Milling Problem

Climb mill it if possible, from the look of the burr in the picture chip thinning may be at work which never ends well.
Increase the feed rate and step over.
 
What brand of end mill are you using? I'm asking because I bought some inexpensive end mill from China. You get what you pay for! I have to run these MUCH slower than a good USA brand. If the end mill says HSS with an AL after it you're going to have to slow things way down IMO.

I can take the cutting edge off one of these Chinese mill very quickly if I don't run it about 1/2 the speed, or less, than I run my good ole M42 cutters.

I have a small chop saw that I use to cut the bad ends off my end mills and this is where I can really tell the difference! On the Chinese mills I can cut through them like butter. The nice USA quality brands I get past the flutes and the grinding wheel just sits there and burns until the metal gets red hot and then it will cut the rest of the way though...

YMMV,
Ted
 
For cutting steel, I use a can of this from the local hardware store in the area with black pipe and fittings.
They sell it for pipe threading.
http://homehardware.ca/en/rec/index...7n/No-216/Ntk-All_EN/R-I1142043?Ntt=oil&Num=0

-brino

Thanks Brino. I'm going into the city on Tuesday and will pick some up. Do you just brush it on?

DOC ..... I initially tried taking 0.050" passes but found it was too much, then went to 0.025" but the problem persists. The end mills are chinese and are labeled HSS (no AL) on the end mill.

This is the jig I use to sharpen the ends (courtesy of Harold Hall) and I checked the settings again this am. Primary cutting angle is 5* secondary angle is 25* and the rake is 2*.

1510504785716.png
1510504833539.png

Here is a pic of the 2 end mills that are now dull.

1510504921417.png

Wreck - what is "chip thinning" and how is it avoided?

Billh50 - is there a simple way to determine is that is the case? Like a file test? I kind of think that is what is going on but I don't have the experience to know.
 
Can you mount the work piece differently so you can use the entire side of the end mill? This would remove more material with less of it passing over any particular part of the mill. Often tips get dulled very quickly leaving the majority of the cutting tool still good.

I do a lot of 3D detail milling so I have little choice but to use the end of the mill, but yesterday I did a project where I used the side of an end mill that the tips have been completely broken off.
 
not enough back rake looking at your setup. leave the edge about 1/32 flat but mildly raked the rest rake up away.
Also while the metal is probably not the problem, consider annealing that piece if you can. It is probably a hard piece of steel.
 
Bob; Only problem with that is, if I damage the sides I have no way to sharped them (yet) and the end mill will be useless then. I can easily sharpen the ends though.

Jeff; please explain "back rake". Is that the primary cutting angle or the radial angle from the edge to the center?
I don't think the metal is hard because I can easily file it.
 
Since they are in fact Chinese end mills, I would suggest slowing things down. I run 1/2" ones at 248 RPM and I use a mister while doing so. Much faster and I've found they dull up quickly on steel. YMMV. You could also try reducing the width of the primary grind a little more to see if that helps. I'd suggest shooting for around .040" max.

Good luck,
Ted
 
Bob; Only problem with that is, if I damage the sides I have no way to sharped them (yet) and the end mill will be useless then. I can easily sharpen the ends though.

Jeff; please explain "back rake". Is that the primary cutting angle or the radial angle from the edge to the center?
I don't think the metal is hard because I can easily file it.


All cutting tools wear. Given your propensity to sharpen rather than replace mills I am guessing you have more time than money. (Not intended as a jab or a dig.) If it takes me half an hour (I have no idea how long it takes) to sharpen a 20-30 dollar end mill I have lost money. A 50 dollar end mill would likely have a coating on it, so resharpening it would do me no good. Alleast not for its intended purpose. That makes it the equivelant of a 20 dollar end mill...

Anyway, you will get a lot more use out of your endmills between sharpening and/or replacing them if you use the sides. If you also want to use the tips so you can resharpen them then use the sides futher up away from the tip.
 
I just came back from the shop and tried a few things. I reduced the width of the primary grind and I used some Rapid Tap fluid brushed onto the work. I also slowed the feed to about half of what I was doing before. I took one 0.050" pass over a new section. It was better but the finish was horrible and was very uneven. I could see and feel the undulations on the surface. So I took a 0.005" pass, very slowly, using more Rapid Tap and that cleaned up the surface pretty well but I could tell the bit was getting dull again. Just for the heck of it I tried another 0.025" pass but I could feel some bad vibrations starting and stopped the mill just as something moved.

Ted, the next thing I try will be to turn the rpm down plus use some cutting fluid.

Bob, not sure how long I have left on this side of the grass so I can't say if I have more time than money or not, lol. But being retired and the cheap SOB I am I prefer to sharpen the end mills as opposed to chucking them out, especially the way things are going for me with this project. I could never do this for money because I am waaaaaaaay too slow and inexperienced but if I were capable and wanted to earn money by machining I would certainly not be dicking around with cheap tooling and spending hours or days making jigs, collet blocks, lining tools, etc. I understand your point about time being money and when I was working, time was a very valuable commodity. This is a hobby for me and most of the time I really enjoy making something from scrap yard steel. It's a great learning experience but can be very frustrating at times. Glad I can get help from the members here or I would probably just go back to one of my other hobbies.
 
Slow it down! Get the RPM down to around 175-225 and you need some kind of cutting fluid to help. If that is a piece of 41xx and heat treated, you need to cut the RPM's in half, just my rule of thumb I use.
 
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