How Long Should An End Mill Last?

[catsparadise]

Hi All. I have been reading this forum for a while now and have a question that I haven't found an answer to. In short, how long should I expect an end mill to last?

More details - It's a TiN coated 12mm HSS end mill from a reputable UK supplier. I'm cutting mild steel (making some more tool holders for my lathe). Cutting without coolant or lube, SX2 mini-mill. Speed is just below the point where the chips start to go straw coloured, so they're coming off silver. DOC is 0.75mm (less for the last couple of passes) as at 1mm and above the machine vibrates. The tool has only had light use before (it wasn't brand new).

I've machined 10 rebates in preparation for cutting the dovetails. Each one is 24mm in the direction of cut x 6mm deep x 15mm (cut in two passes). At the end of this the end mill sounds like it's knocking rather than cutting smoothly as it was when I started.

I'd have hoped it would have lasted longer than this. Is that unreasonable, or with the info provided, am I doing something wrong?

Rob

 

[DSaul]

Use some cutting oil. I'm still using the same set of cheap TiN coated end mills I bought over a year ago and they are still sharp. I use the thread cutting oil I get from the home improvement store for steel and WD40 or similar for Aluminum. I wouldn't think of cutting steel without lubricant. No need for anything fancy, I just brush some on the area with a chip brush.

 

[Ed ke6bnl]

I believe in thread cutting oil as stated above. when building our first buggy we ate up a lot of hole saws for coping, we started using oil on them and we built an entire buggy with one hole saw and it is still going fine. no reason it would not apply to the milling tooling, I fine the same results for my band saws.

 

[catsparadise]

Cutting oil ordered (I've been using motor oil for threading up to now) plus replacement end mills. Thanks for the advice.

Rob

 

[MSD0]

Definitely use oil. Your tools will last longer and the surface finish will be better as well.

 

[Andre]

2 flute? 4 flute? What RPM's are you running? What steel? How fast are you feeding?

I have a old bridgeport with a loose spindle, and cutting steel can be a challenge sometimes. I find using 4 flute endmills, light DOC (maybe 3o thou) and really pushing the endmill is the best solution. The more the tool is loaded in a consistent fashion the better, but obviously not to the point of breakage. It also keeps the spindle splines nice and quiet.

When finishing the shoulder of a slot or groove, take very light passes climb milling.

Use the correct cutting speeds, they really help if you have no experience in hearing and feeling the cut. Over time you tend to get a feel for things.

 

[Tozguy]

The weak part of regular end mills is the pointed tip. Maybe a hogging end mill would work better for the roughing and save the regular one with sharp tips for finishing.
I used up a few end mills prematurely before catching on to the roughing ones.

 

[george wilson]

You seem to have a VERY LIGHT mill. And are taking very light cuts. Taking too light a cut is also bad for holding an edge on end mills. But,I'm afraid you are stuck with what the machine can handle till you get a heavier machine.

DO use cutting oil as suggested. I have also used those cheap sets of end mills you see in most catalogs. You can practically see through the TIN coating! The biggest problem is that some sets are quite sharp,and some are not sharp enough. So,you take a chance on buying them. Chinese HSS is plenty hard,but therefore on the brittle side. Some pro shops actually like them because they will cut steel that other end mills will not. Sounds strange,but this is factual. But,on your light machine,I'd advise against them because of their brittle nature. Your machine will snap them off easily compared to a larger,more rigid machine. The irregular quality control on sharpness is bad for any machine,but especially for a light machine.

The best you can do for now is use cutting oil.

 

[4GSR]

Going along with George has said, I would suggest using roughing end mills, as they will "peck" off very small chunks of metal at a time instead of shearing off a long sliver of metal. Which requires just a little more rigidity in the mill to handle. Stay with the smaller sizes under 1/2" and give it a try. You will find the roughing end mills will hold an edge much longer than conventional end mill will. May not get as much vibration from them too.

 

[Wreck™Wreck]

One drawback when brushing on cutting oil is that it causes the chips to stick to the tool and work where they are then recut, this is more of a problem with conventonal milling as the chips are deposited in the direction of cut. Climb milling ejects the chips opposite the direction of cut yet they will still cling to the tool with static oil brushed on.
The best method is flood oil/coolant with enough pressure and flow to evacuate the chips entirely, however this is often not possible with an open machine in a hobbyist setting. If you were to do so you would find a remarkable increase in tool life at higher feeds, speeds and DOC with improved finish and repeatability. Try an air blast to blow the chips out as an alternative but they will wind up everywhere in the shop.

This is why when you watch vids of machines running fast an hard there is so much coolant being flung around one cannot even see the tool. promotional vids will show them running dry for clarity but the tools will not last long. Some inserted face mills are run dry on steels by design as well as hard turning tools.