Thread: Sharpening coated end mills

Does anyone re-sharpen coated end mills?

I can understand that industrial users may not bother re-sharpening coated carbide or HSS (especially smaller sizes) but how about hobby machinists?

Is re-sharpening a viable option given that end mills from China seem to be getting cheaper and cheaper?

Is the substrate material sufficiently robust to perform once the coating has been "sharpened" off?

I sharpen larger size (12mm +}TiN coated HSS after they dull too much. They work quite well but not for very long.

I have not tried to re-sharpen coated carbide as I have only smaller ones (10mm and smaller).

Obviously, end mill manufacturers target industrial use and are constantly using better and better coatings but is this to the detriment of the substrate? Can they use lower quality substrate because the coatings are so good and users throw them away when dull?

Hope this post generates a useful discussion.

Thanks, Kevin

I sharpen my end mills occasionally, but only the ends using the lathe and a die grinder. Only takes a couple of minutes. 3/16 two flute is the smallest I've done.

Yes, if a HSS slot drill has sharp flutes, but the corners are chowdered (7/10 because I dropped it during a change, 2/10 G00 Z-1, 1/10 genuine wear), then I'll chuck it on the Quorn and touch up the ends back to a sharp corner. Only takes 5 minutes, and might double or triple the life of a $20 endmill.

Angles aren't critical, it cuts just as well. -2° end clearance, 10° primary clearance, 25° secondary clearance. Then I usually do a center thinning op but I can't remember the exact angles there. Grind one lip 25% longer than the other to keep it center cutting.

Anything smaller than 6mm however goes into the cutter scrap bin. Getting them properly sharp at that size is a bit finnicky, you need a very hard wheel (probably CBN would be best), they no longer center cut after the sharpening, and good sharp carbide endmills off banggood are <$8 each. I'll only attempt it if I desperately need one that size that day.

Under all that 'Chinese gold', HSS is still HSS.

Eccentric Engineering have kits, drawings and fully built up versions of a cutter grinder which you may find interesting. There are numerous youtube videos from several different uploaders, including Garry from Eccentric Engineering. The kits are a bit expensive, but being assembled by hand in a labour intensive production system , that is not surprising, and if you want to home brew one the drawings are under Au$40. It would be much easier to build than a Quorn, and I imagine simpler to use as well, all in all well worth a look in my opinion.
https://www.eccentricengineering.com...d=36&Itemid=53
Rob.

Honestly, in spite of owning one:

Sod the bloody Quorn and all the fetishization that goes along with it and all those bloody ball handles. Much respect if you complete one from castings, but Christ on a bike does that thing embody the masochistic nature of the British model engineer.

Is it that the grinding of a worn endmill is only to the clearance side of a cutting edge, and the "working face" is not touched?

So, removing the worn edges by grinding back the clearance faces to restore sharpness results in working faces that retain their coating.

Never done this, just thinking.

Jordan

Originally Posted by Precious Mettle

Yes, if a HSS slot drill has sharp flutes, but the corners are chowdered (7/10 because I dropped it during a change, 2/10 G00 Z-1, 1/10 genuine wear), then I'll chuck it on the Quorn and touch up the ends back to a sharp corner. Only takes 5 minutes, and might double or triple the life of a $20 endmill.

Angles aren't critical, it cuts just as well. -2° end clearance, 10° primary clearance, 25° secondary clearance. Then I usually do a center thinning op but I can't remember the exact angles there. Grind one lip 25% longer than the other to keep it center cutting.

Anything smaller than 6mm however goes into the cutter scrap bin. Getting them properly sharp at that size is a bit finnicky, you need a very hard wheel (probably CBN would be best), they no longer center cut after the sharpening, and good sharp carbide endmills off banggood are <$8 each. I'll only attempt it if I desperately need one that size that day.

Under all that 'Chinese gold', HSS is still HSS.

Many end mills won’t centre cut from new, and none are designed to be used that way. Centre cutting end mills can plunge straight down, but it’s not a good idea and why on CNC machines the plunging op ramps down and on manual machines you should pre-drill. Ramping down enables a non centre cutting end mill to plunge as it’s cutting on the corners.

”HSS is HSS”, just like all steel is steel right? In fact there are many grades and quality of HSS. I think the OP question is good, and using a coated tool should enable lower quality HSS to be used, but I don’t know if that’s the case, or even if there is a definitive answer to that. I expect it will depend on the manufacturer and chances are if it’s not a high quality brand in the first place they won’t bother quoting the HSS type.

Whether it’s viable is also is a loaded question with no answer. I have an end mill sharpener and it doesn’t take long to sharpen the cutters. Is it “viable”, sure, why wouldn’t I? Is it “viable” for somebody with nothing more than a bench grinder and a milking machine? Maybe not. It’s probably not viable for somebody time poor who wants to just make “stuff”; just because somebody is doing it as a hobby doesn’t mean their time isn’t valuable! On the other hand the whole process of sharpening an end mill can be just as much a part of somebody else’s machining hobby. Only each individual can answer that question for themselves.

I've always regarded those coated drills and endmills as a gimmick, surely once sharpened the nice goldy coloured stuff plays no part in the efficiency or said bit.. I've sharped larger endmills by hand, they worked alright but I wouldn't expect them to last too long, be that accurate or do that good a job.

