I saw an old thread discuss this, but it was back during the UA version, so I’m not sure if anything new was clarified by now. But it's fun to think about the science behind magic, so I felt like walking through my own thoughts on it.
Normal foci are not magical items themselves. They can just have magic channeled through them as a means of funneling it out into one spot. The caster must supply the magic themselves in order to complete the process. Each class may have slight variations, but all of them utilize the focus in the same way.
Wizards pull magic from their surroundings/the weave into themselves, then channel that magic through the focus, shaping it into the given spell as it exits.
Clerics, Paladins, and Warlocks use the same method, but draw magic from a deity or other magical being, instead of the general arcane magic flowing everywhere. Their foci being a tangible representation of their loyalty/pact to the being.
Druids do the same, but pull from nature itself as the source. Their focus is a piece from nature, serving as a direct connection to easily pull more nature magic in.
Bards just play music, which is a universal language of its own (as old as magic in some ways), thus they’re capable of tugging at the weave without needing to understand the intricate code like a wizard does. This concept is used on a smaller scale in the verbal components of all spellcasting. The magic is funneled through the instrument after being pulled in, similar to the other class foci.
Sorcerers have the magic already within them, so they skip the drawing in phase and just expel the magic through the foci conduit into the form they desire.
Now we look at Artificers. Their spell casting is noticeably different from all other casters. Spells for them are having their magic put into a device, and that device replicating the spell effect. Their focus is required to be an artisan tool (a sort of “T” component to add to the V, S, M list). But artisan tools are quite an odd thing to use for this purpose, at least mechanically.
Tinker’s Tools are a set of scrap metal/leather, thread, hand tools like pliers/screwdrivers, and even a pot of glue (if the description I found is correct). You obviously don’t need to hold the whole 10-pound set when casting, so it can be implied that you just take the pliers or screwdriver in hand. The same can be said with the other tool sets (a flask for alchemy, a chisel for wood, a pick for thieves’, etc.). This isn’t explicitly written, but I doubt anyone would expect otherwise (similar logic will be used later).
So maybe they have an arm-mounted device that shoots a Fire Bolt cantrip when they tighten a screw with their tool (I know it doesn’t have an M component, but you get the idea). This process starts similar to the other casters in that it pulls in magic and channels it through the tool, but differs in that the magic is then imbued into a gadget that does the spell shaping instead of just being expelled out into existence. This serves as a precursor to their core trait of infusing items. Those infusions are magical items, compared to normal foci. The Artificer fills the object with magic and it stays there. The object can then be used for a specific effect now that the magic is ingrained into its structure.
This is why all infusions can be used as foci for Artificers, per the description, not just the ones you hold directly in your hand. Their magic has already been baked in, so they don’t need to physically touch it with a free hand, since that step is just to flow magic through a foci that lacks magic. They only need to focus their thoughts through the infused item for the spell to manifest. The item is still on their person, and often worn, so it’s not like the item is going anywhere. And having to reach down and touch a pair of boots seems ridiculous. This way of viewing the infusions isn’t explicitly stated (like the tool focus above), but it does say all infusions, so it's not surprising that a similar application of logic is needed here.
This also makes sense when thinking about magic items in general. You don’t need any foci when activating an item, or to touch an item being worn. It just does the effect when you focus on it, because the magic is already in there.
However, this creates a strange case for the Homunculus Servant infusion. Every other infusion is either worn or held as a weapon, while this one is a construct that is separate from you. But the homunculus acts similarly to another existing creature, the familiar. In both cases the caster can cast a touch spell through the creature/construct. This makes sense since it’s the exact same science as discussed above. Magic is already flowing through the construct, thus the bond/connection can be tapped into for passing along a touch spell. Using the homunculus as a focus would then follow a similar understanding, though I could see it still needing to be within 5-10 feet of you to properly act as a focus, instead of the “up to 120 feet” used in the Channel Magic trait.
So does this mean a Wizard could theoretically use a familiar as a focus? Unlikely. And the reason lies in the core way each caster casts. While the familiar is a creature made of magic like the homunculus, the Wizard is not versed in the application of magic like this. Meanwhile an Artificer’s whole style is centered around utilizing magic through an item, so they can easily pull off the more complex application of a construct being a focus.
The only aspect of the artificer that seems off in this setup is the Alchemist subclass needing specifically the alchemy supplies for their later features. I’m not sure why they don’t indicate infusions as an alternative, especially since you’d have to constantly swap out foci based on what you were doing. An easy fix I see is having the Homunculus hold the supplies, wear a pouch with them, or even have the set “built” into its body (meaning you can’t get it back without destroying the homunculus). Regardless, this seems like an odd distinction to have made, considering the high likelihood people would be using an infusion as focus.
