An Ultimate Hand Scraped Surface Plate

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
 
Dubbie said:
How would you even scrape something that large? What would you use as a reference? Enlighten me please!
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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?
 
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!
 
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
 
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.
 
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?
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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".
 
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
 
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
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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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