Originally Posted by Precious Mettle

go be disingenuous somewhere else.

That sounds pretty harsh to me Precious Mettle, I don't think Pete F was in any way being a smart A, just giving a considered answer to the OP. While he may have missed your reference to slot drills, (I did myself) the original post was about sharpening end mills, which is what I assumed he was referring to.
Finally, I think that it behoves all of us to choose our words carefully, if we want this forum to remain a friendly space for the pleasure of all.That's my 2 cents worth anyway,
Rob

Originally Posted by newmanwoodlands

Does anyone re-sharpen coated end mills?

I can understand that industrial users may not bother re-sharpening coated carbide or HSS (especially smaller sizes) but how about hobby machinists?

Is re-sharpening a viable option given that end mills from China seem to be getting cheaper and cheaper?

Is the substrate material sufficiently robust to perform once the coating has been "sharpened" off?

The reason industry treats some endmills as 'throwaway' is just economics - why have someone you can charge out at say $100 per hour spending 10 minutes sharpening a $10 cutter (yes, I know it does not take that long to do the actual sharpening but set up, getting organised and all that take time. If I gave you 5 cutters to sharpen, you would not be done in 5 minutes - probably more like 20)

Hobby machinists can do what they like as their time has zero cost, so if you want to resharpen cutters, go for it (as I do).

Usually the primary benefit to a coating is on the surface that has the chips running on it, so just like a coated twist drill, sharpening by taking off a sliver of clearance surface off will resharpen the cutting edge with only a minor effect on the cutter.

At a previous employer we used to discuss Chinese supplies frequently because it was a constant concern impacting on the end product we had going out the door. This is a typical example of the concerns that we voiced. The problem is not so much that the underlying substrate is nominally HSS, but that the processes used to produce that material are not always consistent (whether that be purity of the input metals, control over the melt, or even post pour heat treatment). As a result the stuff that they sell as HSS could greatly vary in its properties. It is likely that the cheaper the cutter, the more the 'HSS' could vary from what a name brand manufacturer would be prepared to supply. I would expect though that in this case the overall cutter life would suffer whether it was coated or not - after all the cutter does the cutting - the coating is just to help chips not stick, cope with wear, make the surface harder and other nice things. No amount of coating will help if the underlying substrate has the strength of week old cottage cheese.

Finally, to comment on the end mill/ slot drill point raised, a CNC machine will typically ramp in an endmill in rather than plunge with a slot drill simply because the centre of rotation of a cutter has zero linear cutting speed and so is horribly inefficient. Twist drills typically scrape rather than cut material away with their web, hence the use of pilot holes. A slot mill can 'drill' in but with other options available to CNC programmers they don't bother much with them. I use slot drills myself occasionally but normally for side cutting rather than plunging in.

Michael

Originally Posted by Ropetangler

That sounds pretty harsh to me Precious Mettle, I don't think Pete F was in any way being a smart A, just giving a considered answer to the OP. While he may have missed your reference to slot drills, (I did myself) the original post was about sharpening end mills, which is what I assumed he was referring to.
Finally, I think that it behoves all of us to choose our words carefully, if we want this forum to remain a friendly space for the pleasure of all.That's my 2 cents worth anyway,
Rob

That's ok Rob, although I was quite taken back by the person's extraordinary rudeness, I think he's quite new to machining so probably doesn't realise there's a difference between an end mill and a slot drill. The hint is in the name, but no harm - no foul, it's all good, and I guess everyone has their bad days

As you suggested, I was answering the OP's original question about END MILLS, some of which can be centre cutting and some are not, but all can be made to plunge if required.

It sounds as if Michael's experience is similar to my own, and unfortunately going for the cheapest bid on the day probably means a jump into the lucky-dip barrel and taking your chances with what pops up. Overall I think it's worth giving sharpening at least the ends of end mills a go. A little like promising to replace a dull drill because it's not worth sharpening, invariably they'll get used beyond when they should. If they can be sharpened easily they are more likely to be kept sharp.

I use one of these sharpeners shown in this thread. End Mill Sharpening Tutorial Have have not read the thread to verify accuracy of the method explained, I just use an ER32 version of the tool


Ausee Machines & Tools

I found when the late John Stevenson said anything, it was worth listening to and take notes.

I posted this before but being a new member it was submitted for moderation, obviously, it has been mislaid so in case it comes up again, you'll know why.

I've always regarded these coating as a gimmick, I've never found the nice gold ones cut any better than the silver ones. Also, once you sharpen the bit the coating is removed on one side (underneath) of the cutting edge.

Originally Posted by onanonanon

I've always regarded these coating as a gimmick, I've never found the nice gold ones cut any better than the silver ones. Also, once you sharpen the bit the coating is removed on one side (underneath) of the cutting edge.

For cheap coatings that are a bit on the thin side you may be right, but properly applied coatings do help, although the help may not be all that noticeable to a casual observer. They would not be used industrially if they did not work. As noted above, the substrate does matter and without a decent substrate, the coating can not really do much.

Michael

Assuming that it isn't a gimmick, removing by grinding the underneath (clearance) side ought not to affect the actual working face, yes?

Jordan

Originally Posted by onanonanon

I've always regarded these coating as a gimmick, I've never found the nice gold ones cut any better than the silver ones. Also, once you sharpen the bit the coating is removed on one side (underneath) of the cutting edge.