manhole cover """camelback""" dovetail straight edge
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    Default manhole cover """camelback""" dovetail straight edge

    First time posting here, doing a lathe rebuild and finding the need for a dovetail straight edge. Funds being that of a college student i have ethically sourced a manhole cover. I possibly have access to a large enough heat treat oven at school to do some stress relieving. Currently it is 29in long, but will probably shorten it to 16in to get closer to the camel back look. Posting this here for advice/comments as well as to share my results working with a not so ideal cast iron. There is a pretty big inclusion at the center of the SE, will probably just mill it out unless any other advice is given.

    thanks,

    -arthur
    cise2.jpgcise3.jpgcise4.jpgcise5.jpgcise1.jpg

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    It looks like a long, dirty, hot, ugly job with an abrasive cutoff, so kudos to you for pulling it off.

    Don't fret the inclusion. Smooth out with the disk grinder, putty it up and paint it. Strength is not going to be an issue in its new incarnation. You might argue that if vehicles have been driving over it without breakage that's more stress than you'll ever put on it. Stress relief is a good idea under the circumstances.

    Failing the oven availability you could use Richard's suggestion to hang it up and beat the crap out of it with a soft hammer.

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    Quote Originally Posted by arthurptj View Post
    First time posting here, doing a lathe rebuild and finding the need for a dovetail straight edge. Funds being that of a college student i have ethically sourced a manhole cover. I possibly have access to a large enough heat treat oven at school to do some stress relieving. Currently it is 29in long, but will probably shorten it to 16in to get closer to the camel back look. Posting this here for advice/comments as well as to share my results working with a not so ideal cast iron. There is a pretty big inclusion at the center of the SE, will probably just mill it out unless any other advice is given.

    thanks,
    Well, you are indeed entitled to recieve an award for resourcefulness and ambition.

    1)You answered one question I was actually thinking about today---are manhole covers grey cast iron or ductile? I think from your first picture you cut most of the way through the casting and then broke it the rest of the way. That is perfectly reasonable and understandable. The key finding is that the crystal pattern of the iron looks to be grey iron. That is good as it may scrape a little easier than if it were ductile. Had it been ductile you would have had a good deal of trouble breaking it.

    2)I would strongly encourage you to thermally stress relieve the section you intend to use as a straight edge. I say this as the only scientifically proven method (there are numerous anecdotal reports about other methods with often conflicting results and even disagreement among observers of the same "demonstration." So beware of other methods unless you can find equally strong scientific evidence---as long as you think science should answer such questions). I think it is safe to say that thermal stress relief unequivocally does just that. All you need to do is find a large electonically controlled pottery kiln. Put it in there, raise the temp maybe 300 degrees per hour until you get to 1150. Hold it there for 90 to 120 min and then let the kiln cool slowly over 8 to 12 hours. That will do the trick as proven by the US Navy in 1948. I'll bet your school owns a large enough kiln. Otherwise, if there is a foundry nearby, you may be able to get them to heat treat the piece for 10 bucks or so when they throw it in with their next grey iron stress relief load.

    https://apps.dtic.mil/sti/pdfs/AD0620556.pdf

    3) As a small-foundry caster of grey iron straight edges I can say the "inclusion" is not an inclusion. It is a vacuum defect caused by the molten metal shrinking as the casting cooled. There was no riser at that point (a very thick segment in the middle of the casting) to feed metal into the casting at that critical point. So, the metal shrinkage was so strong that it simply did the only thing it could and formed a vacuum defect in the center of the casting. This occurence is by no means rare. I have had to learn how to prevent it in my own castings and I know of multi-ton casting used in bridge construction that suffered internal voids for the same reason. As others have said, it probably is not structuraly significant. Do not try to fill it in by welding the casting. This can be done by an expert (true epert cast iron welders are very rare), but it is more likely to be screwed up by someone who "knows how to do it." Attempts at welding are likely to really mess up your cast iron. Don't do it.

    Denis

    Added: That manhole cover is very likely to be full of stress. The goal of the manufacturer was to make a structurally sound crude casting. He did. But likely it was removed from the mold just as soon as it was solid. No problem for a manhole cover, but not at all right for a straight edge. I am very careful to let mine cool to 150 degrees or less in the sand. Then I pull them out and then THERMALLY STRESS RELIEVE every one. Doing so will allow that retained stress to relax and all will be well.
    Last edited by dgfoster; 01-18-2021 at 09:55 AM. Reason: typo

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    Wow! That’s thinking outside the box. I think Denis covered a lot, I would only add scrap yards can be a great source of heat treated, old, stable, low internal stress cast iron that can be cheap and repurposed. Look for mill tables, small planer tables and arms, etc.

