Help with broken endmills

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I had the silly idea to try and cut some brass with my home made cnc machine. I've cut AL about a dozen times without coolant and it worked great, even held about 8 thou in tolerance.Albeit, this was with a 3/8 2 flute flat end mill.yesterday i figured i try and mill a small intricate design in brass. did a test run in a piece of scrap maple  :http://tinypic.com/r/122ywwx/5The above was cut using a 0.03125" 2 flute 1/8" total cut length kyocera end mill that is supposedly spec'd for metal/plastic/etc. I figured 0.0125 depth cuts would be ok in brass. (using < 1/2 the diameter of the bit a s rule of thumb). However about 30 seconds in using an ultra low 10ipm the first bit went bye bye. Next bit, bye bye after even less time. Now, I didn't use ANY lubricant this first round. Would lubricant have made that much of a difference? Maybe using bits this small is beyond my crappy machines capabilities.As an experiment I tried 0.0125 depth cuts with a 0.125 carbide ball end mill and things worked well. Even without coolant i was able to rip through the brass anywhere from 10ipm to 30 ipm at around 20k rpm. Had some wd-40 on hand so i gave the tool a quick squirt ever 30 seconds or so. but here were talking about a much larger bit.ive only got 3 of the small 0.03125 endmills left so ... ESAB Heliarc 252
Reply:If your using carbide tooling for milling use compressed air.. If your using high speed tooling use flood coolant..  brass can be very abrasive, brass expands and contracts quite a bit also, when drilling and reaming use coolant... i'll add: if your machine is somewhat loose the high speed tooling might not be able to take the abuse and just breaking, where carbide might be able to handle it..also if the kyocera tool is high speed, cut your speeds and feeds in half probably..Last edited by brucer; 03-24-2012 at 01:18 PM.tackleexperts.comwww.necessityjigs.comhttps://www.facebook.com/groups/mach...dingequipment/
Reply:I'm not going to do the math, but to me, 10 inches/minute travel for a 31/1000" bit, even at high spin speed, sounds like too much bite per flute. Have you done the calculation or looked it up in tables? BTW, you didn't give the spin rate.  Any chance the brass is building up on the bit, in effect dulling the edge? Maybe 'welding'  on from heat?What kind of spindle bearings? Does the machine use a high quality router or something similar, or is this all jury-rigged?
Reply:also.. its not good to rapid cool a tool like you did with the carbide and the wd40..that is a good example of thermal shock...  If your doing a lot of milling/routing metals i would run an compressed airline with a 1/2 turn valve on it with some snaploc line and nozzle..tackleexperts.comwww.necessityjigs.comhttps://www.facebook.com/groups/mach...dingequipment/
Reply:I am thinking that you are breaking them when you are "Climb Milling"...Thats the term used when the mill is not under a "Push" mode..It's when the mill is cutting on one side but the play in the table lets it catch and it tries to "Take Off"..You should tighten up the bed locks slightly so it dont freewheel when the mill is cutting on the free side..If you can understand what I mean..And another thing..Brass is very "catchy"..You will have better results if you slightly dull the flutes with a stone..Like a drill..The mill will catch and try to pull itself into the material with sharp edges..I slightly dull drills when doing brass so they dont catch and rip themselves to death.....zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:I also agree with zap on dulling the corner of the endmill, also a bullnose would be even better than a flat bottom endmill..tackleexperts.comwww.necessityjigs.comhttps://www.facebook.com/groups/mach...dingequipment/
Reply:thanks for the replies thus far... Originally Posted by Oldiron2I'm not going to do the math, but to me, 10 inches/minute travel for a 31/1000" bit, even at high spin speed, sounds like too much bite per flute. Have you done the calculation or looked it up in tables? BTW, you didn't give the spin rate.  Any chance the brass is building up on the bit, in effect dulling the edge? Maybe 'welding'  on from heat?What kind of spindle bearings? Does the machine use a high quality router or something similar, or is this all jury-rigged?
Reply:if you have another piece of carbide, just drag it on the edge, just enough to break the sharp edge.. they make a small diamond file for this also.. you need to find some way to make your router variable speed, maybe rig up a potentiometer or vfd.tackleexperts.comwww.necessityjigs.comhttps://www.facebook.com/groups/mach...dingequipment/
Reply:Brass alloys require negative rake on the tools.  Aluminum on the other hand likes positive rake.  Unless you have edges cut to the right angle you will have the tools grabbing and feeding into the brass.   Possibly you have noticed drill bits grabbing when you drill brass?
Reply:I have to ask.....are you sure your machine is even capable of running that small of an end mill?  You mentioned being able to hold .008" tolerance.  Then you said you are using a .03125" end mill.  .008" is about a 1/4 the diameter of your end mill.  Wouldn't take much slop in the table to bend that little end mill to the point of submission.My name's not Jim....
Reply:Originally Posted by lotechmanBrass alloys require negative rake on the tools.  Aluminum on the other hand likes positive rake.  Unless you have edges cut to the right angle you will have the tools grabbing and feeding into the brass.   Possibly you have noticed drill bits grabbing when you drill brass?
Reply:Originally Posted by BoostinjdmI have to ask.....are you sure your machine is even capable of running that small of an end mill?  You mentioned being able to hold .008" tolerance.  Then you said you are using a .03125" end mill.  .008" is about a 1/4 the diameter of your end mill.  Wouldn't take much slop in the table to bend that little end mill to the point of submission.
