1) Would it be possible to get a top view of your beam? :
2) And to carry out the following measures:
3) Do you have metal brackets and rods at your disposal?
4) What exactly will be the function of your inclined pan? Is it intended to hold attachment points for your hands, and if so, will their position be permanent?
A fortiori there is an inconsistency in the measures you have taken.
With rafters of 10, as they are placed on your beam, it is impossible to have this value of 9cm. It should be around 10.4cm
The value of 13 is possible but if the margin of error is the same, it is necessary to count 1.4cm more. Also, if I trust your photo (in a good way), the inclination of the chevrons seems closer to 16° than 11°. That is to say a measurement closer to 14.4cm than to 13.
Unless the rafter is "recessed" into the beam, and although your picture shows that it is certainly not 14 mm, a close-up of the corner where they touch (area circled in red on my plan) would be useful.
So I will ask you to take the measurements again, especially one that will be easier to take and sufficient, the space highlighted in red (the 40.14 blue) on the map. Thank you.
Thank you. The measurement on the second photo is well taken but not the one on the first. The ruler rests on its outer corner for an internal measurement ;) This still allows me to estimate the difference of half a cm and to see that the measurements of my plan are almost correct. The inclination should be 15°.
I'm going to prototype a removable panel on these bases.
Regarding your openwork board, should it be attached to your removable panel?