TL;DR – The unusual use of tools as a focus, along with the distinct description of how the magic manifests (compared to the descriptions for other classes) shows the Artificer doesn’t necessarily follow the exact mechanics of spellcasting given years prior for the other classes. So the idea of infusions as a focus, even if not in the hand, still makes logical and even lore sense. This even includes the Homunculus, especially when taking into account the Channel Magic feature in the stat block (though probably best to limit its distance away from you when used as a focus).
Look at what you've done. You spoiled it. You have nobody to blame but yourself. Go sit and think about your actions.
Don't be mean. Rudeness is a vicious cycle, and it has to stop somewhere. Exceptions for things that are funny. Go to the current Competition of the Finest 'Brews! It's a cool place where cool people make cool things.
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Where did you get the idea that artificers can use their infused items as focuses? Why is it so odd that Alchemists use alchemy supplies?
Are you high?
I think OP is confused about a great many things, but at the bottom of the "Tools Required" subsection of the artificer's Spellcasting feature, the following text is plain:
After you gain the Infuse Item feature at 2nd level, you can also use any item bearing one of your infusions as a spellcasting focus.
Every artificer spell has a material component - they have to have their tools in hand to cast any spell whether that is cantrip or a leveled spell. Artificers can also use any of their infusions as a spell focus and the armorer artificer can use their arcane armor as a spell focus. The spell focus replaces required material components when there is no cost associated with them.
So, mechanically, the only difference between a wizard and an artificer is that the artificer has to have a set of tools in hand or have an infused item or their arcane armor for an armorer in order to cast any spell. This means every artificer spell implicitly has a mechanical component. That is really the only difference between a wizard and an artificer casting a spell.
All the rest, is a DM justification trying to explain why things work that way in their world. Rules wise the difference is spelled out above. Lore wise it is whatever the DM wants to create. The PHB gives some examples of things an artificer could do to "cast" spells but their are no mechanics relying on those descriptions. If an artificer or a cleric casts cure wounds, it does the same thing in the same way and the only difference is how you choose to describe the magical effect being produced. That description has no mechanical side effects. You could not prevent an artificer from casting a ranged spell by interfering with however they describe the magic working.
I saw an old thread discuss this, but it was back during the UA version, so I’m not sure if anything new was clarified by now. But it's fun to think about the science behind magic, so I felt like walking through my own thoughts on it.
Normal foci are not magical items themselves. They can just have magic channeled through them as a means of funneling it out into one spot. The caster must supply the magic themselves in order to complete the process. Each class may have slight variations, but all of them utilize the focus in the same way.
Wizards pull magic from their surroundings/the weave into themselves, then channel that magic through the focus, shaping it into the given spell as it exits.
Clerics, Paladins, and Warlocks use the same method, but draw magic from a deity or other magical being, instead of the general arcane magic flowing everywhere. Their foci being a tangible representation of their loyalty/pact to the being.
Druids do the same, but pull from nature itself as the source. Their focus is a piece from nature, serving as a direct connection to easily pull more nature magic in.
Bards just play music, which is a universal language of its own (as old as magic in some ways), thus they’re capable of tugging at the weave without needing to understand the intricate code like a wizard does. This concept is used on a smaller scale in the verbal components of all spellcasting. The magic is funneled through the instrument after being pulled in, similar to the other class foci.
Sorcerers have the magic already within them, so they skip the drawing in phase and just expel the magic through the foci conduit into the form they desire.
Now we look at Artificers. Their spell casting is noticeably different from all other casters. Spells for them are having their magic put into a device, and that device replicating the spell effect. Their focus is required to be an artisan tool (a sort of “T” component to add to the V, S, M list). But artisan tools are quite an odd thing to use for this purpose, at least mechanically.
Tinker’s Tools are a set of scrap metal/leather, thread, hand tools like pliers/screwdrivers, and even a pot of glue (if the description I found is correct). You obviously don’t need to hold the whole 10-pound set when casting, so it can be implied that you just take the pliers or screwdriver in hand. The same can be said with the other tool sets (a flask for alchemy, a chisel for wood, a pick for thieves’, etc.). This isn’t explicitly written, but I doubt anyone would expect otherwise (similar logic will be used later).
So maybe they have an arm-mounted device that shoots a Fire Bolt cantrip when they tighten a screw with their tool (I know it doesn’t have an M component, but you get the idea). This process starts similar to the other casters in that it pulls in magic and channels it through the tool, but differs in that the magic is then imbued into a gadget that does the spell shaping instead of just being expelled out into existence. This serves as a precursor to their core trait of infusing items. Those infusions are magical items, compared to normal foci. The Artificer fills the object with magic and it stays there. The object can then be used for a specific effect now that the magic is ingrained into its structure.
