Cutting Force During Milling

[KyleL]

Hi All, I'm designing a mill and for the life of me could not find any data on cutting forces. Specifically I was trying to figure out what kind of force may act against a column while milling, after some hunting I stumbled upon Google scholar search and reading a few papers later I found these gems:

http://www.cadanda.com/CAD_4_1-4__35.PDF
http://www1.gantep.edu.tr/~dereli/turkce/dynarefe-1.pdf

I'm making one important assumption as neither of these papers actually measure the force against the column or spindle, but feed force required to complete the cut. My assumption is, this force is transferred equally in magnitude to the spindle, and subsequently the column.

The first one, on page 7 shows a graph with with the y-feed force for a 2-flute 1" end mill, 3.47mm (~1/8") depth of cut, full width, at 1337 rpm, over a range of feeds cutting 6061 T6.

The maximum feed force required was about 700N.

The second paper, starting on page 8, shows a variety of tests with a 2-flute 0.25" end mill, 75% step over, 0.25" depth of cut, rake angle of 14 degrees also cutting 6061 T6.

Over the variety of tests the maximum force was just shy of 600N, with optimized feed rates resulting in forces of 200-300N. On average, about 350N was used for this cut over the range of feeds/speeds.

Both papers are rather interesting, though the math went over my head a bit lol! Enjoy

Thanks,
KL

[altaic]

Good question! I was just looking for this kind of information last week, and I managed to find a paper by Weh-Hsing Lai from the University of Kansas, entitled Modeling of Cutting Forces in End Milling Operations. Unfortunately I got side tracked, so I didn't try to extrapolate the cutting force data to my situation.

I would guess Machinery's Handbook would have tables of this kind of stuff, but I haven't had the chance to check it because a friend of mine is borrowing my copy.

Will

[wildwestpat]

Hi KL

Have a look at theis thread power of milling motor.

The way forward is I believe to work from tables giving the horsepower for machining the type of metal you need. From the horse power convert to tangential cutting force reaction and from there into the forces on the machine mechanics.

I have my copy of the Machinery's Handbook in front of me and page 1742/5 covers this for both drilling and miling. I recall seeing this sort of information on tooling makers sites and I think Sandvic might have some thing on their insert tooling pages.

However the type of milling operation - cutter form - material being cut all have an effect.

Hope this helps

Pat

[Dean448]

Metal cutting machine require extreem stiffness. A rule of thumb for spindle stiffness is 1 million pounds per one inch deflection. This is a tool capable of running face milling type cutters.

[handlewanker]

Hi Kylel, when you decide on the maximum diameter type of slab cutter/end mill the spindle will mount and the material you want to cut along with the maximum size of cut you can take, then take the maximum height you will raise the cutter up the column from the table to, you can decide what dimension the TOP of the column must be.

IE, if you calculate (?) decide(?) that the column at the very top must be 300mm X 300mm square in cast iron with a wall thickness of 25mm or in imperial, 12" X 12" with a wall thickness of 1", to resist the torque forces on the column at that point, then like a stick which the higher up you go the more it flexes, you will be somewhere aware that all the forces of the slabbing mill, whatever, will affect the column at this setting.

Anything below which it just gets better, which will be the maximum capability of the mills ability to not vibrate when cutting, taking into consideration that there must be a safety factor of at least 2 or maybe 3, meaning all the calculated forces are doubled or tripled against the column dimensions and shape, a square column will resist deflection better than a round column.

Once the top of the column size is decided the column can then be tapered down to give it form which probably makes the base part 300mm X 400mm.

If you go to a round column you are sunk because the higher you go the bigger in diameter you MUST go, something like a british postal service pillar box, big and dumpy.

Calculation wise, empirical formulars are usualy the starting point and when the design prototype fails it just gets improved at that point, until it doesn't fall down under it's own weight...LOL.

Experience is a big factor in machine building, and I do not know of any machine tool builder that has been capable of designing a machine from scratch without prior experience to work on.

The DIY wannabe machine designer/builder is indeed a lamb in the slaughterhouse when it comes to getting it right FIRST time and only time.

Best advice is to build it as strong as you think it needs to be, halve your expectations and live with your shortcomings.

The cost of DIY prototyping is a dream turned to a nightmare most times.

At all costs, avoid the round column design horrors so beloved of the early Taiwanese mill/drills that aren't worth the metal they are made from.

The other factor is CNC.....which means more light cuts and less force....no need to allow for brute force.....so a much lighter machine.

If you're keen on seeing a small mill I have, I'll post the pics of the design which is a small Beradi jig borer of Italian make, and has a column of about 300mm wide by same depth, 800mm high, with vee slides on the front of the column.

The motor, attached to the head moves up and down inside the column.
Ian.