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Posted by Steve R. on March 23, 2008, 11:19 pm
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>
>> On Sat, 22 Mar 2008 18:22:04 -0000, "Steve"
>> wrote:
>>
>>>I've managed, through nothing but carelessness, to break a 1.5mm drill
>>>bit
>>>in the cylinder head of the little glow motor I'm (still) making. Only
>>>one
>>>hole left to complete and I broke the soddin' bit into the head. I've
>>>been
>>>dripping sulphuric acid into the hole for the past couple of days,
>>>without
>>>seemingly much progress.
>>>
>>>Any better ideas for getting the broken bit out? Is there anything
>>>better
>>>than H2SO4 to do this job?
>>>
>>>I can bodge it , but rather not without trying.
>>>
>>>Steve
>>
>>
>> If it were carbon steel in an aluminium head then dilute nitric acid
>> would get
>> the steel out without harming the aluminium. HSS is, I think, more work.
>> Can
>> check tomorrow.
>>
>>
>> Is the hole for a head mounting screw? If so, how about:-
>>
>> Is the drill broken off flush? if not then drill 1.5mm into a bit of
>> steel
>> bolted to the drill press table to act as a locator, then put a pin in
>> the
>> hole to locate the buggered hole with. Failing that, make a template with
>> the
>> hole locations out of a bit of scrap and screw that to the underside of
>> the
>> head with some of the existing holes.
>>
>> Once you've done that, carefully drill from the other side until you meet
>> the
>> broken screw. Then punch the broken screw out with a 1mm, or less, punch.
>> Finally, clean up the hole.
>>
>>
>> Mark Rand
>> RTFM
>
> What've got is an aluminium head machined from bar stock, and the hole is
> one of four for holding down the exhaust manifold flange. The drill is a
> 1.5mm HSS hertel and its broken off below the top of the hole (only just).
>
> I can't get at the hole from the other side.
>
> I'm using conc sulphuric, hadn't thought that diluting it would actually
> work faster! The anodising trick sounds interesting.
>
> Not sure how to acquire smal quantities of Nitric acid locally either.
> Our local chemist is nervous about selling me 500ml bottles of IsoPropyl
> Alcohol, so asking for Nitric will probably give him a heart attack.
>
> Thanks for the accumulated wisdom - back into the shed to have another go.
>
> Steve
>
Jewellers supply firms usually sell a nitric acid paste. This is used by
watch and clock repairers to remove broken screws. Mine is a white paste.
Just put a dab on the end of the offending object, and warm over a flame.
Repeat as needed. Not sure how effective it is with HSS though.
Steve R.
--
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