I'll admit it - I cut a 6x6 fir post 7/8" too short. I don't relish buying a new one because of cost, it being the weekend, and the attachment to the base pier is with a knife-style simpson connection which took some time to get right. The fir is not pressure treated - it's an inside application. Can I safely cut a 7/8" slice off of the left over fir post and glue it in there with PL? The beam is being attached using 5" L brackets on either side.
If I was making a shim, I would not want the grain running the short way since it will tend to disintegrate under load and time. Ideally 7/8 plywood, partly because it is harder wood... otherwise plane or rip 2x6 or two 2x4s to the desired thickness, or 1x6 if the thickness will suffice. I would also glue and screw it.
I don't see why not. Just don't trust any glue & put some screws in it to keep it permanently secured. No need to joint or key it in either, unless it's an angle cut. If it is, then the shim should be applied to the flat bottom instead.
Simpson PL9-5X5.5 (or equivalent) is a 1/2" steel plate, 5"x5.5". Or if you have a good steel place nearby, you could probably get even closer to your desired 7/8".
Depends on 1) the amount of load on the beam/post and 2) how it’s loaded, (i.e.: uplift, lateral load, vertical load only, etc.)
1) You can’t use a post that’s too short if the connection is fully loaded. Connectors are designed with certain “edge distance clearances” , “end distance clearances”, etc. When the post is too short, it does not allow the connection to develop “full strength”.
2) I don’t think being 7/8” too close to the end of the post is important, unless there is a significant uplift.