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  • #31
    Grim, I realize you are in Scotland, but there must still be some Screw Machine operations or vendors around.
    They have beautiful blank steel or cast iron rounds up to 10 inches in size that can be quickly cut into gears without any prepping or refacing. The material is superb
    see this example
    https://www.sommatool.com/catalog/ac...cam.blanks.asp

    Rich
    Green Bay, WI

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    • #32
      Originally posted by grim_d View Post
      10 inch diameter pieces of any material aren't exactly thick on the ground around here. Thus my problem!
      Don't you have mail order suppliers somewhere in the UK or Europe?

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      • #33
        Originally posted by vpt View Post
        I recognize that chart! What happened to the number 3 slot (.0063)?

        Hi Andy
        The hole appears to be obscured by a stray shadow, a tribute to my poor photography skills.
        Location: Long Island, N.Y.

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        • #34
          Originally posted by grim_d View Post
          ...
          My biggest concern is how brittle the cast aluminium is. I thought initially I had overheated it and by not degassing or fluxing that was affecting things but I have made some ingots from known 7075 and another batch from random scrap and both are the same. I am using soda for degassing and lite salt for fluxing.
          ...
          It's been a while since I've done any casting, so what little I did know is a bit faded, so I won't comment on fluxing n' stuff. I will say that I never had the problem that you're describing and it wasn't because of my expertise. I did always use scrap & didn't know the alloy, but it was always something that had been cast. E.g., lawnmower engine blocks, pistons, "alloy" wheels.

          There are very knowledgeable hobby casters and I'm sure that you can get the help that you need. After all, this is about the simplest possible casting.

          Bob

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          • #35
            Originally posted by Rich Carlstedt View Post
            Grim, I realize you are in Scotland, but there must still be some Screw Machine operations or vendors around.
            They have beautiful blank steel or cast iron rounds up to 10 inches in size that can be quickly cut into gears without any prepping or refacing. The material is superb
            see this example
            https://www.sommatool.com/catalog/ac...cam.blanks.asp

            Rich
            I certainly don't know of any. Nobody wants to sell to the public!

            Originally posted by lakeside53 View Post
            Don't you have mail order suppliers somewhere in the UK or Europe?
            Sure, if I want to pay more in shipping and tax than the material costs, which I won't do.

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            • #36
              May I recommend that you get an alloy specifically for casting? 7075 is known to be "not weldable" due to micro fractures. I suspect that's what is happening when you are melting and casting it.

              Info on castable alloys.

              https://www.dynacast.com/aluminum-die-casting

              https://en.wikipedia.org/wiki/Alumin...oy#Cast_alloys

              Dan
              Last edited by danlb; 10-28-2017, 01:01 AM.
              At the end of the project, there is a profound difference between spare parts and left over parts.

              Location: SF East Bay.

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              • #37
                Originally posted by danlb View Post
                May I recommend that you get an alloy specifically for casting? 7075 is known to be "not weldable" due to micro fractures. I suspect that's what is happening when you are melting and casting it.

                Info on castable alloys.

                https://www.dynacast.com/aluminum-die-casting

                https://en.wikipedia.org/wiki/Alumin...oy#Cast_alloys

                Dan
                Possibly, I do know 7075 isnt ideal for casting so i have tried using other types such as 6000 series with the same problem, grain refinement seems to be what I need to investigate.

                I suspect that by the time I obtain enough proprietary aluminium for casting I would be just as well buying a peice of plate!

                I have read that adding boron to cast aluminium can help tighten the grain structure...foundry's use bars of titanium-boron aluminium for this, but obtaining a small peice for hobby use is seemingly impossible.
                Last edited by grim_d; 10-28-2017, 01:26 AM.

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                • #38
                  Please note the addition to my post. 7075 is NOT weldable due to micro fractures. Castable alloys tend to have high levels of Si as well as other traces.
                  At the end of the project, there is a profound difference between spare parts and left over parts.

                  Location: SF East Bay.

