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I've been reading the wiki to try to find out the optimal Stone Furnace to Electric Drill ratio and after some math I thought I found that 7 Stone Furnaces were enough to smelt all the ore that 4 Electric Drills could mine. The proportion was calculated using the following logic: I got the throughput pretty much right (118.9/min), however it seems the ore starts to accumulate slowly in the transport belt until it reaches the drills and then the energy use starts to fluctuate (due to the drills stopping). Is it that the drills are slightly faster, are the furnaces slightly slower or is there a variable I'm ignoring?

Electric mining drills produce 1 ore each 1.905s.

DaveMcW wrote:Electric mining drills produce 1 ore each 1.905s.

I see, thank you.

Ratio is 2 furnaces to 1 drill. So 8 furnaces would stop the ore from backing up with 4 drills.

So it's either 114 or 115 ticks. Could probably do some testing with a train and wagon to time it precisely. The ratios would be:
For 114 ticks (1.90 secs) - 19 Electric Drills to 35 Stone Furnaces (38 Electric Drills to 35 Steel or Electric Furnaces)
For 115 ticks (1.92+ secs) - 23 Electric Drills to 42 Stone Furnaces (21 Steel or Electric Furnaces)
Or For Xterminator = "Suffusion of Yellow"

Some quick scripting confirms it is 115 ticks.

ore mined at tick 188
ore mined at tick 303
ore mined at tick 418
ore mined at tick 533
ore mined at tick 648
ore mined at tick 763
ore mined at tick 878
ore mined at tick 993

The rule of thumb is 2:1 (likewise, 1:1 for steel and electric furnaces). As it turns out, it's extremely close to the perfect ratio until you do mining ops of the size that completely swallow ore deposits, at which point you've reached such a scale that you're probably feeding the furnaces by train from multiple mines and probably aren't worrying too much about the ratios.

I decided to math it out. To fill in the blanks, copper and iron smelting takes 3.5 seconds in stone furnaces, which is 210 ticks. That makes the ratio 42:23.

Let's throw it in a spreadsheet to see how it works out. If you round in favor of furnaces (recommended), it's:

• Perfect 2:1 for 1-5 drills,
• Subtract 1 for 6-11 drills,
• -2 for 12-17 drills,
• -3 for 18-22 drills
• At 23 drills, it becomes 42 furnaces, reaching the perfect ratio.

Just for fun, let's do steel/electric furnaces too. They're twice as fast, cutting the recipe time in half, so 1.75 seconds, or 105 ticks, making the ratio 21:23. (Yes, I could've just divided by 2, but I wanted to demonstrate why that works.) Again rounding in favor of furnaces:

• Perfect 1:1 for 1-11 drills,
• 1 less furnace than drill for 12-22 drills,
• At 23 drills, it becomes 21 furnaces, reaching the perfect ratio.

This all is, of course, theoretical; it's what the math says. The game may have unexpected factors that change the actual behavior.

I calculated most optimal ratios for electric drills and electric furnaces, you will need to use Tier 1&2 speed modules to achieve intended speed boost.

Ratios for mining-smelting iron and copper:
4x 90% Electric drills = 5x 40% Electric furnaces (ratio divergence 0,25%)
6x 90% Electric drills = 7x 50% Electric furnaces (ratio divergence 0,25%)
7x 40% Electric drills = 6x 50% Electric furnaces (ratio divergence 0,01%)