How to calculate machining times

I am just starting a new position at my company. I will be estimating machining projects. I need help on how to calculate times. Any formulas or reference material I can use? I have never worked in a shop so I am very limited on machining processes and formulas.

jimcncmachiner said:

I have never worked in a shop so I am very limited on machining processes and formulas.

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I don't see how you can possibly estimate machining jobs if you don't have any experience doing machining. There are no formulas, that would be effective on standard machined parts. For fabrication it can be feasible to run calculations based on how much tonnage of steel is used, but for machining, the work time can be 1x the material cost, or it can 20x. If you absolutely have to start with some calculation, for standard aluminum parts, figure material cost + 4x material cost for the machining. Then, after a few jobs, you can vary the multiplier based on complexity.

The other way to do it is to learn CAM and actually program the part and look at the simulated runtimes -- but you need some machining experience to be able to do this unless you can get someone else in the shop to program the CAM.

Sorry, that's all I got.

Regards.

Mike

calculate the time for a tool by dividing the feed distance by the feedrate and multiply by 60. For example, a drill or end mill cutting (feeding) 3" at 60 IPM, (3/60) x 60 = 3 seconds. Then add in any non-cutting time such as positioning and tool changes. Do this for each tool used for the job and then factor in Load/Unload time and programming, engineering and set up time. There is usually an efficiency factor to consider too, that will be for machine down time during refreshing tools and operator breaks etc...

The facts:
1. You posted in a fabrication forum, asking about machining.
2. You didn't list specific machines.
3. You being the one to "make or break" the company
of your employ.

Get it too high, lose the bid.
Get it too low, lose the company.

sounds like your boss is on his way out of business.

Why do I get the feeling he has the same last name as you?

BROTHERFRANK said:

calculate the time for a tool by dividing the feed distance by the feedrate and multiply by 60. For example, a drill or end mill cutting (feeding) 3" at 60 IPM, (3/60) x 60 = 3 seconds. Then add in any non-cutting time such as positioning and tool changes. Do this for each tool used for the job and then factor in Load/Unload time and programming, engineering and set up time. There is usually an efficiency factor to consider too, that will be for machine down time during refreshing tools and operator breaks etc...

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What he said. I have a spreadsheet I created to help with that internally, but you still need a machining background or you can get whatever numbers you like. I think it would be best for you to quote any material, hardware, outside processes, but rely on someone with a machining background to get you estimated cycle times.

There are formulae but they only apply to large businesses with several dozens to hundreds of machinists working 100 percent and they’re from times before CNC. Today most machine controls include a program run time read. From there you can know something, the rest must be gathered by observation, prepping stock, tools, machine, everything. Plus programming plus discussion plus mishaps

In my experience there is a lot of optimization to be found in even moderate production runs so decreasing run time on a part by a factor of two vs your first CAM attempt is quite possible when there is substantial uncertainty. Once you have a lot of experience with a a particular machine particular cutters and particular materials, you can probably get it closer on your first draft but that's only going to come with even more experience.

Actually this question was asked on the general forum some years ago and whether there was some overall magic formula. It would certainly be possibly to find feeds and speeds for modern tool paths, in the tooling catalogs perhaps, and build a general model where you have the stock, the roughed part and the finished part and you integrate, find the differences in volume and work out the time, but this would would best for a general process like surfacing and it would be trickier to bring in clever and efficient other methods like using a drill here and there. Possible though. How are your Excel or maybe Python skills?

My brother worked for GM for a time and that was part of his job. the old timers had created a book of task and time. Without that long time data keeping it is a crap shoot to figure. Speeds and feeds is a start..inches per minuet rough machining, finish machining , adding lay-out. You might start looking for books on the subject, I do remember such books, some of my old books may have some data on such... but perhaps now with CNC that would add factors..Good luck.

Here find a rough start:
http://web.mit.edu/2.810/www/files/readings/Polgar_TimeEstimation.pdf

When you think you have a too long operation it’s perhaps time to deliberate different processes. To cut from solid is not always necessary. One can cast, mould, forge, press, stamp, form cold. I know customers not always like to be presented with radical departures from their ideas. Some are open, most aren’t.