Most weapons have a general range of grind limits that can be assumed for the most part, however, rares are the big ones when it comes to grinders, as their limits are more sporadic and random, no matter what rank or rarity they are. For example, the "ally" weapons (Axeon-series gunblades) do not share the same grind-max matrix the other two (Ogi's Garland-series rifdles or Reve's Romulus-series double-sabers), in which it goes 10-20-30 for the Axeons (in order: 3*->5*->7* weapons), however, it's 50-40-30 for the other two. Armors are a great one too, in which due to grind maxes, the Pizza Box (4* Lv14 armor with meager ungrinded stats) is the second-best all-class armor n the game defensively due to its NINETY-NINE (99) grind limit. At level 14, that's some pretty friggin' sweet armor, I tell you.
Anyways, for the most part, you'll generally see the grind limits being around this much, for most of the weapons in this rank:
1* - 60-40 (rares, no matter what level, can be upwards of 90, such as Grow Shower (1* handgun)
2* - 55-35 (and Valiant (5* JP-passcode claw) and as high as 50 or so for 7*'s, even, however, they vary
3* - 50-30 (exceedingly, AND can also be as low as ZERO (0), however the only ones that are in the game
4* - 45-25 (that cannot be grinded are all 7* rares, and are all conspicuously named as the
5* - 40-20 ("Zero" weapons in game to tip you off, though the Fuma Shuriken, a rare 7*
6* - 35-15 (slicer weapon is another no-grind, though it's just an odd-man-out; the only armor in the game
7* - 30-10 (that cannot be grinded is the 6* Spirit Garb, just as a tip...)
Just giving my little answer for this question, though as Daggart said, all the exact weapon/armor grinding limits can be found in the
Weapons and
Armor databases on this website. Simply click on the above highlighted texts to search through the specific grindables you like. ;P