SQD – Stupid Question Day project build.
Pb – as in the periodic table and not as in…..peanut butter.
Fail…..as in fail !
Blog time : it’s Easter 2021 (when i wrote this piece) and as i write, a bright, hard and cold day with a biting northerly wind that has chased me out of the workshop and garden and back to the keyboard. In real time i still don’t have any of the actual materials to either start the build or even to begin cementing in posts for the outside shelter…..both the simple result of everything shutting down even more at this time of year. As always here i had plenty to get on with in the veggie garden as it’s the busiest time of year but i really wanted to get on with something for the project so……in the spirit of new build blog format here it is in bench time, admin tasks, tools used and what mistakes made/what i learned.
When i opened up the plans for the first time last week i focused on the construction details for making the centerboard and it’s case because i might still make them first, whatever, that section of the plans calls for a 20 Kg cast lead weight to overcome the bouyancy of the centerboard that has to be set into the aerofoil section board. I knew i had 4 old Lead-acid batteries kicking around and i figured that between them they would have enough lead given that each one weighed in at over 25 Kg once i’d emptied out the dilute sulphuric acid…..it’s ok , i had my safety shorts on !. Last week i broke down one of the batteries , separated out the plates and the insulating sheets and ended up with a heavy bucket load of material ready to go.
My long-arm roofing torch arrived in the post and a local mate gave me a Propane bottle that he was getting rid of complete with a good few kilo’s of gas still in it so ‘good to go’. I had an old cast iron Dutch oven that i haven’t used in years and i also found a cast iron grate that we used to use as our cooking surface when i taught bushcraft skills many years ago, with those , a concrete slab and a couple of buckets of old fire bricks i made a temporary hearth and set to with the burner ; damn but that thing is hot and loud !.
The first thing that happened is that my cast iron grate cracked in a couple of places so i stopped and altered the supports slightly as i really didn’t the Dutch oven tipping over with a load of molten lead in it but…..i just didn’t get much molten lead happening even after 20 minutes or so ; some but nothing like as much as i was expecting. At that point i stopped again , took a break and let the whole thing cool down while i had a brew and thought about what was going on. When i looked at one of the plates from the battery again and knocked it about some i noticed that it isn’t a sheet of lead but a fine metallic grid supporting small blocks of something else…..and now i think that the blocks are not metallic lead but dry lead sulphide paste which i have no chance of smelting.
What i hoped to show you today was how i went about the first stage of making the cast lead weight for the centerboard…..my plan for the weekend having been to cast some simple ingots first and then explain my proposed set up for the 20 Kg melt and pour of the actual weight. In real time i’m nowhere near that as i worked out that i have nowhere near enough metallic lead to work with.
I clearly did make some molten lead except that i had no way of separating it from the rest of the dry junk in the oven so i couldn’t go ahead and make even one small ‘muffin tin’ ingot…..of note, i failed to find a stainless steel kitchen skimmer of any kind in either of the supermarkets in town so i had nothing to sift out the junk and slag with. What i did instead was spend some time researching what exactly it was that i was dealing with that is a clearly heavy material but isn’t soft metallic lead. It seems that battery construction isn’t as i assumed in the shape of lead sheets separated by sheets of some other material but as i found out – a small lead grid supporting dry blocks of lead sulphide . While i can melt lead with my roofing torch (about 350 C) there is no way i can smelt and reduce lead sulphide because that process needs oxygen , charcoal and about 900 degrees of heat. I might be able to do that if i built a crucible and furnace but i would then have to be able to run the metallic lead off and i would be producing extremely toxic fumes so as far as i can see the job is a no-go at this stage.
This job was the first one where i really had no idea where to start so aside from watching some scary Youtube video’s of shooters and fishermen casting ‘bombs and bullets’……and i note in some cases having not grasped the basic problem of free surface effect of molten lead in a cast iron frying pan ffs…..i sh*t you not !….so i SQD’d it. For those that don’t know what that’s all about i am in the habit of posting a stupid question on designer John Welsford’s social media page when i don’t know something , which is every week, and where another builder probably has done it or knows how to do it so…..
This post will go back on John’s site as a summary and response to members answers and also what i took from them and tried myself so what i’d like to do is sum-up the answers and responses that i got and what i tried/ will try next time around.
First group….definitely said ‘don’t even try that’ especially in my case of not knowing anything about melting and casting lead and some of those responses even set out to remind me just how dangerous and toxic melting lead could be , let alone handling it and/or pouring that much. The pour would , i agree, be difficult and need a lot of careful thinking about which is why i just wanted to gain some experience in making smaller ingots first which i could just ladle from the Dutch oven with an old and unused stainless steel kitchen ladle. My problem though is that i almost can’t proceed with that approach because i’ll never get anything done if i don’t learn how to do anything that iv’e not done before ; do remember that accounts for most of the build so in a circular kind of way i will only know how to do something once iv’e learned how to do it !
