Granite plate refurbishing.

[Shox Dr]

The reason he was getting spurious readings is because he was using electronic levels to measure variations. My best level will move if I walk around the surface plate because my workshop floor is quite thin. All he had to do was stand in one spot for the whole length of the test and his results would be unaffected.

My autocollimator doesn't suffer that problem because it sits on the plate itself. If the plate (or floor) tilts, so does the measuring instrument.

With that in mind you would be able to see what happens when the supports are moved, if at all?

 

[Pete.]

With that in mind you would be able to see what happens when the supports are moved, if at all?

You mean could I measure any difference in the plate between supported on it's feet and supported for instance on it's edges?

Yes, for sure.

 

[Agroshield]

Crazy stuff.

Indeed. It is instructive to ponder on the implications of questions 5 and 7 here:

Precision Granite FAQs

www.starrett.com

 

[mtt.tr]

im sure somewhere from one of the granite manufactures they said that smaller plates are not big enough to deflect an amount that is significant so the 3 point only apply to larger plates

i think it was mitutoyo but im probably wrong


my small cast iron plate had 3 points but thats relatively bendy

 

[Pete.]

Indeed. It is instructive to ponder on the implications of questions 5 and 7 here:

Precision Granite FAQs

www.starrett.com

Marketing buswah. A spritz of brake cleaner won't draw nearly enough specific energy out of the plate to 'distort' a plate surface by any amount measurable by mere mortals. Perhaps they can see it on their laser interferometer or whatever device they use but that guy cleaning it before rolling out more blue - he's never going to. I actually tested this with my repeat-o-meter. I set the gauge down on the plate and sprayed a buch of brake cleaner on it. No visible effect. I'm not saying no effect, but you'll need some serious metrology to measure it.

Better never touch that plate with your hand

 

[Pete.]

im sure somewhere from one of the granite manufactures they said that smaller plates are not big enough to deflect an amount that is significant so the 3 point only apply to larger plates

i think it was mitutoyo but im probably wrong

I just made a video be along with it shortly.

 

[mtt.tr]

Marketing buswah. A spritz of brake cleaner won't draw nearly enough specific energy out of the plate to 'distort' a plate surface by any amount measurable by mere mortals. Perhaps they can see it on their laser interferometer or whatever device they use but that guy cleaning it before rolling out more blue - he's never going to. I actually tested this with my repeat-o-meter. I set the gauge down on the plate and sprayed a buch of brake cleaner on it. No visible effect. I'm not saying no effect, but you'll need some serious metrology to measure it.

Better never touch that plate with your hand

i took that to be measure to fractions that are well in excess of the home workshop,

 

[Pete.]

i took that to be measure to fractions that are well in excess of the home workshop,

Like I said marketing buswah. Being true and being relevant are totally different things.

 

[Shox Dr]

You mean could I measure any difference in the plate between supported on it's feet and supported for instance on it's edges?

Yes, for sure.

So what could that difference be. How about bedding on sand, or lead shot

 

[Pete.]

So what could that difference be. How about bedding on sand, or lead shot

I never said there would be any mate I just said I could measure it if there was.

Here you go. I put a couple of bits of steel under one edge not quite touching then lifted the other end with a lever - 3 lifts and no movement on the 1 micron dial. Then I put a 10kg weight in the middle of the plate and did a couple more lifts - no movement again.

Dropbox

www.dropbox.com

The autocollimator could measure with more sensitivity but TBH if my 1um gauge isn't even twitching and a AA plate allows for 3um what's the point?

 

[mtt.tr]

I never said there would be any mate I just said I could measure it if there was.

Here you go. I put a couple of bits of steel under one edge not quite touching then lifted the other end with a lever - 3 lifts and no movement on the 1 micron dial. Then I put a 10kg weight in the middle of the plate and did a couple more lifts - no movement again.

Dropbox

www.dropbox.com

The autocollimator could measure with more sensitivity but TBH if my 1um gauge isn't even twitching and a AA plate allows for 3um what's the point?

be interesting to know at what size plate it becomes significant, though that would be doable with some math

 

[pressbrake1]

YouTube has made people aware of degrees of measurement that can’t be measured outside of a lab but causes them great concern
As I said to Pete the other day you now have people wanting grade aa plates for marking out with a scribing gauge or height gauge

I use a old grade b for all that kind of stuff. As they say grade b for working on , A for measuring off!

 

[mtt.tr]

YouTube has made people aware of degrees of measurement that can’t be measured outside of a lab but causes them great concern
As I said to Pete the other day you now have people wanting grade aa plates for marking out with a scribing gauge or height gauge

I use a old grade b for all that kind of stuff. As they say grade b for working on , A for measuring off!

Brilliant isnt it.

Really knocked the price of grades b down, possibly the only benefit of YouTube

Im after a crown plate just as a momento

 

[Kayos]

YouTube has made people aware of degrees of measurement that can’t be measured outside of a lab but causes them great concern
As I said to Pete the other day you now have people wanting grade aa plates for marking out with a scribing gauge or height gauge

I use a old grade b for all that kind of stuff. As they say grade b for working on , A for measuring off!

Its the same with radio stuff, seems a lot of people spend more time testing and analysing than actually using the gear

 

[Pete.]

The whole purpose of this work I'm doing is BECAUSE I use it

 

[Shox Dr]

I never said there would be any mate I just said I could measure it if there was.

Here you go. I put a couple of bits of steel under one edge not quite touching then lifted the other end with a lever - 3 lifts and no movement on the 1 micron dial. Then I put a 10kg weight in the middle of the plate and did a couple more lifts - no movement again.

Dropbox

www.dropbox.com

The autocollimator could measure with more sensitivity but TBH if my 1um gauge isn't even twitching and a AA plate allows for 3um what's the point?

Thanks, interesting results

 

[Screwdriver]

For my first degree I build a laser interferometer from scratch and produced sandwich holograms which would map deformations easily within 1/2 wavelength of light. About 10 millionths of an inch depending on the laser.

You take a hologram of an object, develop the plate, then take another hologram with the original developed hologram "sandwiched" to it. Any deformation in the object being measured shows up as light and dark bands like a contour map of the deflection. The practical part is super easy, lots of mirrors, big solid table to isolate vibrations, a neat trick to replace the holographic plates (perfectly). The theory and the maths are pretty horrible.

Cheap as chips tho.

 

[Screwdriver]

It is still a thing too, remembering when I did it, lasers were pretty new and still only being used to cut up James Bond.

From: https://www.semanticscholar.org/pap...mson/23e2b034835a951c1bb46601e456d1631f9d269f

What this image shows (I think) is how you can displace the two holograms relative to each other, just by rotating the sandwich in the beam. The rotation causes an offset due to the thickness of the glass (a precise, known amount) and a relatively large crude angle which is easily measured accurately, causes a series of fringes to be generated. Each fringe is 1/2 the wavelength of light. So you can measure angles, rigid body motion, complex distortion etc. with a relatively easy to measure process. Simply count the number of fringes to take your required measurement.

 

[Brad93]

Unless you’re in a temperature controlled clean room, a AA plate is going to be more than accurate enough for anything us mere mortals are likely to do.

 

[brightspark]

dunno why some folk need all this critical accuracy not as if there into aerospace territory . can anyone on here show us piccys of what they are producing that need it