More hammering and casting.

May 10th, 2014

Yes, yes, I know. Still bloody hammering! But I am getting there. I bolted the fire wall on to make sure that sill fitted. It didn’t so some holes needed filing and the T nut in the floor needed removing and moving about 1/4 inch to line up. Things are slowly getting smoother. I fixed up under the tail and am slowly getting around the cockpit smooth. Not too many photos since it looks the same in all of them. It occurred to me what I see in the pictures (an ok looking car) is how most people see the car in real life. They don’t look at the miniscule details I focus on.

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To prove this my neighbour went past walking her dogs and stopped in to see how I was doing and she thought it looked great. My mate Dave is the same, he sees a car. So I am getting there. I have got the front corner, that was pretty battered, fairly smooth. Not perfect but the not perfect look is really growing on me. I am making an old car, not a new one so it’s all good.

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Apart from the constant, endless bloody hammering (which I am starting to finally get a feel for) I decided to start looking at the engine. I have stripped several of the old block Joss gave me to clean up. One looks in great condition (only one broken off stud) so I may end up using that one.

I also started looking at doing some metal casting finally. I started playing with metal casting a couple of years ago. I made a furnace and got as far as casting ingots. I decided it was time to cast something useful. I decided to start with something really simple, the little adapter block that goes between the carb and the blower.

First I made a little wooden pattern from MDF. A couple of bits were cut out based on the shapes of the blower port and carb outlet (I used the gaskets to trace around) and a little body filler smooths things out.

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A coat of poly seals the wood.

I was hoping to do the casting yesterday but the weather was bad so I spent some time practicing the actual mold making part. I have some proper greensand from a foundry near where I used to work. I am not entirely sure I have the moisture content of it right yet though. I’ve never done this before, or even seen it done in person, so I am guessing a bit. YouTube was actually a help here. Getting the sand right is called tempering and I suspect my sand is a little too dry.

I am glad I practiced since it’s all a bit tricky but today, since the weather was great (it has been since I ‘retired’ actually and it only rains on the days I actually do real work) , I went out and tried my first actual casting.

Now casting is a funny business. Every has fancy pants names. Like ‘tempering’ the sand. Then the box you make the mold in is called a flask and it’s made of two halves, the cope (top) and the drag (bottom). You start with the drag on a board upside down. Upside down is important as I found out in my practice runs .

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The pattern goes on the board. There are all sorts of things to know about in pattern making I won’t go into here. I didn’t get photos of every step since I was too busy doing things so this isn’t a tutorial!

The pattern and the board are dusted with parting powder which stops the sand sticking. I used talcum powder in an old sock which makes a great poofer (I don’t think that’s a proper casting term but that what I call it). It’s funny, you’re outside, raging furnace going, doing manly, metal working things and the whole time you smell like a baby’s bum (the clean kind) because you’re poofing talcum powder about all over the place.

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Next you sprinkle sand all over the pattern in the drag. I am using a kitchen sieve to do this but since we’re metal casting it’s not called a sieve it’s called a ‘riddle’. Why, well that’s a guessing game.

You press the sand down around the pattern. I think I need practice doing this as getting the sand compacted around the pattern without moving it is tricky. You want nice, fine sand all around the pattern. I keep saying sand and it is but it’s actually sand mixed with clay so it is actually more like dirt. They call it greensand but it’s actually dirt coloured. The green refers to the water in it I think.

Once you have riddled sand all over the pattern you add more sand and tamp it down with a rammer.

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My ‘rammer’ is a bit of wood with the corners sanded off. This again takes practice since you want the sand compacted down and in good contact with the pattern but not really packed in hard since when you pour in the metal the steam from contact with the damp sand needs to escape somewhere. It needs to be in there hard enough that you can lift up the drag and the sand won’t fall out.

Once the drag is full you smooth off the top with a steel bar. Apparently this is called ‘strickling’.

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You then put a board on the top (actually bottom) of the drag and flip it over.

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And then you can see the pattern in the sand. Now my first casting was meant to be simple but there is a minor complication. Mine is hollow in the middle. So what I have to do is a process called ‘coping down’ where you dig the sand out of the drag then later when we add the cope it gets refilled in. I removed the sand from the middle then tamped it down.

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I then put the cope on, added the sprue pin and put in more sand and tamped that down and smoothed it off.

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I totally failed to get pictures of the next part but you then pull out the sprue pint and remove the cope from the drag. You can then carefully remove the pattern from the sand. I found I definitely had to spray the sand with water first to stop the corners crumbling (this they call ‘swabbing’). You can then cut a channel between the sprue hole and the pattern. This is called the gate. I also added vent holes thought the cope using a steel rod passed right through it.

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The vent holes allow gas to escape as the metal fills the void left where the pattern was. The cope is them set back onto the drag. Now of course there is no pattern just a pattern shaped hole in the middle of the sand.

I used the same pin and made a little sand filled can to make a little head for pouring the metal in.

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I fired up the furnace which now works much better with a metal grate in the bottom and a steel air inlet tube. I am using charcoal since I find it much safer to use than gas.

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I just used some of the ingots from my previously melted down aluminium scrap.

This is the first time I tried using a flux in the metal and it definitely helped. The flux is a washing soda and potassium chloride (solds as low salt at the supermarket). You put a little of each (I used about half a teaspoon) in a bit of tin foil then drop it in the melt. It seems to clean the metal and more dross came to the top.

