New Surface plate.

New to me anyway. Came with no history. Left behind in warehouse. New tenants worked around it for many years. As they grew, they needed the room and it was so heavy they waited and waited. Finally made arrangements and one of the employees took it. He called my cousin who then called me. He had two already. Its a 3x4x4.5" and weighs like 4 or 500 lbs. I'm not a machinist or metrologist. Just getting into wood working and am on a budget because im poor. Wanted to make as many of the tools as I could including straight edges. In the process of researching, a lot of videos came up about scraping and sanding and surface plates etc. I was fascinated with it all. Especially when I saw a vid of a hooby machinist getting his 3 plates redone. And how precise they can make them. I had bought some plate glass to line with sandpaper and started resurfacing some vintage planes then the plate just fell in my lap. Was going to buy some tools to check it. >003mm gauge and a block stand to slide it around. Quickly learned that isnt good enough. Can take it 50 miles to Standridge in SoCal for a B grade for 140 so decided to save up for that. And am just leaving it in my Jeep till i do. Its too heavy. Lol. Enough history. Oh. It came with a stand and cover. the stand has the 3 mounts that are adjustable. Place for adjuster or casters on leg bottoms. Cover had a name on but the plate had no tags. The name one cover is LMS or something and I called them. They are a distributer for Starrett plates. I looked up starrett and they have plates like mine. Black granite but there stands are different. and no 4.5" thickness. Mine could be really old and they may have offered those back then I dont know. Or maybe they just bought the cover seperately from LMS. Precision stands look more like what mine looks like. So I dont know. Would like to know and maybe standridge can I.D. it for me.

My question is, can I line it with sandpaper to flatten things. Straight edges. Planes and tools and whatever. I was going to protect the area not being used by masking paper over it to keep the sanding debri off it. My thought is since the nmaterial being surfaced is only contacting the paper and not the granit, it wont wear the plate. I am also aware that the debri is abbrasive and simply clean, wiping it off could cause wear. I want a reference table and I want to take care of it. But I need a dead flat surface to sand on. And for straight edges I will use the blue marking stuff on the table and drag them accross it and spin etc. Thinking that will wear it more than paper and sanding.

Thanks in advance.

With great care, you can do what you propose. If using multiple sheets of sandpaper to cover an area larger than 8.5" x 11" you'll need to butt the edges closely and make sure they stay flat, end even then some debris will get between the sheets and cause wear, so frequent lifting and cleaning may be needed to limit damage. Larger sheets of sandpaper would help. Lots of posts on cleaning surface plates here on PM, a little searching will find them.

Be aware that at 4.5", the plate is relatively thin and "flexible" for its size, so once the plate is flattened and calibrated you'll want to support it again exactly as it was during that work. Be sure the three bottom pads are firmly attached and won't be knocked off during transport. If you ever put heavy objects on the plate you may distort it past nominal flatness, calculations for how much can be done using some basic data on the modulus (stiffness) of granite and the distance of the load from the supports.

Wait a minute, you said you're going to use it for woodworking stuff? The plate is likely to be flat enuf for that already, you don't really need Grade B tolerance, which is less than a thousandth. Can you borrow or even buy a precision straight edge just to be sure? A good 3 or 4 foot straight edge is very useful for checking out and setting up woodworking machines, every shop should have one.

Lapping planes and tools flat on abrasive paper on the plate can be done, but it's very hard not get a slightly rounded surface (convex), especially at the edges. And its very easy to slightly deform a long plane body with hand pressure. You'd be better off to learn to scrape them, or at least to scrape a bit hollow first before lapping to avoid rocking.

That being said, I have a dedicated old 18" x 24" cast iron plate that I use for lapping wood or metal parts with sandpaper. I buy surplus sanding belts on ebay and just cut them up for longer length pieces. To hold the abrasives to the plate, I made some 12" and 24' aluminum bars with magnets epoxied in them. Works great, fast on and off, with no tape or adhesives. We're not talking toolroom tolerances here...

PM member Frank Ford, of frets.com, has the converse(?) solution - he drill holes in a cheap import granite plate and epoxied his magnets into the granite, and uses steel bars to hold the paper. That's what inspired my idea.

