Question about roughing or ripper end mills

I have a question regarding the ends of roughing end mills. As can be seen in these pictures, of this particular 3 flute Presto cutter, that due to form of the cutter when the ends are ground they don't all come to a point like a standard cutter.

So does this mean that when in use, for example cutting an inside corner for say a tee-nut, does the sharpest corner take more abuse than the others and act a bit like a single point cutter?

Thoughts welcomed,

Craig

Craig

Best to use the roughing cutter to remove excess material and leave an allowance to machine off with a finishing cutter.

Emgee

The operation of these roughing cutters are that the 3 flutes cut grooves at different positions along the length of the cutter. So a bite will be taken and then another just below it and then one below that. This repeates for the length of the cutter which makes for a very free cuttting action. The roughing cutters I have used have all been bevel ground on the tips which makes for a longer life and does eliminate the chip loading on the sharp corner (basically by avoiding sharp corners). This one looks like it has been reground. They are not really for finish cuts.

regards Martin

The tip has a progressive depth of cut on the tip corners, as previous it is used to a depth using the flutes, corner edges may be chamfered also. For more information look at Guhring or similar roughing cutters.

They are not really for finish cuts.

A bit of an understatement there?🙂

By definition they remove metal with a ‘rough’ cut. They are just for fast removal of metal with no pretences of a fine finish.

Thanks for the replies so far.

I am aware they are for roughing out and not finishing which really is what got me thinking about the ends because unless you are just using the flutes to remove material from the periphery of something thinner than the depth of the flutes then the ends and therefore corners are going to be doing some work. And by definition these cutters can be worked hard so I was just curious about the vulnerability of the ends, imparticular that one sharp corner.

Yes this cutter has had a regrind but im sure I have seen new ones with a standard grind on the end in the same fashion as this one, happy to be corrected if this is infact not true

Because the outside profile is a rounded single start thread form, there will never be a perfect end corner on all the flutes. If anybody was to make a 3 start thread form with 3 flutes, all of them could have an identical square end. I have a solid carbide 10mm endmill with the roughing profile and the "thread" pitch is about 2mm with 4 flutes, I haven't tried it out yet.

A roughing cutter has lower cutting forces, so can be run at higher feedrates. A big advantage is that the swarf produced is in the form of chips rather than long and thin chips, so the swarf is easier to clear. While roughing cutters do not leave the best finish it is adequate for many applications. To sharpen roughing cutters the flutes need to be ground on a helix, which is why the the lead is listed on the cutter shank.

Andrew

Most, but not all, of mine are radiused at the end to prevent the flute with the end of the thread taking too much load.

I do like them, because the chips they produce are far less painful than the needles produced by finishing endmills.

WARNING:

Ensure that roughing cutter is securely fitted to the mill because the spiral flute tries to pull the cutter out of the collet in the spindle and can dig into the work (or mill table) Don't ask how I know

I have not personally used these but from what I have observed at work, they can leave a finish slightly like that of a shaper - lots of fine, parallel lines. Since these work-pieces were for high-precision or otherwise highly-specified parts, some cut from large pieces of thick aluminium-alloy plate, a decent finish was desirable, but as I recall that left by ripping-cutters was often tidy enough to be acceptable.

The point is that the finish is not only a matter of the tool, nor is a polished finish always necessary; and in many cases fine tooling-lines left by conventional milling, turning and shaping cutters ( used preferably with self-acting feeds if possible), are not out of place.

Maybe the term "ripping" is a bit unfortunate, although that is on the cutter's box label!

"the term "ripping" is a bit unfortunate" but the term "roughing" is and is. Ripping is not term that is normally associated with precision. (eg. Ripping a piece of paper instead of cutting a piece of paper).

I regularly rip wood on my table saw. To a woodworker it just means cutting with the grain, and doesn't necessarily imply a lack of precision.

I would say yes one tooth is cutting leaving a larger radius in the corner than the other two but that also means that the tooth that comes to a full radius and a sharp corner has less work to do.

Bill Phinn I agree woodworker do tend to call what you describe as a ripping cut but unless you are not worried about a finish it will 9 out of 10 times leave and undesirable finish and it would need to be put through a planer or if that way inclined a hand plane to get an surface that is needed for fine furniture.

Except that when ripping timber, one automatically thinks about the timber warping as the cut proceeds. With a cross-cut saw (across the grain), that problem does not normally arise.

I may just stone a radius on the sharp flute.

This however sparks another question, I have a number of standard end mills where the sharp point has burnt up, blunted or chipped and I always assumed these would require the attention of a T+C grinder but, as discovered with these roughing cutters, if differences in the tips doesn't effect the functionality of the cutter (which is obvious as they wouldn't sell any) then can I hand grind a chamfer or fillet on to the corners of these old end mills to get them cutting satisfactory again?

So long as you are using the flutes for most of the work and not just the end.

We home folks tend to burn up a number of endmills before we realise that they do their best work with the full length of the sides rather than the very ends. DAMHIKT!

As ripper mills are primarily intended to cut sideways rather than end on as a slot mill, you can simply grind the end square to shorten it. This would get rid of the tip which is normally the first part to go blunt.

Back to the Craig 2's question about the end grind: One of the flutes will extend to center while the other stop short of center. It is capable of plunging.

One thing I especially like about roughing mills is that the chips are granules rather than the needles produced by conventional end mills.