The Kinetic Magnet Clock was designed by Ben Light for Bantam Tools.
This project walks you through building a clever Kinetic Magnet Clock using magnets, a clock mechanism, and some parts you can make with the Bantam Tools Desktop PCB Milling Machine.
In this intermediate-level project, we assume you have some experience with the Bantam Tools Desktop PCB Milling Machine and Software. If you're just getting started, we recommend first starting out with the three Getting Started Projects that come with the milling machine.
See the Kinetic Magnet Clock in action:
Tools
- Bantam Tools Desktop PCB Milling Machine
- Computer with Bantam Tools Desktop Milling Machine Software installed
Materials
-
Battery, AA
Files
- plate_mechanism_outside.svg
- plate_mechanism_center_hole.svg
- plate_back_smallholes.svg
- plate_back_insidehole.svg
- plate_back_outsidehole.svg
- plate_top_holes.svg
- plate_top_grooves.svg
- plate_top_outside.svg
- hand_center_hole.svg
- hand_recesses.svg
- hand_outside.svg
Custom Tool Libraries
- Aluminum_tool_library.json: Custom tool library for milling aluminum
- 1_16_flat_acrylic.json: Custom tool created to mill acrylic
Note on Materials: The material links provided above aren't the only sources. Just about everything can be substituted with something comparable, but results may vary. I suggest buying more material than you think you need. A good rule of thumb is to take the amount you think you need and multiply it by pi!
Note on Safety: This tutorial assumes you have basic working knowledge of how to safely use the Bantam Tools Desktop PCB Milling Machine. Always clean the machine before starting a new project, take care to properly attach the material to the bed, and never leave a the machine unattended while it's milling.
Milling the Three Acrylic Plates
The Kinetic Magnet Clock has three main pieces that are made of acrylic: the top plate, the mechanism plate, and the back plate.
Milling the mechanism plate and back plate is pretty straightforward. We'll use double-sided tape to secure the black acrylic to the mill bed. Then we'll use a 1/16” flat end mill to make the cuts.
Of note, when cutting through the full thickness of the acrylic, instead of using the software's Cutout setting, we'll use the Engraving setting to mill all the way through the material.
The Engraving setting can be used to cut all the way through the material if the engraving depth is the same value as the Material Thickness (Z) setting. For instance, if the material is 0.25" thick, and the engraving depth is also 0.25" thick, then the mill will effectively cut all the way through the material.
If you're new to using SVG files with the milling machine, or want a refresher, take a look at the Engraving Dog Tags with SVG Files project.
Acrylic mounted to the mill bed.
Step 1: Create a custom tool to mill acrylic.
First, create a custom tool in the Tool Library. Name this new tool “1/16 Flat Acrylic”, and give it the following settings:
- Feed rate: 43.3 in/min (1,100 mm/min)
- Plunge rate: 1.81 in/min (46 mm/min)
- Spindle speed: 16,400 RPM
- Stepover: 50%
- Max pass depth: 0.003" (0.08 mm)
In the software set Material to Generic and Material Size to 4.5” x 4.5” x 0.125”.
The double-sided tape we use to attach the acrylic to the machine's spoilboard is 0.003” thick. In the software, set Material Placement for the z-axis to 0.003”.
The tape you're using might have a different thickness, so use digital calipers to measure the thickness of the tape you're using. Then enter this tape thickness value in the Material Placement (Z) field.
Now it's time to get the mechanism plate SVG files loaded into the software and ready to mill.
Step 2: Mill the mechanism plate.
To mill the Mechanism Plate, use the files below and follow the steps.
Download these files:
Follow these steps:
- For all the files, choose the custom tool we created, “1/16 Flat Acrylic”.
- For all files, under Advanced, set "Scale from" to “Document bounds”.
- For plate_mechanism_outside.svg, unclick the Engraving option.
- For plate_mechanism_small_holes.svg, unclick the Cutout option.
- For plate_mechanism_small_holes.svg, set Engraving Depth to 0.125”.
- For plate_mechanism_center_hole.svg, unclick the Engraving option.
- For plate_mechanism_center_hole.svg under Advanced, set Cutout placement to Inside.
- Click "Mill All Visible".
