Is it the end mill or the machinist??

Jake2465

Jake2465

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The other day I was doing some slot milling with a .250" 4 flute carbide end mill that I had purchased in a set of 5 from eBay. I believe they may have been from "online carbide" or something like that. anyway, these slots were .350" deep, .275" wide and 2.000" long. I usually have my mill running 3000rpm with a 24ipm feed rate which gives me a .002" chip load. My depth of cut was .075" deep and this material was regular hot rolled with the surface layer removed. I had my program set to run a 2 deg ramp angle and to get my .075 depths, so no plunge cutting. With this setup I was able to make it through 6 slots before I started hearing changes in noise and a few sparks. I checked the end mill and the corners of the corners were all chipped. One of the HM members suggested that I may just be going way too fast and should try again with less chip load. Sounded like a good idea to me.

I guess my impression was that carbide liked an aggressive cut and could handle hot rolled with no trouble. The performance made me start to wonder if perhaps those end mills are not very good or possibly just my zeal for watching end mills eject purple colored chips like a lawn mower.
 
Normally you slot with a 2 flute End Mill not a 4. Also carbide usually fairs better when it has a small corner radius.

I don't have a CNC mill, but I know a lot of guys that do like to buy stuff from Lakeshore carbide.
 
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- Were you running any coolant?
- What was the type of material being slotted?
 
Carbide is brittle. Nature of the beast. Hard but brittle. It takes a rigid machine and setup plus proper feeds and speeds to use carbide end mills successfully. You are cutting hot rolled steel, no grade specified, perhaps "regular" means mild steel. If it is HR mild steel, I think you would be much better off with HSS cutters for working with it. Tell us about your mill...
 
I agree with hss, and need 2 flute as well. Would never use carbide for anything less than very hard material unless in very rigid machine.

For your slot I would drill a hole at end of slot to near final depth, put in hss 2 flute center cutting and plunge to about .345, then move over .125 and replunge, move another .125 and plunge again. Keep it up till you get to the other end, then go back and forth at full depth to clean the sides up to your. 275. Using the end mill that way if it starts to dull you can touch up the bottom on the bench grinder and keep going.
 
My mill is a Bridgeport R3E3. Basically a boss 8. It uses those Erikson NMTB-30 tool holders.

The nice thing about HSS is that it is cheaper. I guess I have not really considered it because I have concerns about tool deflection and long cycle times. I believe the material was 1018. I don't ever use cold rolled on a mill because I had too much trouble with warping.
 
That's what I was wondering. So much for that idea.
No shock or interrupted cut in doing keyways, so, what the devil...?
 
Another thing I noticed was that the first ramp maneuver started kicking up a burr after a couple of parts. So, perhaps the tool was getting dull for some reason?
 
There's nothing wrong with running a 4-flute end mill for cutting slots unless it has to be dead on. Then use a 2-flute end mill. In your case, running a .250" diameter end mill to cut and finish a .275" wide slot no problem using a 4-flute end mill..
In my case, I used to run .502-.505" wide slots 1.250" deep using a .500" long 4-flute end mill. Material was 4140/45 with a 110-140K yield. A two flute end mill would snap off in a heart beat in this material. Took five passes to get the slot to depth.
Now, if you are cutting aluminum, yes, use a 2-flute end mill.

Ken
 
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