Machining Time Calculation

During a production run, to machine a 36" X 84" X 1-3/4" slab door for 3 Ea 4-1/2" butts and a Gov't type 161 lock is about 4 minutes. We use a Norfield Magnum. This time can be reduced with the use of of a Magnum Loader and Unloader, but we don't have one.

Can you tell us what you might be machining?

Kind of an open-ended question. How accurate of an estimate do you need? Do you want the dollar cost of a finished item, or the cost of just one operation cycle? If it's a short production run, then machine setup times can be a large proportion of the production.

Start here -- http://lmgtfy.com/?q=machining+cost+calculator

To get the basic cost of machining per item, run your production process for an hour, then count how many items were made. Take the total cost of your production time per hour, and divide by the number of items machined. This is your base cost for machining each item, if no extra costs must be factored in (setup time, amortizing equipment cost, etc. )

Suppose you machined 100 items per hour. The cost of electricity was $10 and the cost of labour $40 for a total of $50. Cost of machining per item is 50/100 or $.50 cents each. You might have other overhead cost besides electricity, such as rent or mortgage. Divide your mortgage cost by the number of productive hours per month, to get an hourly overhead rate, and add it to other costs to get the total production cost per hour.

If the setup time is a factor, you must decide, how many hours production run you will be doing between setups. You have to design a production run that is big enough to minimize the cost of setup time per item, if changing setups is a factor.

For example, suppose the setup time is one hour, and you choose to do a production run of seven hours, before the setup needs to be changed. You already know how many items produced per hour from your test run - 100. For 1 hour setup plus 7 hours machining you will produce 700 items. Setup hour cost $40, machining hours cost $50 each for a total of 40+350 = $390. Cost per item is 390/700 or around 56 cents per item.

For amortizing the cost of equipment, the calculations are scaled up to spread the cost over a year, or two years, or however long you decide.

That's a good overview, but I think he's trying to determine the cost of machine time.

Milling and turning operations are too variable to offer a "rule of thumb". Material type, depth of cut, spindle speed, feed per tooth, and so on.

As usual, ambiguity rules in the question department! Still, what I outlined can be reduced to a formula, if not a rule of thumb, for any machining operation.

bn * prh/smh + prh = n

where bn = base number of items produced per hour in trial run, prh = production run hours, smh = setup and maintenance hours for the production run, and n = true number of items per hour. Custom jobs and small production runs will be more costly per item because of the increase in setup costs per run, but the formula is still applicable to any operation, to get the number of items per hour for a specific length of production run with specific setup and maintenance time, if the goal is to calculate the cost of machining time per item.

As for the cost per hour of "machining time", it would include

ma/h + oh/h + e/h + l/h = mtc

where machinery amortization per hour, plus overhead (rent)/hour plus electricity/hour plus labour per hour have been reckoned, for total costs per hour of machining time mtc. Setup time involving machining tests or trial runs would be charged at the same rate (unlike my example where I left out electricity for setup).

After all that calculating has been done, divide the cost/hour by the number of items produced/hour for machining time cost per item.

mtc/n = machining time cost per item.

More like a rule of fingers than a rule of thumb eh. Maybe the cost of an accountant should be reckoned in as well.

Cost of time to plan the machining steps x time to fixture x time to remove undesired material to produce part.

Keep records.

Thumb rule is; if you're not a machinist, ask one.

Other wise, simulators in modeling software have a time estimator for CNC cutting operations. Generally you have to fill in the rest of the story. See Artsmiths posts

Get a stopwatch and repeatedly time the damn machinist(s) doing certain X & Y operations....get an average production time......KISS!!!

Don't forget to include labor costs, benefits costs, electrical costs and machining parts replacement costs in your total cost analysis!