# An Ultimate Hand Scraped Surface Plate



## jmhoying

I was at a shop today that does machine rebuilding.  I was admiring the awesome surface plate that they use and got a few photos.  The base is from a Minster Machine punch press and the top is 6" x 4' x 8' cast iron, hand scraped to with 4 tenths.





They also had a Bridgeport that they just finished rebuilding to original Bridgeport specs. (other than paint).
How pretty is this table and ways?



Jack
Fort Loramie, Ohio


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## Ulma Doctor

Wow!
both projects took someone a lot of time!
beautiful work
thanks for sharing


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## Franko

Thanks for sharing that, Jack. That is an awesome chunk of iron!

Was 4-tenths a typo, or did you mean 4 ten-thousandths?


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## T Bredehoft

One would assume that 4 tenths meant .0004 inches.


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## Tony Wells

Basic UoM for machinists is one thousandth of an inch, so "a tenth" is assumed to be 0.0001 inch.


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## jmhoying

Franko said:


> Thanks for sharing that, Jack. That is an awesome chunk of iron!
> 
> Was 4-tenths a typo, or did you mean 4 ten-thousandths?



Yes, I meant to say 4 ten-thousandths.
Jack


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## Franko

I thought that might be the case, Jack. I just wanted to make sure. Thanks for the new (for me) info on machinist lingo.


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## EmilioG

Awesome.  That is one solid heavy table.  The one I used at work is the same size but granite.
That is a monumental piece of work in both photos. Thanks.


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## Dubbie

How would you even scrape something that large? What would you use as a reference? Enlighten me please!


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## jmhoying

Dubbie said:


> How would you even scrape something that large? What would you use as a reference? Enlighten me please!


  This company rebuilds large punch presses, so they probably didn't have much problem working on it.  In their shop, they had quite a few large precision straight edges  (4" x 4" x 8', etc.). ,so that is probably what you would use for something like this.


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## cazclocker

Thanks for sharing, jmhoying. I've always been fascinated by the process of scraping. It must be incredibly tedious and exacting. Scraping and checking against your reference plate (or edge) over and over and over again. Until you've achieved a state of nearly perfect flatulence. Sorry, I've been waiting to use that joke for years! Yeah, I know, I shoulda kept waiting...!!!     
...Doug in Arizona


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## intjonmiller

Franko said:


> I thought that might be the case, Jack. I just wanted to make sure. Thanks for the new (for me) info on machinist lingo.


I had that same confusion a couple of times when I first encountered that terminology. By now I'm accustomed to it so I don't notice anymore, but I remember that feeling. It clicked for me when I realized that nobody would mention "accurate to four tenths" (or whatever amount for whatever situation). Home center plywood is often flat within four tenths of an inch. Four tenths (of the usual 0.001" standard unit) is orders of magnitude more impressive. 

I want to see the process of printing the plate in the scraping process. I can't imagine they had another 4'x8' plate, already comparably flat, and they put one on the other with some prussian blue and slid it around to print the high spots. How does one approach such a large piece?? I can think of several possible ways, all of which have potential failings.


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## Dubbie

Yeah that was what I was curious about. I can't really see how you can make something planar with just a straightedge.


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## Dresden

At Mpls Honeywell we had three identical plates about 3x5 feet, we had them at three different locations, you could always check with a straight edge but we would get the other two and scrape them in as a set using the three plate method
if needed. At one location we had a six by eight pink granite about a foot thick
that was used for rebuilding.


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## johnh

I used to work at a university that had a steel optical table, probably a little larger than the one shown (perhaps 10' x 6'), that was scraped flat using optical interferometry techniques (back in the 1960's). Eventually the table became superfluous for the laser optics research team and a few years before my time it ended up in the workshop I managed - as a welding table!
It's an amazing set-up surface for welding but what a waste of a lot of some poor sod's time spent scraping.


