Machinist

With total focus, the exhausted machinist, turns a cog for the last time. She closes the hatch on her new creation and flips a switch on her Aetherconverter. In an instant the metallic automaton whirrs to life and stands to its feet, waiting to receive its first orders. At that moment, an explosion can be heard nearby with a horde of goblins breaking into the laboratory looking for loot. The machinist gives a sly slime, loads her gun, and speaks "Good... I was hoping to do field tests today."

Gunner

When you adopt this specialization at 3rd level, you gain proficiency with smith's tools. If you already have this tool proficiency, you gain expertise instead.
In addition, you create a Machinist Firearm. A Machinist Firearm is a one-handed ranged weapon that deals 1d10 piercing damage, has a range of 30/90, and has the loading property. If your Machinist Firearm is lost or destroyed, you may create a new one by expending a spell slot. If you do, the lost or destroyed Machinist Firearm ceases to function.
Lastly, any firearm (both magical and non-magical), can be turned into a Machinist Firearm, by upgrading it during a long rest.

Machinist Spells

Starting at 3rd level, you always have certain spells prepared after you reach particular levels in this class, as shown in the Machinist Spells. These spells count as artificer spells for you, but they don't count against the number of artificer spells you prepare.
3rd Hunter's Mark, Faerie Fire
5th Silence, Misty Step
9th Haste, Lightning Bolt
13th Dimension Door, Fire Shield
17th Hallow, Conjure Elemental

Heat Gauge

Beginning at 3rd level, you gain a Heat Die that can overheat your weapon to power your machines. When you take the attack action with your Machinist Firearm or cast a spell, roll 1d4 and gain an amount of Heat equal to the number rolled. You can gain Heat this way once per round and can hold up to a maximum of 4 Heat. You can expend Heat to power weapons from the Machinist Kit by paying the corresponding Heat Cost

Machinist Kit

HEAT COST	MACHINIST ACTION	Description
1	Scatter gun	As a bonus action, each creature in a 15-foot cone must make a Dexterity saving throw. They take 2d6 piercing damage on a failure, and half as much on a success.
1	Peloton	As a bonus action, you emit a burst of revitalizing energy. All allied creatures within a 10-foot radius benefit from the Longstrider spell until the start of your next turn.
3	Gauss Round	As a bonus action, you fire your weapon in a straight line up to 60 feet. Every creature in that line must make a Dexterity saving throw, taking 2d8 force damage on a failure.
4	Slug Shot	You fire large slugs that home in on targets. The slugs deal 1d4 + (your Intelligence Modifier) force damage. You fire a number of slugs equal to your Intelligence Modifier.
5	Flamethrower	As a bonus action, you spray fire from your weapon. Every creature in a 25-foot cone must make a Dexterity saving throw. A creature takes 4d6 fire damage on a failure or half as much on a successful save.
6	Bioblast	You spray toxic and corrosive gas from your weapon. You choice a point within 20 feet of you. Every creature in a 15-foot radius, with that point in the center, must make a Constitution saving throw. A creature takes 3d10 poison damage, and 1d10 acid damage on a failed save, or half as much on a successful one. At the end of each of the affect creatures turns, a target can make another Constitution saving throw to remove the acid. On a failure of this save, it takes yet another 1d10 acid damage. On a success, the acid is removed.
7	Tactician	As a reaction, you can bolster your allies defenses. You grant resistances to all incoming damage to a creature within 30 feet of you as a reaction. It only lasts until the start of your next turn.
8	Wildfire	You fire a kinetic detonator at a target within 30 feet of you. Every hit on the creature which the detonator is attached, gains one charge. At the start of your next turn, the target must make a Dexterity saving throw, taking an equal amount of magical radiant damage equal to the amount of charges times your Intelligence modifier. They take half as much on a successful save.
10	Drill	You fire a kinetic drill at a target within 90 feet of you. Make a spell attack roll against the target. On a hit, the drill deals 6d6 magical piercing damage and 6d6 magical force damage.

Extra Attack

Starting at 5th level, you can attack twice instead of once whenever you take the Attack action on your turn. Moreover you can use one of your Machinist Kit options in place of one of those attacks. Additionally, your Heat Die increases to 1d6 and your maximum Heat increases to 6

Master of Metal

Starting at 9th level, your dedication to the machines has grown deeper. You gain the following benefits:
Barrel Stabilizer - As a bonus action, you can increase your Heat by an amount equal to your Intelligence Modifier. This ability recharges on a short or long rest.

Your Heat Die increases to 1d8 and your maximum Heat increases to 8.

Automaton Queen - As an action you can magically summon an automaton that is bound to you. It appears in an unoccupied space of your choice within 15 feet of you. The automaton is friendly to you and your companions, and it obeys your commands. See its game statistics block in the accompanying Automaton Queen stat block below, which uses your proficiency bonus (PB) in several places. You can determine the cosmetic characteristics of the automaton.

Once you create an automaton, you can't do so again until you finish a long rest or until you expend a 3rd level spell slot to create one. You can have only one automaton at a time. The automaton shares your initiative count, but it takes its turn immediately after yours. It can move and use its reaction on its own, but the only action it takes on its turn is the Dodge action, unless you expend 3 Heat at the end of your turn to power it enough to take another action. That action can be one in its stat block or some other action of your choice. If you are incapacitated, the automaton is inactive. The automaton disappears if it is reduced to 0 hit points, or after 1 minute. You can dismiss it early as a bonus action.

Note: You will have to make your own automaton queen using the statblock below and filling in the numbers where applicable, on critterdb. This is due to the fact I am unable to make a universal one for everyone in dndbeyond/critterdb. Inconvenient I know.

Armor Class: 13 + Proficiency Bonus (Natural Armor)
Speed: 40ft
Damage Resistances: Poisoned
Senses: darkvision 40 ft., passive perception 10
Condition Immunities: Charmed, Frightened, Exhaustion, Incapacitated, Paralyzed, Petrified, Poisoned
Languages: It understands the languages you speak
Actions
Slam Melee Weapon Attack: + your spell attack to hit, reach 40 ft., one target. Hit: 1d10+4 bludgeoning damage.
Pile Driver (Recharge 5-6) All creatures within a 15-foot cube originating from the automaton must make a Dexterity saving throw with a DC equals to your spell save DC. On a failed save, the creature takes 8d8 thunder damage and is pushed 10 feet away from the automaton. On a successful save, the creature takes half as much damage and isn't pushed.

Overdrive

At 15th level, your mastery of machines has reached its pinnacle. You gain the following benefits:

Your Heat Die increases to 1d10 and your Heat maximum is increased to 10.

Overheat - When you reach your maximum Heat, you enter an overheated state. For a number of turns equal to your Intelligence Modifier, your attacks score a critical hit on a roll of 19 or 20, and you add your proficiency bonus to the damage rolls of any Machinist Kit option.

Crowned Collider - When Overheated, you can cause the Automaton Queen to use all of its energy to create a powerful blast that can destroy a target. The target can be a creature, an object, or a creation of magical force such as the wall created by a wall of force. The automaton causes a creature to make a Dexterity saving throw against your spell save DC on a hit with its Slam attack. On a failure, the target takes 10d8 + 40 force damage.