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Hss Vs Solid Carbide End Mills, Lessons Learned, Questions.

Jwest7788

Jwest7788

Joshua West
Administrator
So, My recent haul of used machine tools and bits has given me lots more to learn with.

While working yesterday on making some t-slot nuts, I was switching through different end mills trying to find what worked best for the particular job.

Essentially, one issue I noted was that the HSS end mills (new) I used really had some bad chatter taking 0.020 depth of cut, 1/3 the cutter doing the work (1/2" 4 flute end mill) in some off the shelf cold rolled square bar.
--> Using cheap "cutting oil" from Princess auto.

I noticed that it seemed to be re-cutting chips pretty badly, which I assume was the issue.
It seemed to me that the cutting oil was not allowing the chips to leave the cutter, and thus re-cutting the chips, causing the whole process to go slow, sound and feel bad, and in general not be pleasant.
Note: By the end of the cut, the part was still cool to the touch, and I could see the cutting oil was muddy with micro-chips.

This bring me to the first set of questions:

No matter the bit material or cutting fluid, I should expect the chips to "eject" from the work area, correct?
--> I was getting a shoddy muck of cutting fluid, micro chips, and some small chips, but all in the work area.

What viscosity should cutting oil be for this application? (I think the cheap **** I have may be intended for another purpose, it's pretty viscous.) 10w30 thick, but appears to be dedicated cutting oil.

Should cutting fluid be constantly applied, or should I just put a light coat on the work piece before I begin?
--> Seems like my brush may have been helping to keep the chips on the cutter?

Can you mill with HSS bits without cutting oil? Or will I quickly destroy the bit?

I'm still learning the whole speeds and feeds thing, but what are the signs that I am working at too high an RPM?
--> I am unsure if the noises my mini mill are normal, or alarming, so I fear I am either over working, or under working the machine's capabilities. I suspect under working the machine, due to the lack of chip ejection, but on that same note, the machine is making some noises I am not yet comfortable with.




Carbide end mill was used as well. Same process as above, but without cutting fluid.
Chips were flying, turning light brown, all was good. Cut twice as much material at three times the rate.

Obviously, am much happier with the carbide end mill and would love this capability from all of my HSS tools too.

So what were the differences between the carbide, and HSS tests:

Both 1/2" end mills
Both 4 flutes
(Same or better depth of cut)
Carbide vs HSS
No cutting fluid




I have so many HSS tools, I need to figure this out, but I am tempted to just switch to using carbide all the time based on yesterday's results. Need to learn! Help!
 
Tom's Techniques has a great chart on machining speed. I've printed it off and have it on the wall, I look at it often.

http://tomstechniques.com/reference/
Scroll down....

A few things you might try. You didn't mention tightening all the gibs. That might help.
The material you are machining is what? 1014 or 1018? or who knows? Massive difference in performance for different materials. Some materials are very poor to machine, and if you are using whatever you can find, this is problem. Metal supermarket . com has a summary document on materials and their suitability for machining. Try machining with no fluid and keep going slower and slower till you have no discoloured chips.
 
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I would bet that the reason the carbide seemed better is because you were not using the "cutting fluid".

My person thoughts on your questions above are:

1) Yes, the chips MUST eject from where you are cutting. This could be an issue of the cutting fluid not being correct - Also, try switching between conventional and climb milling (change the direction you come at the cut). On my machine I've noticed that there is too much play in the nut and if I am going one way, the cut will feel a lot better than the other.

2) Go to busy bee and buy a gallon of coolant, sounds like your cutting fluid is more of a tapping fluid which doesn't flow very well. It'll last you a long time with what you are doing.

3) I personally prefer a flood coolant. It keeps everything nice and cool, which heat is the enemy in machining (unless you are using ceramic, then it doesn't really matter). Be very careful though, with carbide you either need to have constant coolant, or none at all. Carbide is great only it can handle high temperatures and is hard, but it is brittle and if you are cutting and give it a shot of coolant you can destroy it (I haven't done this yet, but I'm not about to try either).

4) I use HSS more than I use carbide. Carbide is expensive, and on most machines not very useful since they won't have the HP and speeds that it needs to be productive. My personal opinion is to say only use HSS on your machines as it'll save you money and you shouldn't notice a difference.. the only exception to that is that is if you decide to try and machine really hard materials (stainless probably) or if you pick up pre-brazed tools like boring bars. Check out a speeds and feeds chart and compare carbide to HSS, unless you can get inside the carbide range then don't bother. One more thing to note - Carbide doesn't like interrupted cuts on the lathe. You will likely find that HSS tooling in general is a better option for you.