- The milling machine will mill the plate.
All of the settings to mill the mechanism plate.
Milled mechanism plate.
Step 3: Mill the back plate.
To mill the back plate, use the same material size and placement settings as you did for the last mill job, open the files below in the software, and follow the steps.
Download these files:
Follow these steps:
- For all the files, choose the custom tool we created, “1/16 Flat Acrylic”.
- For all files, under Advanced, set "Scale from" to “Document bounds”.
- For plate_back_outsidehole.svg, unclick the Engraving option.
- For plate_back_insideholes.svg, unclick the Engraving option.
- For plate_back_insideholes.svg under Advanced, set Cutout placement to Inside.
- For plate_back_smallholes.svg, unclick the Cutout option.
- For plate_back_smallholes.svg, set Engraving Depth to 0.125”.
- Mill the plate.
All of the settings needed to mill the back plate.
Milled back plate.
Step 4: Mill the top plate.
Milling the top plate is a little more involved. Just like the first two plates, attach the frosted acrylic to the bed using double-sided tape, use the same material size and placement settings as you did for the last mill job, and start with the custom 1/16” Flat Acrylic tool we created.
To mill the Top Plate, use the files below and follow the steps:
Download these files:
Follow these steps:
- For all the files, choose the custom tool we created, “1/16 Flat Acrylic”.
- For all files under Advanced, set "Scale from" to “Document bounds”.
- For plate_top_outside.svg, unclick the Engraving option.
- For plate_top_holes.svg, unclick the Cutout option.
- For plate_top_holes.svg, set Engraving Depth to 0.125”.
- For plate_top_grooves.svg, unclick the Cutout option.
- For plate_top_grooves.svg, set Engraving Depth to 0.035”.
- Run the milling operations for plate_top_outside.svg and plate_top_holes.svg.
- DO NOT run the operations for plate_top_grooves.svg yet.
Here’s where it gets a little tricky. For the plate_top_grooves.svg, use a 1/8” ball end mill (NOT the 1/16” flat end mill) to engrave the two circular grooves.
The tricky part is that you'll tell the Bantam Tools software that you're using the 1/16” Flat Acrylic end mill, but you'll physically load a 1/8” ball end mill into the milling machine.
After you physically load the 1/8" ball end mill, make sure to do a tool touch-off. You can read more about how to do a tool touch-off in the the Inserting and Locating a Tool Guide.
With the Engrave operation selected for plate_top_grooves.svg, click Start Milling.
All of the settings needed to mill the top plate.
Before you remove the acrylic from the spoilboard of the machine, clear off the chips and dust and test that the spherical magnet rides nicely in the tracks.
If the spherical magnet slips out of the tracks easily, then we want to make the tracks a little deeper. To cut the tracks a little deeper, mill plate_top_grooves.svg again with all the same settings, except make the engraving depth a little deeper — somewhere between 0.040” – 0.045”.
When you're happy with how the spherical magnet rides in the track, remove the acrylic top plate from the spoilboard.
Note: Acrylic has a way of melting to the end mill if you don’t get the speeds and feeds just right. If you use a dull end mill, the quality of the cuts might be poor. If you use new sharp end mills and follow the recommended feeds and speeds in the Acrylic Guide, then the cuts turn out very well.
Step 5: Make the magnet clock hand.
The following is a technique Tom Igoe and Ben Light came up with to mill thin, delicate aluminum parts and not destroy them when pulling them off the milling machine spoilboard.
Using double-sided tape, fasten the aluminum to the PCB blank.
The aluminum/PCB sandwich.
Use digital calipers to measure the thickness of your aluminum/PCB sandwich, and enter this number as your material thickness in the software. Ours came in at 0.086”, but yours may vary, so it's always best to measure.
Then tape the sandwich, PCB side down, to the milling machine's spoilboard. The PCB acts as an additional spoilboard for the clock hand.
Now let's do a little math to get the Z offset for Placement.
Take the sandwich thickness (0.086”), add the thickness of the double-sided tape you use to mount the sandwich to the mil bed (0.003”), subtract the thickness of the aluminum (0.025”), and you get the Z offset for Placement (0.064”).
