Getting a handle on things (part 2)

The time had come to cast this bad boy!

Preparations

I had a free day recently so decided the time had come to try casting the stove tool. But before I did, there were a couple of things I needed to turn my attention to.

Raw material

The first of these was making sure I had enough copper and tin to charge the crucible with. It would be a poor show if the end result was a partial casting due to my own mis-calculation. I measured the complete original tool – I can’t remember the precise weight now but rounded up to 1Kg to allow extra for the pouring cup and riser. I have my ingot mould so could always pour any excess off into that.

However, looking at the quantity of material, something was nagging the back of my mind. It didn’t look anywhere near enough and then it dawned on me. The size and volume of my rope handle is significantly larger than the original handle, so I would need way more molten bronze than I had allowed for. After some serious head scratching I decided to double up the quantities. Another kilo was measured out giving me 2Kg of bronze in total.

For the record, I used a 9:1 ratio of copper to tin for the bronze alloy. The tin I used was plumbers lead-free solder which I obtained from Ebay for a bargain price. 🙂

Core mould

The head of the tool is a reasonably complex shape so it was quite obvious I would need to fashion a core mould to accommodate this. To do this, I carved some fire-brick which is soft and easily shaped.

The above photo shows part of the core mould but I had to make a second piece to completely define the recess of the tool. This meant that the core was in two parts and I realised at the time this probably wasn’t ideal. I decided to continue with it anyway as I didn’t have any other options open to me at the time if I wanted to proceed. And after all, at this stage, this is as much about the education as it is about making stuff!

With raw materials measured out and cores prepared, it was time to start packing the flask.

We rammin’ (I wanna ram it with you)

I do enjoy a bit of Bob Marley occasionally. 🙂

Because of the unusual shape of the tool, it wasn’t possible to easily pack the sand around the piece in the inverted drag. So I resorted to mostly filling the drag and then packing the pattern into the top of the sand.

The above also shows the two part core mould.

The ramming was a little fiddly around the pattern but I got there in the end. The photo below also shows the pouring sprue (left) and riser (right). The whole thing was dusted with parting powder to prevent the sand in both halves of the mould from sticking together.

Next, the cope was placed on top and that was also packed with sand and rammed.

A few minor setbacks

After finishing the ramming and admiring my efforts for a few minutes, I withdrew the sprue and riser and carefully separated the two halves of the mould. It was at this point I had my first problem …

My sand had stuck together! I can only believe this was due to not using enough parting powder. So, after scraping the sand off the failed cope, I repaired the drag and re-rammed the cope again from scratch. I made sure to use bucket loads of parting powder and it worked better the second time around.

Quite a bit of sand broke out along the parting line when I pulled the pattern. I knew this would be a problem along the handle since the sand would want to adhere to all the nooks and crannies of the rope. Quite a bit of sand also broke out from around the tool head but I was able to repair this, which can be seen as the clear sand in the photo above. Gates were cut into the sand and the two halves of the mould were placed back together.

Time to melt metal

The time had come to fire up the furnace and start melting some metal.

Once all the raw material was molten and at the right temperature, the mould was poured.

The bronze only just began to fill the riser and as you can see, I emptied the crucible. I wouldn’t have wanted any less molten bronze for this pour.

After the pour …

I need to do something about burning my flasks!

After allowing a little time for cooling, the exciting time had come to break the mould open to view the results.

Upon first inspection, the cast looked pretty good in that it was complete. Both the sprue and riser had filled with bronze (but only just) and the rope effect on the handle wasn’t looking too bad either.

After a little more clean up …

You can clearly see where the parting line failed along the handle in the above photo.

Closer inspection

After some further cleanup and removal of the sprue and runner, we can make a more objective evaluation of the result.

Given that this was my first major, solo cast, I am quite pleased with how it turned out. It was not straightforward and maybe a little ambitious but I have taken away many lessons from this already. I did anticipate some of the snags but certainly not all … however I am now wiser!

As you can see from the above photo, there is significant flash along the parting line where the sand broke away when the pattern was pulled from the mould. The rope texture provided a great key for the sand to bind onto so this would need to be addressed for any future attempts. The flash could be cleaned up but I think it would be very tricky and time consuming to blend the edge neatly into the rope effect.

The above photo shows the tool head. The interior of this form was largely defined by the core mould but as you can see, there is quite a lot of excess bronze here. Some of the excess having crept in between the two combined core mould parts – which I sort of knew would happen.

This cast has already taught me a great deal. But rather then spend a lot of time cleaning it up, my plan is to use the lessons and try to produce another much cleaner cast.

Take away

Unfortunately, not the Chinese variety but rather some key lessons learnt from this experience. Here are the things I reckon I can improve upon next time …

1. Coat the rope handle with something smooth (i.e. – paint) to make it less attractive to the sand. This may result in a small loss of definition of the rope effect but this will probably be necessary to preserve the parting line of the mould.
2. Produce a single core mould for the tool head to give a more accurate reproduction of the part.
3. The complete bronze tool is actually quite heavy (~1.5Kg). I think it would be good to cast it with a hollow handle to reduce the weight. This will require another core mould and I would need to work out how to support it within the cavity of the mould.

Lots to think about! Until next time …