Fracturing HSS end mills

I wrecked two 1/2" two flute center cutting end mills in a row. I"m trying to figure out what happened.

A friend gave me a couple of cast iron clamps from his tractor wheels to mill 1/2" keyways in.

I had intended to "drill" down with the end mill and produce a series of overlapping holes, and then side mill the slot - cheapo me - I can sharpen the ends of end mills, but not the sides, so I try to put my wear on the ends.

I moved the table up until the end mill was just touching, then started to pull down on the quill handle. I was putting a fair amount of pressure on to get it to cut and it just grabbed and fractured. The first time I could blame it on the vise and work piece not being clamped tight enough. The second time the cast iron work piece moved less in the vise when it grabbed than before, but it still moved when the end mill grabbed. After this I did the slot in the conventional way, side milling out the metal. I didn't feel any hard spots when I came in from the sides.

What happened? Doesn't cast iron like to be drilled with an end mill? It seemed to work ok when I was feeding the table up to get into bright metal, but when I pulled down on the quill handle, it broke apart. Did I put too much pressure on with the quill lever? Thoughts?

RWL

Reply to
GeoLane at PTD dot NET
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You were cutting through the as-cast surface? The cast surface is "chilled" by the sudden contact of molten metal to cold mold sand, and may include a bit of sand, too. This is HARD stuff, and REALLY tears up an HSS cutter. I have been forced to do the same, but I EXPECTED it to total the cutter, and rather quickly, too (and it did). If finish in the area is not important, you may be able to use a grinding wheel, or even a Dremel and stone, to remove a little of the "skin" off the casting where you are going to cut it. Once that hard skin is removed, the end mill should be able to cut it quite easily.

Oh, and, of course, is it REALLY cast iron, or cast tool steel? A file or hacksaw blade will tell the difference real easily.

Jon

Reply to
Jon Elson

The hard skin is often visible as a whiter and shinier surface layer when you grind a cross-section.

I have trouble drilling sometimes unless I tighten the quill lock's drag enough that the bit or end mill won't jump downwards. That doesn't happen if you lock the quill and raise the knee.

Jim Wilkins

Reply to
Jim Wilkins

White cast iron?

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Reply to
guillemd

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White is very brittle, and is only left in the "white" state for wear applications with very low or no tensile loads. Typical uses are things like grinding-mill parts. Most white iron is cast that way for conversion to malleable iron by heat-soaking for extended periods.

Gray cast iron that grabs sounds like it has uneven hardness or outright hard spots. I remember a piece that had a HSS end mill cast into it, which destroyed two good end mills until we found it.

-- Ed Huntress

Reply to
Ed Huntress

I tried to find the melting point of any alloy called HSS to compare it to melting point of cast iron. Did this actually happen to you?

Wes

Reply to
Wes

Cast iron approx. 2150 deg. F. M2 high speed steel approx. 2600 deg. F

Yup. We couldn't see what it was until we'd wrecked the second cutter and the workpiece. Finally we cut through it with a cutoff wheel, and then we found the milling cutter inside.

That was a piece of cast iron bar stock. The supplier made good on it, including an allowance for the wrecked cutters.

-- Ed Huntress

Reply to
Ed Huntress

That is cool. The only reference (old) I could find was this:

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Looked like there was some headroom for this to happen. I've heard that ball bearing in steel or CI too many times that I'm a bit skeptical when I hear about embedded metals.

Wes

Reply to
Wes

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Back when remelted scrap first started to be used for graded steel bars, odd things appeared in them from time to time, I've heard. I only worked in that shop for a couple of years and the CI bar was the only example I ever saw.

We did a lot of work for Princeton University's labs in that shop, and they specified electroslag remelted steel and even vacuum-remelt for many of their projects, for just that reason. Some of the parts we made went into very expensive experiments and defense-related research. It drove the materials costs 'way up, but it was cheap insurance from their point of view.

