Induction Plate Using Permanent Magnets

Using magnets, an electromotor, some lasercut MDF and itemprofiel, we made a small sized induction plate. The aluminum plate gets heat to around 40-45 degrees Celcius.

This project was made for the course DEF, Design Engineering voor Fysici, as part of the Bachelor of Applied Physics at the TU Delft.

Materials:

• 30 magnets (link)
• 0.181 m^2 MDF (6mm thick)
• 2 pieces of 15x15 cm (for the magnet wheel)
• 4 pieces of 24x10 cm (for the shielding sides)
• 1 piece of 20x20 cm (for the shielding bottom)
• 20x20x0.3 cm Perspex (for the shielding top)
• Two bearings, the size of the metal rod
• A metal rod with screw thread on the end (8 mm in diameter, 40 cm long, M8 screwthread on one end)
• One nut, has to screw on the metal rod
• Itemprofiel (link):
• Profile 20x20 (link):
• 6 pieces of 10 cm long
• 16 pieces of 20 cm long
• 4 pieces of 40 cm long
• 10 flat pieces (link)
• 40 corner pieces (link)
• T-Slot Nut (link)
• 90 screws short (link)
• 32 screws long (link)
• 4 flat head screws, used to secure the bearings (link)
• 4 flat head screws, used to secure the electromotor (link)
• Electromotor (link)
• Two Aluminum plates of 4x4x0.3 cm
• Press-in nut with screw thread on inside, has to screw on the metal rod (M8 to match the metal rod screw thread)
• Connecting clamp/nut between the metal rod and the electromotor (see photos step 4, 4mm to 9mm)
• 2 power cables, connecting the electromotor to the power supply

All the sizes and dimensions of our materials are up for change depending on how big you want to make everything. These are just the sizes and the configuration that worked for us.

Tools used:

• Laser-cutter
• Sandpaper
• Loctite
• Drill
• Inbus screwdriver set
• Vice
• Glue

Skills:

• Making or changing .svg laser-cut files, using Inkscape for example

First, laser-cut the file for the magnet wheel (the .svg file is included). This will result in two, same-sized circles, both with a 0.9mm hole in the middle, but one of the circles also has 30 holes for the magnets around the sides, see the pictures. Put the wheel with the magnet holes in a vice, with the press-in nut. Press them together to ensure a smooth and straight fit, this will be essential to minimize the wobble of the wheel later on.

Afterwards, the magnets can be pressed (don't do this in the vice) into the holes. The wheel is divided into ten rows, each consisting of three magnets. The orientation, of the south and north poles, needs to be switched up every row. So first one row all three magnets south, then the next row all three magnets north. DO THIS BEFORE GLUEING THE TWO WHEELS TOGETHER. If the orientation of one of the magnets is wrong, this can still be fixed if the wheels are not glued together yet. The fit is very tight, so this will take some strength and patience. After securing all the magnets and checking for the right orientation, the two wheels can be glued together. Let it dry using glue clamps to ensure a good connection.

The wheel is now finished. The magnets should all stick out a little bit, around 2 mm.

In this step we will create the frame in which the induction plate will be housed. To do this, we need to use the Item materials. While doing this it is important to keep an eye on inserting the correct amount of T-slot nuts into the itemprofiel bars. Remember, for every screw you see, you need a T-slot nut already slid into the itemprofiel bar right underneath the screw, or else the screw has nothing to screw into.

The first step is to make a square of four 20 cm Itemprofiel bars, connected in the corners by four 40cm itemprofiel bars perpendicular to the square. Before connecting them, make sure to add two additional T-slot nuts in the groove on the inside of all 20 cm bars and one in the groove underneath to leave room to mount the plexiglass later on. Now connect the corners as shown in the picture. This should look like a stool when done properly. Now we want to construct a second square around 10 cm above the first one, connecting four more 20 cm bars as shown in this picture. Again make sure to leave two T-slot nuts on the inside of every 20 cm bar and adding one underneath every bar. This will allow us to mount a sheet of MDF later on. 

