One of the bows I've been using for teaching the local scouts how to shoot has a shelf that angles downward. This angle (see Pic 1)and makes it a little tricky to keep the arrow on the shelf during the draw. I was wondering if it is OK to reshape the shelf to make it more perpendicular to the riser. If it's OK then would it be better to do so as a flat shelf (see pic 2 with yellow lines) or slightly rounded like in Pic 3 with the red lines?

It won't hurt anything to slightly modify the shelf.  As an alternative, you might try adjusting the rug material on the shelf and side plate; building it up a little near the outer edge of the shelf and leaving a gap for fletching clearance in the corner.

If your gonna do it I go with picture 1 and while I was at it I'd radius the shelf from front to back

Thanks for the ideas. I hadn't thought about front to back and it makes sense.

Benoli,

Be careful not to square the shelf off as in your first picture.  You want more of a rounded shelf as below.  It can still be flat, but the corner should be rounded to prevent the riser from cracking along the grain lines.

Just another thought.....If you're teaching them traditional/instinctive shooting, have them cant the bow.  No rework involved at all.  Bow doesn't need to be straight up unless you're using sights.  Another option for no rework is to add a stick-on rest and don't shoot off the shelf.  Yeah, I know, that's blasphemy to some people, but it sure is an easy fix and is absolutely no risk to the bow.

Well I went ahead and cut the shelf. Here is what it ended up loking like:

It looks like it should be just fine.  How does it work for you?

Along with having them cant the bow, the alteration makes a big difference. Thanks for the help!