You're buying 3 printers at $600 each, so day one you're out $1,800. Each machine runs up to 12 hours a day, 25 days a month, for 900 print hours of monthly fleet capacity.
A typical order takes 4 hours to print and uses 50g of filament (raw cost: $1.00). You price it at $55.33. After the 0% platform fee, 3% payment processing, 10% failure buffer, and $2.00 in shipping, each job contributes $50.47 toward fixed costs.
At full utilization you'd ship 225 jobs a month and bring in $12,077 in net revenue. Subtract $200 in fixed costs, $30.00 in printer maintenance, and $2,250 to pay yourself at $20.00/hour, and you're left with $8,875 per month, a 73% operating margin.
Starting from 15% utilization and ramping over 9 months, the business pays back the $1,800 fleet cost around month 1.3. After 24 months you're sitting on $172,357 of cumulative cash, a 9575% return on the initial $1,800 spend.
The sneaky line item: your own time. Every job costs 30 minutes of you between designing, prepping and shipping. At steady state that's 113 hours a month, so the business earns $98.89 per hour of your time, before you pay yourself.
GrandpaCAD