The next step is to create two identical mounts for the bearings to attach to, for the axis to fit into later on. To do this, exactly copy the frame in one of the pictures twice. The Itemprofiel bars used are all 20 cm long. Make sure to use the flat head screws to mount the bearings in place. It is important to make sure the center of the bearings aligns with the center of the 20 cm bars. This means the axis will be perfectly centered once we put it in place.

The next step is to put these mounts into place. To do this, simply slide them into the frame somewhere above the squares we created earlier and mount them using a cornerpiece. See the pictures for the final product.

We still need to make a mount for the electromotor. To do this, take a 10 cm Item bar and put it down horizontally. Mount two more 10 cm bars vertically to the first one, using angle brackets. See the second to last picture for what I mean. Repeat this step one more time. Now that you have two of these structures, we will connect them together. To do this, put them next to each other, around 20 cm apart. Now put a 20 cm Item bar between each of the pairs of vertical 10 cm bars, as shown in the last picture. These 20 cm bars can later be used to mount the motor on, so adjust the height to make sure your motor fits perfectly aligned with your axis. When this is all put together, you can connect the horizontal 10 cm bars to the frame using flat connecting pieces as shown in the second to last picture.

For most of the shielding, it is as easy as laser-cutting all the MDF and plexiglass in the right sizes and with pre-made drill holes where necessary. The shielding consists of 6 plates, 4 on each side, the top and the bottom. The four sides are straightforward: Laser-cut them all, make sure the ''screw thread parts'' are already installed in the itemprofiel, line everything up, and screw it in. On one of the plates we also placed an aluminum plate, this way you can feel the difference in temperature between the two plates. For this we also lasercut a 4x4 cm hole in one of the side panels and forced the plate into the hole, without using glue.

The top and bottom are a bit more complicated. We wanted the top to sit flush with the itemprofiel for two reasons. First, it simply looks better, and second, because the gap between the magnets and the aluminum plate needs to be minimalized and should not exceed three millimeters. The top plate is made of plexiglass, so you can see the wheel and the mechanism inside. The aluminum plate needs to be inserted in the plexiglass. So when the aluminum plate is manufactured, measure it precisely and go back to Inkscape to change the size of the square gap in the plate before getting it cut. Make sure to make the gap smaller than the plate is, this way you can sand it down yourself and ensure a perfect fit, so it won't get loose. Glue can also be used, although this was not necessary in our case. The bottom plate can be laser-cut with a hole for the metal rod.

The top and bottom plates are secured using screws and small plates which are both screwed directly into the itemprofiel, see the photos. Using these two items, the plates can be squeezed between them, which will keep them securely in place. This also serves as a handy way to fix things if anything gets damaged, you can unscrew the plates very easily.

Down below the .svg laser-cut files can be downloaded.

We'll start by assembling the middle metal rod with everything connected to it.

Take the magnet wheel and the nut, which should both be able to screw on the screw thread of the rod. First place the nut on the rod followed by the magnet wheel. They should be screwed in until the top of the magnet wheel sits flush with the rod. Measure till where the screw thread of the rod was used, unscrew everything and start applying the Loctite. Smear some drops on the rod itself and some drops on the inside thread of the nut and the wheel. After applying, screw everything back and let it dry for at least 90 minutes. We recommend doing this step in a vice.

After having secured the bearings, the bottom shielding MDF plate, and having the rod dried completely, the rod can be slit into the contraption. Hover the top plate in place and screw the bearings tight when the magnet wheel is around 2-3 mm away from the top plate. When the rod and magnet wheel are secure, the top plate can be placed on top and secured as well.

Now all that's left to do is take a drill, fasten it around the rod, and test if everything spins as it should. The magnet wheel should have minimal wobble and the bearings should be perfectly aligned.

Optionally, if you want the entire setup to sit on its own, an electromotor can be used, see the photos. We will use this in our setup. So first things first, we need to connect the electromotor to the metal rod. For this we had a specialized piece which goes from 8mm (diameter metal rod) to 4mm (the size of the bit of the motor), the piece can be seen in the photo's. It has 2 little screws in the side which will clamp both axis. The electromotor (12V, 3.5A) will also have to be connected to a power supply, so connect two power cables to the electromotor and connect them to the supply.