What Size Surface Plate

Just a hobbyist. Maybe someday it could turn into something more.
I just think it would be good to have a nice flat reliable reference.
 
I've had a 10"x18" for several years and have always thought it was too small. Earlier this year a friend was downsizing a commercial shop. He had a 36"X 48" and 24" x36" granite plate, and a 24" x36" cast iron plate. He kept both the granite plates and sold me the cast iron (Challenge brand) one for an excellent price. I now have a plate that can handle almost anything I need to measure.
 
Just a hobbyist. Maybe someday it could turn into something more.
I just think it would be good to have a nice flat reliable reference.
True enough, however there are probably better ways to spend money so buy a plate when you begin doing work that requires one.
If you are Hooked On Accuracy© a plate may open a can of worms that you do not expect.
 
I have the Lee Valley 9x12. Its adequate but I plan on getting a 12x18.

Greg
 
Duane, if you have a Woodcrafter store near you, they sell a Grade A 12 X 16 surface plate for under $100.00. It comes with a surface map. I just bought one of these the other day. I also have a 9 X 12 Starrett toolmaker's flat and it is very good but I use it mainly for laying out, not for gauging stuff on.
 
I have an 18 x 24 x 3 that I got on the local Craigslist. Back then, I could move it myself, admittedly, with difficulty. Now, not so much.
 
I'm happy with my little 12" x 18" plate. It's large enough for pretty much everything I do and doesn't take up much room in my shop (clear flat surfaces are at a premium!). Any plate is better than no plate, but I'd be frustrated if the only one I owned was any smaller than what I have now.

I only have one thing to add to everything that's already been said: no matter what size your plate, you should rest it on three points. To go the extra mile, you can put the rests on Bessel points, but that's not nearly as important as ensuring the bottom is resting on a flat plane. Three points guarantees a flat plane.

Even a 4" thick piece of granite can eventually get out of flat if you just rest it directly on, say, a child's desk with a thin 3/4" sway-backed wooden top. But only a complete idiot would do that. :rolleyes: (I finally realized the error of my ways.)

For a small plate, up to say 18" x 24", any three small pieces of metal or wood placed somewhat evenly inbound from the edges will suffice. I've just got three chunks of scrap wood under mine, but have considered using some 1" steel balls with a flat milled on one side. If I ever do go that route, I'll probably put the flat sides against the bottom of the granite and the round bottoms against the table to avoid putting too much point stress on the granite.

For a larger plate you should locate the 4 Bessel points to support the plate. Two of the points should be supported directly. The other two should be supported by a rocker arm of some sort, and then the center of that rocker arm supported. That gives you three points of rigid support to define a plane.

I understand that better plates have the Bessel points already marked on the underside, but you can calculate them yourself pretty easily. Just measure each dimension, length an width. Multiply those dimensions by 0.5594 and that should be the distance between the support points (just measure half those distances from the center lines to locate the points).

A real support stand should also protect the corners of your plate to prevent anyone from knocking it off the proper support points.

Dale Derry has a nice series on the stand he built for his plate.
 
I am just a hobbyist, and a newbie at that. In the Starrett literature I read early in my initial steps into this hobby it was made very clear to get the best that you can afford. I kept my eyes open and picked up a grade B Starrett 36 X 24 black plate for $200 Canadian (so like $130 US lol). I am a hobbyist as I said, but I have not once though to myself, "gosh I wish that this surface was smaller" (No I don't move it). My shop is only 12 x 14 so it does command a fair amount of real estate, but worth it, completely. I started with the Lee Valley plate and it was just fine. Happened across this Starrett and sold the LV for $50CAD. I did pick up a 12 X 18 Starrett for lapping, again on Kijiji (like Craig's list) for $90CAD. It is grade A and had I found it first would have made do, but again my point being that go as big as you can. Just my 2cents.


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My two 12x14 stepped sides have three 2" round 1/4" thick high density felt strategically glued under them
 
Like me and most of my stuff, my surface plate is rather ancient. Its a 12 x 18 cast iron plate with lifting handles on both ends, its easy for even this old coot to move around. Quite adequate for anything that I ever need it for. Picked it up from a precision machine shop that was shutting down to move elsewhere. Just happened to be in the right place at the right time. The surface is as close as I can measure to being perfect. No dings, dents, or major scratches. I think I paid $30 for it back in the '70's. Never really had need to use it until I finally started playing around with doing my own machining. It just occupies a spot on the back of my work bench with my stereo microscope and its accessories sitting on top of its well worn and oiled wood cover. Nary a spot of rust ever. Perfect size for all of my needs. I think that a 9 x 12 would just be too tight to easily use.
 
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