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## benmychree

Dubbie said:


> Yeah that was what I was curious about. I can't really see how you can make something planar with just a straightedge.[/QUOTEI think one would use bridge straightedges for overall accuracy and surface plates for the local flatness, or, an autocollimator for accuracy of any part of it.  Incidentally, those of us who have taken Rich King's scraping classes can appreciate the fact that the knee on the Bridgeport should have been finish scraped and NOT flaked as this one has been "decorated"; the flaking allows grit to be pulled into the interface.  If flaking is done, and it should be done, it is properly done on the places that you cannot see, such as the underside of the saddle surfaces and gib, where it holds oil, but does not invite grit to be drawn in.  U&lmadoc can testify as to this issue as he has also taken Rich's class.


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## fmj1911

I'm an old (maybe 52 isn't old, old) machine tool rebuilder/retrofitter that started a year out of high school. I was fortunate to apprentice with an old(er) gentleman (His name was Gene - we called him Gene, Gene the dancing machine) who had been doing it since the 50s. He was a true craftsman and artist. Together we scraped a number of projects so he could teach me the principle of 'because you can'. Once we scrapped the heads and block of an old v-8 so flat that headgaskets were not required. It was typical to scrap some parts like gears and bores not just  to tenths but to microns. You can easily get two parts so flat that adding a drop of oil causes a hydraulic lock that 'glues' them together. You could only get them apart by sliding them apart sideways and shearing the bond.

That was all done by hand scraping. The half-moon flaking seen in the pictures above used to be done by hand but most people do it with a power flaker now because of the time involved - it's just not cost effective to hand scrape machines any more other than to touch up spots or gibs (or flaking for cosmetics and picking up oil). Machines have become more accurate now as well with CNC controls so grinding is also more accurate which also eliminates the need to scrape as much.

It's sad to see that skill going away. More and more folks like myself are aging out of it and true Artists like poor Gene - are long gone and with them special skills, tricks and tips that will never come back. 

I've scraped in so many machines over the years that I've lost count but here where I live - I don't know of another single person that still does it. So while I've scraped in my machines in my garage, kept all of my hand scrapers, power scrapers, camel back straight edges, indicators, masters and even my hidden supply of red lead...  my sons, now grown chose different paths so I imagine when I die, my wife will give them to someone who doesn't know what they're for and will scrap it all. Well, that's progress I guess - sniff, sniff! 

Thanks for those great pics though. It's nice to know the art is still alive in a place or two.


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## intjonmiller

'm currently mourning the loss of tooling for my grandfather's roughly WWII (I think) era tool & cutter/surface/universal grinder because my father or brother didn't recognize them (thinking this machine was just a surface grinder) and tossed them. It pains me to think about it, especially when I wonder what else may have also been thrown out. 

So if you're honestly concerned that your family will toss them feel free to send them my way. I promise I will put them to use learning and preserving those skills.


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## Ulma Doctor

intjonmiller said:


> 'm currently mourning the loss of tooling for my grandfather's roughly WWII (I think) era tool & cutter/surface/universal grinder because my father or brother didn't recognize them (thinking this machine was just a surface grinder) and tossed them. It pains me to think about it, especially when I wonder what else may have also been thrown out.




a cold chill ran down my back at the thought...


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## intjonmiller

So according to my calculator this plate should weigh over 7100 pounds (assuming it's solid, not webbed). I really have trouble imagining this or any comparably sized plates getting flipped and rubbed/printed multiple times in the scraping process. But I don't have any scraping experience so what do I know? Can a localized approach with a smaller reference plate achieve this grade? I would love to understand the technique even though I can't imagine ever using it.


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## jmhoying

Besides the top weighing 3 1/2 tons, I was told that the base is close to 3 tons also.  This company does a lot of work with Minster Machine (one of the leaders of the punch press industry) and was given the base and plate for one of their shared projects.  The top of the base was ground flat, as was the back and top surface of the top.  It was then bolted down to the base with 6 countersunk bolts, that were plugged with cast iron plugs.  At that point, the surface was scraped.  It's impossible to find the plugs. 
 Hanging on the wall in this shop are an amazing array of huge straight edges.  One that I saw was a 3/4" wall box tube of cast iron 4"x4"x8', all scraped in.  They had a cylinder square there in a nice case that you need a crane to lift it! (over 300 lbs)
Jack


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## LEEQ

Dubbie said:


> How would you even scrape something that large? What would you use as a reference? Enlighten me please!


