manhole cover """camelback""" dovetail straight edge - Page 2
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  1. #21
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    Maybe Arthur can clarify, but I didn't think the void opened onto a functional surface. It was only exposed in the interior when he cut away a side rib. If that's true body putty and paint is all he needs if anything at all.

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  3. #22
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    throw it in a big Bonfire and remove it in a day or two.

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    Quote Originally Posted by quasi View Post
    throw it in a big Bonfire and remove it in a day or two.
    be careful, iron at orange-red is pretty bendable. make sure it is well supported while at temperature.



    dee
    ;-D

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    To stress relieve grey cast iron you need to heat it to 1150F. Here is a graph of various metals including cast iron vs temp:

    Temperature and Strength of Metals

    strength-temp.jpg


    You can see that at 1150 cast iron retains 40% of its room temperature strength. I have stress relieved many straight edges and have never found any evidence of deformation due to stress relief. They are often stacked so as to maximize load size in the kiln and are not evenly supported. At 40% strength I would expect one of my 18" straight edges to deflect about .0005" due to its own weight if supported at its exteme ends only..

    Denis

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  7. #25
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    I used to have a crappy foundry that didn't mix and properly pour the molten Iron, Lucky can testify to that...lol..the old foundry would use Allen cap screws to supplement his iron powder recipe and they would not melt and bingo bango when someone machined it they would hit the hardened bolt. That guy would also cast in air pockets...I told the customers to fill them, and we have had the best results using solid core solder and cleaning the hole with a lot of flux. We used a propane torch and didn't get it to got. I now have a better foundry. I contacted Northfield Machinery who make professional wood making machines and I use the foundry they use. It costs more to use them, but well worth it.

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  9. #26
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    So how did the manhole straightedge look after machining? All the talk about cast iron aside, I think it's a pretty damn clever idea.

    metalmagpie

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    Sweet job OP! My buddy gave me an old manhole cover already chopped up on the demo saw, layed out a nice arrangement of squares, straight edges, and raw stock to turn the chunks into, but never got around to actually cutting it all up. He also gave me a gas main cover that I ground and scraped into a really nice indicator stand/comparator. I also turned some of the smaller chunks of the plate into whatever I could, little scrapping flats and a ruler square.

    Super difficult to get through that weathered/work hardened surface/scale, but worked pretty well after that!

    Good luck!
    Corey

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    Now that the OP is probably in the scraping or using the SE phase, how does it handle? This is something I didn’t think about when buying SE castings, but one that I think about often while using them. A stable, reasonable weight, stiff straight edge that feels nice in my hands gives better, more consistent prints. That is why I enjoy using Denis’s 36” and Richard’s HKA 24 so much. And dislike my Challenge straight edges. This is also why I modify my hand scraper handles... and file handles, saw handles etc. to feel natural to me. So that I can do better work with them.

    L7

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    A+++ to the OP for his effort.

    Based on on avg. past posts, it seems about 10% of those who try ever get to make and show a flat straight edge or a flat generated via some method like lappping three together.

    So I think there is 10% probability the OP will finish a straight edge and show the results.
    And I am NOT being negative.
    I commend the OP on his work with a 10 for effort.

    I really hope some further work and info is forthcoming from the OP.

    Good luck OP !!!

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    Now it's only a matter of time until someone tries to turn a manhole cover into a round surface plate. It's already nicely ribbed on the bottom.

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    Quote Originally Posted by TGTool View Post
    Now it's only a matter of time until someone tries to turn a manhole cover into a round surface plate. It's already nicely ribbed on the bottom.
    On a tour of Beijing our guide cautioned us to be extra alert when walking. Especially of an evening in poor lighting. As the "locals" already ARE. To stay alive.

    Seems Beijing was losing over 900 cast-iron manhole covers a year to theft- some so large as to require team lift or a powered hoist to open.

    Not ALL were being scrapped.

    Some had been recovered from "Mongolian BBQ" where they were cooking on them, the upper surface machined flat for use as a griddle.

    Given that other recce's deep into China's hinterlands had included SOE primary metals industry?

    We decided to also avoid "Mongolian BBQ" as if it, too, were a dangerous hole in the ground!!!

    Mystery metallurgy thing.