0.086” + 0.003” – 0.025” = 0.064”
Use the 1/16” flat end mill to cut and engrave the aluminum.
Milling aluminum requires feeds and speeds that are different from the feeds and speeds we used to mill the acrylic. See our recommended feeds and speeds for aluminum.
You can also download the aluminum tool library, and then import it into the software. (File > Tool Library > Import > select Aluminum_tool_library.json). Read more about this process in our Custom Tool Library Guide.
Settings for a 1/16” flat aluminum cutting bit.
Step 6: Mill the magnet clock hand.
To mill the clock hand, use the files below and follow the steps.
Download these files:
Follow these steps:
- Choose the bit “1/16 FEM Alum” for all files. This is very important. If you accidentally choose the default 1/16" flat end mill, the feeds and speeds will be too fast for aluminum, and the end mill will probably dull or break.
- For all files under Advanced, set "Scale from" to “Document bounds”.
- For hand_outside.svg, unclick the Engraving option.
- For hand_center_hole.svg, unclick the Cutout option.
- For hand_center_hole.svg, set Engraving Depth to 0.03”.
- For hand_recesses.svg, unclick the Cutout option.
- For hand_recesses.svg, set Engraving Depth to 0.015”.
- Click "Mill All visible". The machine will mill the clock hand.
- You won't cut all the way through the PCB.
All of the settings to mill the clock hand.
The aluminum has been cut through, but not the PCB.
Gently pry the aluminum/PCB sandwich from the mill bed. DO NOT pry the aluminum from the PCB.
Polish the aluminum clock hand with the scouring pad while it's still attached to the PCB. Take care while polishing because the clock hand is very delicate.
Next, submerge the aluminum/PCB sandwich into acetone for about an hour. The acetone will dissolve the tape, and the aluminum clock hand will be released from the PCB. Use acetone and a paper towel to remove any sticky residue left on the hand. If you're using the high-strength double-sided tape, you can use 91% isopropyl alcohol to release the clock hand from the tape.
Note: You only need one clock hand for this project, but the setup is somewhat involved, and the parts are delicate, so we made a few just in case.
Why make only one, when you can make three using the same setup?
Step 7: Attach the magnets.
We'll use two-part epoxy to glue the disc magnets to the two recesses on the clock hand. Mix your epoxy per the package instructions.
Use a toothpick to put a small dab of epoxy in the center of each recess. You don’t need a lot. Place a disc magnet in each of the recesses.
If you do this step on top of a magnetically attractive surface (a steel sheet), the magnets stay in place, with no clamping is necessary.
Allow the epoxy to dry fully before handling.
Step 8: Attach the clock hand post.
Carefully remove the small brass post from the second hand that came with your clock mechanism.
To do this, we drilled an 5/32” hole in a scrap piece of wood, placed the the second hand face down on the wood (making sure the brass post is over the hole), and lightly tapped the brass post with a hammer.
Insert the brass post into the aluminum magnetic hand you milled. If necessary, use a little epoxy to keep it in place. Apply with a toothpick. Allow the epoxy to dry before handling.
Brass post inserted into magnet hand.
Step 9: Assemble the Kinetic Magnet Clock.
Follow the instructions that came with your clock mechanism to secure it to the mechanism plate.
Clock mechanism attached to the mechanism plate with a nut and washer.
In each of the three holes on the mechanism plate, attach a 1” standoff to a 7/8” standoff. The 1” standoffs should be on the top of the plate, and the 7/8” standoffs should be on the bottom.
Note: In the pictures there are two short-stacked standoffs in place of the 7/8” standoffs.
Flip the assembly over and screw on the back plate using three screws.
Flip the assembly over again, and fasten the magnetic clock hand to the clock mechanism. Simply press the second hand post onto the mechanism.
Screw on the top plate using the three screws. You now have a fully-assembled Kinetic Magnet Clock.
Insert the AA battery into the clock mechanism. Then place a spherical magnet into each of the groves on the top plate.
You’re done! The Magnet Clock can lie flat, be placed at an angle, or hand on a wall using a nail.
If you have any questions, don’t hesitate to contact us at support@bantamtools.com. We’re here to help. And if you do make the Kinetic Magnet Clock, be sure to share it with us. We’d love to see it!