    Good luck with your project!

    L7

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    You definitely deserve an A for effort! Curious, how long did it take? How many cutoff wheels?

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    Reminds me of a thread we had several years ago when I think it was Pete in the UK. He made a straight edge out of a window weight. The old fashion weight that hangs from a rope in the wall to counter-balance the window. UK rebuilder as it didn't work so good.

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    Quote Originally Posted by Richard King View Post
    Reminds me of a thread we had several years ago when I think it was Pete in the UK. He made a straight edge out of a window weight. The old fashion weight that hangs from a rope in the wall to counter-balance the window. UK rebuilder as it didn't work so good.

    After all that time as a hanging weight it had taken a set and was only good for spotting vertical surfaces maybe?

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    Quote Originally Posted by TGTool View Post
    It looks like a long, dirty, hot, ugly job with an abrasive cutoff, so kudos to you for pulling it off.

    Don't fret the inclusion. Smooth out with the disk grinder, putty it up and paint it. Strength is not going to be an issue in its new incarnation. You might argue that if vehicles have been driving over it without breakage that's more stress than you'll ever put on it. Stress relief is a good idea under the circumstances.

    Failing the oven availability you could use Richard's suggestion to hang it up and beat the crap out of it with a soft hammer.
    Will probably try out the hammer method in-between machining stages, thinking I'm going to machine out the inclusion as well as other sections along the SE to decrease weight and increase moment of inertia, thus ridgidity

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    Quote Originally Posted by dgfoster View Post
    Well, you are indeed entitled to recieve an award for resourcefulness and ambition.

    1)You answered one question I was actually thinking about today---are manhole covers grey cast iron or ductile? I think from your first picture you cut most of the way through the casting and then broke it the rest of the way. That is perfectly reasonable and understandable. The key finding is that the crystal pattern of the iron looks to be grey iron. That is good as it may scrape a little easier than if it were ductile. Had it been ductile you would have had a good deal of trouble breaking it.

    2)I would strongly encourage you to thermally stress relieve the section you intend to use as a straight edge. I say this as the only scientifically proven method (there are numerous anecdotal reports about other methods with often conflicting results and even disagreement among observers of the same "demonstration." So beware of other methods unless you can find equally strong scientific evidence---as long as you think science should answer such questions). I think it is safe to say that thermal stress relief unequivocally does just that. All you need to do is find a large electonically controlled pottery kiln. Put it in there, raise the temp maybe 300 degrees per hour until you get to 1150. Hold it there for 90 to 120 min and then let the kiln cool slowly over 8 to 12 hours. That will do the trick as proven by the US Navy in 1948. I'll bet your school owns a large enough kiln. Otherwise, if there is a foundry nearby, you may be able to get them to heat treat the piece for 10 bucks or so when they throw it in with their next grey iron stress relief load.

    https://apps.dtic.mil/sti/pdfs/AD0620556.pdf

    3) As a small-foundry caster of grey iron straight edges I can say the "inclusion" is not an inclusion. It is a vacuum defect caused by the molten metal shrinking as the casting cooled. There was no riser at that point (a very thick segment in the middle of the casting) to feed metal into the casting at that critical point. So, the metal shrinkage was so strong that it simply did the only thing it could and formed a vacuum defect in the center of the casting. This occurence is by no means rare. I have had to learn how to prevent it in my own castings and I know of multi-ton casting used in bridge construction that suffered internal voids for the same reason. As others have said, it probably is not structuraly significant. Do not try to fill it in by welding the casting. This can be done by an expert (true epert cast iron welders are very rare), but it is more likely to be screwed up by someone who "knows how to do it." Attempts at welding are likely to really mess up your cast iron. Don't do it.

    Denis

    Added: That manhole cover is very likely to be full of stress. The goal of the manufacturer was to make a structurally sound crude casting. He did. But likely it was removed from the mold just as soon as it was solid. No problem for a manhole cover, but not at all right for a straight edge. I am very careful to let mine cool to 150 degrees or less in the sand. Then I pull them out and then THERMALLY STRESS RELIEVE every one. Doing so will allow that retained stress to relax and all will be well.
    Thanks for your detailed reply!
    From my research prior to breaking it apart it seems there is a mix of grey and ductile manhole covers. This particular one was from some abandoned WWII installations where I live.

    The kiln situation will soon be worked out fairly confident Ill be allowed to use one of the heat treat ovens at school 'RIT'.

