To try and keep the response shorter.
Copper is hardest, cause it doesn't really get you anything extra - just a bare minimum profit margin, no "surplus"
You can kinda get a little extra if you mine the copper instead, like you say you do, but its just basically covering "spares"
Ideally, to really keep the progress rolling - you want to get the best handles for Copper, and maybe tin,. Yes. They're hard to keep in stock - and you could buy the insanely cheap ones, but its harder to make a buck off of.. well.. a buck.
1$ handle is only making 0.15$ with 10+5% mark up (markup and charisma)
a 9-20$ handle is at least close to a buck to 2 bucks.
You'll also want to keep the bellows hot after day 19/20 or so somewhere between 13-20, the customer wait period drops to 60, or so it seems
And pre-make a few tool heads- Personally. I focus on pre-making 3ingot tool heads - they take the longest to prepare on the anvil, the longest to hammer, and they sell for the best profit margin - so having them "rushed" for the most - is most beneficial - where as daggers, are the least, and quickest.
Just make sure to keep 3 ingots on the forge of your current metal tier, at all times, to be prepared to make any item you don't have in stock.
At this current version, you'll also want to make sure its /only/ tool heads. and not actual weapons and tools.
Reloading forces you to have to reassemble them if they were assembled before reload. - and after you have more than 1 tier metal - they can distract the npc from the correct item. - which wouldn't be a problem, if yes, they would accept any metal.
Example
Tin Greatsword is requested
You have a copper and tin greatsword both on counter, but the copper one is in front of customer, and the tin one is off to side.
Customer will lock onto the copper one - its a "greatsword" and thats what they want, so they reach for that, but can't accept "copper for tin" - thus they get kinda stuck in an infinite logic loop, until that improper greatsword, is removed from their reach, and they're left with the correct one. which they'll then take.
Specializing
I also dabbled in specializing for when I would go mining.
Create one or maybe two types of items,and place them handle-wrap in under the cloth on the counter.
Greatswords are great for this, you can stick 2-3 on the top shelf (blade pointed at bed, handle at shelving unit)
and 3-4 on the middle shelf - all of which the customer can reach, immediately buying and taking off - provided, there's no interference.
Like the aforementioned tin vs copper greatsword - All Tin, or all copper, or all etc. - at least for now.
This way, you can leave the shop open while mining, sure you'll hear a lot of empty customers
But there'll be a few where you hear an immediate purchase, you're 50+$ richer now, sure you'll spend half that on a handle - but you didn't have to have /no sale/ while mining.
also doable
Spears - Dagger blade to the shelving - handle directly under cloth - What's important - is the wrap, the bottom of a pole - is nothing, the wrap just under the blade is the customer's area. - which is why they have to be flipped
Dagger tip#3 makes it even easier to fit them in the top shelf - and you can have a few of them there.
A Pole-sword (glaive)/(Pole + guard(none or any) + 1h blade) - might also fit, but the area of reach may not. - Pole+greatsword doesn't fit anywhere. - its massive :3 - you'll have to hand those to a customer, potentially knocking over a lot of other things.
But yeah. That's some things you can do to increase profits, keep pace, etc.
I ramble/d, I totally meant for this to be shorter....