This is why all infusions can be used as foci for Artificers, per the description, not just the ones you hold directly in your hand. Their magic has already been baked in, so they don’t need to physically touch it with a free hand, since that step is just to flow magic through a foci that lacks magic. They only need to focus their thoughts through the infused item for the spell to manifest. The item is still on their person, and often worn, so it’s not like the item is going anywhere. And having to reach down and touch a pair of boots seems ridiculous. This way of viewing the infusions isn’t explicitly stated (like the tool focus above), but it does say all infusions, so it's not surprising that a similar application of logic is needed here.
This also makes sense when thinking about magic items in general. You don’t need any foci when activating an item, or to touch an item being worn. It just does the effect when you focus on it, because the magic is already in there.
However, this creates a strange case for the Homunculus Servant infusion. Every other infusion is either worn or held as a weapon, while this one is a construct that is separate from you. But the homunculus acts similarly to another existing creature, the familiar. In both cases the caster can cast a touch spell through the creature/construct. This makes sense since it’s the exact same science as discussed above. Magic is already flowing through the construct, thus the bond/connection can be tapped into for passing along a touch spell. Using the homunculus as a focus would then follow a similar understanding, though I could see it still needing to be within 5-10 feet of you to properly act as a focus, instead of the “up to 120 feet” used in the Channel Magic trait.
So does this mean a Wizard could theoretically use a familiar as a focus? Unlikely. And the reason lies in the core way each caster casts. While the familiar is a creature made of magic like the homunculus, the Wizard is not versed in the application of magic like this. Meanwhile an Artificer’s whole style is centered around utilizing magic through an item, so they can easily pull off the more complex application of a construct being a focus.
The only aspect of the artificer that seems off in this setup is the Alchemist subclass needing specifically the alchemy supplies for their later features. I’m not sure why they don’t indicate infusions as an alternative, especially since you’d have to constantly swap out foci based on what you were doing. An easy fix I see is having the Homunculus hold the supplies, wear a pouch with them, or even have the set “built” into its body (meaning you can’t get it back without destroying the homunculus). Regardless, this seems like an odd distinction to have made, considering the high likelihood people would be using an infusion as focus.
TL;DR – The unusual use of tools as a focus, along with the distinct description of how the magic manifests (compared to the descriptions for other classes) shows the Artificer doesn’t necessarily follow the exact mechanics of spellcasting given years prior for the other classes. So the idea of infusions as a focus, even if not in the hand, still makes logical and even lore sense. This even includes the Homunculus, especially when taking into account the Channel Magic feature in the stat block (though probably best to limit its distance away from you when used as a focus).
Where did you get the idea that artificers can use their infused items as focuses? Why is it so odd that Alchemists use alchemy supplies?
Are you high?
Edit: Whoops I'm blind.
Look at what you've done. You spoiled it. You have nobody to blame but yourself. Go sit and think about your actions.
Don't be mean. Rudeness is a vicious cycle, and it has to stop somewhere. Exceptions for things that are funny.
Go to the current Competition of the Finest 'Brews! It's a cool place where cool people make cool things.
How I'm posting based on text formatting: Mod Hat Off - Mod Hat Also Off (I'm not a mod)
I think OP is confused about a great many things, but at the bottom of the "Tools Required" subsection of the artificer's Spellcasting feature, the following text is plain:
There is fluff and there is mechanics. :)
The OP seems to be mostly talking about fluff.
Every artificer spell has a material component - they have to have their tools in hand to cast any spell whether that is cantrip or a leveled spell. Artificers can also use any of their infusions as a spell focus and the armorer artificer can use their arcane armor as a spell focus. The spell focus replaces required material components when there is no cost associated with them.
So, mechanically, the only difference between a wizard and an artificer is that the artificer has to have a set of tools in hand or have an infused item or their arcane armor for an armorer in order to cast any spell. This means every artificer spell implicitly has a mechanical component. That is really the only difference between a wizard and an artificer casting a spell.
All the rest, is a DM justification trying to explain why things work that way in their world. Rules wise the difference is spelled out above. Lore wise it is whatever the DM wants to create. The PHB gives some examples of things an artificer could do to "cast" spells but their are no mechanics relying on those descriptions. If an artificer or a cleric casts cure wounds, it does the same thing in the same way and the only difference is how you choose to describe the magical effect being produced. That description has no mechanical side effects. You could not prevent an artificer from casting a ranged spell by interfering with however they describe the magic working.