    Vacuum makes sense, to mitigate this would you put a riser above and below? Also was originally thinking to braze the hole but the difference in expansion rates would probably be annoying it would only be accurate at the temp I scraped it at I believe.

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    Quote Originally Posted by lucky7 View Post
    Wow! That’s thinking outside the box. I think Denis covered a lot, I would only add scrap yards can be a great source of heat treated, old, stable, low internal stress cast iron that can be cheap and repurposed. Look for mill tables, small planer tables and arms, etc.

    Good luck with your project!

    L7
    That's a good tip, I'll keep that in mind if I ever need a longer one

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    Quote Originally Posted by dalmatiangirl61 View Post
    You definitely deserve an A for effort! Curious, how long did it take? How many cutoff wheels?
    Actually cuts pretty well with the minigrinder, had to toss a few wheels due to fractures but if I had been more careful I could have done it with just one. If anyone else is going to do it definitely do it outside and I'd advise with respirator lest you end up with black boogers as did I.

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    Quote Originally Posted by Richard King View Post
    Reminds me of a thread we had several years ago when I think it was Pete in the UK. He made a straight edge out of a window weight. The old fashion weight that hangs from a rope in the wall to counter-balance the window. UK rebuilder as it didn't work so good.
    I have a few of those weights that I use as ...... weights. ;-)

    Like manhole covers they are manufactured to the lowest casting standard possible. No criticism for that as their function is so basic and time wasted making them better than needed for the job is time wasted, indeed. Mine are composed of "white iron" which is amazingly hard. Using a sharp carbide spotting drill, slow speed, and very high pressure it was very difficult to drill a 1/4" hole even a quarter of an inch into them.

    I figure they became white iron because they were likely popped out of the sand just as soon as they congealed enough not to deform. They may even have been sprayed with water or dumped into water. But, that rapid cooling converted them to extremely hard "white iron." (This chilling principle is followed when machine ways are flame hardened like my EE.) You can actually see the difference in grain structure on white iron because the fractured surface is very finely grained and is very bright and sparkly where grey iron is dull grey with grain structure size inversely proportional to cooling rate.

    However, if the weights are annealed by putting them in a kiln and raising their to temperature to 1750F. That is only a few hundred degrees less than melting temp. Then hold them at 1750 for an hour or two and slowly let them down over 8 to 12 hours and they should convert to soft grey iron. I've done this and it works. Trace metals in the original weight can affect how well they may revert to soft iron, but it should work nearly all the time.

    Denis

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    Quote Originally Posted by Richard King View Post
    Reminds me of a thread we had several years ago when I think it was Pete in the UK. He made a straight edge out of a window weight. The old fashion weight that hangs from a rope in the wall to counter-balance the window. UK rebuilder as it didn't work so good.
    Do you know if he properly heat treated it? I had a box of window weights to use as munition for a trebuchet built many years ago, every one of them was easily broken into smaller pieces except one. Maybe if he used this blessed stronger window weight he would have been more successful

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    My earlier contribution was obviously facetious.

    To come to the point it would have been more useful advice to point to the actual thread of the prior problem OR to repeat what the problem was for comparison to your current situation. There is sometimes very good, specific advise for newcomers but to say someone else tried something with a part different than yours but possibly similar in some respect and had some non specified difficulty and leave it at that is just about as much use as the proverbial tits on a boar or testicles on the pope.

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    Quote Originally Posted by arthurptj View Post

    Vacuum makes sense, to mitigate this would you put a riser above and below? Also was originally thinking to braze the hole but the difference in expansion rates would probably be annoying it would only be accurate at the temp I scraped it at I believe.
    You are very fortunate to have a chance to be a student at RIT!

    A riser above the center would very likely have solved the problem If I were making the riser, I would try one about 2" in diameter and 3 inches high located above the rest of the mold. Risers placed below a mold should in theory work, but in practice seem to have not worked well for me and also not well for folks I have discussed them with. Having gravity on your side seems to be a plus. The lift you might expect to get from air pressure on an under-mounted riser might just be reduced or eliminated by gas production in the mold at time of pouring.

    Denis
    Last edited by dgfoster; 01-19-2021 at 08:52 PM.

