LMS HiTorque Mini Mill - Stainless Steel Work

[DHerman304]

Morning/Afternoon all!

Well I finally got a mini-mill, I've squared my vise along with all other pre-setup and even got some decent cuts on steel and aluminum but I've trashed 3 bits on stainless very quickly. I'm looking for advice on what end mill to try next, as well as confirmation that 2500 rpm should suffice on a 1/2 mill? Any help would be great! The next task is getting workpieces to stay firm in the little rotary table.

Thanks,

Danny

 

[Peyton Price 17]

here is a chart for carbide end mills in different metals and cuts.

 

[DHerman304]

here is a chart for carbide end mills in different metals and cuts.

This is a great starting point, thanks!!!!

 

[Peyton Price 17]

This is a great starting point, thanks!!!!

your welcome

 

[Badabinski]

Do you know what kind of stainless steel you have? 303 isn't too bad to machine, but 304 is a horrible pain and loves to work harden. I've destroyed several endmills when machining 304 because I didn't push the cut hard enough, leading to rubbing and work hardening.

Just something to keep in mind. I found I had to keep my DOC pretty shallow in order to get the feed rate I needed.

 

[DHerman304]

Do you know what kind of stainless steel you have? 303 isn't too bad to machine, but 304 is a horrible pain and loves to work harden. I've destroyed several endmills when machining 304 because I didn't push the cut hard enough, leading to rubbing and work hardening.

I think that's exactly what I did on the last end mill I burned up. Unfortunately, I'm not sure what grade it is, I'll ask the next time I'm at the metal suppliers.

 

[markba633csi]

Most stainless can be challenging to machine if you haven't worked it much. A 1/2" endmill is asking a lot from a mini-mill no matter what kind of steel you are trying to cut, and those are expensive to ruin. Get some smaller sizes like 1/4" and 3/8" both carbide and HSS cobalt and practice at some slower speeds and feeds, don't try to force the machine to cut faster than it is comfortable with, but fast enough to prevent work-hardening. Use a cutting fluid of some kind too.
-Mark
ps make sure your machine's gibs are snugged up as firmly as possible to avoid chatter, which is a cutting tool killer

 

[DHerman304]

Most stainless can be challenging to machine if you haven't worked it much. A 1/2" endmill is asking a lot from a mini-mill no matter what kind of steel you are trying to cut, and those are expensive to ruin. Get some smaller sizes like 1/4" and 3/8" both carbide and HSS cobalt and practice at some slower speeds and feeds, don't try to force the machine to cut faster than it is comfortable with, but fast enough to prevent work-hardening. Use a cutting fluid of some kind too.
-Mark
ps make sure your machine's gibs are snugged up as firmly as possible to avoid chatter, which is a cutting tool killer

my machine only goes to 2500 rpm, I see 1/4" recommends 2600. Think this is a big problem?

 

[markba633csi]

Many of the speed charts are geared toward high volume production work where the most material needs to be removed in the shortest time. You can usually go slower in a hobby setting
-M

 

[mikey]

Well I finally got a mini-mill, I've squared my vise along with all other pre-setup and even got some decent cuts on steel and aluminum but I've trashed 3 bits on stainless very quickly. I'm looking for advice on what end mill to try next, as well as confirmation that 2500 rpm should suffice on a 1/2 mill? Any help would be great!

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 ...