# Coated end mills for hobby shop manual mills



## wildo (Mar 22, 2017)

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:

Going with carbide
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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## mikey (Mar 22, 2017)

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.


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## wildo (Mar 22, 2017)

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.


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## mikey (Mar 22, 2017)

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.


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## JimDawson (Mar 22, 2017)

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.


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## wildo (Mar 22, 2017)

JimDawson said:


> 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.



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


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## Bob Korves (Mar 22, 2017)

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?


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!


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## wildo (Mar 22, 2017)

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!



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.


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## JimDawson (Mar 22, 2017)

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



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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## wildo (Mar 22, 2017)

JimDawson said:


> I probably have 200 to 300 endmills in stock at any one time, from 0.032 to 2.00 dia.



Whaaaaaaa!!?? I have 18 end mills so far, and nearly $425 invested. Good God that's quite a collection you have...  I don't think I can afford this hobby! LOL!


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## george wilson (Mar 22, 2017)

Many of you guys are too carbide happy! Most of the machines we use in the home hobby shop can't even use carbide cutters to their full potential. And,unless you have diamond grinding wheels on your tool and cutter grinder, you can't sharpen them.

Fortunately for me,I have so many surplus USA HSS cutters,I don't really need any more till I croak. There was a used machinery dealer in Richmond for many years,whose low prices enabled me to build up my shop vastly more than I could,if I had to pay retail prices. He has just retired. A sad loss.

The trouble with Chinese cutters is lack of quality control. Some of their cutters will be fully sharp. Some will NOT be fully sharp. I've HAD to use import cutters in the museum I worked in for 40 years as toolmaker. Budget constraints,you know. I have bought several of those 20 piece sets over the years,and have found big variations in how sharp they are.

Many of those sets of HSS cutters are coated. But,you can see through the coatings,so thin are they applied!! Might as well not be there!

At least,I have been able to sharpen them with my K.O Lee "Knock Out" tool and cutter grinder and my VERY old,but still quite functional Weldon cutter grinding attachment. Not one of the nice air bearing outfits,but it gets the job done.

But then,the original diameters of the cutters is altered,of course.

It seems to me that Chinese HSS is harder than USA HSS. The guys at Wholesale Tool told me that some customers prefer the Chinese HSS,as they will cut material that the softer USA HSS will not. I believe that,as I have found the Chinese HSS harder,but also MORE BRITTLE. Not as brittle as carbide,though. If they are fully sharp,they seem to perform pretty well.

So,my advice is not to buy Chinese HSS unless you can actually FEEL their cutting edges and see that they are sharp. That probably means a trip to Harbor Freight. I think that Harbor Freight picks the cheapest of the cheap Chinese stuff to sell,though.

My purchases at Harbor Freight are usually limited to acid brushes,twine,and sometimes their cheap ceramic kitchen knives. The knives are very sharp,except abut 1 1/2" from the tips of their knives,their grinding is not sharp,and you can actually see flat spots on the cutting edge of the blade. I can grind those flat spots away myself,though most can't. I had one of their knives' handles ,made of some kind of hard plastic/rubber(?) split open,and the blade fell out. But,that was on an older knife,and for $9.00 I can make a wooden handle,or just chuck it! Chinese plastic is always questionable. And,some times it actually STINKS. I have a drawer full of screw drivers,which emits an unpleasant odor when opened as it contains a few plastic handle screw drivers. Recently I have just gone back to steel knives. Those ceramic blades are VERY brittle,and you don't dare twist with them,no matter what they cost.

BTW: FORGET about buying Chinese files!! They NEVER are any good. The Mexican Nicholsons seem to have gotten their files fully hardened by now. GREAT news for those of us who use files a lot.


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## JimDawson (Mar 22, 2017)

wildo said:


> Whaaaaaaa!!?? I have 18 end mills so far, and nearly $425 invested. Good God that's quite a collection you have...  I don't think I can afford this hobby! LOL!



That represents many years of collecting endmills.  When I buy for a job, I just buy a few extras.  I also find deals on Craigslist occasionally.


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## wildo (Mar 22, 2017)

I just found this video which addresses my initial question, actually. He runs the carbide endmills at the same feeds/speeds as a HSS one and they far outperform the HSS variety. I think the entire point of the video was to prove that while the carbide CAN run at much higher RPM than typical hobby mills can spin, they still perform exceptionally well at "normal" HSS speeds. This is super interesting...