Having the chips come off golden isn't bad at all, it means you are right in the range that you should be but once they start to turn before they are ejected you are going to have issues with your HSS tooling breaking down and chipping. On a good note though, I did just buy an endmill sharpener so once I get it working well and all figured out you can come re-sharpen all the damaged "learning" tooling and try again.
 
Thanks for the replies guys.

I was doing some more milling last night, I think you're right that the cutting fluid is partial cause of the issues I was having.

Additionally, I tried pushing the machine a bit harder and actually had better chip ejection and results.

An end mill sharpener? That's awesome. Didn't know they made them. I received like 20 or so dull HSS end mills recently, so that would be amazing. Haha


JW
 
It's at protospace, just had time to bring it in and then had to head out.. You'll see it tonight it sounds like, along with the mill, lathe and plasma.
 
kylemp said:
It's at protospace, just had time to bring it in and then had to head out.. You'll see it tonight it sounds like, along with the mill, lathe and plasma.
Click to expand...
Meetup is June 30th, not today!

But yes, I think I will see it then. :D Haha

whoops, I meant "Link to it" in my last post. Hoping to see how much I would need to invest to get one!
 
Jwest7788 said:
Thanks for the replies guys.

I was doing some more milling last night, I think you're right that the cutting fluid is partial cause of the issues I was having.

Additionally, I tried pushing the machine a bit harder and actually had better chip ejection and results.

JW
Click to expand...
I find milling cuttings may not spit out depending on the material and how you are cutting. Progressive slotting for example captures a lot of swarf near the cutter.

Cutting oils are used to prevent the chips from welding / adhering to the cutter, where as coolants such as water soluable oils are used for three purposes: remove the head of cutting (hence coolants), flush the chips from the part (they are less viscous, and constantly applied) and protect the part / machine (when the water evaporates the oil film left behind stops corrosion).

I tend to over-oil but a bit of a good quality cutting oil brushed on will prevent damage / welding to the cutter in most cases. Oil can increase the chip hanging on to the part.

HSS can cut dry, depending on the material and amount of cutting, but lubricant is best if you are doing a lot. I use WD40 with aluminum, or sometimes aluminum tapping fluid. For steel, I have a few oils, including some dark sulfur based threading oil I bought a Princess. These tend to improve finish. I have used hypoid gear oil in a pinch; it is a high pressure lube with sulfur.

As for the chips, I blow / brush them away with as I go.

Just my nickel!

Brad.

PS: I have kicked around the idea of flood cooling etc. but don't like the idea of the mess / cost. Found this, will see how it works...

http://www.ebay.com/itm/400893699974

BH
 
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End mills (4 flute) work the best at low rpm's and a high feed rate,, they need pressure to keep chatter away,, get some nice thick slices coming off and Bob's your Uncle. Slot Drills (2 flute) can be run faster at a slower feed rate, and are the tool of choice for keyways.
 
I am a bit late to the discussion but my experience with a mini mill and the HSS and Carbide is identical to the OP.

One of the reasons I am adding a large brace to my mini mill is the chatter - way too much without the brace. With a brace people are reporting improvement equal to double or in some cases triple the depth cut.

This is why we are having "strange" things happen - cannot run low rpm and high feed rate if your mini mill is about to chatter itself to death.

The chatter doesn't help with carbide as well - through my 1 flute carbide end mill still cuts better than the 4 flute HSS... Guess how I got one flute ;) As long as it cuts its good.

I am hoping the mini mill will become more serious tool like my lathe with the extra 10kg of steel added to its back.
 
I've been experimenting with roughing end mills lately. I wish I would have discovered these a long time ago. They remove material with less effort than my regular (good quality) spiral end mills & produce a very nice chip vs. shooting swarf like a sprinkler. They are not for finishing of course, but 90% of my milling time is working up to the last couple thou anyway so I can swap in a good cutter fro that. For less critical things like squaring off a bar end that doesn't require a mirror finish, I just use the fine tooth version (they generally come in coarse or fine). My understanding is they are mostly designed for production & feed high rates, but I personally think they benefit lighter weight mills because the cut seems more efficient. Maybe a real machinist can explain or confirm. I've tried a couple styles & brands & coatings, mostly all Asian knockoffs except for one Niagra that I got off ebay. For the most part they seem to perform the same.
 
I also have few roughing end mills - have to do some more work with them to actually confirm your observations.
 
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