Flattening a Lapping Plate

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Flattening a Lapping Plate Scrim 01-30-2010
Posted by Scrim on January 30, 2010, 10:54 am
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I've got a used iron or steel lapping plate 10 inches diam. by 1 1/2 inches
thick which has roughly concave faces - I measure the dip in the middle of
each face to be 0.25mm and 0.1 mm. I was hoping to use it as both a surface
plate and lapping plate (lapping mainly by using it to support lapping film
to avoid wearing it) but it obviously needs work. Can I fix this myself by
hand?
Thanks,

Alan


Posted by Steve R. on January 31, 2010, 6:15 am
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> I've got a used iron or steel lapping plate 10 inches diam. by 1 1/2
> inches thick which has roughly concave faces - I measure the dip in the
> middle of each face to be 0.25mm and 0.1 mm. I was hoping to use it as
> both a surface plate and lapping plate (lapping mainly by using it to
> support lapping film to avoid wearing it) but it obviously needs work. Can
> I fix this myself by hand?
> Thanks,
>
> Alan

Yes! You need two more plates! Lap them against each other until all three
are dead flat. Optical flats are often made that way.




Steve R.



Posted by Scrim on January 31, 2010, 9:48 am
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Thanks Steve, What about when you only have one plate?
The techniques I have in mind is grinding the lap on a sheet of float glass
first with silicon carbide grit to get rid of the worst of the error and
then scraping the surface whilst using a sheet of float glass as a reference
with engineers blue to spot the high points. Does this sound practical?
Or would the lapping plate and two sheets of glass work with the three
plates technique?
Thanks,

Alan


>
>> I've got a used iron or steel lapping plate 10 inches diam. by 1 1/2
>> inches thick which has roughly concave faces - I measure the dip in the
>> middle of each face to be 0.25mm and 0.1 mm. I was hoping to use it as
>> both a surface plate and lapping plate (lapping mainly by using it to
>> support lapping film to avoid wearing it) but it obviously needs work.
>> Can I fix this myself by hand?
>> Thanks,
>>
>> Alan
>
> Yes! You need two more plates! Lap them against each other until all three
> are dead flat. Optical flats are often made that way.
>
>
>
>
> Steve R.
>


Posted by Steve R. on February 1, 2010, 1:18 am
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> Thanks Steve, What about when you only have one plate?
> The techniques I have in mind is grinding the lap on a sheet of float
> glass first with silicon carbide grit to get rid of the worst of the error
> and then scraping the surface whilst using a sheet of float glass as a
> reference with engineers blue to spot the high points. Does this sound
> practical?
> Or would the lapping plate and two sheets of glass work with the three
> plates technique?
> Thanks,
>
> Alan
>
>
>>
>>> I've got a used iron or steel lapping plate 10 inches diam. by 1 1/2
>>> inches thick which has roughly concave faces - I measure the dip in the
>>> middle of each face to be 0.25mm and 0.1 mm. I was hoping to use it as
>>> both a surface plate and lapping plate (lapping mainly by using it to
>>> support lapping film to avoid wearing it) but it obviously needs work.
>>> Can I fix this myself by hand?
>>> Thanks,
>>>
>>> Alan
>>
>> Yes! You need two more plates! Lap them against each other until all
>> three are dead flat. Optical flats are often made that way.
>>
>>
>>
>>
>> Steve R.
>>
>
The problem may be with the differing hardness, and embedability of the two
materials. Cast iron to cast iron does work, but as I said, 3 are needed.
each plate needs to be lapped against the others. you also need some way of
checking so that edges do not get rounded. Best to read up on it first, as
it has been many years since I have done any optical work.


Steve R.



Posted by the wizard on January 31, 2010, 11:37 am
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> I've got a used iron or steel lapping plate 10 inches diam. by 1 1/2 inch=
es
> thick which has roughly concave faces - I measure the dip in the middle o=
f
> each face to be 0.25mm and 0.1 mm. I was hoping to use it as both a surfa=
ce
> plate and lapping plate (lapping mainly by using it to support lapping fi=
lm
> to avoid wearing it) but it obviously needs work. Can I fix this myself b=
y
> hand?
> Thanks,
>
> Alan

Do you know anyone with a surface grinder, which might get it near
enough?
T.W.

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