This is a section of our Laserpanel tutorial at hertzlovers.com/laser-absorbent-panel
"They are designed so they can not be mounted the wrong way. If they fit, you're doing great. We recommend that you fit the pieces together while pressing them horizontally in a table. Repeated task are some times a good idea. Think of preparing frames for all the panels you can produce in a day (between 10-20). "