-- Ed Huntress

Reply to
Ed Huntress

You don't need to cast HSS in, all you need to do is have your buddy, the welder, TIG weld the crack in his cast iron automobile head using stainless rod and tote it over to you, "just take a light cut off it to level it off". Takes the end right off a HSS fly cutter. Cheers,

Bruce (bruceinbangkokatgmaildotcom)

Reply to
Bruce in Bangkok

Chromium carbide?

I thought pure nickel was recommended.

Reply to
Jim Wilkins

Sure, but they didn't have any of that stuff. But he did have a bunch of 316 for welding airplane ducts and it welds a pretty bead...... and apparently absorbs humongous amounts of carbon because after I ate the end off my fly cutter I got smart and hit it with a file - skated across the weld like it was a diamond.

I finally got it strapped down on the surface grinder, had to jury rig some clamps on the magnetic chuck cause the studs were still in the head and had to put it up on parallels but I finally got a light cut off it and took it back. "Gee, it looks nice" he says and then starts to speculate about getting some more busted heads and fixing them and selling them. We'd both get rich! I just walked off.

Cheers,

Bruce (bruceinbangkokatgmaildotcom)

Reply to
Bruce in Bangkok

I used to work at a place where we milled large plates of mild steel. Our Mazak operator looked to see why his end mill had crashed. Embedded in the middle of the 1" plate was a steel file.

David

Reply to
David R.Birch

I didn't mean it as criticism. What would you buy a little of to be ready for unexpected small repairs?

Reply to
Jim Wilkins

Is it possible that you don't have a center cutting end mill? Did you try using a drill bit to see if the material is "drillable"? I try to avoid "drilling" with an end mill because you really need to have things solidly held. Even loosening the quill enough to get the quill handle to move can allow the spindle to wiggle enough in my old mill to create a problem that way. You didn't exactly say whether you are using a milling machine or a drill press for this operation. If you are using a drill press, then I think i'd drill first. I have been looking at those (usually solid carbide) drill/milling cutters lately. They sound pretty neat for the kind of application you have there, but the are pretty pricey. The one time that I was prepared to spring for one, they didn't have them in the exact size I needed. One other thing: Not to criticize your ability to "sharpen the ends but not the sides": I'd bet that ANY lack of symetry between flutes would be a cause for this problem.

I'd like to hear what you finally find, Pete Stanaitis

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GeoLane at PTD dot NET wrote:

Reply to
spaco

melting point

Ive got a customer with a mold on display in his office. After it was about 3/4 completed..many hours into it....they found the big tap cast into the "billet"

If I remember, Ill take a picture next time Im in there....

Gunner

"Upon Roosevelt's death in 1945, H. L. Mencken predicted in his diary that Roosevelt would be remembered as a great president, "maybe even alongside Washington and Lincoln," opining that Roosevelt "had every quality that morons esteem in their heroes.""

Reply to
Gunner Asch

Yup. Rust and all.

Good suggestion for the future.

The project's done now, so I don't have the castings to try that on. Milling from the side in the conventional fashion worked pretty well.

RWL

Reply to
GeoLane at PTD dot NET

Would it have worked if I'd raised the table to get through the skin and then used the quill handle. How thick is the skin typically?

RWL

Reply to
GeoLane at PTD dot NET

No. It was a two flute center cutting end mill.

No, but having had this experience, I might the next time ;-)

Bridgeport 2J head Hand feeding with the quill handle.

I use one of the tilting fixtures that you put on your magnetic chuck and sharpen the end on the surface grinder. I am admittedly still on the learning curve, and gashing doesn't look very pretty, but they seem to work - at least when fed in sideways in the usual fashion.

Entered the cut from the side and milled the slot in the conventional fashion. It actually machined pretty nicely that way.

RWL

Reply to
GeoLane at PTD dot NET

Spark plug porcelain, stainless cable, taps, can all be found in steel bars and plates. I had one order of 4140 material that had certs and came from romania that had a bunch of crap in it. Little pieces of hard stuff that was killing inserts and leaving little pits where it fell out.

John

Reply to
john

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