Help! Problem cutting steel with 3 Flute EM!

[damae]

It seemed like such a simple task! I wrote a simple program to cut two slots in a piece of mild steel using a 1/2" EM. Using the ME Consultant calculator, I tried cutting at 800 RPM and 7 IPM, but the chips looked pretty rough (not smooth). So I tried taking lighter cuts and experimented with different RPMs, up to 2200 RPM and 20 IPM. But no matter what I do, I keep burning out my end mills! I had 6 of these things and burnt out 4 of them. I can tell by sound when they are ruined because the machine starts squealing pretty bad. It usually happens after just one or two passes at .025" deep. I'm entering the material from the side (not center-cutting).

First question: Is this the wrong kind of endmill for steel? 3 flutes seems unusual, but they are all sharp. I cranked the knee up slowly as I spun the spindle by hand and was able to make nice clean, smoooooth cuts into the material.

Second question: What is the appropriate speed/feed for this? I am using a series I Bridgeport with 2J head. If ME Consultant is right and I need to cut at 800RPM and just 7 IPM, then how deep shoould I reasonably be able to cut in one pass? Today I just want to get the part done. But eventually I'd like to remove material in the most efficient way possible.

Third question: Looking at the photo of the endmill, can anyone tell me what caused the failure? Was it an impact failure? Did I drive the EM into the material too fast? Or could something be loose and chattering around?

Fourth question: What kind of coolant should I be using? For the moment, I've just been spraying WD-40 on it.

I know these are fundamental simple questions and I'm probably doing something very wrong. But I'm very concerned that I'll kill my last two 1/2 endmills before I even finish this simple part! So I'll wait for some advice before I attempt any more cutting!

[mrainey]

Off the top of my head:

I would suggest you verify that the workpiece material is really what you think it is.

Three-flute end mills are fine for slotting steel. Yours appear to be far longer, and less rigid, than necessary.

You're clamping across the entire height of the slots, which is bad practice. You could be squeezing the slot and putting additional pressure on the tool as you're cutting.

[lakeside]

you biggst resaon for failure from reading your post would be the lack of flood coolant if you look at the endmills in photo you can see bue(built up edge) the chip is welding itselt to end mill and wear out edge

[kalmah]

Originally Posted by damae Third question: Looking at the photo of the endmill, can anyone tell me what caused the failure? Was it an impact failure? Did I drive the EM into the material too fast? Or could something be loose and chattering around?

THe local charge on the peak is too high. Why do you use uncoated tool ?? I would use TiAlN coated tool.
If you don't have coated tool, decrease the feed.

Originally Posted by damae Is this the wrong kind of endmill for steel? 3 flutes seems unusual, but they are all sharp. I cranked the knee up slowly as I spun the spindle by hand and was able to make nice clean, smoooooth cuts into the material.

I think that it's the wrong end mill.
Here is a mill for slotting. Strong flute, high helix angle, special flute.
http://www.niagaracutter.com/solidca...vie_quick.html

If you use the cutting parameters given by your end mill provider, it should work.

[damae]

Thanks for the great replies guys!

Originally Posted by mrainey ...I would suggest you verify that the workpiece material is really what you think it is...

Good point. I am cutting that block down to become a T-nut for my new toolpost on my lathe; The material came with the toolpost kit. The kit instructions expect you to customize this block to fit your lathe. It is steel for sure, but it's true that I don't really know what grade of steel.

Originally Posted by mrainey ...Three-flute end mills are fine for slotting steel. Yours appear to be far longer, and less rigid, than necessary....

I agree it should be shorter. Unfortunately, that's what I had on hand. My next tool order will include some stub-length EMs.

Originally Posted by mrainey You're clamping across the entire height of the slots, which is bad practice. You could be squeezing the slot and putting additional pressure on the tool as you're cutting.

I guess it shows -- I'm green at this! Next time I'll probably clamp down to the table. Or else use the vise and clamp lower on the block.

[damae]

Originally Posted by lakeside you biggst resaon for failure from reading your post would be the lack of flood coolant if you look at the endmills in photo you can see bue(built up edge) the chip is welding itselt to end mill and wear out edge

Hehe. I suspected that could be a factor. I started looking at flood coolant systems (tank + pump), just before I typed my "help" message. My mill already has a coolant tray built-in and outlets for the coolant to be recycled into the pump.

[damae]

Originally Posted by kalmah THe local charge on the peak is too high. Why do you use uncoated tool ?? I would use TiAlN coated tool. If you don't have coated tool, decrease the feed.