Second group were equally a bit bold……in that several members suggested doing the pour straight into the centerboard blank. Now, that would surely ‘fill the hole’ and i can well imagine the molten metal bonding with the timber except for 2 things : first that i would be then greatly concerned about the molten metal breaking down the eopxy-wood joints between the lamells and secondly, wouldn’t the lead casting shrink as it cooled and potentially break away from it’s ‘mold’….TBH i don’t know but this way of going about the job seems a no-go to me until i see one already done and in all of my searches i never saw a video of this one being done.
The third group of answers i felt had a much better solution and that is to not (hot) melt and cast the lead but rather to do a cold casting with lead shot and epoxy resin which would definitely bond with the timber and should easily hold the lead shot together. I think iv’e come across fin keels on IOR boats in the past, i think the OOD34 was one, where the keel was a GRP shell filled with a lead shot and resin matrix ; that from having worked on the keel repair of the OOD34 that i crewed on after the owner pranged it on a rock just outside the Menai straits !. I like the sound of that technique because i can see a way to cut the basic shape out of the centerboard and then rout a groove all around the inside edge of the cut which would create an extra concave surface for the epoxy/lead shot mix to settle into and bond with. The slight downside of this approach is the cost of lead shot which in the UK works out at some £10 a kilo and having also done the calculations myself i would need around 15 Kg just to neutralize the natural bouyancy of the board ; this then naturally segues into the learning section of this week’s post so…….
Take 2, second attempt with video.
You can probably tell from the beginning of this post that i started it over a month ago but what happened then is that my shelter building materials did arrive so i put aside the side projects and got on with my main April job which was to get the shelter built. Now, in real time it’s the end of the month, the shelter is up and iv’e even done most it’s side project which was to box in one corner of the garden to obscure the view into the build area somewhat, then, on a day when i was waiting for more materials i was casting about for things to do so i had another go at melting and casting some lead ; this time using some scrap lead sheets which i sourced via the internet and which came home at about a tenth of the cost of lead shot so it wouldn’t be a huge loss if it was a failure.
I also decided that as it was a single job for an afternoon session that i may as well set up and try filming the whole process as at least some of it would be like waiting for the kettle to boil, also and unlike my previous attempts at video i had a go at just taking lots of clips and then editing most of that just to show what i was trying to do and with very little chat.
What i did….
For those that prefer video iv’e linked the video version below, for those that like this sort of thing in written form then here goes.
First……i made a new hearth using the same fire bricks that i used last time and the same concrete slab to lift the whole thing off the Tarmac of the drive with an air gap under the slab and more bricks supporting the cast iron grate above the slab. I packed some loose charcoal around the upper fire bricks as i intended to light that first and use the ember bed to thoroughly heat the cast iron Dutch oven before applying intense heat to it from the Propane powered roofing torch.
Second…..emptied out all of the lead sulphide blocks from the Dutch oven and peeled the small amount of molten lead out of the bottom and I then spent a good hour just cleaning out the Dutch oven and getting it back to a ‘black iron’ finish so as not to end up with any ferrous waste in the lead if i succeeded with the melt this time.
Third….got all the kit together, lit the torch and fired up the charcoal bed with that and let the Dutch oven heat up slowly for about 20 minutes before adding any of the lead sheets and/or before really applying direct heat from the Propane torch.
Then….I started with just 2 thin sheets of lead in the bottom of the Dutch oven and slowly started bringing up the heat by playing the Propane torch all around the melting pot……it took about 15 minutes of gradual heating to produce the first bead of molten lead in the bottom of the Dutch oven ; once i was happy that everything seemed to be going ok , nothing seemed to want to go bang or produce noxious fumes i put all of the lead sheets (10 Kg) in the pot and set the roofing torch in such a way as to apply a medium heat to the Dutch oven – in around another 20 minutes the whole lot slumped and melted to form a pool of molten lead with some obvious dross on top. To get the dross out i skimmed through the now molten lead with a stainless steel kitchen skimmer and then got ready to attempt a pour into my mold – in this case an Aluminium loaf tin, and that’s where i went wrong.
As soon as i took the weight of the Dutch oven and it’s 10 Kg of molten lead (by it’s bail) the whole lot instantly tipped to one side and i lost a good Kilogram of molten lead straight over the side – luckily away from me and i was able to put the whole thing straight back down again. Funnily enough i was pre-aware that the free surface effect could be a problem but i thought i would be able to control it…….i couldn’t and that was a vital lesson to learn !. In the actual video there’s a long pause at that stage (edited out) during which i ran up to the house and ran back again with a stainless steel ladle to use instead. I re heated the pot for a while, skimmed it again and then just experimented with ladling out the molten metal – that went ok apart from it’s tendency to cool and solidify too quickly on the ladle and in the mold ; my lesson there is to maybe not use Aluminium for the mold unless i get that hot first and/or to put the mold back over the ember bed to encourage the lead to become a more consistent mass as it cools.
Given what i lost down the back of the hearth that’s about an 8 Kg ingot of fairly clean and bright lead – as a second experiment i’m happy with that until i work out what i’m going to use as an actual mold.