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[4]

Granite Lapping Plate

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ddickey

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#1
Could you buy one of those cheap B grade small granite plates and convert it to a lapping plate by cutting the groove in it somehow? Maybe with a radial saw with a diamond blade?
 

Hukshawn

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#2
I am currently interested in making some lapping plates due to watching some Tom Lipton videos.
How would you keep the granite lap true?
The 3 lapping plate methods of keeping them true Seema easy enough, but how would you maintain the surface?

As far as cutting the groves, cutting with a wet saw would be necessary. Trying to cut dry, either with a grinder or with a radial arm saw, would cause the blade to chip the edges as it cuts. Cutting try produces a rough cut.
A high quality belt driven wet saw produces a better cut, but good wet saws are expensive and a lot of saws, the blades don't raise that high. My target tilematic could probably do it. But it's a lot of weight on the table.


Interesting idea.... The b grade plates are only $50 around here.
 

Ulma Doctor

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#3
you can simply wet the back of a piece of wet/dry sandpaper of your choice and stick it to the surface plate.
you then can lap until you can't lap no more.
when you are finished lapping, remove the wet/dry sandpaper and put another on for the next operation
 

benmychree

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#4
My take on this subject is that lapping plates and any other type of lap depend on being soft enough to imbed abrasive in their surface; granite does not possess this ability. Cast iron is the material of choice for flat laps. Laps are not a replacement for surface grinding, but rather a finishing touch for finish and geometry (this I add because of a similar thread currently on HSM).
 

benmychree

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#5
you can simply wet the back of a piece of wet/dry sandpaper of your choice and stick it to the surface plate.
you then can lap until you can't lap no more.
when you are finished lapping, remove the wet/dry sandpaper and put another on for the next operation
That is quite true; I have done it many times, but it would not equal the accuracy of a well maintained cast iron lap, charged with abrasive.
 

ddickey

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#6
I am currently interested in making some lapping plates due to watching some Tom Lipton videos.
How would you keep the granite lap true?
The 3 lapping plate methods of keeping them true Seema easy enough, but how would you maintain the surface?

As far as cutting the groves, cutting with a wet saw would be necessary. Trying to cut dry, either with a grinder or with a radial arm saw, would cause the blade to chip the edges as it cuts. Cutting try produces a rough cut.
A high quality belt driven wet saw produces a better cut, but good wet saws are expensive and a lot of saws, the blades don't raise that high. My target tilematic could probably do it. But it's a lot of weight on the table.


Interesting idea.... The b grade plates are only $50 around here.
$30 shipped on eBay.
 

Hukshawn

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#8
Here you go. The best was -
B plate $54 USD. $129 to ship.
The most was AA $125. $850 shipped.
 

Joe in Oz

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#11
you can simply wet the back of a piece of wet/dry sandpaper of your choice and stick it to the surface plate.
you then can lap until you can't lap no more.
when you are finished lapping, remove the wet/dry sandpaper and put another on for the next operation
I think that is called sanding - or at best honing.... the results are flat within microns at best. Lapping is at least one order of magnitude finer. The results are measured in fractions of wavelengths of light....
 

Ulma Doctor

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#12
I think that is called sanding - or at best honing.... the results are flat within microns at best. Lapping is at least one order of magnitude finer. The results are measured in fractions of wavelengths of light....
thank you for trying to correct me but i'll use this definition in my shop, you can use whatever term you want in your shop
Lapping is a machining process in which two surfaces are rubbed together with an abrasive between them, by hand movement or using a machine.
 

Bob Korves

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#14
Granite would make a horrible lapping plate. Lapping plates are supposed to let the grit become embedded in the surface, then when the two plates are rubbed together the lap holds the grit while the work gets abraded. A granite plate would not do that. Both surfaces would wear. I also see some some of us recommending placing sanding paper on the surface plate, grit upwards I assume, for lapping stuff. That is a great way to make your certified flat surface plate no longer flat. Keep all grit and other abrasives well away from a granite surface plate. I use plate glass with sandpaper wet down and stuck to the top of the glass for that sort of lapping.
 

ddickey

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#15
After reading these posts I agree that granite would not be a good choice but my pic I posted shows that some companies do make them for whatever reason.
 

Bob Korves

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#18
Embedded abrasive lapping is by far the most common method, but rolling or 'loose' abrasive lapping does exist. Perhaps granite laps may be intended for this technique?

http://www.engis.com/pdf/Flat-Lappi...ramic-surface-to-precise-dimensions-may11.pdf
Perhaps the disconnect here is in the two separate goals of "lapping." One is for making a surface shiny, the other is for making the surface flat. My use of it is for making things flat. The method in your link does not achieve flatness to a high standard. It does produce shiny surfaces to a high standard, and perhaps economically as well. Machinists can be looking for either or both, and the average person does not know the difference, thinking that a mirror finish must be exceedingly flat and accurate, which is not necessarily the case. Matt finishes can be to a very high flatness standard. "Monkey likes shiny." Science and technology often find flat more useful.
 
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