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Choice of Milling Cutters

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Brian O'Connor23/11/2015 15:33:37
71 forum posts
18 photos

I have quite a large collection of milling cutters, both two and four flute, that are blunt or at least well past their best. I also have a few three-flute carbide cutters which I find stay sharp for much longer. I have no means of sharpening the cutters so my question is this: can I replace all my two and four flute cutters with carbide three-flute centre-cutting cutters or are there some circumstances where a two-flute or four-flute cutter would be advantageous? I am particularly keen to get rid of the two-flute cutters as I find that even with a fairly substantial mill (VMC) and everything locked down I still get appreciable vibration when using the larger sizes.

Regards, Brian

colin hawes23/11/2015 15:40:36
543 forum posts
18 photos

I have often sharpened the end of 2 flute cutters on the off-hand grinder. Colin

David Clark 123/11/2015 16:03:21
3357 forum posts
112 photos
10 articles

Make sure the three flute cutters are centre cutting.

Chris Evans 623/11/2015 16:34:04
1960 forum posts

Big downside of three flute stuff is measuring the things once they are re ground. I can't justify the special micrometer required.

Emgee23/11/2015 17:18:35
2158 forum posts
265 photos


Do a full width cut and measure the slot, even with new cutters if not top quality you may find a discrepency in the width cut.


Tim Stevens23/11/2015 18:24:29
1468 forum posts

This cut-and-measure method will only give accurate answers if you can eliminate all the flex in the machinery. One side of the cutter is working up-hill and the other side downhill, and the working part between works sideways, shoving the mill head etc all over the place. Perhaps one answer instead is to drill a slightly undersize hole, and then to ream it with the 3-blade cutter at the same position, so it cuts evenly all round. Measure this hole and I suspect you will get a more useful answer.

Not that I know anything about it, you understand.

Cheers, Tim

Chris Evans 624/11/2015 20:31:24
1960 forum posts

I know there are work arounds, to much faff when you want to measure a cutter to give a known size.

Brian O'Connor25/11/2015 09:50:03
71 forum posts
18 photos

Thanks for all your responses chaps, but I'm still not clear what disadvantages there are, if any, of ditching all my old and blunt 2 and 4 flute cutters and using only centre cutting 3-flute ones (which I won't be able to resharpen) from now on.


John Stevenson25/11/2015 10:45:08
5068 forum posts
3 photos

No disadvantages at all.

3 flute are a good compromise between two and 4 flute.

David, could you post a picture of a NON centre cutting 3 flute cutter please? Not saying they don't exist, there are always exceptions but I have never seen a non centre cutting 2 flute or 3 flute cutter.

4 flute is a different animal.

Andrew Johnston25/11/2015 11:00:58
6279 forum posts
677 photos

I use all three types, although I use 3-flute centre cutting by default. For cutting accurate slots in one pass 2-flute cutters are recommended. That's possibly less important now with carbide cutters that are much stiffer than HSS.

It also depends upon the material. For aluminium, with high chip loads, I use 2-flute or 3-flute cutters to minimise choking of the gullets. For harder materials with lower chip loads, like steel, I use 4-flute cutters to maintain the metal removal rate.

I suspect that the introduction of 3-flute centre cutting tools has been largely driven by CNC, where they are a compromise between chip removal and overall metal removal rates. Centre cutting tools also make it much easier when engaging the workpiece with CNC than non-centre cutting.


Brian O'Connor26/11/2015 09:47:36
71 forum posts
18 photos

Thank you, John and Andrew, very reassuring. I now feel confident to raid the piggy bank and give myself a Christmas present of a range of carbide 3-flute cutters.


AlanW27/11/2015 15:33:50
83 forum posts
10 photos


I have acquired a variety of cutters over the years, some sharp but the majority in need of refreshing. Most have clearly had the flutes sharpened in a professional environment (because the diameters are undersize). With no T & C grinder and a reluctance to spend the required time to build one, I opted for Harold Hall's solution using a bog standard bench grinder. It is probably a bit tedious to set up for grinding the secondary clearance, a job best done in 'batches' but the principle works surprisingly well. See how simple it is here:


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