Suppose you have a 3D printer that you use to provide a service. In calculating the rate, you would include the amount of material used for a job, and the labor involved in executing it. That is easy enough to determine. You also have to consider the cost of the machine itself and the amount of time it spends running (which may be directly related to the amount of material). How do you factor that into a “per time” or “per material” rate?
Do you figure the number of months or years you want to spend making that cost back, and spread it over the amount of time you think the machine will be running in that interval?
How do you incorporate capital and overhead costs that aren’t directly related to the use of a machine into a rate based on time or size of a job?
These sound like pretty standard cost accounting issues; a college textbook in basic cost accounting would help you sort it out. You’re on the right track with the direct materials and direct labor; the rest is overhead applied using the most logical cost driver, be it machine time, labor hours, units produced, etc. I took the course last year but would have to review a bit to get more detailed.
As bahia says, that’s how you calculate costs.
Calculating the rate to charge is much simpler: what rate will make you the most money. If you already have the machine, you have to make sure to charge a rate that covers the marginal costs (labor, maintenance, materials). If you don’t have the machine, then you have to see how long it will take to return your investment. But the calculation of rate is more “what the market will bear” than “what it costs to provide this service.”
Tack it on to the labor rate
Well depending on the tooling in question it should pay for itself within its useful life and then some. If the printer costs $5000 but needs to be replaced every 1000 hours of use then make sure you add at least $10 per hour to the labor rate to cover that, any mid stream repairs/upgrades, etc.
Accountants are good for this kinda stuff in many cases. One important thing is to always be looking at the big picture. In any business, revenues must exceed expenses (including your income) or you are dead.