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## woodchucker (Mar 22, 2017)

wildo said:


> 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.



Well like everything else, there will be multiple opinions. I would use crap when I have something I won't risk a good cutter on. But a good cutter will cut better than a POS cutter.  Sometimes you can ruin a piece of work with a bad cutter. Sometimes a crappy cutter will do... again, different situations, different opinions..  I would prefer to use higher end cutters.


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## Bob Korves (Mar 22, 2017)

wildo said:


> 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.


If I can buy tools at half the cost, I can have twice as many tools.  When I can get tools for pennies on the dollar, I can (and do) have a whole shop full of tools.  I love making old and neglected tools useful and looking nice again, often better than new.  It takes a lot of elbow grease, but it is most satisfying.  Often under the grime and surface rust you find names like Starrett, Browne & Sharpe, and other fine brands.  Never pay retail!


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## Bob Korves (Mar 22, 2017)

wildo said:


> I just found this video which addresses my initial question, actually. He runs the carbide endmills at the same feeds/speeds as a HSS one and they far outperform the HSS variety. I think the entire point of the video was to prove that while the carbide CAN run at much higher RPM than typical hobby mills can spin, they still perform exceptionally well at "normal" HSS speeds. This is super interesting...


Carbide is very brittle.  If you have less than a truly rigid machine, it loves to chip and break.  HSS and cobalt tools are much more forgiving.  Carbide does not respond well to ham-fisted operators, either...


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## pdentrem (Mar 22, 2017)

I was doing a job a month or so ago that the end mills would die in about 30 minutes. Standard carbide 2 flute 0.020" stubby @ 60k rpm with 25 ipm feed. This was going to get expensive so we looked at something different. Ended up using a coated 4F 0.020" stubby at the same rpm and feed. Now I could get through 3-4 times as many parts with one end mill vs the uncoated ones. So yes coated can run faster but not required in all cases.
Pierre


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## mikey (Mar 22, 2017)

wildo said:


> I just found this video which addresses my initial question, actually. He runs the carbide endmills at the same feeds/speeds as a HSS one and they far outperform the HSS variety. I think the entire point of the video was to prove that while the carbide CAN run at much higher RPM than typical hobby mills can spin, they still perform exceptionally well at "normal" HSS speeds. This is super interesting...



That's why I said to just use them. You will find they cut fine. We have to keep costs in mind or things can get out of hand. My approach is to use a good cutter in HSS whenever I can (to keep costs down), and use carbide when I need carbide. I think I go through more roughing end mills than most so my finish end mills last a long time. Hope you come to a happy place on this one because there are so many different opinions. In the end, it will come down to what your experience is and that will be the best guide.


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## darkzero (Mar 22, 2017)

wildo said:


> I just found this video which addresses my initial question, actually. He runs the carbide endmills at the same feeds/speeds as a HSS one and they far outperform the HSS variety. I think the entire point of the video was to prove that while the carbide CAN run at much higher RPM than typical hobby mills can spin, they still perform exceptionally well at "normal" HSS speeds. This is super interesting...



You should watch all of Stefan's videos. He's actually a pretty knowledgeable guy. Don't let his age fool you (I'm not sure how old he is but he doesn't look old). It was hard for me to overcome his heavy accent at first but I think his English actually pretty good, English is not easy to learn as a second language. I always look forward to his videos.


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## intjonmiller (Mar 23, 2017)

Stefan is one of my top 3 favorites for machining. He's affectionately referred to as "Mr Precision" (though that could probably be more accurately applied to Robrenz). 

My personal philosophy on the subject of "I'm just a hobbyist so I don't need the best" is that because I'm a hobbyist and have very limited time for my hobby it is important to me to make that time as productive, efficient, and effective as possible, to the extent my budget allows. 

And I buy what I can at discount rates whenever possible, especially through eBay, classifieds, and a local industrial liquidator.


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## Bob Korves (Mar 23, 2017)

darkzero said:


> You should watch all of Stefan's videos. He's actually a pretty knowledgeable guy. Don't let his age fool you (I'm not sure how old he is but he doesn't look old). It was hard for me to overcome his heavy accent at first but I think his English actually pretty good, English is not easy to learn as a second language. I always look forward to his videos.


In one of Stefan's earlier videos he said he learned English from watching YouTube videos.  I think his English is damn good, much better than my German...  He even has colloquial English down better than many who were born into it.  He is one intelligent, hard working, and clever guy.


