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Endmill Selection
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Author:  Andy Birko [ Fri Feb 18, 2011 4:41 pm ]
Post subject:  Endmill Selection
The thread on dry machining Al prompted me to post this question which has been on the backburner of my little brain for a little while.

Are there any cutting edge geometry differences between endmills for wood vs. Al or Steel? Are you guys buying bits specifically for your material or are you going with what's readily available. If there are differences in geometry, is the difference significant or not that big a deal.

I'm about to buy a selection of flat and ball end mills for my soon to me machine and was planning on going with the cheap stuff at first assuming I'll probably break a few to begin with. After I figure things out a bit though is there any benefit to buying "wood" bits which tend to be about 4x in price?
Author:  cyborgcnc [ Fri Feb 18, 2011 6:40 pm ]
Post subject:  Re: Endmill Selection
Wow....now you did it!! Opened up the can, and all the worms are out!

:-)

Just kidding, and I am sure others will chime in, but yes, there is a difference.

If you read the replies on the aluminum post, and cutting with no fluids, you will see that there are a LOT of factors to consider, when you choose one mill vs another, and the material you are cutting.

Over time, manufacturers have figured out that different shapes work better for different materials. You have number of flutes which are different, different spiral shapes, sizes, angles, sharpness, thickness, materials, and the list goes on and on. When this ends, you now also have different coatings as well....

Sticking to the fundamentals, and understanding chip load, speeds and feeds, will help you to decide on the type of tool you will need, for the type of material. Let me give you an example:

Let's say you want to cut say Lexan, or some sort of plastic. Using a 3 or 4 flute mill, will probably not be a good choice, since at a given speed and feed, the flutes will basically generate heat (there are many more going by), and the stuff will quickly begin to melt. On the other hand, a 2 flute mill, and now one specifically made for plastic, will not create as much friction, and hence allow you to cut the material. Off course, all this depends and is directly correlated on the speed of your spindle, and the feed rate.

I have found the following discussion to be helpful in the past:

http://precisebits.com/tutorials/calibr ... speeds.htm

It talks about how one can go about finding the "sweet spot" in a mill, and although the discussion is meant for smaller bits, it does apply to larger ones.

Now with the mills you bought, you usually get what you pay for. Cheap ones tend to dull quickly, but for starting out, I am sure they will be fine. I have bought some mills from ebay in the past, and some are really good, while others, not so good.

I think this should get you started. All in all, "just start cutting" after paying some attention to some ideas and fundamentals as discussed here, and you will quickly develop your own experience on what works well, and what does not. Take some notes along the way, and you will be fine!
Author:  Andy Birko [ Fri Feb 18, 2011 7:14 pm ]
Post subject:  Re: Endmill Selection
cyborgcnc wrote:
Wow....now you did it!! Opened up the can, and all the worms are out!

Using a 3 or 4 flute mill, will probably not be a good choice, since at a given speed and feed, the flutes will basically generate heat (there are many more going by), and the stuff will quickly begin to melt.


I'm good at worm can opening!

I should have mentioned that I do know that there are geometry differences. I've seen specs with the differences in angles between even bits for Al vs. steel. It's more, is there a practical difference for us.

One thing I learned a while ago and was reinforced by a couple of pros is that you want to increase your feed rates pretty much to just a few clicks below what the max the bit will take before breaking. This is easily illustrated with a router on cherry - go slow and you burn like crazy. Speed it up and you get no burning (albeit with some scalloping). One thing that most people don't realize is that the chip is taking away a lot of heat with it. Bigger the chip, the more heat it's taking with it (not really but it's a good way to explain it)

This extends to just about everything - I use the max feed rate on my drum sander and just make sure I don't take off so much it bogs it down - no burning ever.
Author:  Bob Garrish [ Fri Feb 18, 2011 11:53 pm ]
Post subject:  Re: Endmill Selection
The aluminum optimized cutters work well on wood. Steel optimized cutters will work worse than general purpose cutters.
Author:  Stuart Gort [ Sat Feb 19, 2011 7:33 pm ]
Post subject:  Re: Endmill Selection
Andy,

None of the considerations that apply to the geometry required for metal are going to apply to wood....it's THAT much easier to cut through. You just need to be sure you have sharp cutters. To that end, I'd ony buy carbide tooling. I've use aluminum optimized cutters too but frankly, I don't see a great deal of difference between conventional end mills and the ones claiming a special helix for aluminum.....even when cutting aluminum. Besides that, most of the specialty tooling I use has a conventional rake and I haven't noticed any particular lack of performance on wood. If you think in terms of only using aluminum optimized tooling I think you'll have a hard time locating everything you need...diameter wise...# of flute wise...length of cut wise....ect.

http://www.monstertool.com/ ....the best quality for the best price that I've found over many years.

http://www.mcmaster.com/#carbide-end-mills/=b3v0w1 ....always in stock...good quality...a little higher priced.

https://www.onsrud.com/ ...best quailty...highest price....but they have speciality stuff that I can't do without. For instance, I make heavy use of reverse direction cutters and Onsrud actually has a stock selection of these....not easy to find.

http://www.cetdirect.com/catalog/produc ... _id=221692 ....large selection of tiny cutters. These guys will alter a tool to suit your needs. For instance, Their standard .023" endmill that I use for fret slots doesn't quite have the depth of cut that I need....so they grind the shank up a ways so the cutter can achieve the .09" depth I need.
Author:  Bob Garrish [ Sun Feb 20, 2011 7:34 am ]
Post subject:  Re: Endmill Selection
I should specify suppliers, too. The aluminum cutters from Ridiculous Carbide http://www.ridiculouscarbide.com/ and Iscar http://www.iscar.com/ do make a difference in wood in my setting, but things definitely differ based on setup. On aluminum there's no question; a regular mill would gall 2" into the cut at the feeds I can run the aluminum mills at.

That said, I'm pretty sure Stuart has mentioned using really low spindle speeds on wood, whereas I use 10K, 65K, or 90K and tend to push my tools pretty hard. On a router, you're likely to be using high spindle speeds and not pushing the tools (if you're using a 1/2" @ 24K, 400IPM would be a conservative feed on wood) and so your experience could be different from both of ours. HSS is junk, just get carbide. Buy a few cutters for what you need, and you'll probably never do enough cutting for your stuff to wear one out.

In general, I'd recommend Ridiculous for most stuff and Iscar only if you've got a really good local distributor (ie: one that gives you cut rate pricing) and you need a particular tool they have. Reduced neck extended reach 3-flute cutters are magically delicious, but they're crazy expensive. The Ridiculous stuff is quite reasonably priced.
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