Surface plate mounting question

shapeaholic · Sep 18, 2018

I have just bought a 24x36 2 ledge granite plate to replace the plate I currently have.
I know that the plate needs to be sitting on the airy points which are specified in the standard GGG-P-463c

The question I have is, having a plate with ledges, do I use the dimensions of the top of the plate ( 24x36), or the bottom of the plate (24x30), to determine where the airy points are?

OR, am I just overthinking this?

Peter

lucky7 · Sep 18, 2018

Are there no pads at the Airy points on the bottom of the plate? Or marks from where they were?

L7

shapeaholic · Sep 19, 2018

lucky7 said:
Are there no pads at the Airy points on the bottom of the plate? Or marks from where they were?

L7

WELL, I would have checked, but;
A) I haven't received it yet,
B) those potential marks are on the bottom of a 600 lb rock that is currently sitting on the floor.
SO... Not like I could just flip it over and have a look now could I??

I was asking the question so I could get a head start on the stand, so that I could lift it into place when it arrives (lift it once)

Peter

TGTool · Sep 19, 2018

Calculate from the full size of the plate. In theory you could figure for the different weight distribution owing to the absent mass of the ledges but it's not that critical. An inch one way or the other from the theoretically ideal spot is going to be immeasurable by equipment that any of us have in our shops.

You are overthinking it. You're doing the right thing by arranging the correct mounting but as one of my co-workers used to say, "It's not particular to a dog's dick". I don't think I ever figured out exactly how much that was but I did get the general idea.

Paolo_MD · Sep 19, 2018

Not easy to give you an answer, unless you know the dimensions of the ledges and you calculate the distribution of the weight.
In reality, unless you need to do extra accurate work, it doesn't matter too much: being in the neighborhood of the right place is good 'nuf.
It is not necessary to lift it completely and flip it upside-down to see the pads (once you get it): jack up one end and inspect underneath with a flashlight and a mirror.

Paolo

ironsmith89 · Sep 19, 2018

On the plates I've dealt with, it is based off of the bottom of the plate. It really doesn't matter if the plate will get lapped as long as it's on those points all the time. Most likely if it's a used plate there's wear in the middle, if you move the points closer together based off the bottom, the plate may go convex just a hair which could work in your favor. Ultimately it wont matter if you have it calibrated. I run the calibration dept. at my work and I have yet to encounter a surface plate calibration tech who knew what airy points were, they only check to see it's on three points. If it's been sitting on the floor a while it can take several months to relax fully, I have run into this multiple times.

thermite · Sep 28, 2018

shapeaholic said:
I have just bought a 24x36 2 ledge granite plate to replace the plate I currently have.
I know that the plate needs to be sitting on the airy points which are specified in the standard GGG-P-463c

The question I have is, having a plate with ledges, do I use the dimensions of the top of the plate ( 24x36), or the bottom of the plate (24x30), to determine where the airy points are?

OR, am I just overthinking this?

Peter

If you were overthinking it you would have bought a FOUR ledge plate!

Still doesn't come out "even", though, as the ledges are fixed width, not percentage-of-span width.

Which is why I'd work off the bottom shape/dimension.

Search

Largest Manufacturing Technology Community on the Web

Search

Surface plate mounting question

shapeaholic

Stainless

lucky7

Titanium

shapeaholic

Stainless

TGTool

Titanium

Paolo_MD

Stainless

ironsmith89

Aluminum

thermite

Diamond

Similar threads