A trip to the library to look at "Foundations of Mechanical Accuracy " Will open your mind. They show some Very large surface plates that they hang from above and move down onto the work. Pretty amazing the lengths the company has gone to in the name of accuracy. A note about the scraping on the top of the knee. As I understand, "to Bridgeport spec's" would include flaking the top of the knee. I think Rich's way of looking at it makes more sense from a wear standpoint, but the machine was said to be taken back to Bridgy Spec. I am curious as to the reasoning behind flaking the top of the big surface plate. To my way of thinking, the deeper flaking wipes out high points as well a low. This would reduce points per inch, increasing the rate of wear. I don't see a benefit to this practice that would justify increasing the frequency of treating the surface of the surface plate. I would love to know other than pretty reasons for the flaking. Any one?


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## Ulma Doctor

oil flaking is used for deeper oil pockets. 
the oil pockets trap oil and use the oil as a bearing surface to reduce wear.
this process works off of the hydraulic principle that a liquid can't be compressed, it becomes a bearing surface.
oil is not likely to be put on this surface plate, nor will it be likely that the base will be incorporated into another machine.
my thought is that the flaking is purely decorative, and it's not serving it's intended purpose of trapping oil.
another purpose ,i suppose, is to look really cool-
that they nailed!


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## jmhoying

I returned to the shop today that has this surface plate and talked to the 73 year old owner of the company. (who is in the photo above)  He described to me part of the process of scraping in that table, and a 3' x 5' table that sits nearby.  He got out an 18" Lufkin machinist level and put it on the surface and said that it was used to do almost all the leveling of the surface.  (with is carbide tipped hand scraper)  I'm not saying that I understand his process completely, but this is what he told me.  The 3' x 5' table was done in a similar manner and at one point, it had to be certified for a government job they did.  It was within 90 millionth over the whole surface.  Even the inspector couldn't believe how it could be so accurate.  That is when they tested the large table and found it to be within 4 tenths.   He said that he learned his techniques over 50 years ago and they prove out.  And all is not lost, as they have a couple younger guys in the shop who are quite capable in the art.
Jack


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## Dubbie

Thanks for following up Jack.
I'm still mystified at how he can get it so accurate without a larger reference surface which they clearly don't have.
If anyone else can explain it to me in simple terms I'd be very grateful.

Regarding the foundations of mechanical accuracy, I can completely understand how you can flatten a surface when you have an even bigger plate hanging from the ceiling. I can also understand how you can make 3 identical  plates.
But making one plate standalone with straightedges only, baffles me.


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## intjonmiller

LEEQ said:


> A trip to the library to look at "Foundations of Mechanical Accuracy " Will open your mind. They show some Very large surface plates that they hang from above and move down onto the work. Pretty amazing the lengths the company has gone to in the name of accuracy. A note about the scraping on the top of the knee. As I understand, "to Bridgeport spec's" would include flaking the top of the knee. I think Rich's way of looking at it makes more sense from a wear standpoint, but the machine was said to be taken back to Bridgy Spec. I am curious as to the reasoning behind flaking the top of the big surface plate. To my way of thinking, the deeper flaking wipes out high points as well a low. This would reduce points per inch, increasing the rate of wear. I don't see a benefit to this practice that would justify increasing the frequency of treating the surface of the surface plate. I would love to know other than pretty reasons for the flaking. Any one?


Thanks! That book looks great. Unfortunately it's only showing up at university libraries, but I'm going to set it up to notify me when one shows up on Amazon or eBay. $150 from the publisher is a bit steep for my "needs".


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## LEEQ

Mine is a used college library copy and I wound up having to give more for that than I ever thought of paying for a used book. Libraries around here do an inter-library loan of books. You sign up for the books you want and they get them to your library. You might try that.    Either way, good luck


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## Inflight

http://www.totallyscrewedmachineshop.com/documents/FoundationsofMechanicalAccuracy.pdf


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## astjp2

Its not as dry of reading as I was expecting...


