power values. There are five holes and one slot. The three top holes need to be able to fit an M5 screw, M4 screw, and M3 screw respectively. The middle holes need to be able to fit the 12mm linear rod and the cylindrical barrel of the linear bearing. The slot should fit an M4 screw. The M3 heated insert slot should be able to fit the narrow end of a heated insert. See the image below.
<aside> 📎 Set up the test piece such that you cut it out very close to the corner or your acrylic sheet. This is to make sure you have plenty left for making your plates. Often, you can find small scraps of 1/4” acrylic near makerspace laser cutters. Using a small scrap is even better than using your brand new sheet of acrylic for testing.
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The holes for the M5, M4, and M3 screws should be somewhat tight. They should be greater than but close to 5mm, 4mm, and 3mm in diameter, respectively. The holes for the linear rod and linear bearing should have plenty of room around them. The narrow end of an M3 heated insert should sit in the M3 heated insert hole, but the whole insert should not be able to pass through.
Keep cutting out this sample part until you are satisfied with the settings. If you are cutting out many of these parts, see the below example placement images for the carts. You will want to make sure you are cutting out the sample parts such that you can still fit all needed plates on the material.
Once you are satisfied with your test piece and all parameters, it is time to lay out the actual plates. The images below are an example for how you could cut the plates if you are building a three cart CTR and using 2 sheets of 1/4” acrylic. If you are using 1/2” acrylic, you need half as many parts. If you are only building two carts, you need 2/3 as many cart plates.
The below setup gives you two extra slots incase you make a mistake and need to redo a plate, or in case you used up a significant portion of the acrylic doing tolerance testing.
<aside> 📎 It is best to cut the plates out one at a time. This might take a bit more time, but it is worth it to be able to check each plate before proceeding to the next one.
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You should familiarize yourself with the specific 3D printer that you are using. Learn how to load and unload filament, apply glue to the print bed, wash the print bed, and remove a part from the print bed. Learn about slicing software that works with the printer, and familiarize yourself with different settings: wall thickness, infill percentage, and support material settings.
Once you are familiar with how the printer works, you can start printing pieces. Similar to laser cutting, you will want to print a few parts at a time until you are sure that your process is reliable.
To set up a print, you will need to load an STL or a STEP file into your slicing software. You should always orient your part such that it requires the least amount of support material.
<aside> 📎 There a few exceptions to this rule. If you have some small, delicate features, you may want to position your part differently. It is best to position small holes perpendicular to the print bed if you need a constant diameter. Printing holes parallel to the print bed can result in an oblong shape that will not conform to your tolerances.
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See the image below for a suggestion on how to print each of the parts for this system.
Make sure to enable support material for both of the pulley pieces. Other pieces do not need supports. However, if you are struggling to print some of the small pieces because they keep coming off the bed, it might help to enable a brim. The printer will outline the edge of the part with a few extra lines. This often helps smaller parts stick to the bed.