[bshahi]

Hi CNC Experts
Firstpost

I am a design engineer and have no experience with machining , but i am working on a project to make an excel calculator for milling sprockets
what i have learned so far is in order to calculate milling times we need need SFM and FPT based on Material and tool (i guess this is how mastercam do it )
so my approach is to get feed rates and rpms from these SFM and FPT then dividing total path length with feed rate and get milling time (then will add finish pass, lead in/ lead outs)

So i collected SFM and FPT for few material that i have noted down (for HSS inserts) but when i plug in those values i get really high mill time with stainless steel does my sfm and fpt are wrong
also suggest if this is right approach to go

Thanks

[peteeng]

Hi bshahi - There are many free cam packages that will calculate toolpath time, why reinvent the wheel. Try camotics. Plus tool suppliers will provide tables with suggested DOC and feed rates for different materials. ...Your trouble will be that a tool does not have constant feed speed. The CAM velocity planner adjusts the tool velocity depending on the path curvature (eg around a 90deg turn) , acceleration settings and even jerk settings so it's not as simple as it seems...Peter

[Jim Dawson]

I machine a lot of 304 SS and for HSS I would say your speed and chip load are about correct, but I think a HSS cutter would not last long. In real manufacturing you will be using the proper carbide cutters and run about 200 FPM at a 0.002 chip load, about 18 IPM feed.


I think your approach is correct.

[bshahi]

Than you peter for your response, reason being is we cut sprockets which usually have involute profile so not very sharp turns (assuming acceleration won't change drastically), but profiles are very custom hence it takes time to generate dxfs and then importing into software to get times, but i manage to calculate path lengths of those profiles and now i need to calculate times for that path lengths but i have to get my sfms and fpts correct. that is why i am here so guys like you can help me determine what sfms and fpt are practical in machining world for the materials i mentioned in attached image. Thanks once again

[bshahi]

I machine a lot of 304 SS and for HSS I would say your speed and chip load are about correct, but I think a HSS cutter would not last long. In real manufacturing you will be using the proper carbide cutters and run about 200 FPM at a 0.002 chip load, about 18 IPM feed.


I think your approach is correct.

Thank you very much Jim, yes you are right that we rarely use HSS, considering carbide tooling would you like to suggest SFMs and FPTs for materials i have mentioned in image.

[Jim Dawson]

For aluminum, we normally run the spindle at 6000 RPM for any size end mill, simply because that is our maximum spindle speed. Feed rates up to 180 IPM depending on what we are doing. Using carbide aluminum cutting endmills and heavy flood coolant.

I can't really help you on the other materials. The best I can say is to look at the cutting tool catalogs to get the proper feeds and speeds and cutter type for a specific material. The cutting parameters also depend on what your machine is capable of.

[peteeng]

Hellp Bshahi - yes accelerations do change drastically unless you cut very slowly and thats usually not the commercial reality. Peter

[bshahi]

For aluminum, we normally run the spindle at 6000 RPM for any size end mill, simply because that is our maximum spindle speed. Feed rates up to 180 IPM depending on what we are doing. Using carbide aluminum cutting endmills and heavy flood coolant.

I can't really help you on the other materials. The best I can say is to look at the cutting tool catalogs to get the proper feeds and speeds and cutter type for a specific material. The cutting parameters also depend on what your machine is capable of.

so recently i checked at our machine while it was running 4140 and was running at 624 SFM and 0.011 FPT with a 1.5" dia indexable 6 inserts end mills (calculated rpm 1600, feed rate 104.87), just one last query so i think its good approach to look into tool catalogues but my concern is will diameter of tool affect both base sfm and fpt or only one, so far what i have seen is tungaloy catalogue gives a range for sfm but give specific number for fpt as per end mill dia , but now using constant sfms or of bigger end mill given high rpms on smaller dia endmills (in my calculator ) what i am doing wrong ? should i get sfm and fpt both for all sizes and materials? once again thanks

[Jim Dawson]

The SFM is common to the material and the cutter, the diameter of the cutter has no effect on the SFM, only the spindle RPM changes per the cutter diameter.

FPT is really controlled by the mechanical strength of the cutter. Your 1.5 inch indexable insert endmill is very strong and will take a heavy radial load, thus allowing the 0.011 FPT. But 0.250 diameter endmill would instantly break if you attempted to cut with that FPT, just won't handle that much radial load.

[peteeng]

Hi BSH as Jim says the surface speed of a tool is a function of tool wear, friction and the material. Its about an economic and non destructive application of the tool.

https://en.wikipedia.org/wiki/Speeds_and_feeds

The chip load is a function of the tool design that allows the tool to clear chips effectively. Plus for some materials that strain harden it indicates the minimum cut required. If you cut too light the tool just scuffs and does not cut. See

https://cimquest-inc.com/what-is-chip-load/

As machinists what we are really concerned about is Metal Removal Rate MRR. We want to remove as much metal (or material for the plastic and timber people out there) as fast as possible without too much wear and tear on tools or machines. We want to find the sweet spot of surface speed, chip load and DOC that maximises MRR and gets the job done as fast as possible. This either brings smiles to the hobbyist or $$$ to the commercial operators.

Peter