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## Uglydog

jmhoying said:


> He got out an 18" Lufkin machinist level and put it on the surface and said that it was used to do almost all the leveling of the surface.  It was within 90 millionth over the whole surface.  That is when they tested the large table and found it to be within 4 tenths.  Jack



I've got a meager tired 36x36 cast table I got off CL for $100. Still has flaking over the entire surface. But, its clearly worn in the center. Am I to understand that if I got the plate perfectly level I could use a level to identify the high spots and scrape her in myself?

Daryl
MN


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## 4GSR

That's what I hear, too.  I think I would want to have a scraped straight edge to use along with the master level.  Richard can tell you his way of doing it.  Which I would trust before using a level to scrape to...


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## DaveSohlstrom

Two things that I observed. 1 I do not understand why they flaked the surface plate. Surface plates are normally scraped to 40 points per square inch or better and 70 percent contact. Also 4 tenths on a surface plate is like having the grand canyon on your plate. Plates are normally scraped to less than 1 tenth.
2 Machine ways are normally only flaked on surfaces that point down so they do not collect dirt and grime in the flakes that point up like we are seeing on the bridge port. That dirt and grime that is collected turns into lapping compound and speeds the wear on the machine.


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## Primitive_Pete

So anyone want to hazard a guess how you might scrape plate to 90 millionths without a larger plate?


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## chevydyl

I watched a video where the they were rebuilding a large granite plate, it's on YouTube, I do remember them doing quadrants, and checking with surface gauges until all areas were the same


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## benmychree

Ulma Doctor said:


> oil flaking is used for deeper oil pockets.
> the oil pockets trap oil and use the oil as a bearing surface to reduce wear.
> this process works off of the hydraulic principle that a liquid can't be compressed, it becomes a bearing surface.
> oil is not likely to be put on this surface plate, nor will it be likely that the base will be incorporated into another machine.
> my thought is that the flaking is purely decorative, and it's not serving it's intended purpose of trapping oil.
> another purpose ,i suppose, is to look really cool-
> that they nailed!


Yes, correct about the decorative scraping, it is quite superficial so far as depth is concerned I can see that it is done with the Biax flaker at a low angle; if a higher angle is used, it cuts way deeper and much narrower; I have seen this technique used by rebuilders for oil flaking the undersides of sliding elements with the re scrape of the exposed surfaces lightly flaked for decoration.  I find it hard not to do the decorative stuff on my own work, but I do my best to not get carried away with it.


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## giantswede

Franko said:


> Thanks for sharing that, Jack. That is an awesome chunk of iron!
> 
> Was 4-tenths a typo, or did you mean 4 ten-thousandths?


Well, let's see.   Scraped within 4/10" would be just less than 1/2".   I think that would be kind of rough for a surface plate.


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## middle.road

One would have to assume and imagine that it is 0.0004" over the entire 48"x96" area.
That's pretty good over that area. And who knows the method used in measurement.
For inspection grade you would want 0.0001"FIM 
Toolroom grade would be 0.0002"
Those are tight numbers from the Starrett Spec, there are other specs out there that are looser.


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## stupoty

Dubbie said:


> How would you even scrape something that large? What would you use as a reference? Enlighten me please!



Surely you just pick it up and rub it on the other 8x4 foot surface plate you have blued up and go from their, errrrr yeah i see what ur saying 

Stuart


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## chevydyl

Those are pretty loose specs from starrett, and 4 tenths is equal to 400 millionths, my new Standridge grade A inspection plate is accurate to .000050 or 50 millionths, grade AA lab plates are 25 millionths, or .000025 my plate is said to repeat to 25 millionths, the double a repeats to 17 millionths.
Another thing to note is that you can only expect a part you scrape to the surface plate to be half as accurate as the plates accuracy, in my case my tested parts would probably calibrate to a tenth, depending on how good it am lol.


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## hman

Inflight said:


> http://www.totallyscrewedmachineshop.com/documents/FoundationsofMechanicalAccuracy.pdf


Durn it!  Somebody complained about something, so they removed a whole section's worth of documents, including this one.

... but there it is, in the sticky threads!!!  Many thanks to whoever put it there.


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