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## EmilioG (Mar 23, 2017)

Good strategy to use roughing end mills first and to use HSS un coated EM.  I was given this advice long ago by a very talented machinist.
My first experience with a carbide end mill was a very expensive, 6 flute Guhring 1/2" EM, Firex coated, super cool looking.  I chipped a few cutting
edges running it too slow.  Good thing it was a free sample from Guhring. I felt bad anyway. 

Now, I buy mostly NOS Niagra cutters. HSS and Cobalt.
The bright finish let's me use them on any type of metal and are less expensive. Niagra is now moving away from un coated HSS end mills., so I buy what I can
at reduced prices as they come up., new, never used. I can barely sharpen a large HSS drill! 

I use BP mills, so I can spin the smaller carbide cutters fast and
not ruin anymore Carbide EM's.  The talent, wisdom and experience here is awesome.  As I work more, my respect for talented machinists grows. Especially
the old school methods. Cnc work is something else., I imagine.

Interesting video. Would like to see a similar shoot out using larger EM's.


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## Bob Korves (Mar 23, 2017)

When you are using a HSS or cobalt end mill and it is becoming dull, and it is the only one you have of that size to finish the job with, it is quite possible to give it a bit more life by carefully stoning the cutting edges and flutes.  Try to hold the original angles and to remove the same amount of material from all flutes so they all keep cutting.  Leave any chips in the cutting edges as they are.  It certainly won't make them like new again, but it can get the job finished...  I typically use fine grit square India stones with mineral spirits and/or fine diamond laps (Eze lap.)


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## intjonmiller (Mar 23, 2017)

Bob Korves said:


> In one of Stefan's earlier videos he said he learned English from watching YouTube videos.  I think his English is damn good, much better than my German...  He even has colloquial English down better than many who were born into it.  He is one intelligent, hard working, and clever guy.


No kidding. His commentary and (undeserved) self-deprecation are subtle and nuanced. My favorite phrase of his is "pretty okay". I love how This Old Tony uses it as well as many other Stefan references.

There are few better ways to better understand your own language than to study another one. It forces you to really focus on the various mechanisms of language and why the pieces work together the way they do. Precious few people ever do that with their own language without such a prompt. While it's terribly rusty from about 15 years in storage, I still speak at least survival Japanese. It is a fascinating language, beautifully structured with very few exceptions to the well-defined rules. I consider myself fortunate to have not been in the position of starting with such a disciplined language and then trying to learn English, as unruly as it is. When someone makes a point of really studying English to be truly conversant and effective in communication their thoughts they tend to become more proficient and articulate than the casual lifelong speaker. Even when Stefan stumbles on word selection or pronunciation I still find him far easier to understand than a number of native English speaking YouTube video creators.


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## darkzero (Mar 23, 2017)

Bob Korves said:


> In one of Stefan's earlier videos he said he learned English from watching YouTube videos.



I missed that, wow, that's pretty impressive!


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## T Bredehoft (Mar 23, 2017)

I found some TiN coated 2 flute 1/4" shank 1/8" endmills on Ebay yesterday, 4 for $22.50, that's $5.62 each,  to add to my collection of small end mills. I have to make some 1/8 slots in Lucite, these should work well.


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## Rustrp (Mar 23, 2017)

I am asked, when the customer wants to drill their own holes, and have been asked many times; "Do I need a special drill bit to drill stainless steel?" I just tell them you need a good quality drill bit and lubricant. The reason they ask is their experience(s) based on lack of experience are many dull, low quality drill bits. Quality HSS steel cutters have parameters that fit a wide range where speed and feed make the difference, along with lubricant making the difference in how long they last, how many holes, etc. We have many discussions on the use of carbide cutters and the supporting arguments come across as someone making excuses for a prodigal child.  Buying anything used leaves one guessing, especially in regards to how it was used, is it dull and so on, but if the deal is good, go for it. There's no experience gained in using a dull cutter with no knowledge in what or how it happened to be dulled. If I start with new I learn; **Don't do that again** if I dull it, or buy this again if I'm still making holes after 100+. Buying new on the other hand should be done to fit the job you have, not the job(s) you may have.

With the full understanding this is a hobby, there's too many charts available showing materials and cutting tools to use for there to be any second guessing. A known quality tool is hard to beat. Coatings on cutting tools (my experience) may improve the cut or assist with chip control, but if there is significant cost involved I'll pass. My experience to date puts coatings in general, into a sales feature category. I prefer to spend on a lubricant suited for the material.


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