How fast to run endmills in 304 stainless?

Patrice Lemée

Patrice Lemée

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Aug 13, 2002
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I just broke three 1/8 endmills trying to slot a guard 1/2 an inch thick 304 stainless. :mad:

Turning at around 730 RPM. Just plain HSS endmills. First one I admit I took 0.010 passes so maybe that was the problem but the next was a 0.003 pass. :confused:

Patrice
 
You need to give us more information about the endmills in question. 2,3,4 flute? How long?

I don't envy you...304 is nasty stuff....
 
Look into using a slotting saw for guards. I know that MSC carries them. They may cost a bit, but will outlast 15 different 1/8" endmills.

Mike L.
 
The cutting speed for 304 stainless is around 120 sfpm. The formula for RPM is CSx4/D = 120*4/.125 = 3840RPM. But that is for a single cutting edge. I believe you divide that by the number of edges (ie. a 4 flute cutter would run at 960 RPM).

I've only done machining in High School, so someone please correct me if I gave any mis-information.
 
I've been told 303 stainless is better than 304.
(memory trick .303 British the rifle cartridge)

The one time I used 304 because it was easily available it was horrible and gummy to work.

Have you considered "plunge milling"? - treat the end mill like a drill = no side load breakage
(only if it is a centre cutting endmill)

Have you considered a Woodruff Key Seat Cutter ?
08449980.jpg

The tooth width would be 1/8 and cuts in the opposite axis that an endmill does.
Especially useful if you want one side of the guard open and the other with square corners.
jzcp390_guardslottedbrass_cv.jpg
 
i would over size the back side of the hold so that you only have ot mill say 3/32 thickness of that guard thats how i ended up doing a Ti guard that was over .5 thick

also i have become a real fan of the little dremmel carbide (ball endmill) they are for cleaning grout and stuff but work great for me (think they have liek 10 flutes)
 
SFM dictates RPM. RPM, number of teeth and feed per tooth dictates feed rate. SFM for a HSS cutter in 304 should probably be around 70 SFM.

For a 1/8" HSS cutter in 304, you should probably be turning around 2000 RPM. You should feed about .001" per tooth. That is hard enough that you're not rubbing, but not so hard to overload your cutter. A four flute that is probably around 10 IPM (wild guess) or 5 IPM for a two flute.

Your depth of cut should be shallow enough that your setup doesn't chatter at your RPM and feed rate. Your small mill should probably be .010" per pass.

304 work hardens badly, so you should avoid rubbing such as dwelling in one spot or feeding too slow. Avoid high RPM because chatter will cause hardening. 2000 is nice and slow for 1/8" cutter. Cutting oil with chlorine and sulfur (the stinky stuff, not WD40) can reduce galling and work hardening from friction. Avoid dull cutters.

Plunging with an endmill in SS can be iffy. I'd drill out the ends with a 3/32" drill so the mill can plunge mostly in air. I'd also use an undersize cutter for stock to clean up with finishing cuts. Lift into the air to feed over in Y for the finish cuts.
 
I was using 4 flutes endmills.

I will take all your good advice and try them on mild steel for a while. That stainless is much too hard to work doing something that I thought would be simple. But seeing your advices I find it much more complicated.

Thanks again.

Patrice
 
Patrice
Iusually scribe the lines for my slot on the guard,then on the bandsaw cut out between the lines,then use the mill to clean up the sides to proper width.Lot less metal to miil out that way.
Stan
 
I use my Sherline mini-mill to 1/4" slot 3/8" thick 416 stainless.

I've found the best way is to first mill a 0.003" deep slot as guidelines:

guidelines.jpg


Then I drill a series of holes (a few sizes smaller):

drilled.jpg


These are then milled out (with a 1/8" end mill, followed by a 1/4" end mill):

milling.jpg


Here's the finished slot:

slotted.jpg


On guards that are pushed on from under the ricasso, I use a 4" wide HSS slitting saw (after removing most of the material with a metal cutting bandsaw). McMaster Carr sells them. I also use plenty of Cool Tool II cutting fluid.
 
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Sbuzek, I am doing a slot in the middle of the guard so I can't use the bandsaw.

Butch, I hear you. I've been using using WD40 and should really get some real coolant.

Flatgrinder, that is prefect. I'll give it a shot.

Thanks again folks.

Patrice
 
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Opps Misunderstood, on hidden tangs I also do like Flatgrinder,I also buy cobalt end mills and turn them about 900 rpm.
Stan
 
Try using a 1/8 stub end mill, the cutting length is less so you will have to mill from one side then flip the piece over, then use a standard length cutter to finish the slot. Drilling undersize holes in the ends of the slot will help alot, so your not cutting with the face of the end mill. 500-600 rpm SLOW FEED, try .005 -.010 per pass. You need a good heavy cutting oil not wd-40, something sulpher based, cool tool works I just hate the smell of it. Stainless does not dissipate the heat, which turns the cutter blue and then it snaps. Be patient
304 stainless is more corrosion resistant than 303 (303 machines easier though) ,if you really want to curse try 316
:D
 
You can even try a slower rpm at first, if the cutter gets dull it aint cutting anything. Those fast rpm's are for flood coolant to get the heat and chips away. If your just putting it on wuth a brush, which most of use are go slow.
Keep the slot free of chips also, blow it out often.

good luck hope this helps

:D
 
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