A (not so) Little Freebie Turned up in my Driveway

graham-xrf

H-M Supporter - Gold Member
H-M Supporter Gold Member
Joined
May 27, 2016
Messages
3,452
It kind of went like .. a phone call. "Hey Graham, there is this granite block thing. Somebody dropped something hard on it, and it got damaged. They have a replacement now, so nobody wants it anymore. Too heavy to just put in the trash. Do you want it"?
What?? !!
So OK, I have to at least get a look. Can't really see the "damage". How to get it to my place? "Oh - that's OK. We have one of the company van drivers drop it off at your place while on his way South"
Good Lord - delivered as well!
Then.. "Er - it's on this angle iron stand - I take it you mean to keep it on the stand frame".
Pinch me, I'm dreaming! "Well yeah - they go together".

So, in my self-isolation during these stressful times, this happens..

GraniteBlock1.jpg

GraniteBlock2.jpg

GraniteBlock3.jpg

Then, later, my son arrives with the last bit..

GraniteBlockStand.jpg

The strong lad who brought it hefted it out and onto my trolley easily enough, but I can't lift it without help. Even between two, it's awkward, and the three-point pads under are not thick enough to stop the fingers becoming at risk.

The "damage"? I found it. Catch the light reflecting off the top, and there is a ding, about 3mm across. Also, in the surface, a few tiny pits. I am thinking that a steam clean + a few careful tiny dabs of JBWeld, and minor scrape-back, and a check with the good side of my 6"dia x 1" thick optical flat here and there, and I end up with something that is way "good enough" for my needs, even if would be shown the door at the likes of Mitutoyo!

Yay! I can hang out here somewhat rural and play with it until things get better!
 
sweet score!!!
the beautiful part about granite plates is that if they are damaged,
the damage is usually local to one spot on the plate and doesn't disrupt the overall accuracy of the plate.
if chunks are somehow dislodged, the damage will only very rarely create high spots or not at all.

lucky guy!!!
 
Dumb newby question here. What do you use one of these granite plates for?
 
Free tools and they are delivered too. Cant beat that.
 
W. O. W. !
That’s a total gift!


Sent from my iPhone using Tapatalk
 
Dumb newby question here. What do you use one of these granite plates for?
OK Mike - do I get the name right? It was a guess
Having a surface plate is the ultimate reference for anything you need to measure or mark out. Most commonly, you would use a height gauge, or a adjustable scriber base to mark out the centres of where to put holes, and the edges of where to cut material away, on any part you are making. The scribe marks can be incredibly fine, especially if marked in very thin deposit plating or blue ink coating, or even on a thick underline done with a sharpie-type marker.

See one in use HERE -->

The surface of most "B" grade, or engineering toolroom grades is that the surface is guaranteed flat to within 0.0001", or "a ten thousandth" across the plate, (0.00254mm). Many are much closer than that! More expensive higher grade plates are used for calibration of instruments, and inspection of gauges. These can have accuracies ten times tighter, and the very best are tested in terms of how many interference fringes of light wavelengths.

Many are made of cast semi-steel (very stable), because they can be easily checked and maintained. Just like grinding telescope optics, there are techniques of making a perfectly flat reference plate from scratch using just the fact the only surfaces that will slide over each other are two spheres, or two planes. Granite surface plates are made by first grinding, then lapping, and metal surface plates are made by first grinding or milling or shaping, or some combination, then scraping.

Gauge blocks, lapped to optical millionths accuracy can be placed on the plate, so comparison dial gauges can be set up on them, and the size of parts checked by passing them under the gauge.

Anybody who needs to restore, check, or true up slideways of any kind would use the surface for "spotting". That is, putting a (very) thin layer of indicator ink colour on the plate, and placing the part (carefully) on it. Then, move it slightly so as to mark all the high spots to be removed by scraping. The whole procedure is a skill, and one has to carefully stone off any burrs, between spottings. There is a whole section in this forum about machine restoration and way scraping. In this forum, you will find @Richard King 2 , and read to your hearts content about what it takes to scrape a machine surfaces to often better than when it left the factory!

YT Link --> Blue Dye and Height Gauge Use

I know you were asking about what they are used for. I am sure that if you look at the other stuff that comes up on YouTube, you will be overwhelmed with choice.

It is easy to get distracted on YT, and I found ROBRENZ totally absorbing as he does amazing stuff to a very large Starrett granite block with a huge cast iron lap and diamond powder.

ROBRENZ --> DIY SURFACE PLATE LAPPING PART 1
I think this next bit is PART 2..
ROBRENZ --> DIY SURFACE PLATE LAPPING ANSWERS TO PART 1 QUESTIONS

I can tell you that I got completely distracted looking at what he does to properly rebuild a spindle, and what is different about precision ground toolroom stones, and what is a "repeat-o-meter", and generally all that stuff well out of my league!
 
Last edited:
Back
Top