Thanks Dave and Bob the scotia moulding is quite expensive and has to be altered to get what I need. I had assumed that making them with a router would be quicker and more cost effective but now you have made me think about it the router bit was more expensive than the scotia.
The other reason to change to the routed version was to raise the sides or deepen the slot depending on your point of view. I am thinking I should try to adapt my current method rather than spending anymore time on this.
2020-01-16_04-43-41 by my0771, on Flickr
I am sharing my plan to make the whole project clearer to everyone including myself. I am going to cut a groove top and bottom on opposite sides to allow the trays to stack in threes. The trays for the pens will be 25 mm high as you can see from the drawing the gap is 28mm this will allow the bottom of the middle and top bases to have a pad underneath, this will stop the pens moving around in transit.
Another question does adding the spline to the mitre increase the strength of the joint.