Chipping the carbide?

Frequent quote: "intermittent cuts will chip carbide inserts"

apt ("mini index" and several other manufacturers have on offer single fluted (single insert) carbide end mills. Single flutes are common on the smaller diameter inserted end mills that are a typical size for the machines that many of us use.

Is there a "special technique" that must be used to overcome chipping these carbides? Higher than recommended rpm? Slower feeds? Limited depth and width of cut?

What is your experience (recommendations) with single fluted end mills?

Appreciate all input.

Paul

I've not really had any inserts chip from intermittent cuts be it on the lathe or mill, usually only if you knock them or wind the tool into the stationary work.

Plenty of insert flycutters and face cutters that all have interupted cut and no issues. I use a 3 tip 40mm cutter a lot on castings and it goes through hard chilled spots no problem.

J

That mirrors my experience; I've never chipped an insert during actual cutting.

As an example the tapers on the conrods for my two traction engines were turned on the lathe using one 5mm carbide button insert for both:

I started with the roughed out shape at the top, and finished with the one at the bottom. The interrupted cuts were done at 800rpm and 8 thou/rev feedrate, so no pussyfooting around. The speed was increased, and feed decreased, for the finishing cuts.

In general for carbide run it hard and fast; it's happy running hot, so you might as well do so. For milling, avoid step overs around 50% to reduce shock loading as the inserts enter the cut. Less, or more, is fine, but not in the middle.

Regards,

Andrew

"For milling, avoid step overs around 50% to reduce shock loading as the inserts enter the cut. Less, or more, is fine, but not in the middle."

Could you elaborate on the above quote? Is a "step over" a movement of the mill table where 1/2 of the diameter of the cutter is cutting? It is therefore acceptable to have say 1/4 of the diameter cutting or 3/4 of the diameter cutting when moving into the cut.

Thank you,

Paul

I just remembered I uploaded this the other day, first cut on an iron casting using an insert tool in the boring head, just one of the set of 3 that Glanze do.

Paul: I think you've got it. To clarify; a stepover of 50% means that for each pass the cutter is moved over half it's diameter, so for 20mm diameter cutter that's 10mm. I normally use a stepover of less than a third, or more than two thirds. If you have a fair depth of material to remove, it is probably better to use a deeper depth of cut and use a smaller stepover, say 10-20%. After all, you're paying for the whole length of cutting edge, so might as well make use of it. You can even up the feedrate, to take account of chip thinning.

See this page: **LINK**

Regards,

Andrew

To get back to the original question, the easiest way to chip a carbide tip, is to switch off the machine spindle with the feed still engaged. This applies to the mill and lathe. Disengage the feed, then switch off the spindle. I was taught this during my apprentiship, and rarely chip one following this principle, unless all hell breaks loose, and one has to hit the emergency stop.

Chris Gunn

THANK YOU!

I want to thank each of you for your contributions. You have certainly answered my question and more.

Partial summary:

There are ways to chip carbide while cutting, but intermittent cuting is likely not one of them. The following will likely cause chipping:

Turn off a lathe or mill in the midst of a cut without first withdrawing the tool from the cut.

Stepover 50% while milling.

While not cutting, touch the carbide tool to the work. Or allow the carbide tools to touch each other or a hard surface during storage and handling.

Paul

I have used large slotting machines in the past for machining steel etc. using HSS and also wrought steel tool bits. However, stick in a carbide tipped tool and stand by for failure. The problem with the slotting machines that I have used is that, unlike shaping machines, the tool is NOT raised from the work piece on the return stroke. The carbide tips seem to resent being dragged backards and chip very easily. Never did find out why and not likely to as I have no plans to use one of these machines now or in the future. (That somehow gives me a warm glow inside) -------Rik

I have used carbide tipped tools with good success on my shapers. The tips were used ones from a fellow club member who commented much later that they were no good... I sharpened them with a diamond wheel and found them excellent, although I quite likely have not worked them as hard as they would have in commercial use. The shapers have clapper boxes, so although they are dragging across the job on the return stroke we seem to get away with it. Might be different as above if the clapper box was locked.

There is of course no shortage of guys who will state unequivocably that carbide is no good in a shaper. I think the grades we get these days might be a bit better than some of the early stuff.

John