Thumping cast-iron

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Thumping cast-iron

anotherid

07-31-2008

Re: Thumping cast-iron

Dave Baker

07-31-2008

Posted by anotherid on July 31, 2008, 6:36 am

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I need to mark some hole positions out on a cast-iron lathe backplate -
is it OK to use a transfer punch and give it a good wallop? Or could it
fracture? I've never worked with c.i. before but vaguely feel it might
be "brittle".

Brendan

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Posted by Dave Baker on July 31, 2008, 6:48 am

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>
> I need to mark some hole positions out on a cast-iron lathe backplate -
> is it OK to use a transfer punch and give it a good wallop? Or could it
> fracture? I've never worked with c.i. before but vaguely feel it might
> be "brittle".

It's quite brittle compared to steel but you won't fracture a big lump of it
with a centre punch. In fact you can straighten bent cast iron with a sharp
whack. A guy I know who regrinds cast iron car engine camshafts checks them
for straightness first on a dial gauge fixture and then gives the high spot
a whack with a cold chisel. Surprisingly this persuades them it's in their
best interest to lose the curvature. I wouldn't have thunk it myself until I
saw it being done.
--
Dave Baker

Posted by newshound on July 31, 2008, 4:21 pm

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>>
>> I need to mark some hole positions out on a cast-iron lathe backplate -
>> is it OK to use a transfer punch and give it a good wallop? Or could it
>> fracture? I've never worked with c.i. before but vaguely feel it might
>> be "brittle".

>
> It's quite brittle compared to steel but you won't fracture a big lump of
> it with a centre punch. In fact you can straighten bent cast iron with a
> sharp whack. A guy I know who regrinds cast iron car engine camshafts
> checks them for straightness first on a dial gauge fixture and then gives
> the high spot a whack with a cold chisel. Surprisingly this persuades them
> it's in their best interest to lose the curvature. I wouldn't have thunk
> it myself until I saw it being done.
> --
> Dave Baker

Yes but crankshafts are spheroidal graphite (SG) cast iron, also known as
ductile cast iron (because it is ductile, which is why it is OK to use for
things like drain covers). Your lathe back plate will almost certainly be
grey cast iron, and pretty brittle. That said, a sensible use of centre
punch should be OK. A light tap, not a good wallop.

Posted by Dave Baker on July 31, 2008, 5:20 pm

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>>>
>>> I need to mark some hole positions out on a cast-iron lathe backplate -
>>> is it OK to use a transfer punch and give it a good wallop? Or could it
>>> fracture? I've never worked with c.i. before but vaguely feel it might
>>> be "brittle".

>>
>> It's quite brittle compared to steel but you won't fracture a big lump of
>> it with a centre punch. In fact you can straighten bent cast iron with a
>> sharp whack. A guy I know who regrinds cast iron car engine camshafts
>> checks them for straightness first on a dial gauge fixture and then gives
>> the high spot a whack with a cold chisel. Surprisingly this persuades
>> them it's in their best interest to lose the curvature. I wouldn't have
>> thunk it myself until I saw it being done.
>> --
>> Dave Baker

> Yes but crankshafts are spheroidal graphite (SG) cast iron

What do crankshafts have to do with the price of fish? I'm talking about
camshafts.
--
Dave Baker

Posted by newshound on July 31, 2008, 6:35 pm

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>>>
>>>>
>>>> I need to mark some hole positions out on a cast-iron lathe backplate -
>>>> is it OK to use a transfer punch and give it a good wallop? Or could it
>>>> fracture? I've never worked with c.i. before but vaguely feel it might
>>>> be "brittle".
>>>
>>> It's quite brittle compared to steel but you won't fracture a big lump
>>> of it with a centre punch. In fact you can straighten bent cast iron
>>> with a sharp whack. A guy I know who regrinds cast iron car engine
>>> camshafts checks them for straightness first on a dial gauge fixture and
>>> then gives the high spot a whack with a cold chisel. Surprisingly this
>>> persuades them it's in their best interest to lose the curvature. I
>>> wouldn't have thunk it myself until I saw it being done.
>>> --
>>> Dave Baker

>> Yes but crankshafts are spheroidal graphite (SG) cast iron

>
> What do crankshafts have to do with the price of fish? I'm talking about
> camshafts.
> --
> Dave Baker

Sorry, mis-read the post. Even so, grey cast iron doesn't sound the right
material for a camshaft to me, except perhaps for a Lister.

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