mills and End Mills

[alan camby]

Like most of you, I like to do small projects in the garage in my free time.
I have a small benchtop mill that I mostly use to add slots to metal to allow adjustment in whatever i am building. Not building anything for NASA. Have no formal training on how to use this machine. My last employer had a full size Bridgeport that i spent some time tinkering around with.
Anyhow, I see most mills chucked up with 4 flute end mills. Why not 2 flute?
I have been using 4 flute HSS USA mills. Seem to work fine.

Does anyone use a chart to select the spindle speed when going to different diameter mills? I would think that the flute number would factor into this speed also.

Any other tricks to the trade that anyone whould like to give to the hobby mill operators.

Lets say, for example, that I wanted to mill the side of a 1/2" metal plate. How many thousands can I hog off in one pass. How about the final pass.
Should the final pass have the same spindle speed and feed rate?

Thanks, Alan

 

[Watchwatch]

Software that will do the work for you
http://www.cnccookbook.com/CCGWizard.html

The math behind it all
http://www.endmill.com/pages/training/spdfeed.html

More flutes take more horsepower.

How deep of cuts can you make? Like everything it depends. I wouldn't take more than .010 on a little benchtop mill. But I've never ran one before. And .010 is probably too heavy of a cut in soft steel.

A few tips and rules of thumb

The bigger diameter the cutter, the slower your RPM should be

Ideally, your endmill diameter should be 1/3 bigger than your work piece. Ex: millling a 1 inch square bar, you would want your cutter to be 1.333 diameter.

Don't put endmills in drill chucks!!!!!

Learn the difference between climb milling and conventional milling. You don't want to climb mill on a benchtop(or Bridgeport).

 

[alan camby]

My benchtop has a 2hp motor and has no problems with power. I break the end mill before i would stop the machine. Of course the largest end mill i have is 1" and i think that is all the machine would like to turn, mainly due to the machines limit on rigidity.

I am sure that all my terminoligy is wrong. Did not mean chuck, quess it is called a collet.
Think mine is R8. Don't own a drill chuck for the machine.

Will check out the links. Thanks

 

[Jim Johnstone]

Do a google search for speeds and feeds for milling. There are formulas that you have to take into account the material, the type of end mill (ie HSS or Carbide), the diameter of end mill, the # of flutes. And after all that, it comes down to feel and experience.

As for the depth of cut, that is a LOADED question. How many HP is your machine, how heavy is your machine, how rigid is the machine, how rigid is your work holding setup, how much of the end mill is extended out of the spindle. The point is, this will come down to experience and feel. For a small benchtop mill, you aren't going to be taking very deep cuts.

As for the speed/feed difference between roughing and finishing, I've known guys that use the same speeds/feeds for both, but I prefer to run higher speeds, with shallower depths of cut for finishing.

Another thing to mention with 2 vs 4 flute end mills, is that 2 flutes end mills are better for gummy materials like aluminum, because the extra space lets the material release, where as a 4 flute end mill will pack up in aluminum faster. In steel, 4 flutes tend to work great.

 

[alan camby]

How much does chip color tell you. How do i read the color.

 

[Jim Johnstone]

How much does chip color tell you. How do i read the color.

Cutting steel, goldish to a light blue is good. If you get dark blue and purple, you're too hot.

Cutting anything else, colour won't help.

 

[Provincial]

One strong point for 2-flute end mills is plunge cutting. Plunge cutting involves moving the cutter straight into the work like a drill bit. It is usually done to start a cut like a slot in a plate or to start a keyway on a shaft where the keyway doesn't extend to the end of the shaft. The fewer flutes clear the chips better.

Some 4-flute end mills are "center cutting", meaning that they will plunge cut like a 2-flute end mill because two of the end cutting edges extend all the way to the center of the cutter. The other two stop short of the center. Many 4-flute end mills are not center cutting and none of the flutes extend all the way to the center. You cannot feed these bits straight down into the work.

 

[Trucky]

Hopefully helpful stuff in red.

Like most of you, I like to do small projects in the garage in my free time.
I have a small benchtop mill that I mostly use to add slots to metal to allow adjustment in whatever i am building. Not building anything for NASA. Have no formal training on how to use this machine. My last employer had a full size Bridgeport that i spent some time tinkering around with.
Anyhow, I see most mills chucked up with 4 flute end mills. Why not 2 flute?

I mainly use 2 flute only when cutting softer metals (mostly limited to aluminum, brass, copper, etc.) because the high rpm and feed creates a lot of chips. 2 flute end mills are great at clearing chips and not "gunking" (welding) up with the metal you're cutting. 4 flutes for mostly everything else. Most all 2 flute end mills are "center cutting" (as mentioned earlier), but not all 4 flutes are. I never plunge with a 4 flute that isn't specifically made to do so, and most of my 2 flutes are used just for that. Keep it mind it is good practice to drill a smaller hole than the end mill and THEN plunge into it and mill in the other directions. This keeps the center nice and sharp, and lowers stress and possible overheating of the more outward cutting edges.