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                  • #39
                    Your lack of local suppliers sounds like a real challenge. Perhaps you could look for a water jet or laser cutting facility that can cut your blanks from sheet/plate. Let them worry about finding the stock to cut them from. As for alloy, I would look for a leaded one, at least for my first attempts. And they may even have some drops laying around that they can cut them from.
                    Last edited by Paul Alciatore; 10-28-2017, 01:50 AM.
                    Paul A.
                    SE Texas

                    And if you look REAL close at an analog signal,
                    You will find that it has discrete steps.

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                    • #40
                      Grim,

                      In the USA most towns and cities have cast iron covers in streets and near sidewalks for access to water shut off valves and other utility services. If you pay a visit to the water or sewer department with a case of beer you might come away with an old discontinued or damaged cover. I have a water shutoff valve cover about 8" in diameter that will become a small lapping plate one of these days. I found it in the ditch in front of my house. It must have fallen out of a city truck because we are all on privates wells and septic systems where I live.

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                      • #41
                        Originally posted by nc5a View Post
                        Grim,

                        In the USA most towns and cities have cast iron covers in streets and near sidewalks for access to water shut off valves and other utility services. If you pay a visit to the water or sewer department with a case of beer you might come away with an old discontinued or damaged cover. I have a water shutoff valve cover about 8" in diameter that will become a small lapping plate one of these days. I found it in the ditch in front of my house. It must have fallen out of a city truck because we are all on privates wells and septic systems where I live.
                        No chance. Around here you can't even take things from the dump. Because health and safety. Councils are terrified.

                        I've just had a thought though, I do have a bunch of cast aluminium, gearbox housings and the likes that will likely cast better, I'll give that a try!

                        I still want to add boron to the other stuff but the only source of it I can find is in health supplements, not sure if suitable, not much to lose by trying though

                        Comment


                        • #42
                          Originally posted by grim_d View Post
                          I still want to add boron to the other stuff but the only source of it I can find is in health supplements, not sure if suitable, not much to lose by trying though
                          You can find borax ( sodium borate ) as a laundry cleaner. I'm unaware of what brand names it would go by in Scotland. Here it's Borax, Boraxo, 20 mule team Borax and other brands. Often used as a flux in metalworking.

                          Dan
                          At the end of the project, there is a profound difference between spare parts and left over parts.

                          Location: SF East Bay.

                          Comment


                          • #43
                            There's a home foundry supplier in Liverpool, I think they do additives and such.
                            I think I've still got addresses of the boron nitride supplier in the uk, or one of them
                            LSM metals, I think they do a lab sample size bag, couple of hundred grams of boron
                            You don't need a lot to grain refine cast aluminium, parts per million works.
                            https://www.artisanfoundry.co.uk/about_us.php
                            Mark

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                            • #44
                              Originally posted by boslab View Post
                              There's a home foundry supplier in Liverpool, I think they do additives and such.
                              I think I've still got addresses of the boron nitride supplier in the uk, or one of them
                              LSM metals, I think they do a lab sample size bag, couple of hundred grams of boron
                              You don't need a lot to grain refine cast aluminium, parts per million works.
                              https://www.artisanfoundry.co.uk/about_us.php
                              Mark
                              I will try and contact LMS for boron nitride. I see it's also popular as a powder in cosmetics, might be easier to get a hold of.

                              Apparently about 0.002% (20ppm) by weight is sufficient! A few milligrams per kilo.

                              I have seen artisan foundry a lot, i would like to order some degassing tablets from them despite their prices being high but the only available shipping option available to me is £20!!

                              I've received your message, I'll come back to you later on as right now it's time for bed!
                              Last edited by grim_d; 10-28-2017, 06:07 AM.

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                              • #45
                                If you have access to a scrapyard or a friendly garage, another handy source of big flat round pieces of cast iron is car engine flywheels. You would have to turn up a centre boss depending on pilot shaft hole size unless you were lucky though. I have made up bespoke for a job faceplates to swing in my lathe's gap area from sacraficial car flywheels and there's always a couple tucked away behind the lathe ready as I have a friend who when he pulls a old engine to replace it with a replacement engine that arrives with one fitted will let me take the clutch side flywheel, and who also saves halfshafts and other handy stock bits too. But then I'm one of life's natural scavengers :-)

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