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

graham-xrf

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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!
 

Ulma Doctor

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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!!!
 

mickri

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Dumb newby question here. What do you use one of these granite plates for?
 

NCjeeper

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Free tools and they are delivered too. Cant beat that.
 

graham-xrf

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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!
 
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middle.road

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Now that's a SCORE!
Perfect size also.
I want one! :grin:
 

graham-xrf

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Oh yes - the value of something like this just sort of "happening" is not lost on me. I have my repaired + refurbished vernier height gauge all ready for it, though I still have to sort out that the (several) carbide scriber parts in the box it came with are from some different gauge.

Sadly, the lady of the house did not quite get it. She said the granite stone would go just fine under one of her pot plants in the garden. I had to move fast to divert the black block from a weedy future!

Now if my driveway could just play host to the arrival of a nice 42" camel-back with 45° wedge on one side.. :)
Yeah!
 

middle.road

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Oh wait, not this type of camel-back... :cool 2:
0514182032_Rc.jpg
I keep going out to the end of our driveway, still no 'drop-offs'...
 

Reddinr

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Nice! Maybe chock those wheels! :)
 

graham-xrf

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@middle.road : Hee Hee - I am still trying to figure it. A pillar drill - right?
My freebie granite still awaits a suitable height gauge to match it's quality.

A while back, I picked up a auction deal off eBay for about £27, being two gauges, one in a wooden box. One was Shardlow, and the other a Chesterman, now known as Rabone Chesterman. It came with a cylindrical precision 1.5" calibration gauge.The Shardlow needed repair. Some ham-fisted git had turned the adjuster knob on the back while it was locked in precision worm gear mode with such force it sheared the two 1/16" pins in the keyway.

New territory for me, I took it apart, refurbished it, pushed out the two pins, and made up some new ones. The several carbide scribers that came with it all were clearly quality, and in great condition, but not the right height to set all the way down to the surface.

Then I found --> THIS

Given that these gauges go for around £40 for a single beat-up used, with most around £75 for one a bit less beat up, £100-£150 for various new, and the quality fancy Mitutoyo at about $450, I think I did OK. The eBay 25mm high carbide scriber leaves only 0.4mm to calibrate out. I will set it down on "driveway freebie", and move the verniers to zero it. There looks to be enough calibrate shift to be able to do it. At worst, I can turn 25mm into 25.4mm by raiding my feeler gauge set, and have 0.4mm feeler donate some of itself, re-purposed into a shim spacer.

Slowly, steadily, I am acquiring the basic stuff to do anything precision. The granite block on a stand is a huge boost to that end.
 

graham-xrf

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Nice! Maybe chock those wheels! :)
Two of the red wheels have a lever brake. Without, it would have gathered speed pretty rapidly, even over that old concrete. The trolley is actually leftover as a totally OTT solution to a different cause now no longer. There is a stiffener structure of 2" x 2"s between the 18mm plywoods that does not leave very much ply area between supports, and the wheels are 900kg rated bolted right through into recessed nylocks.

And yes - there has been an occasion when I ended up running after it as it used all that gravity could supply to accelerate, and try for an overshoot off the cutting, and down onto the road!
 
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