LMS HiTorque Mini Mill - Stainless Steel Work

[bill stupak]

One rule for stainless. ABC - Always Be Cutting

 

[DHerman304]

Danny, congrats on the new mill! Always cool to have a new machine.

There are a few things about milling stainless steel that you need to be aware of.

• The particular alloy series you're working with matters. There are Austenitic (200 and 300 series) and Martensitic (400 series) stainless steels and they have different machining characteristics, among many other differences. The most common SS used is the 300 series and of those, 303 has sulfur and is the easiest to machine. 304 and 316 and their variants are harder to machine and work harden much more readily. SO, you have to know what you're cutting.
• The kind of cut you're making matters - slotting or profiling. Speeds and feeds vary with each. Moreover, the number of flutes on your end mill will vary with which kind of operation you're doing. For slotting, a 2-3 flute end mill is preferred due to better chip clearance, while for profiling a 4 flute end mill will usually work better in most steels.
• There are two parameters you need to be concerned with to find the speeds and feeds you need with a MANUAL MILL: The axial depth of cut and the radial depth of cut. Axial depth of cut refers to how much of the flute length you're using and radial refers to how much of the diameter of the cutter you're using. Your speeds and feeds will vary with both of these parameters.
• Austenitic SS will work harden if you do not keep the cutter moving. The reason for this is because unlike most steels that get rid of heat in the chips that come off in a cut, SS tends to retain heat. Much of the heat remains in the cutter and most of the rest of the heat remains in the work piece. If the work piece gets too hot, it will work harden and you must cut under this hardened layer to machine it further. 303 tends not to work harden nearly as much as the other 300 series alloys, which is why it is preferred for manual machining. However, if you have sharp tools, use coolant or cutting fluid, take cuts that your machine can handle while it moves along in the cut at an adequate feed rate then all the SS types can be cut with a manual machine.

I am attaching a speed and feed chart from Niagara Cutter for stainless steel. Have a look and view it in light of what I said above. Hope it helps.

Oh, and no, you will not be running at 2500 rpm ...

Thanks for the write-up! I just got back from my metal supplier, looks like most aluminum is 6061, Steel is A-36, and stainless is 304. Looks like I need to slow way down.

 

[mikey]

You have to keep in mind that all the feed/speed charts are intended for use on industrial machines, not a little LMS benchtop mill. If the numbers suggest a given speed, it may or may not work well for you because you just don't have the rigidity and power to use those speeds as calculated. The same is true on a lathe; the calculated speeds are close but not all that accurate.

Us hobby guys have to eventually learn that speeds, feeds and depth of cut (all three are called your cutting conditions) are inter-related. A given depth of cut will require a particular speed and feed rate in order for your cutting tool to work well and there is NO formula that gives you this ideal combination on YOUR machine. YOU are the one that has to know how to adjust to the cut as it happens at the point of cut. This is true on any machine.

You will find that lighter depths of cut at slower speeds and faster feeds not only rough better but finish better and more accurately, and your tools will last longer on a small machine. On a lathe, the tool is held pretty rigidly so if there is deflection the work piece is usually the one to flex. On a mill, the work piece is usually rigid and guess what? Yup, its the tool that deflects so as you take bigger cuts at faster speeds, the feed has a massive effect on how much cutting force the tool experiences. Get it wrong and the end mill can snap.

What I'm trying to say is to slow down the speeds, lighten up on the depths of cut and learn how fast a feed your machine can take and still be happy. For milling machines, especially little ones, this is a better general approach.

Before I forget, use 303 SS whenever the job allows. It is far easier to work with.

 

[MrWhoopee]

Your supplier summed it up perfectly. Unknown stainless flat is almost always 304 (might be 316 if used in food processing). 303 flats are available, but not generally seen at your LSS (local steel supplier) because of poor weldability. Stainless rounds might be 303, or 304, if precision ground then 316 or 416 (pump shaft).

My eyes bugged out when you said 2500 rpm for a 1/2 in. cutter in stainless with no mention of carbide. Too fast even with carbide. Spend some time learning cutting speeds before spending more money on cutters.