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  17. #32
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    Quote Originally Posted by TGTool View Post
    Now it's only a matter of time until someone tries to turn a manhole cover into a round surface plate. It's already nicely ribbed on the bottom.
    Always wanted to make a surface plate out of one in my younger years. The only drawback, did not have access to a large VTL or Big lathe to machine it flat. I missed my chance of buying one from Alamo Iron Works back in the 1980's when we were buying volumes of iron castings from them. They were cast with the "Alamo" emblem on them, pretty cool if you ask me. I'm very surprised they haven't start disappearing off the streets of San Antonio for keep sakes!

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    At the risk of derailing this thread I will mention that Seattle has taken it a step further.

    Click this link, for example. Walking Seattle Neighborhoods: Manhole Cover Art

    I am anxious to see how the OP is progressing with his clever use of “junk.”

    Denis

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  20. #34
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    Quote Originally Posted by dgfoster View Post
    At the risk of derailing this thread I will mention that Seattle has taken it a step further.

    Click this link, for example. Walking Seattle Neighborhoods: Manhole Cover Art

    I am anxious to see how the OP is progressing with his clever use of “junk.”

    Denis

    Now that's interesting. Kudos to Seattle for investing in street art. I'm always in favor of things that make the world around a little more varied or interesting or that bump you out of routine. Often traces back to interesting people of which this forum has its share.

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    Quote Originally Posted by 4GSR View Post
    Always wanted to make a surface plate out of one in my younger years. The only drawback, did not have access to a large VTL or Big lathe to machine it flat. I missed my chance of buying one from Alamo Iron Works back in the 1980's when we were buying volumes of iron castings from them. They were cast with the "Alamo" emblem on them, pretty cool if you ask me. I'm very surprised they haven't start disappearing off the streets of San Antonio for keep sakes!
    We have a sewer lid in our scrap pile, I think our of New York. I'm not sure if it was scrap or a souvenir, but I don't envy the guy who tries to finger one out of the street.

    Concerning their machinability and stability, I remember it coming up in a previous thread that some foundries had some different tricks to make them less prone to corrosion, and that usually gave them a very tough skin. It's probably all dependent on who made it, but I think the others above are on track with getting it stress relived and normalized.

    I bought a used 48" dovetail straight edge a while back that was finished and worn, but had almost a 1/8" twist to it. swatkins was tenacious enough to save it via a trip or two through his oven and then his plainer, and now it's flat and waiting for me to scrape it in, but the casting still has some voids in it that I plan to fill with epoxy or lead. One of which seems to have a hardened Phillips head screw in the bottom, so you never know what they throw in the melting pot. The straight edge was a no-name one and it's pattern was included with the sale, so I think it was a one-off. Whoever made it probably went with a cheap foundry and didn't do any stress relief to the casting, so it twisted after it was first plained and scraped.

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  23. #36
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    Quote Originally Posted by Richard King View Post
    I used to have a crappy foundry that didn't mix and properly pour the molten Iron, Lucky can testify to that...lol..the old foundry would use Allen cap screws to supplement his iron powder recipe and they would not melt and bingo bango when someone machined it they would hit the hardened bolt. That guy would also cast in air pockets...I told the customers to fill them, and we have had the best results using solid core solder and cleaning the hole with a lot of flux. We used a propane torch and didn't get it to got. I now have a better foundry. I contacted Northfield Machinery who make professional wood making machines and I use the foundry they use. It costs more to use them, but well worth it.
    These stories of finding screws and bolts etc in castings boggle the mind. Steel immersed in molten iron melts so fast that this seems impossible. Since I expect disbelief of this assertion, a couple hours ago I was melting iron to pour a 36 camelback and a couple 8” straight edges. To demonstrate how rapidly steel melts in iron I stuck a 3/8” diameter steel round rod into the not-quite-pouring-temp iron for 15 seconds. Here is how it looked when I pulled it out—-nearly completely dissolved.

    img_7807.jpg


    Since it went in cold, it took half that time to get close to the temp of the crucible. So, in another 5 to ten seconds it would have been completely gone. So, how can screws etc thrown into the pot survive as identifiable pieces? Like I said, boggles the mind.

    Incidentally, this melting off of a steel rod is a well known in foundry circles. Measuring how much of a 1/2" steel reinforcing rod melts off in a given time when stuck into the molten metal is a quick and dirty way to approximate the crucible temp. It is not a method I use, but it is described in books on the subject.

    Denis
    Last edited by dgfoster; 02-26-2021 at 10:50 PM.

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