Surface plate

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Black_Moons
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Surface plate

Post by Black_Moons »

Hi I just bought a really cheap surface plate and was wondering, should the top be polished? the sides are.. the top is unpolished however, has that sorta dusty 'dry' look, though feels rather smooth.. definately goes darker like the sides when wet..
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easymike29
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Post by easymike29 »

A freshly lapped surface plate has a what I call a nap. It feels a little rough for awhile but soon disappears with use. We always saved our freshly ground straight edges so that we could lap the knife edge with this nap. Actually the knife edge was a .005 radius. Lapping the radius produced a straighter edge than grinding alone. Just a few strokes is all that is necessary.
Gene
Jose Rivera
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Post by Jose Rivera »

Surface plates are not polished. They have a very smooth sating finish.

Also it should show the grade and tolerance.

I was given a piece of granite (I still have) that was polished.

Doing a flatness check this piece of granite was not flat at all with .018 error.

I assume that what you have is a real surface table.
I ended up buying small one 18" X 12". More than flat enough for what I use it for.
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Black_Moons
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Post by Black_Moons »

ahh cool thats good to know. whats all that cool stuff on your surface plate? I recongise the height gauge but the rest is..
Inspector
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Post by Inspector »

The surface is honed and even coordinate machines are the same just a bit finer. By any chance did you get it from Busy Bee for about $75 or so and about 12 x 18 x 3 or 4 inches of black granite? If so they are tool room grade and good for .0002 per foot if memory serves.

Pete
kapullen
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Post by kapullen »

Jose Rivera wrote:
I was given a piece of granite (I still have) that was polished.

Doing a flatness check this piece of granite was not flat at all with .018 error.

use it for.
Jose,

I would say that .018 would be flat enough for storing all that stuff on.
:lol:

Kap
Fadal Turn, Fadal Vmc 15, Prototrak 16 x 30 Cnc Lathe, Pratt and Whitney 16 x 54 lathe, Pratt and Whitney Vertical Shaper, G & E 16" Shaper, B & O Electric turret lathe, 36" Doall band saw,
Enco B.P. Clone, Bridgeport CNC Mill, Delta 12" Surface Grinder.
Jose Rivera
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Post by Jose Rivera »

Yeah, it probably was a tombstone at one time.
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Black_Moons
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Post by Black_Moons »

lol yea I got a busybee grade B special, like $45 on sale.
good to know its 'proper'. I did'nt feel like spending $100 on a slab of rock im not even sure what to do with yet. (looks like it might make a good drafting table lol)
Jose Rivera
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Post by Jose Rivera »

:D :D

Surface tables are mostly used for inspection.
On shop use they're excellent for lay-outs using Dikem and then scribing lines at precise distances.

During all the years that I worked as a machinist none of the shops had one.
I got introduced as soon as I started working as a final machined parts inspector.
I found out how useful one can be but I don't always use it.
There are things that cannot be done unless you have one, but still falls into the double checking level.
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Black_Moons
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Post by Black_Moons »

I realise the height guage deal, that seems very cool.. can scribe on the side of something at precise height (well, distance from any flat edge!) reguardless of contour.

I can also understand useing hispot on the plate and laying something on it to then find out where the high spots are and grind them down flat
(you can get all that hispot dye off afterwards right?.. seems like there might be tiny pockets in my plate..)

And then theres the TDI on the height guage for messureing multiple points from the flat surface to some other height and getting a +- error.

Then theres that weird stand with the scribe looking arm stand... no scale or anything on it... not exactly sure how useful that is unless the height gage gets in the way sometimes?

Any other neat tricks I can do with a surface plate?

I assume I should get one of those double collumn height gages and not the rectangle looking ones.. (for rigidity..). Not sure if I should get a digital one or just one of the dial ones with the counters on it..
Jose Rivera
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Post by Jose Rivera »

I've seeing them being used (non kosher) for sticking sand paper and used to hone woodworking tools.

Door stop is another :lol:
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BadDog
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Post by BadDog »

Black_Moons wrote:Any other neat tricks I can do with a surface plate?
Off the top of my head:

Quantify non-flat condition using shim/feeler.
Quantify squareness using surface gage (or various other).
Quantify parallel/taper condition.
Sandpaper held with water for low precision or finish applications.
Layout as stated.
Transfer/Spotting for as stated (though usually for scraping).
Comparative measurement using gage blocks or the like.
Transfer using surface gage and gage blocks to adjustable parallel or planer gage.
And so on...

I use a smallish dial height gage, or larger vernier height gage, one of several surface gages, planer gages, gage blocks, adjustable parallels, etc. I really see no need for a double beam or digital height gage...

And generally you don't use a DTI for quantitative measurements. Not bad for close to zero as long as the arm is set very near perpendicular to measurement, but beyond that cosine error starts to show more and more. Of course that depends on your accuracy needs. Also, if the arm is changed for longer/shorter, then values are off anyway. Generally a DI is much preferred for quantification, or using a DTI for comparison against a standard of same dimension (to avoid the error).
Russ
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