# what makes end mills and drill bits dull quicker than normal



## SE18 (May 15, 2014)

I was just browsing through some of the posts and like the one I saw on how to sharpen end mills. One guy was using a dremel in a video to do it. I didn't want to post the question there so I created this thread just to learn more about what makes drill bits and end mills dull, assuming you are using cutting oils and going at the right speed/feed rates.

I quickly dulled some drill bits going thru some carbon steel even using right speed and smaller bit followed by larger bit. Bedframe are particularly nasty.

I quickly dulled a new end mill while milling some railway spikes and tie plates. I think there was some carbon content in that steel.

Anyway, if anyone has some general info on this topic, much appreciate. Costs money to replace drill bits and end mills and I've tried sharpening them with some success but not complete success.


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## Don B (May 15, 2014)

One thing that can certainly take you cutting edge off a tool is letting it dwell and rub against the material your cutting, if your tool isn't making chips get it out of there )


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## xalky (May 15, 2014)

Don B said:


> One thing that can certainly take you cutting edge off a tool is letting it dwell and rub against the material your cutting, if your tool isn't making chips get it out of there )


A heavy cut, within reason, will be easier than a light cut on a cutting tool too. It will also give you a better surface finish. The cutting edge works best when it can get below the surface and shear the material off.

No matter if you do everything perfectly, eventually, a cutting edge just wears out, and eventually has to be resharpened or replaced. All we can hope to do is extend that time in between sharpening.


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## SE18 (May 15, 2014)

thanks; this already has been helpful. Guess I wasn't aggressive enough. Now that I think of it perhaps excessive dwell can work harden the piece as well, making things worse?!

I'm glad this forum hosts beginner questions as well as advanced!


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## Andre (May 15, 2014)

I'm that dremel guy...
It works, but there are limitations. It will never give a factory grind, but good for touch ups and almost factory sharp.
I also discovered you can sharpen them on a bench grinder (you can also sharpen the ends of reamers) with some time and practice. 

As for dulling them in the first place, bed frames are a nasty material. Who knows whats in them. And watch out with railroad spikes, there are two different kinds. One for straightaways (lower carbon content) and one for curves (higher carbon content). You need to machine them with carbide of possible.


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## SE18 (May 15, 2014)

Thanks, Andre, I'll keep that in mind! Your video was simple but inspiring.


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## Andre (May 15, 2014)

SE18 said:


> Thanks, Andre, I'll keep that in mind! Your video was simple but inspiring.



Thank you )

You'd be amazed what you can do with a few things around the shop. No Bill Gruby's cutter grinder though!
You can also use a small oil stone to tough up the ends and flutes.


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## Rbeckett (May 15, 2014)

The main reason mill bits dull faster is because more ot the bit is in contact with the material to pll a chip away from the base materialcooling, running the correct speed and chip loads will go a long way to help this and bedframe metal id ungraded and has hard and soft spots all through the metal so it is really tough to save bits if your using that as a source of material for a project.  If you need any help understanding chip load PM me and I will give you my down to earth views on that too.  Good luck and hope to hear from you soon

Bob


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## SEK_22Hornet (May 15, 2014)

I'll throw this out there for what it's worth - I use a Drill Doctor to touch up and regrind drill bits. It is quick and easy and seems to work very well for general purpose. I'd hate to be without mine now. I can grind a bit by hand and there are a multitude of grinder attachments from very simple to complex - some worse and some probably much better than the Drill Doctor, but for the money, it makes quick work of keeping bits nice and sharp. Obviously that doesn't address keeping them sharp - all good suggestions in the posts so far on that subject. I was always taught to keep drills cool, apply just enough pressure to get a good cut, and to stop trying to drill when they stop cutting.


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## middle.road (May 15, 2014)

SE18 said:


> I was just browsing through some of the posts and like the one I saw on how to sharpen end mills. One guy was using a dremel in a video to do it. I didn't want to post the question there so I created this thread just to learn more about what makes drill bits and end mills dull, assuming you are using cutting oils and going at the right speed/feed rates.
> 
> I quickly dulled some drill bits going thru some carbon steel even using right speed and smaller bit followed by larger bit. Bedframe are particularly nasty.
> 
> ...



My 2¢ worth: most bedframes are really cruddy material, and even tough to weld sometimes. As for rail spikes and tie plates, I believe that they are 
formed and not machined and also worked when the material is still hot.

_Dan


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## AlanR (May 15, 2014)

One thing I did in the hopes of extending the life of milling cutters was to buy a Noga Minicool which I use with Koolmist. The Noga unit is really nice and easy to use, the misting is well worth the trouble.


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## Hawkeye (May 16, 2014)

Keep in mind that carbon content isn't the only issue when choosing cutting speeds. The actual hardness of the material will have the biggest effect. I think most charts are assuming that the steel is in its normalized state for machining.

Bed rails have a higher carbon content than mild steel angle iron because you don't want them suddenly buckling under the normal stresses experienced by a bed. For this reason, they are also hardened and tempered. Really nasty to drill or machine, unless you soften them through heat treating first.

If you are trying to machine materials that are hardened, you need to use lower speeds than the charts show for normalized metals. And probably use carbide very carefully instead of HSS.


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## george wilson (May 16, 2014)

Back in the 70's,I was walking down the railroad track with a friend. You could actually pull the spikes out with your fingers(though we did not go pulling them out and leaving them out!!) It's a wonder that those mile long heavy coal trains do not instantly spread the rails apart and crash. There was a derailment many years ago. In fact,there have been 2 of them.


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## SE18 (May 16, 2014)

George, deferred maintenance was legendary in early 70s. I think railways were at their low point. I tried to get a job then with a number of railroads but they weren't hiring so I joined the Marines and spent 20 glorious years. Sometimes wish I'd been a railroader though


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## Ed T (May 17, 2014)

FWIW, bed rails are gnarly because they are made from reprocessed railroad rails. This produces a high strength, high carbon, angle iron that is pretty tough stuff. Jersey Shore Steel is one company that produces this material and bed frames are the largest user.


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## george wilson (May 21, 2014)

Back in the old days,the Arabs would steal British railroad rails and make them into copies of British rifles and pistols. They did this sitting on dirt floors in caves by hand. I would like to have been there to see how they managed to do that!! And,railroad rails are not the easiest steel to work with.

Of course,in Williamsburg they make flintlocks completely by hand. But those are not as complex as modern fire arms. And,a Webley break top pistol is by no means the simplest pistol to make. It was the only pistol they usually could get their hands on to copy.


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## Don B (May 21, 2014)

george wilson said:


> Back in the old days,the Arabs would steal British railroad rails and make them into copies of British rifles and pistols. They did this sitting on dirt floors in caves by hand. I would like to have been there to see how they managed to do that!!



I would have like to have seen that as well, many years ago I was shown one of these by a Gunsmith, the receiver and barrel where cast as one piece, 303 I think, it may have just been my inexperience but it looked a good copy to me.


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## Hexhead (May 29, 2014)

cold rolled and other steels have a mill scale make sure you take a deep enough cut to get under this or it will dull up your end mills


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## Andre (May 29, 2014)

Hexhead said:


> cold rolled and other steels have a mill scale make sure you take a deep enough cut to get under this or it will dull up your end mills



Aluminum has this, too. Aluminum oxide is very abrasive, but it's so thin you don't notice it when cutting.


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