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Chilled cast Iron - a small Rant

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Tony Martyr01/06/2020 16:59:06
188 forum posts
37 photos

The job of machining two small valve chamber covers should be a nice simple task - in fact the job was saved for a relaxing evening.
But the whole outer edges of both cast iron pieces are chilled and can't be milled. A tipped lathe tool makes an impression but tends to 'bounce' leaving high spots. I have reverted to rubbing the machined surface on a blued-up surface plate and carefully grinding the high spots with a Dremel. A surface grinder would be nice!


JasonB01/06/2020 17:03:18
18113 forum posts
1995 photos
1 articles

Good luck drilling them!

heat is probably your best option and being thin it should not bee too hard to get then red hot (850deg)

old Al01/06/2020 17:22:02
166 forum posts

send them back

mechman4802/06/2020 12:19:59
2663 forum posts
410 photos

I had a similar problem with my S10V having a chilled area on the OD of the standard. I managed to get around it by using a carbide tipped tool & a carbide insert face cutter.

Chilled area around the OD...

s10v casting hard skin (2).jpg


Mark Gould 102/06/2020 12:43:52
212 forum posts
120 photos

I am a novice but was told that the best way around this is to take a heavy cut. Otherwise the tool skates on the chilled outside.


JasonB02/06/2020 13:08:57
18113 forum posts
1995 photos
1 articles

A lot will depend on the depth of the chill which is not quite the same as a hard skin, In the photo above it is just limited to corners and thin edges in bad cases it can be quite deep or go all the way through. Then there is the problem that some castings only give you a very small machining allowance so no deep cuts possible

You can see the shine from the chill on this part even though I have taken a total of 3mm depth of cut. Metal was coming off in long blue ribbons more like steel than iron.

Baz02/06/2020 13:31:57
378 forum posts

Send them back, not fit for purpose.

Tony Martyr02/06/2020 15:19:50
188 forum posts
37 photos

I have consider the 'send them back' option and may do so but if the hole positions are clear of the chill (which is full depth on the edges) they will be usable. It is many years since learning about chemistry of cast iron, I seem to remember that I found it about as boring as the chemistry of boiler feed water in power stations

Grindstone Cowboy02/06/2020 17:35:27
300 forum posts
27 photos

Is heating to red heat and allowing to cool slowly a guaranteed fix for this problem?



Oily Rag02/06/2020 17:51:57
94 forum posts
54 photos

Time for a diamond milling insert cutter. I had a job a few years ago which were a high chromium alloy of cast iron (motorcycle disc brake rotors off a Norton Commando - the chromium was so they wouldn't rust!) The only way to machine them was with a diamond tipped tool. Knife through butter with those inserts!! I then used one as a fly cutter for some chilled white iron castings - again they cut beautifully!!

Maurice02/06/2020 18:07:10
464 forum posts
50 photos

I had this problem on some "Clarkson " castings many years ago. On advice, I put them in our coke stove, banked it up well with fuel, opened the damper to get everything nice and hot, then let it go out and cool overnight. No more hard spots in the castings! I realise that coke stoves are probably rare now, but heating and then slow cooling seems to be the answer.


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