choice of end mill
I have 2 AR15 barrels, one stainless steel, the other chrome moly. I need to put 1/4" flats on each one for set screws FSB's. What type of end mills do I need for each metal type? I have access to a milling machine but will likely need to buy the end mills. I want to have a nice clean cut when I'm done so I'm ok with multiple sizes if I need to work up to 1/4".
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4 flute carbide end mill. 0 -
No need to make the cut in steps; you would want one that is center cutting though assuming you're going to plunge cut. 0 -
I would use a carbide bit...it will do the stainless, and if it will do the stainless, it surely will do the 4140 carbon steel. The number of flutes will determine the number of cutting surfaces, and that combined with your bit speed(rpm's), and feeding speed will determine your finnish cut properties.
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quote:assuming you're going to plunge cut.
Can you tell how the cut was done in the picture I attached? It seems much cleaner than the plunge cut a friend did on one of my other barrels last year.0 -
You do a plunge cut and then move the table in one direction straight out very slowly. 0 -
Your friend must have used a dull tool or his speed was off. 0 -
A carbide or HSS 2,3,4 flute will all work just fine. There isn't any reason not to use a HSS tool for this, but get whatever suits your fancy. Don't plunge with a 3 or 4 flute endmill unless you have too. Endmills walk when they are plunged, it is just the nature of the beast. Get a good endmill, not the crap stuff from Mcmaster Carr or Enco. Buy a Garr, Herter, OSG. Get 2 so if you break one you already have another one, double sided might come in handy.
I would side mill it, your not taking that much material off. Stainless steel will work harden and it is gummy. 410, which is probably what the barrel is is not too bad in the gumminess in comparison to some other stainless steels. Use lots of oil, ATF works well for what your doing. The 4140 will cut better then the stainless, it won't be any harder or softer, do the same thing, speed the cutter up a little bit.
If you have never done anything like this before, practice on a scrap piece of material first.
quote:Thanks to everyone. Thanks to shoff14 for the very detailed info. Any suggestions on the optimal RPM to cut at, or will that be dependent upon what end mill I buy?
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There are a lot of variables that will go into this sort of question. Coolant, type of cutter, angle of edges, type of machine, ect. I would say on a bridgeport type knee mill, with 1/4" HSS endmill your probably going to need a range of 1000 to 1250 ish. I know charts will tell you to run it a faster, but with stainless it is hard on a hand operated machine to keep the feed up so it doesn't get hot and gummy or chatter. With the type of cut your doing you may have to go down to 850 range in order for it not to chatter when the cutter is fully engaged in the corner. With the 4140 or 4150, which ever it is, I would probably run it 1300-1400 and take nice shallow depths of cut (.040"), you will be done with it in no time. The shallower depth of cut will keep it from chattering in the full radius of the cut. If you have chatter issues, slow the tool down spindle speed wise till you don't. But take note, the slower spindle speed you run, the higher chip load the tool will have with the same feed. So with your 1/4" you will have some flex in it, to fast feeding and you will get a nice "tink" by by endmill. Nice smooth movements will help you, use both hands to turn the knobs.0 -
no reason to use carbide. barrel steel not that hard. any good quality high speed steel mill will work. 0 -
Thanks to everyone. Thanks to shoff14 for the very detailed info. Any suggestions on the optimal RPM to cut at, or will that be dependent upon what end mill I buy? 0
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