Coated end mills for hobby shop manual mills

wildo

wildo

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I bought some ALTiN coated carbide end mills for my mill the other day and am just now looking up formulas for how fast to spin them. I'm starting to think that maybe I made a mistake with:
  1. Going with carbide
  2. Going with coated carbide
The manufacturer recommends a SFM of 150 for a 4 flute, 30* helix carbide end mill. Given a .500" end mill, I'd have to spin it at: (3.82 * 150) / .5 = 1146rpm. My mill can spin that fast.

The manufacturer recommends a 40% increase in SFM when the ALTiN coating is applied. 40% increase on 150 gives us a SFM of 210, and an RPM of = (3.82 * 210) / .5 = 1604rpm. Ok, yes, I can still deal with this.

However, when I start looking at smaller end mills like the 1/8" one in the set, being coated- I'd have to spin it at: (3.82 * 210) / .125 = 6417rpm!! This is far outside of the top speed of my mill. Had I bought standard HSS end mills, uncoated, then that 1/8" end mill would spin at: (3.82 * 100) / .125 = 3056rpm which is just a little higher than the max speed of my mill.

So what's the story here? I thought I was buying super awesome, high quality end mills- but maybe I bought a tool that is simply far outside of the capacity for my machine? Are coated carbide end mills better suited for CNC mills that can spin extremely fast?
 
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Yup, you gotta' spin 'em fast. If you do, they work good. Carbide end mills are very stiff so they're good when you need to profile a harder material like alloy steels. I don't like to buy these in smaller diameters because of the issue you just pointed to - you need speed. I have 3/8 and 1/2 end mills with that ALTiN coating (like that sexy black color) that I use for side milling hard stuff.

You have them; use them. Just spin the smaller ones as fast as you can and slow your feed. They will work.
 
So is cobalt a better (or let's say "more suited") end mill material for a manual hobby mill? I think my mill can get down to about 100 rpm and up to about 2600 rpm. Funny, I was buying the fancy stuff thinking that it would cut better and last longer. Oy. So much to learn... but at least I am learning.
 
I would guess about 85+% of my end mills are uncoated HSS. I have a few cobalt end mills and some really good carbide end mills but they don't get used much. I think HSS can take more use/abuse when compared to carbide. The way I think of them, carbide end mills are useful to me when I have to side mill something that is somewhat tall or hard or when slot milling deep. Carbide is stiffer so my edges are more precise.

I think HSS is usually adequate for what I do. More important to me is the maker. I like Niagara, Melin, Keo and OSG the best. I only buy new end mills, never used because you are almost guaranteed to get a cutter that is either dull or a hair's breadth away from it. Coatings don't mean much for me; most of the stuff I mill doesn't require it.

Buy some HSS roughing end mills and use them before pulling out a finishing end mill whenever possible; it will save you money in the long run. High Helix end mills are very good for aluminum as it clears chips better, especially in a slot or pocket, and this also helps prolong edge life.

I'm sure the other guys will chime in with stuff I missed. My needs are pretty simple.
 
What I use the most is 1/4 and 3/8 solid carbide 2 flutes, uncoated for finish work. I have a few 1/2 high helix 2 flutes for aluminum that are leftovers from a job. And I keep a few 1/2 cobalt roughers around. But my go to utility endmills are from Harbor Freight, I buy them with the 20% off coupon. I keep several boxes around. They are not high quality, but most work OK for general work. I also use solid carbide and carbide tipped router bits in everything from stainless steel to wood, use 1/2 shank where possible.

If you need a special endmill for a job, buy two or three, that way you can build up your stock. The easiest way to guarantee that you will break an endmill that you need for a job is to only have one.;)
 
wildo said:
Given your druthers, wouldn't you rather work with higher quality end mills than something that works "mostly ok"? Or am I reading too far into that statement?
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When you are removing metal, you just want to remove metal, the most metal for the least money and grief. The prices of import end mills are a fraction of the cost of high quality end mills. As long as they work, use them and toss them. Save the nice, sharp, quality ones for finishing and special jobs. If you work in a shop where the boss buys the cutters, then of course you only want the best!
 
Bob Korves said:
When you are removing metal, you just want to remove metal, the most metal for the least money and grief. The prices of import end mills are a fraction of the cost of high quality end mills. As long as they work, use them and toss them. Save the nice, sharp, quality ones for finishing and special jobs. If you work in a shop where the boss buys the cutters, then of course you only want the best!
Click to expand...

That all makes perfect sense. I guess my hangup with it is that in a hobby shop, we're under no pressure or deadline (usually) to get something done. It's generally done for the enjoyment of the hobby, right? So if I can use a higher quality cutter that really cuts like butter vs an import (or otherwise) that is mediocre in comparison, it seems like the better cutter would make the hobby more enjoyable. But this is all my inexperience talking. Perhaps the HF end mills, while mediocre in comparison, are still perfectly acceptable and still enjoyable to use.
 
wildo said:
Given your druthers, wouldn't you rather work with higher quality end mills than something that works "mostly ok"? Or am I reading too far into that statement?

And are you talking about these?
http://m.harborfreight.com/20-piece-titanium-nitrade-coated-end-mill-set-5947.html
Click to expand...

It really depends on the job. In some cases I know I am going to destroy one or more endmills on a job. I that case I am going to grab a throwaway end mill, cutting through a weld for instance. I do a lot of stuff that may be uncommon in most shops and I'm not afraid to destroy cutters, they are expendable. For really accurate work, I use the the proper cutter for the job. I probably have 200 to 300 endmills in stock at any one time, from 0.032 to 2.00 dia.

Yes, that is the Harbor Freight set I am talking about.
 
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