I have been using 4 flute HSS USA mills. Seem to work fine.

Does anyone use a chart to select the spindle speed when going to different diameter mills? I would think that the flute number would factor into this speed also.

http://www.endmill.com/pages/training/spdfeed.html

If I were you, I would get a general list of the things you usually cut and write the speed/feeds for them down on paper for reference.

Any other tricks to the trade that anyone whould like to give to the hobby mill operators.

Lets say, for example, that I wanted to mill the side of a 1/2" metal plate. How many thousands can I hog off in one pass. How about the final pass.
Should the final pass have the same spindle speed and feed rate?

You have 2hp to work with, which is what most all Bridgeport style mills and copies of it are rated at. However the table and ram/knee may not be as rigid as the larger mills simply because of construction or mass. With the correct rpm and feed rate (if you don't have digitals, you can do a stopwatch test to determine your average "hand feed". Use tape on the table and a reference point on something that doesn't move next to the table. On the tape, use a ruler to write inch marks down. Crank the handle for a specific number of seconds, count the inches (hopefully down to eights at least), and you can determine your "feed" that way.)

As for passes and "hogging", I'd invest in a decent roughing end mill to take care of that. You can take almost .100" on a decent Bridgeport with a good roughing end mill, but they aren't cheap. Try one from Niagara or other good manufacturer, just try not to kill it too fast. With regular 4 flute HSS end mills, I'd recommend a max of .050 at a slower feed rate, and keep the RPMs reasonable as well. The calc should help with that. For finishing cuts on aluminum and steel (normal varieties. This does not apply to anything tough that work hardens when you cut it. Basic 1018 steel and most aluminum alloys will apply here.), I would leave about .010 left for a finishing pass, at a slow feed. There are specific finishing end mills you can buy, but you should be good with a decent 4 flute HSS end mill. 2 flutes work equally well for finishing aluminum, at a higher RPM.

Thanks, Alan

My benchtop has a 2hp motor and has no problems with power. I break the end mill before i would stop the machine. Of course the largest end mill i have is 1" and i think that is all the machine would like to turn, mainly due to the machines limit on rigidity.

End mill size doesn't really matter all TOO much. Of course trying to cut something rediculous with a 1/16th end mill isn't going to go very well, but try this: Keep about 3/4ths of the cutter in the metal per pass. My most used end mills are .750 diameter.

I am sure that all my terminoligy is wrong. Did not mean chuck, quess it is called a collet.
Think mine is R8. Don't own a drill chuck for the machine.

I advise you to keep a good collection of collets on hand, unless you can keep your variety of screw/bolt sizes to a minimum. The cheap Chinese made ones work just fine, in most cases. Now if you're reaming a hole to 2 tenths, I would get precise ones.

Also recommended is a higher-quality drill chuck. I would have to say Albrecht is on the very high end of those. A good used Jacobs or Rohm will do you just fine.

Will check out the links. Thanks

How much does chip color tell you. How do i read the color.

Color progression on lighter steels is easy. Here's a good link discussing it.

http://www.mmsonline.com/articles/read-your-chips

In general, it starts out by getting darker and darker until a blue starts to form. Then, the blue gets very deep... at that point, unless you're roughing with carbide usually, it's very hot.. too hot for the applications you describe. I would recommend you stop if that happens and adjust your feed/speed rates. The most I usually get on a manual 2hp bridgeport is a darker brown, and that's roughing pretty well. (.075"-.100"). If you're getting dark or even blue chips when taking lighter cuts, your end mill is probably too dull.

Almost forgot. Climb and conventional (Thanks whoever posted it above). On CNC machines, climb cutting is very key to taking minimal number of passes, because it cuts (usually) to size, with good finish, but creates a lot of cutting pressure. On your basic bridgeport or tabletop mill, that is simply too much for the table to handle and it usually doesn't work out too well (exception: lighter cuts on aluminum).

Easy way to remember it: CLimb is CLockwise. Conventional is counter-clockwise around the part.

Important: this only applies for clockwise turning tools. End mill in high gear going in the "forward" direction, for example.

Top-down view of climb (the path the endmill takes)

----->|
^PART\/
<------

--YOU--

Read this page as well: http://en.wikipedia.org/wiki/Milling_cutter

It has some decent info.

If you have any more questions, feel free to ask.

 

[lametec]

Does anyone use a chart to select the spindle speed when going to different diameter mills? I would think that the flute number would factor into this speed also.

I use this chart:
http://www.endmill.com/pages/training/Speed and Feed - HSS End Mills.pdf

For carbide, I just multiply the RPM by 2-4, depending on end mill size and the available RPM on my mill. I'm not doing production, so I don't need to work at the very limit of the tooling.

RPM and flutes are not really related. The tool material and work material decide the RPM. Number of flutes are related to feeds, though, but I go by feel (finishing and general milling) and chip color (hogging).