facing mill insert - what radius - Model Engineer

I have got two facing mills that use inserts. 60 and 40 mm in diameter. Great for cutting aluminium but not so for steel until I use inserts for aluminium ( much sharper and rake angle larger ) for cutting steel. Light cutting only though ( DOC 0.2 mm ). I know the tool life is going to be short but as these inserts are very cheap ( 0.6 pound each ) so I will just live with it. My mill is a light one ( Emco FB2 ) so I believe I don't have much choice.

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There are two choices of tip radius for the insert : 0.4 and 0.8 mm and I wonder which one produce lighter load on the machine hence more steady speed of rotation under the same rate of material removal.

Edited By Y C Lui on 31/05/ 03:11:12

I only run a 25mm facemill on my small SX2P was going to get a 40mm but decided against it thinking that 25mm is enough for a small light mill but it does work very well.

The coated and uncoated inserts that ARC supplied with the cutter work really well to and like Jason I once tried some cheap inserts but they couldn't handle the same depth of cut and also like Jason the machine had a horrible vibration. I have not tried the uncoated on steel though but with ARC inserts cutting very well I haven't found the need to.

+1 for Jasons' suggestion of getting a better breed of insert.

The sharp edge on aluminium specific insets is, by reason of its slender geometry, inevitably somewhat weak. The continually repeating shock loads of a face mill give it a hard life.

Cutting stresses on steel are considerably greater than on aluminium so there is a good chance that the sharp edge will be rapidly battered off if the insert material is insufficiently strong. The made to be inexpensive inserts are likely to be made from a less costly carbide giving an edge that is strong enough to handle aluminium and its weaker alloys when used with care under appropriate conditions. But steel is asking too much of it.

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Professional grade inserts are designed to stand up to production use in CNC machines which drive them hard enough that the shock loads in aluminium can be greater than those encountered on ordinary steels when used in our lighter machines. So they stand up pretty well when used on the wrong material. Some of the harder breeds of steel will faze them tho'.

As ever its a question of price / performance ratio. Leaving aside the uber cheap "probably junk" selections the less costly the insert the more care you have to take to stay firmly inside its safe operating region. So inexpensive aluminium ones should stay on aluminium and be used with care.

None of us are in any real position to definitively evaluate insert performance so its just a matter of common sense and appropriate use. In the "good(?) old" HSS days there was a certain commonality between home shop and industrial use / machinery so intelligent re-appraisal of industrial focused guidelines was easy and appropriate. Not so now where carbide use is generally focused on making more chips per day then most of us manage in a lifetime!

The uber cheap inserts are frequently just grabbed from a batch that failed quality control so its totally dependant on luck and statistics whether you get good ones, bad ones or something in between. No production user will risk inserts that don't have reliable performance statistics so iffy batches are binned on a regular basis. Up to Mr Carbide Scrappy whether the material is re-cycled or sold on for cheap inserts. Whatever is the best deal. Money talks.

Clive

The difference between a fly cutter set up for Ø60 and a Ø60 facing mill is simply the number of cutting edges so the facing mill can remove metal more quickly and needs faster feeding as a result, otherwise you may end up rubbing not cutting. A facing mill may have more than one cutter working at a time so needs more power to keep it working well. For small milling machines, with low rigidity and power, facing mills do not really make a lot of sense. I would suggest keeping the facing mills for use with aluminium but go with a fly cutter for steel unless you get a better machine in the future. Stick a suitable carbide tipped lathe tool in a fly cutter so you do not need to worry about tool sharpening angles.

Martin C

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