Actually this was when I had the only accident of the day. Obviously with molten metal you are very, very careful. I wear all the safety gear and take all the precautions. But when I was making the flux (far away from the furnace)  I was taking the lid off the salt container and it got stuck. When it came loose I ended up throwing low salt right in my face and eyes which stung like a bitch! I had to run indoors to flush my eyes with cold water.

Anyway, once I could see again, I was able to do the pour. While that was cooling I melted some more metal from some old hard drive housings I had. Once the original pour had cooled somewhat I removed it from the sand. I wasn’t sure it had worked but as I poked away the dried sand a shape appeared.

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It actually worked!

I actually made a second mistake here. I put the sand off the first mould right back in the container. Then when I came to do the second mould I of course found the sand was all lumpy with dry bits in it from where the sand had been in contact with the metal in the first mold. The sand needs retempering between used of course.

I went ahead with the second pour anyway and did get another part from it. I set those aside and since there was still a lot of heat in the furnace I decided to make cupcakes!

Out of lead.

I have a bad habit. Whenever I see lead wheel weights on the road I have to pick them up. Been doing it for years and collecting them in a tin. I also had a box of lead flashing left over from when my house was re-roofed last year. I made them leave behind all the old lead flashing and lead headed nails.

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I stuck all that into my second crucible and made a bunch of lead cupcakes. I was wondering about the steel part of the weights being in the lead but of course steel is less dense than lead so when it all melts the steel bits float to the top!

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With everything cleaned up and cooled down I took the two parts I had made and cut off the sprues. The one from hard drive metal was really brittle. I cut half way through the sprue and then was able to snap it easily. The original one was much stronger. The problem with melting scrap is you don’t really know what the metal is. Well, it’s all aluminium, but what else is in it. you can see the difference in the sprues below.

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The scrap metal is the left and the old hard drives are on the right. You can see the right hand one looks more brittle and more ‘crystally’. From this I think I won’t try casting my front plate on the engine but will instead have it machined from flat plate. With my castings I can’t guarantee it would be strong enough!

The second casting I did with the hard drive metal is very rough. Not helped by the sand of course but the metal just seems more brittle. The first one thought, after a bit of filing and clean up is probably useable. I am sure I can do better with practice but I think it’s kind of cool to be able to use my first aluminium casting on my first hand made aluminium car. The whole thing is far from perfect so that works!

It actually cleaned up OK on the sanding wheel. I need to smooth out the inside and drill the holes and add the studs for the carb mounting (which I have ordered) but it should work. It is a little rough and a bit porous but useable.

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This is where this part will go. Between the blower inlet and the SU downdraft carb.

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It’s rough and crude and I know I can do better with practice but I am pretty pleased with that actually. I am actually really pleased my first attempt at casting resulted in a useable part. It seems a simple process but there is a lot of nuance to it and lots of experienced needed I think.

I did find this online (after I did all this) which explains the process step by stem much better than I can. And of course there are entire forums devoted to metal casting online. Look there if you want more info.

3 Responses to “More hammering and casting.”

  1. Barry Morris Says:

    Hi, congratulations on a successful melt and pour, nice job on the patterns, thought I might give you a couple of tips for your safety and better ali castings, firstly “DON’T” look at the molten metal or more to the point the flame too much with out oxy goggles on as it gives a large ultraviolet light which can wreck your eyes over time, the really dangerous part of casting can be when you pour into the mould if it is too wet or moist, water turning to steam expands either 700 or 7000 times it volume…. or something like that, I can never remember… point is the metal will come back out like a fountain and run straight down inside your gloves so next tip is always put your gloves on first then a leather long sleeve coat over them, yes your very correct when you mentioned the quality of the metal and each time ali gets melted it loses some of its additives so yes you need to add them back in, particularly a de-gasser tablet shortly before talking it out of the furnace but finally I have found the best scrap ali to melt is old pistons, they have already been given the additives and will stand a remelt without losing much and will be a dream to machine afterwards, engine re conditioner’s should be able to supply lots , oh and don’t over cook the ali, once it has melted get it out and into the mould.

    your A7 restoration looks great so congrates on a job well done so far

  2. admin Says:

    Thanks for the tips. I do want to get some better safety gear to wear in case of mishaps and metal splashing about. I didn’t know about the UV issue so will be careful about that too thanks. It’s one of those things I won’t be doing that much probably. I just don’t have enough things I need to cast! I am pleased how my adaptor block came out though. I checked the matching of the block to the blower inlet port with the carb off and they line up very well.

    Just starting to get geared up for engine building next.

  3. Jeremy Ashford Says:

    Simon, good to see the casting process has begun.
    I may already have told you my first job out of school was casting lead/tin and aluminium/zinc using the Romanoff process, which employs vulcanised rubber moulds spinning in converted washing machines. Your items may be a bit heavy which can mean hot here for rubber moulds.
    Aluminium is very tricky to cast: too cold and it sticks, too hot and it comes out porous. I don’t suppose you have a thermometer on your crucible. If you don’t you could try some dummy pours to check how it’s going to come out. Cool it til you get a good pour..
    If Joss is over on Sunday I may join you, if that’ okay.
    I think I told you there is a part I need to make for a moka pot, I mentioned engineering it but if you are heating aluminium again, maybe I should think about getting some silicon rubber and making a mould.
    Jeremy

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