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Tools and Equipment

lapping plate?

Discussion of tools and equipment for gunsmithing and refinishing of Mosin Nagant Rifles

lapping plate?

Postby Marauder 1 » Fri Mar 13, 2015 8:31 pm

I went by Industrial Metal Supply today and picked up some material, one of the items I bought was a 12 x 12 1/4 steel plate. I want to make use of it for lapping parts etc. I'm not sure if it is completely flat however. Anyone have an idea on how to check and if not make it flat?

Thanks
Mark
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Re: lapping plate?

Postby jaysny87 » Fri Mar 13, 2015 10:45 pm

It would depend on just how flat you would want it to be. At the shop one method we use to check for flatness is to lay the part to be inspected down onto a precision ground granite slab and run a dial indicator over the surface of the part. But if you have granite counter tops or a flat counter top to rest the metal on you can use a flashlight resting on the surface of the counter behind the part and try to see if any light passes underneath the metal indicating a bend or surface anomaly. Usually if you need something to be 100 percent flat precision grinding is the ticket but you can DIY using sandpaper with a flat backer and get it pretty close if you work the paper from all direcrions. If you have access to a milling machine a skim cut on both sides of the plate would square it up pretty well but the sandpaper and backer should be fine.
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Re: lapping plate?

Postby Marauder 1 » Sat Mar 14, 2015 12:07 am

Thanks, could I use a square to make sure I have a level surface? I was also thinking of painting the surface with that part die I seem to remember using years ago to make sure a surface was even. Painting the entire surface and then sanding with the flat backer might show me the high and low spots. I don't have access to a large mill any more. I think your idea will get me pretty close.

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Re: lapping plate?

Postby jaysny87 » Sat Mar 14, 2015 9:15 am

Yea a level would work. And yes to the dye as well we usually use dykem because regular paint will clog up sandpaper.
http://www.amazon.com/Dykem-80300-Steel ... B0018ACR6G
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Re: lapping plate?

Postby Shepard » Tue Mar 17, 2015 2:10 am

Why steel - the standard poor mans lap is a piece of glass on the coffee table and I've done Harley heads - aluminum and cast iron. 12x12x1/4" or 1/2" is better with a piece of 220 wet sand paper wet and set on the glass.
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