I'm looking to create a rod that can be used as a light hammer and the spider staff seemed like a really great start. When I add the staff as a test item to character, that character gets a melee weapon attack action. When I mess with the type, it will only be a rod or light hammer, never both.
I also tried adding a melee attack and all the relevant weapon properties to a rod, I get the ability to equip the rod like a weapon, but no attack actions.
Storywise, it's really a rod that can be used to hit stuff. My initial plan was to make a hammer and say, "this works as a spellcasting focus". But building it as a rod adds to it's carryover from the preceeding 4e game. It's a thing made by a retiring player character for a new player character.
I guess the real answer is that I'm looking to do it for the same reason the creator of the Spider Staff made their weapon a staff instead of a quarter staff that serves as a spell focus; it fits better with the item's story.
Workarounds like this are always an option (I could even add custom actions to the player sheet), but I'm hoping that there's just something silly I'm missing since it's already been done with a staff and a quarterstaff.
You want a rod that is mechanically a light hammer that has other stuff (like being an arcane focus and possibly other things).
The system allows you to make a light hammer that you can state can be an arcane focus and give it other things and you can then change it's name to "Rod of Whatever" and set it's description to a rod that does these things. This will result in the character having a rod with these magic properties that they can use like a light hammer.
So, you have a system that does PRECISELY what you want it to do but somehow this is not what you want because it's been done before?
I made an item following what I said: Rod of Thunder this seems to do what you wanted: it can be used like a light hammer and shows the attack under Attacks on the character sheet, it has +1 attack and damage, deals 1d8 thunder damage on a hit and can be used like an arcane focus and the user can cast thunderwave out of it.
I am having a hard time understanding why this doesn't seem suitable for you.
I might be overstating the importance of the distinction. The base item in this case is somewhere between an artistic choice and an indulgence of my my anal retentive urge to categorize things elegantly.
I can a totally make it a hammer, but it feels kinda like spagetti sauce on fettuccini. It's going to taste the same and the meal will be fine, but it feels...weird.
Really, what I'm looking to understand is why my efforts to reproduce a thing that exists using the same tools is failing.
That being said, I do legitimately appreciate you taking the time to try to help me find something that works.