In our local saga, a device has been created. Namely A Knife To Cut Both Wood And Stone.
What does it do? What it says on the tin - cuts through stuff, without impediment.
But what ability is rolled to use it?
Not in combat - it's not really designed for that, and if I was used in combat, the answer would obviously be brawl.
but for other purposes? Say, cutting out a chunk of material from eg a wooden or stone pillar.
Hello! My 2 cents, Covenants pg 52, Stone Cutting Knife. It states Finesse with an ease factor of 6. Yes Finesse, its weird but appropriate.
Covenants, page 52?
The standard answer, as already stated, is finesse. It is really the answer to all applications of enchanted items where the result may be more or less satisfactory, and of course, many spells too.
It is not weird, but it is arguably a problem. It is completely consistent, to the extent that the skill becomes almost omni-potent. One skill to replace mason, carpenter, archer, weapon smith, artist, musician, et cetera ad nauseam. Highly abusable, but that's RAW.
That's a pretty good example of how broken the requirement for Finesse is. Instead of using a relevant craft skill for stonemasonry, the operator needs to learn an Arcane Ability. I get that the authors wanted to keep magic items from unduly changing the mundane world but this is really silly.
Sure, but the alternative is silly too. Using a stone cutting knife is very different from using hammer an chisel. A master mason would not be well-prepared to wield it.
The point, really, is that building a consistent and realistic world with magic is bloody hard. The ArM authors have done an amazingly good job of it, but they are not perfect either.
Excellent, thank you. I knew there was a reason I was thinking Finesse.
I would find it reasonable to allow artisans to, over time, become used to using magical implements that take the form of usual tools and to use these magic items with the appropriate Craft skill. Reducing everything to Finesse means we might as well have a stone-cutting thimble rather than a knife or chisel.
That's an argument for continuing to discuss the rules and suggest fixes and other changes. AM5 is a good game, not necessarily the best of all possible games.
I would say there is precedent for multiple approaches, depending on how you want the item to work. Who here has a warrior use Finesse when Edge of the Razor is placed on the warrior's sword? Probably no one. Why can't we have a similarly sharp tool for an artisan and not require Finesse? Personally, I would say you could design a device that cuts more easily or similar but still takes an artisan's skill, and then you use Craft; that device should be the appropriate tool. Meanwhile you could design a device that actually does much of the shaping itself as you use it, and then you use Finesse; that could really be any device at all.
Doesn't the section on Crafting Magic in HoH:S discuss the link between Finesse and the relevant Craft ability? I want to say that the relevant crafting skill is either required, or else you get a bonus if you have the crafting skill, or something like that.
There's the familiarity Bonuses/Penalties table on page 62 of HoH:S - +3 to Finesse if you have relevant skill of 5+?
Yep, that was it - which pretty much I read as "if you're good enough with the underlying skill, you can cancel out the +3 penalty that Finesse has relative to the Crafting skill itself".
Personally, I'd house-rule that to "Use either the relevant Crafting ability, or Finesse. Finesse rolls at a +3 difficulty. If you have both abilities, you may choose to roll either; the character gains a +1 to the ability roll for every level the character has in the secondary ability, up to +3".
Our SG has house ruled that finesse be capped by the relevant craft (except for Creo effects).
Personally, I don't like the idea that Craft 5 gives +3 and Craft 4 gives naught. Generally, I like ability scores to behave linearly ... and Craft 5 is definately not that much better than Craft 4. Capping resolves the main problem, but remains non-linear.
Maybe Finesse + 0.5*Craft (against the +3 ease factor used for finess). That's smooth and linear and pretty, and it matches the stated RAW rules at Craft 0 and at Craft 5 if we round up. But of course, many players will dislike the extra division and addition, which is a valid point.
Isn't the +3 to Ease Factor because Finesse does in a short time what a craftsman does in a lot longer? For a device which in moments makes a finished chair out of a piece of wood, this makes sense. But a device that merely magically assists a mundane action, taking the same time as it usually does?
The knife allows the user to cut through wood or stone like a mundane knife cuts through butter. It does not rearrange things like Craft Magic normally does.
I agree that it makes sense to use Finesse for the Knife, but with Characteristic do you add?
Dex makes sense in a way - steady hands and all - but then again the device does not manually cut off a piece of the stone, it does it magically. And Finesse rolls usually use Per for precision/detail right?
I could also see the use of a relevant, mundane ability (masonry, carpentry) but only provided the user has become familiar with how the magical knife works in comparison with mundane tools.
I think this depends on the design of the knife, essentially related to the trigger action, but really extending to control and not just triggering.
I think you can design such a knife for control with delicant manual dexterity (dex), or for mind control (Int). And yes, an item cannot read minds without a linked Me effect, but enchantments generally support some sort of mind control in that the wielder may maintain concentration for conc duration, so I think it is within RAW. For the latter design, the knife shape may be less sympathetic though.
I am not sure if the +3 Ease factor is because you work faster with Magic or because Finesse is a more generalist ability. I think each reason justifies a +3, so maybe it ought to be +6 
Hi,
Once house-ruling....
Use Form bonus (not Form score) for the thing being crafted both instead of Finesse and Craft skill. Do you have Terram 20? Along the way you've picked up all sorts of useful abilities at 4 with stone, iron, gold...
Anyway,
Ken
I definitely agree with the idea of differentiating 'craft magic' with 'magic to aid crafting'. The example above of a knife to cut stone and wood like it was butter makes crafting a lot easier and smoother, but doesn't make it minutes-instead-of-months. There's a difference between a magic table which does Carpentry for you with a hand-wave, and magic tools which stay sharp and can cut through wood like it was paper. I remember the Grogs book mentioned that having the proper (or better) tools would give bonuses to some utilizations of skills, so it's easy to rule that the Magic Knife(tm) would let a sculptor have a bonus to carving a statue, but would not force - or let - a user substitute Finesse.
Very good observation. But we need to consider what the user wants to cut with this knife.
I the user is a sculptor, we are talking art and the actual cutting of the stone is only a minor part of the work. The knife is very helpful, but probably more to speed than to quality of the work. The critical skill is the craft. Finesse arguably may or may not be relevant, but it is less important.
If the user is a quarry worker, on the other hand, the actual cutting is the major challenge. The question is mainly if the user can cut a straight line. In this case, I find a case to argue for finesse as the primary skill.
I just apply this rule
even to craft magic. There is nothing that says you can bypass it. This means you can't just get ridiculously good stuff with a really luck roll. Otherwise you may have to deal with the weapon-talisman magus with an excellent +20 weapon, yielding bonuses of +20 attack, +20 defense, and +20 to enchant it.
As for the needing an Ability at 5 to get a bonus, is there anything saying you couldn't get +1 or +2 for such an Ability with a score between 1 and 5?
If the item were crafted with Finesse, would you consider that the Craft Ability to be divided by 3?