Reply:Originally Posted by lotechmanBrass alloys require negative rake on the tools.  Aluminum on the other hand likes positive rake.  Unless you have edges cut to the right angle you will have the tools grabbing and feeding into the brass.   Possibly you have noticed drill bits grabbing when you drill brass?
Reply:doent look like it from the picture...  I would try a different brand of endmill, garr or osg..  if your router only runs 25000 rpm your running way to fast for any type of highspeed cutters in any type of metals...   at 25000rpm metal cutting you will have to at least run carbide, another option is, if you can afford it, would be to go to a diamond coated endmill and take even smaller doc but faster feeds, a good brand is Fraisa.. diamond coated cutters are usually brittle though, so if you machine isnt tight they might break from the chatter..tackleexperts.comwww.necessityjigs.comhttps://www.facebook.com/groups/mach...dingequipment/
Reply:Originally Posted by brucerdoent look like it from the picture...  I would try a different brand of endmill, garr or osg..  if your router only runs 25000 rpm your running way to fast for any type of highspeed cutters in any type of metals...   at 25000rpm metal cutting you will have to at least run carbide, another option is, if you can afford it, would be to go to a diamond coated endmill and take even smaller doc but faster feeds, a good brand is Fraisa.. diamond coated cutters are usually brittle though, so if you machine isnt tight they might break from the chatter..
Reply:Originally Posted by BlauSchuhim going to try some different endmills, but these kyoceras are carbide.I'm looking at the followinghttp://www.daycounter.com/Calculator...lculator.phtmlfor brass it says use 400 SFM. To calculate RPM:RPM=(3.82*SFM)/DIAMETER=3.82*400/0.03125 = 48896.0 rpms
Reply:Cutter can break from many factors. You should use coolant or air to clear the chips away from the cutter so it does not clog up. If it clogs up it wont be able to cut correctly and will start to push. Not sure what you min radius corners are , but try to use the biggest cutter possible. But then again not too big if your limited on spindle speeds. You dont want to burn out the cutter.
Reply:A sharp cutting tool will dig into brass and grab, the tool needs a very blunt face, and the brass should then crumble ahead of the tool.  You will always get metal particles spraying from brass, never long continuous curly shavings.As previously mentioned "climb milling" is deadly with brass, the tool rotation and travel direction absolutely must be in opposite directions.Lubricant and cooling may be a factor, but I doubt it.If tools are breaking instead of going blunt, I would say the tool is digging in and grabbing rather than overheating.Cheers,  Tony._________________________________Transmig 310 + Argoshield LightOxy acetyleneOxy propanePrehistoric stick welder_________________________________
Reply:Originally Posted by brucerYes, those formulas might work for ideal conditions..  I run high speed mills at work and we couldn't run that fast in brass, maybe half that, probably around 30k rpm, high pressure flood, probably 15-20ipm..  in a typical cnc mill probably about 6000rpm and about 6ipm..   Your machine isnt an ideal machine for milling metals.. I would start out at about 25,000rpm (because you can not run any slower) and I would run about 6 or 8ipm and probably about .005doc.I would want a 2flute bullnose stub length endmill.. Have you checked the bearings in your router?  put an indicator on the spindle and put pressure on it and see if you get any movement or slop in the spindle and also the Z axis.. Thats probably whats killing you, just bearing clearances promote chatter which kills tooling if theres any kind of cutting pressure.. If your planning on cutting a lot of metal like alum and brass, you might invest in one of those import spindles and a vfd..  also try to get your machine adjusted as tight as you possibly can..
Reply:Here's a handy calculator that may help.http://www.custompartnet.com/calcula...speed-and-feedAlso having a simple feed and speed chart is handy.http://www.cgstool.com/Catalog/Catal...%20CARBIDE.pdfEvery time I get greedy... I break something.  Remember that many of the formulas were developed for very rigid machines. On your machine you will likely need to compromise and use more conservative values.
Reply:blauschuh what kind of machine do you have?   If its a plasma table, that you have converted to use as a router, you might add some weight to the gantry, it might help stabilize it some... also cut the design out near one side or the other, not out in the middle of the table..tackleexperts.comwww.necessityjigs.comhttps://www.facebook.com/groups/mach...dingequipment/
Reply:you might be able to make your router variable speed by wiring in a dimmer switch..I'm no electrician, it might work, might be hard on the motor though..tackleexperts.comwww.necessityjigs.comhttps://www.facebook.com/groups/mach...dingequipment/
Reply:Originally Posted by brucerblauschuh what kind of machine do you have?   If its a plasma table, that you have converted to use as a router, you might add some weight to the gantry, it might help stabilize it some... also cut the design out near one side or the other, not out in the middle of the table..
Reply:Originally Posted by BlauSchuhi see that HF has a motor controller for like $15. I'm seriously considering buying a 2.2kw spindle and vfd combo. for $400 bucks I can get something that will allow me to ditch the hearing protection. also, my office is right above the router, and i (and my wife  ) can hear just about every cut through the floor.
Reply:Aluminum like positive rake. Unless you have a cutting edge to the right angle, you will have to snatch the tools and feeding brass.HDMI Converter | Wall Stickers