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    Quote Originally Posted by arthurptj View Post
    First time posting here, doing a lathe rebuild and finding the need for a dovetail straight edge. Funds being that of a college student i have ethically sourced a manhole cover. I possibly have access to a large enough heat treat oven at school to do some stress relieving. Currently it is 29in long, but will probably shorten it to 16in to get closer to the camel back look. Posting this here for advice/comments as well as to share my results working with a not so ideal cast iron. There is a pretty big inclusion at the center of the SE, will probably just mill it out unless any other advice is given.

    thanks,

    -arthur
    cise2.jpgcise3.jpgcise4.jpgcise5.jpgcise1.jpg
    man

    I thought making one out of a lathe bed was nutz...you win.


    dee
    ;-D

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    Quote Originally Posted by Richard King View Post
    Reminds me of a thread we had several years ago when I think it was Pete in the UK. He made a straight edge out of a window weight. The old fashion weight that hangs from a rope in the wall to counter-balance the window. UK rebuilder as it didn't work so good.
    Richard is right - having no dovetail reference of any kind I thought it would be a good idea to mill a round cast iron sash weight into a wdege/triangle shape then scrape it. What I managed to do was mill a triangle-shaped cast iron banana.

    I can commend the OP for his inventiveness and hope that he gains something more useful than just experience from it, but steele yourself for the reality that even with stress-relief you might not end up with a satisfactory workpiece. Good luck either way, you deserve a 10 for effort.

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    Quote Originally Posted by arthurptj View Post
    Thanks for your detailed reply!
    From my research prior to breaking it apart it seems there is a mix of grey and ductile manhole covers. This particular one was from some abandoned WWII installations where I live.

    The kiln situation will soon be worked out fairly confident Ill be allowed to use one of the heat treat ovens at school 'RIT'.

    Vacuum makes sense, to mitigate this would you put a riser above and below? Also was originally thinking to braze the hole but the difference in expansion rates would probably be annoying it would only be accurate at the temp I scraped it at I believe.
    Please do not braze it. You will very likely create an area of white or at least very hard iron. Fill it in with Bondo or JB weld.

    Denis

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    Quote Originally Posted by dgfoster View Post
    Please do not braze it. You will very likely create an area of white or at least very hard iron. Fill it in with Bondo or JB weld.

    Denis

    That reminded me of something I encountered. I'd gotten an import angle plate with the idea that it could be scraped into accuracy for exercise and experience. There was one small area on one face about half an inch in diameter that was softer than the remainder of the surface. I explored and scraped that spot just a little lower so it wouldn't otherwise disrupt the process. It looks like it was filled in with soft solder. You can usually spot silver braze repairs by the change in color, but this was indistinguishable from the surrounding cast iron. Having sat in the back of the shop through seasonal changes and warm wet air, I found it later to have a rust patina everywhere except that small spot which was some confirmation.

    It's not a surprise that the cheap manufacturer would cheat on that as well, if you can even call it a cheat. They had a surface defect, filled it, hit it once more on the belt sander and it was good. Good enough for them anyway.

    It hadn't occurred to me to use soft solder since strength is usually a prime factor on repairs, but if it's purely a cosmetic problem it wouldn't get into a problematic heat range. And lead was used for auto body repairs before epoxies and polyesters became much more convenient.

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    Quote Originally Posted by dgfoster View Post
    Please do not braze it. You will very likely create an area of white or at least very hard iron. Fill it in with Bondo or JB weld.

    Denis
    Quote Originally Posted by TGTool View Post
    That reminded me of something I encountered. I'd gotten an import angle plate with the idea that it could be scraped into accuracy for exercise and experience. There was one small area on one face about half an inch in diameter that was softer than the remainder of the surface. I explored and scraped that spot just a little lower so it wouldn't otherwise disrupt the process. It looks like it was filled in with soft solder. You can usually spot silver braze repairs by the change in color, but this was indistinguishable from the surrounding cast iron. Having sat in the back of the shop through seasonal changes and warm wet air, I found it later to have a rust patina everywhere except that small spot which was some confirmation.

    It's not a surprise that the cheap manufacturer would cheat on that as well, if you can even call it a cheat. They had a surface defect, filled it, hit it once more on the belt sander and it was good. Good enough for them anyway.

    It hadn't occurred to me to use soft solder since strength is usually a prime factor on repairs, but if it's purely a cosmetic problem it wouldn't get into a problematic heat range. And lead was used for auto body repairs before epoxies and polyesters became much more convenient.
    If you are going to heat treat it, you should soak it at 1020F to 1200F one hour/inch thickness. when you pull it out you could just braze it it will be hot enough to melt the brazing rod, you may want to slowly cool it, as slow as possible can be done. Otherwise, just use epoxy and leave it lower than the rest of the surface
    Last edited by dcsipo; 01-20-2021 at 10:02 AM.


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