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Hardened Lapping Plate?

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cmantunes

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#1
I've been trawling eBay for an used lapping plate and see this listing for a "Nice 4” Lapping Plate .875” Thick, Hardened" which got me a bit confused. I've never used a lapping plate but based on my Internet education, it seems that the consensus is that a lapping plate ought to be softer than the material to be lapped. Oxtool, on Youtube, even made a lapping plate out of copper, for example. Is there any situation in which a hardened lapping plate would be the right tool for the job?
 

benmychree

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#2
That would certainly not allow the abrasive medium to imbed in the plate, you'd be abrading the plate as much as the article being lapped. Soft cast iron is the usual material used.
 

neshkoro

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#3
There are plenty on EBay.


Sent from my iPhone using Tapatalk
 

Mitch Alsup

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#4
I've been trawling eBay for an used lapping plate and see this listing for a "Nice 4” Lapping Plate .875” Thick, Hardened" which got me a bit confused. <snip> Oxtool, on Youtube, even made a lapping plate out of copper, for example. Is there any situation in which a hardened lapping plate would be the right tool for the job?
If you watched the Oxtool lapping plate videos, you see that a lapping plate is nothing more than a regular plate that has groves sawed into the surface; and then lapped into flatness.

Is there a need for a hardened lapping plate--probably.
Are the materials you are going to lap in need of a hardened plate--probably not
Will a hardened lapping plate do you any harm--not if it truly is flat--and therein lies the rub.
 

benmychree

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#5
If you watched the Oxtool lapping plate videos, you see that a lapping plate is nothing more than a regular plate that has groves sawed into the surface; and then lapped into flatness.

Is there a need for a hardened lapping plate--probably.
Are the materials you are going to lap in need of a hardened plate--probably not
Will a hardened lapping plate do you any harm--not if it truly is flat--and therein lies the rub.
And if it is truly flat, how long will it stay that way if the abrasive does not imbed; the plate will be worn much to the extent of the part lapped, in proportion to the amount of its surface area that is used in proportion to the area of the part to be lapped.
 

jlanders

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#6
There are many types of lapping plate, but as already stated in the thread, the most important feature for a lapping plate is that it has been lapped flat. The shape of the lapping plate is mirrored on the part you are lapping so if the plate is convex it will generate a concave part and vice-versa.

The material of the plate depends primarily on what abrasive media you choose to use, and what the material of the component is. Also, what do you want the surface to look like after lapping? Are you only concerned about flatness?

For hard materials the best abrasive would be diamond, but to use diamond, unless the parts are very hard, you should use it in combination with a composite lapping plate. The composite material allows the diamond to embed into the lapping plate.

For softer materials, say stainless steel and softer, you can use a cast iron lapping plate with either an aluminium oxide or silicon carbide abrasive. These abrasives don’t cut by embedding, they tend to roll between the lapping plate and the component removing material from both. This type of process will only generate a matt grey finish, you need diamond if you want a reflective surface.

All hand lapping plates will need re-lapping themselves from time to time, but I doubt whether your usage would require this more than once a year.

Hope that helps. I get stuff from Kemet when I need it.
 

Downunder Bob

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#7
I have used both hard and soft lapping plates and find little difference in the result. I understand the logic of using a soft plate, as in cast iron, and the abrasive material will embed in the plate.

I have also used thick glass plates where the abrasive (carborundum in both cases) can not possibly embed and it works just as well.

the difficulty in both cases is to keep the plates flat. In the case of cast iron or other soft material, it's very easy to set the plate up in a lathe and face it off flat every now and then. Whereas with a glass plate or other hard material it requires a special technique to keep them flat or the tedious process of lapping three plates against each other to generate a flat surface.
 

P. Waller

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#8
Explain exactly why you feel that you need a lapping plate?

If for instance you have work that requires flatness that is beyond what a surface grinder will accomplish this is a good way to go about it, sourcing inexpensive tooling on ebay for sub tenth work is rather foolish, go to one of the companies that produce such tooling and buy what you need.
 
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