Summary

I shrunk the pieces (~17%) and added a recess for gluing in small (6mm) magnets into the base.

Update 2017-12-15: After printing the king, I realized the jewel in the crown was too small and delicate. It looks great in the model, but it snapped off pretty easily when printed. I doubled the jewel size and changed out the file.

Print Settings

Printer Brand:

Monoprice

                                            <p class="detail-setting printer"><strong>Printer: </strong>                     <div><p>Maker Select</p></div></p>                                                                                <p class="detail-setting rafts"><strong>Rafts: </strong>                     <div><p>No</p></div></p>                                                                                <p class="detail-setting supports"><strong>Supports: </strong>                     <div><p>Yes</p></div></p>                                                                                <p class="detail-setting resolution"><strong>Resolution: </strong>                     <div><p>0.1 mm</p></div></p>                                                                                <p class="detail-setting infill"><strong>Infill: </strong>                     <div><p>0%</p></div></p>                                                        <br>                        <p class="detail-setting notes"><strong>Notes: </strong>                    </p><div><p>The knight is the only piece that actually needs supports.</p><p>I recommend using three walls and printing these at 0% infill. They will be very strong and don't need to be heavy, because the magnets ensure they won't fly away.</p></div>

Post-Printing

Magnets

            <div><p>The magnet recess is designed for a 6mm x 3mm disc magnet with a little extra room for tolerance. I used superglue to attach them, but you could use your adhesive of choice.</p></div>

Magnetic Chess Set