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View Full Version : Looking for advice on carbide endmills on a manual mill



beanbag
07-12-2009, 07:47 AM
Hello folks,

Here's some background: I'm not totally new to machining, but I am new to paying for my own tools now and trying not to jack them up. I use a manual Bridgeport knock-off mill to cut aluminum, mild steel, and stainless.

I'm looking for a source of info that can help me maximize tool life given some of the constraints I have. Stuff like speeds and feeds, depths and widths of cuts to take, type of lubrication, tool coatings, etc. I looked at some speeds and feeds charts for some of the carbide end mills I have, but it seems like those were written for high power, rigid CNC machines that can spin up to 30K and flood the area with coolant. Or shoot sparks when machining dry. The best I can do for lubrication is brush on some oil, or squirt a pathetic drizzle of coolant here and there.

Anyway, here's just a random list of some of the questions and observations I built up over the last month. I don't expect somebody to go and just answer all of them (you can if you want, though), but maybe point me to a source where I could figure this out...

1) What if I take the speeds and feeds numbers and just scale them down so that the chip load stays constant? What bad thing will happen, besides that the coating might not heat up to full temperature? And is this even an issue in my case? Is this one of the main determinants of tool life, i.e. how many cuts it takes?

2) What should I do to get good chip removal? Should I try to avoid the 4 flute and higher end mills?

3) I only have very limited experience with a TiN and TiAlN coated end mill, but so far, I have liked their performance. Should I do dry machining on stainless and mild steel with TiAlN? How about with aluminum?

4) Recently I did some plunges in stainless (I think) with a 3/16" 2 flute uncoated end mill, maybe 800 rpm, and some sprayed on coolant. The tip seemed to get slightly dull pretty quick, which lead to more rubbing (without cutting) therefor more work hardening, etc in a bad cycle. What did I do wrong?

5) Using 1/4" 3 flute uncoated end mill on stainless. Rpm is about 1000+ (I forgot), no coolant. Using a depth of cut of 1/4" and pushing the end mill straight into the side of the chunk, it didn't seem very "happy", in that it took a bit of force to push in, I didn't use that high of a feed rate, so there were a lot of very thin chip and dust coming out, and some chattering/squealing noises. I went about .1" into the material. Then when I moved the end mill left to do a climb cut, it seemed "happy", with very little noise and chips just shooting out the back. What did I do wrong in the initial cut?

6) Lubrication/coolant suggestions?

So I guess that's all the questions for now. I'm not too worried about the initial cost of coated end mills, since I can eventually get some for cheap off ebay. Anyway, thanks for the suggestions.

Frank Downey
07-12-2009, 07:56 AM
I can't help you with exact answers to your questions,but if you can get a copy of the machinery's handbook it will answer the questions that you have.I don't have the book in front of me,but I think the feeds and speeds are about the endmill or cutter and not the machine.By the way I just have the pocket version of the book Is there anywhere that I can download the big version of the book online?As for #4 and 5 I always use flood coolant on my endmills and with you buying your own cutters I would take more time and take lighter cuts,also sharpen the endmills before cutting harder metals such as stainless steel.Just my opion

knedvecki
07-12-2009, 09:58 AM
Your main issue here, as I read it, is work hardening of Stainless and plunge cutting. I recommend to 1st: Learn to sharpen drill bits, and then use the drill bit to rough out or hog out material, and then finish cut with your end mill. Drill bits are one of the cheapest / toughest tools around and are easily sharpened by hand on a bench grinder, (and No, they do not have to be perfect). SS usually likes to be climb cut instead of conventional. And by drilling using your quill lever, you can "feel" when the work is getting hard / tool is getting dull and stop and resharpen.

Jim Shaper
07-12-2009, 02:04 PM
Stainless work hardens, so the key to machining it is to keep the edge cutting at all times. Heavy feed is the way to achieve this. Peck drilling may end up putting a hard face on the bottom of your hole and then when you come in for the next peck it's having an adverse effect on your cutting edge, which further work hardens the material, which further dulls your tool, which further work hardens the material, etc...

Use machinery's handbook to get your surface speed in the ballpark and then lay on the pressure when you plunge or pull the cutter out when you're not cutting.

Carbide is a wonderful thing, but it comes in so many grades that it's difficult to find endmills that are tough enough for manual machining (carbide is hard, and brittle). With a CNC, you have ball screws and no backlash, so the machine has complete control of the work/cutter interaction at all times. When you come into the work in a manual machine there's the possibility of the table floating as the cutter pushes it into the acme screw - that's when you chip teeth. Sharp HSS is better than missing teeth carbide.

beanbag
07-13-2009, 06:45 PM
Thanks for the replies so far.

As for drilling vs plunging, the surface is slanted, plus the hole is not very deep, which is why I am not drilling.

I adjusted the backlash of the mill I am using down to about 4 mils on X and Y, so hopefully that is good enough? Perhaps if I stay with end mill sizes 3/8 or smaller, they will not generate enough torque to move the stage?

I have used HSS end mills on stainless in the past, and while not paying much attention to speeds and feeds, they didn't seem to last very long, nor cut well. I have a sense that an end mill is cutting well when it is very quiet, or makes light scraping sounds.

I gave Data Flute a call today regarding what end mills to use, and here is what they had to say:

for aluminum, use one of their finishing "designed for aluminum" end mills with a ZrN coating, 3 flutes. No coolant or a slight amount of coolant is ok. I forgot why he suggested 3 flutes and not two.

For stainless, use a 4 flute end mill coated with AlTiN. A slight spritz of coolant is fine. When I asked about 4 vs 3 flute, they said that 4 somehow seemed to work better on a bridgeport, so I wasn't going to argue. I also thought that slight amounts of coolant were bad for AlTiN coatings due to thermal shock, but again, I wasn't going to argue.

As for the speeds and feeds, the guy confirmed that it was ok to scale both of them down as long as the chip load is the same.

MTNGUN
07-13-2009, 07:23 PM
I rarely mill stainless, so I can't comment on that.

But, in general, small, not-so-rigid mills will be much happier with roughing mills.

Roy Andrews
07-13-2009, 10:28 PM
for stainless i have had best luck with sharp hss slow speed constant feed and coolant. as has been said don't dally in the cut.

plunging and plowing in from the side will cause problems and show off movement of the bit, quill and table. plunge with the biggest/shortest bit possible with the quill up and locked and the table snubbed down tight. when plowing in from the side loosen that axes up just enough to be able to move it with pressure.

accept the fact that stainless is going to eat tooling and go with cheap hss.

macona
07-13-2009, 10:56 PM
For coolant I use one of the Bijur spray mist units. The tank portion can be had for about $80 on ebay and the nozzle can be made. It is a micro drop system kinda like the trico one but built like a tank.

Fasttrack
07-13-2009, 11:36 PM
For the SS issue, like others have said, keep your feed up! You mention a slow feed and that is a real killer when working SS. I have done quite a bit of SS milling in the past year for UHV applications. Usually I used HSS endmills with a heavy feed and relatively low speed. Also used lots of tapmatic because it was readily available and keeping the cutting edge cool and keeping the shearing action of the cutting edge was important.

beanbag
07-15-2009, 04:57 AM
I guess I'll give the ol' HSS a try...