I blame it on a tool shortage! =) I don't own any TiAlN EMs yet, but have a bunch of them circled in the GARR catalog. I can get them locally, no shipping.

Originally Posted by kalmah I think that it's the wrong end mill. Here is a mill for slotting. Strong flute, high helix angle, special flute. http://www.niagaracutter.com/solidca...vie_quick.html

Hey, that's an impressive video! If that is steel, that's an incredible depth to be cutting in one pass!

Originally Posted by kalmah If you use the cutting parameters given by your end mill provider, it should work.

Unfortunately, my tool provider (for this particular tool) is ebay.

[damae]

Thanks to all for the suggestions so far!

I'm going to have another go at it this morning with lower feeds (don't have coolent yet). Translation: I'll report back on how I break my last two end mills!

So given a longer than neccessary, uncoated endmill and lack of flood coolant, do you guys think I should still be able to cut this part (assuming it is mild steel) as long as I get everything else (feeds/speeds, setup) right? Or am I asking the impossible from this endmill.

Surely an experienced machinist could finish this part without toasting the endmill. Is that a reasonable expectation? Or is it impossible?

[Mcgyver]

its hard to tell from the photo what the geometry of the endmill is - it doesn't look like there is any radial rake but that may be just the picture.

what mill and what type of steel?

800 is the max for this - assuming mild steel, remember the basic formula; rpm=fpm*4/dia of cutter. the max assumes ideal conditions - conditions are never ideal much less so with our small or old home shop stuff. perfect mill, flood coolant etc would be need to cut at the max. I'd back off from this, 400 rpm maybe and try with a spray bottle of water soluble coolant (assuming you don't have flood).

Next point, cutting at the max surface speed, ensures max tool wear, its not linear, ie cutting the speed down by 25% might increase tool 50% (i just made up the numbers, but the principle is there). guys in industry covering overhead want to balance through put and tool life to maximize profit, those of us at home are more often just looking at controlling costs

I'm not sure about your remark about the chips looking rough, we don't usually care about the chip finish metal cuts by shearing in a plane in front of the tool, to get a decent finish on mild steel takes a lot more pressure that we're typically able to get with home shop stuff - if you are using 1018 you pretty much can't expect a high quality finish with a home shop mill. From a purely cosmetic view, there's usually going to be tool marks to remove (that's what files are for!) but you only worry about it if you want to.

Try slowing it down, get some coolant in a squirt bottle and don't expect a perfect finish on mild steel.

finally, when cutting a slot, a 4 flute end mill is best, that way there is opposing cutting force. Still, its tough to get a good finish. I always use a cutter small dia than the slot so that i can rough then finish cut, and use a steady stream/low volume of air to clear the chips - the tend to jam between the cutter and work. Use as big a depth of cut as your machine will handle, .100 would be good - figure up to 50% of mill dia if the mill can handle it, otherwise you are just using the bottom .025 of the mill.

[mpstech]

www.kbctools.com carries niagara tools. Just got a new TiCN coated 3 flute cobalt rougher for aluminum. Cuts aluminum like butter. Double check your material, SFM, IPM, RPM they are most important. Most people overlook the SFM. There are usually good charts or tables on the cutter mfg's websites.
Also if you don't want to use coolent look into a trico micro drop.
http://www.tricomfg.com/store/Produc...D=31&ProdSeg=4

Also you can use a can of spray on canola (cooking) oil in a pinch. You don't need alot, just spray the path and hit the tool once and awhile to keep it lubed.

Dry machining, vibration, and poor setups trashes tools fast.

[mrainey]

"when cutting a slot, a 4 flute end mill is best"


I think that's debatable. An enclosed cut in steel often does very well with a three-flute tool. Many companies use three-flutes for milling keyways, because they just work so damn well!

For a finish pass, the four-flute has obvious advantages.

[little bubba]

My recommendations. First is I tend to reserve finishing endmills for finishing and aluminum. I would go with a 4 flute rougher, much less tool pressure and breaks up the harmonics. I guess a variable flute endmill accomplishes part of that but you're still going to have fairly high tool pressure, not a big deal without the harmonics I guess.

The other thing, slow it down, 100+ surface feet with what appears to be a HSS uncoated endmill in mystery steel, dry. You did pretty well getting that much cut. HSS endmill, drop your speed to about half, especially without flood or at least mist coolant.