More Bronze Pour Problems and Cheap Spanners

BRONZE POUR.

I had 3D printed another tree with 4 cannon parts. Brackets. The complete tree fitted into a steel flask 100mm diameter and 120mm high. So I repeated the steps of the last successful pour, and painted the tree with investment slurry, mixed the main investment, degassed it, poured it, and degassed the entire flask, investment and all. That method had worked well before, so I repeated it.

But I was a bit concerned because the investment was only a few mm thick at the bottom of the flask. Would it hold up? Read on.

So then commenced the drying, burnout, and baking cycles in the potters oven. Normally it is about an 8 hour process, and I did not get to start until 12 midday. So I was in for a long day.

But then the oven started to play up. It would suddenly switch off. The temperature gauge would swing wildly. And would not heat above 400ºc and it needed to reach 710ºc.

I did not know the source of the problem. Thermostat? Wiring? Controller? Power supply? I did know that the thermostat wire was not rated for temperatures above 600ºc, but it had worked OK previously. So I turned everything off, and removed the electronics compartment. Changed the thermostat wire to the proper grade (thanks Stuart!), then found a loose main heater element join, so fixed that too. It all took another 1-2 hours.

Started up the oven again. The temperature had dropped to about 200ºc, but the the temperature started rising slowly, so maybe the problem had been fixed? By this time it was 4pm, and there were still 7 hours of heating required, so it WAS going to be a late night in the workshop. Made my peace with SWMBO. She was happily watching the footy, and not too worried about about my travails. (and our team won convincingly!)

To finish this story, I eventually poured the bronze, and my earlier concerns about the thin layer of investment at the bottom of the flask were realised. The bottom fell out, and molten bronze poured out through the breach. I normally rest the flask in a tray of sand when pouring, and fortunately, the bronze seemed to harden when it hit the sand, and the outflow ceased.

This was the result….

Amazingly, the parts seem fully formed, with no voids or bubbles. The ugly lump underneath is the bronze leak through the bottom. Note the length of feeder sprue. And the funnel. If you zoom into the photo you will see that the fine detail of the 3D printing has been reproduced. I will cut the parts off and finish them tomorrow. I got home about midnight. I needed that shot of single malt.
The bronze brackets, after sawing them from the tree. I will add a photo after another session of machining and finishing them.
After some more tidying. The investment powder can be persistent.

CHEAP SPANNERS.

I have several machines which use 40ER collets. I have enough collet spanners, but only one locking spanner for the chucks, and it is always on the wrong machine. So I decided to get some more locking spanners, and I sent my drawing to the laser cutting company. I picked up 4 spanners from them a few days later. Cost $AUD55. (cheap!)

My Colchester, with ER40 chuck. And one of the new stainless steel locking spanners. Drawn up as a dxf file, which was emailed to the laser cutter. The square hole is to lock the carriage to the bed. A few moments on the belt sander removed the sharp edges. Not elegant, but works perfectly.
2 spanners are required to tighten the ER collet. Here I am making a jig which will be used to cut the quadrant gear which elevates the cannon barrel. More about that in a day or 2.