I'm not trying to discourage anyone from recalibrating an old granite plate, just saying it might not be the best use of your resources.

Sandblaster and a rubber stencil, you can make your own headstone.

digger doug said:

Sandblaster and a rubber stencil, you can make your own headstone.

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Have no idea what you are implying here.

richard newman said:

Wait a minute, you said you're going to use it for woodworking stuff? The plate is likely to be flat enuf for that already, you don't really need Grade B tolerance, which is less than a thousandth. Can you borrow or even buy a precision straight edge just to be sure? A good 3 or 4 foot straight edge is very useful for checking out and setting up woodworking machines, every shop should have one.

Lapping planes and tools flat on abrasive paper on the plate can be done, but it's very hard not get a slightly rounded surface (convex), especially at the edges. And its very easy to slightly deform a long plane body with hand pressure. You'd be better off to learn to scrape them, or at least to scrape a bit hollow first before lapping to avoid rocking.

That being said, I have a dedicated old 18" x 24" cast iron plate that I use for lapping wood or metal parts with sandpaper. I buy surplus sanding belts on ebay and just cut them up for longer length pieces. To hold the abrasives to the plate, I made some 12" and 24' aluminum bars with magnets epoxied in them. Works great, fast on and off, with no tape or adhesives. We're not talking toolroom tolerances here...

PM member Frank Ford, of frets.com, has the converse(?) solution - he drill holes in a cheap import granite plate and epoxied his magnets into the granite, and uses steel bars to hold the paper. That's what inspired my idea.

I'm not trying to discourage anyone from recalibrating an old granite plate, just saying it might not be the best use of your resources.

Click to expand...

I will also be using it for precision checking. Yes, i dont need lab or even tool room precision for wood. I do want it for the tools however. I am anal that way. I've done a lot of research on plates and most videos and threads I find are dated. So i am just seeing if there is anything new or important that I have not heard about. I will be buying rolled 3M to counter the gap issue. I will at first be trying to make a precision straight edge. If successful that will be maintained carefully and used as a known reference and to help quickly make others in various sizes. I also plan on dabbling in metrology stuff just for fun. stumble across good deals on blocks and gauges and what not. Precision is important to me. Even when not needed. I can never seem to get anything as precision as i am striving for. I have unwillingly mastered the art of knowing when to except that this is as good as I can do for now. Will i get any satisfaction from taking it to the next or final level. We shall see. A friend of said the other day, "You know wood moves right?" And i do. But it will be straight and perfect for long enough. Been Dabbling in French Polishing. Would like to have a flat top to polish. Every imperfection stands out after polish. And for the most part, the tools. As i have taken crooked tool and used them, then improved their flatness and squarenes with lapping, the results and efforts are remarkable. A dead flat edge edge with a dead flat tight square mouth in a plane and a flat soul, the .001 and less full width shavings are just fun to make. And for me therapeutic. But getting to flat and square is much faster and enjoyable with properly tuned tools. And the finish from a properly tuned tool on wood is much more reflective and beautiful than any that can had with even the finest of sandpaper. I just strive for reaching as close to perfection as humanly possible. So a master plate as a reference would be a treasure to me.

chuckyz2 said:

Have no idea what you are implying here.

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First posting, harry homeshop topic.

Try the Homeshop forums:
General

And

The Hobby-Machinist Forums

Hey chucky, have you seen this video?

Surface Plate Calibration and Conditioning - YouTube

If youre taking it to standridge it might well be these guys doing the work, try get a quick chat with Mike, seems like a very knowledgeable chap whos happy to explain things out.
Re using sandpaper:- Not something id like to do with a nice plate, and as mentioned before the part will most likely come out crowned. If you really want get say a plane flat then youd be better of scraping it in. If you still wana use sandpaper to lap, start by wiping off any residual abrasive on the back of the paper and stick it down with double sided tape, covering the entire surface of the sandpaper. Silicon Carbide will cut granite, albeit pretty slowly. Aluminium oxide doesnt seem to touch in brief tests ive done, worth keeping in mind.
Good luck and let us know how you go at Standridge.