Using a jointer on an end grain cutting board with a side grain border is not recommended, and it may not be safe for the following reasons:
End Grain Structure: Cutting boards made with the end grain facing up are generally more forgiving to knife blades due to the structure of the wood fibers. The knife edge can sink slightly into the end grain, reducing the chances of deep cuts and maintaining the sharpness of the blade. Running an end grain cutting board through a jointer can be extremely dangerous because the rotating cutterhead can catch the wood fibers, causing the board to kick back or even get thrown out of the machine.
Side Grain Border: Side grain (also known as edge grain) borders are typically added to end grain cutting boards for aesthetic purposes and to provide a solid frame around the board. However, side grain wood is not as forgiving as end grain wood when it comes to cutting with a jointer. The jointer's blades can catch on the side grain fibers and cause splintering or damage to the border.
Risk of Damage: Using a jointer on an end grain cutting board with a side grain border can lead to irreparable damage to the board. The machine's high-speed blades are designed to work with long grain wood surfaces, and attempting to joint an end grain surface can cause tear-out, chipping, and ruin the board's appearance.
Instead of using a jointer, end grain cutting boards are typically made using a planer to level and smooth the top surface, or a drum sander to achieve a smooth finish. If a side grain border is part of the design, it's better to work on the border separately and avoid running the entire board through a jointer.
Ultimately, when it comes to woodworking projects involving cutting boards, it's essential to prioritize safety and choose appropriate tools and techniques for the specific type of wood grain being used. If you're unsure about the best approach, consult with experienced woodworkers or follow reputable woodworking plans and guidelines for making cutting boards safely and effectively.