Materials & Preparation

Materials

Lego parts

and/or any parts you feel are right for the job.
For me, building with Lego is a way of expressing my imagination...
I rarely stop to plan a design, it just flows (30+ years of playing :)

Other parts

Generally, I use the B&Q Poly Glue for sticking stuff, and epoxy for setting stuff... one under the other around :)
The poly glue seems to be more flexible than epoxy, and I find that the Poly glue is more resistant to heat expansion differences and stress.
The vice is a Draper hobby vice, it can tilt and rotate on its base... very usefull.
When considering the mold, an important factor is bismuth's expansion factor of 3.3% from liquid to solid. Just like water, bismuth has a larger volume in its solid state than liquid.
The magnets I used for the lifter are grade N45 1" (d) x 1/4" (h) black nickel coated NdFeB disc magnets. Some small NdFeb magnets are also needed to levitate them.

Safety First

Bismuth is non-toxic, however bismuth shot is not pure bismuth.
It is advisable to wash hands after handling bismuth or bismuth shot.

Bismuth melts at 271 degrees centigrade... Very Hot!!!
Great care should be taken when handling molten bismuth and hot tools.

Your health and safety is your responsibility, the methods I describe below can be hazardous, and should only be attempted by a responsible adult.
I accept no resposibility should you try this at home.

Preparation

Mold

The mold I used is made from 20x20mm aluminium U section, cut to 40mm length.
End plates cut from 20mm width aluminium flat.
And a length of wire to hold it all together.
I filed some notches in the end plates to help get a tighter fit.

Click on an image to enlarge in a new window.


mold parts
Assembled mold

This mold has a capacity of 12.58ml;
Internal dimensions are; 40mm (l) x 17mm (w) x 18.5mm (h).

From this mold, the cast block weighs about 135 grammes.

Bismuth

The bismuth shot I aquired is oily, to clean the shot, I used some washing up liquid and kiln dried sand... all in a jug with a small amount of water and stirred it up for a while.

Click on an image to enlarge in a new window.


All the tools & materials.
The cast bismuth block and
the shot needed to make it.

 


Bismuth shot in a 10ml stainless
steel measuring cup.
Bismuth shot melting.

 


Molten bismuth shot.
Molten shot, cleaned.

As the shot melts, there is some solid material that needs to be extracted from the crucible... carefully with tweezers or needle nose pliers.
The shot takes 3 to 5 minutes to melt on a medium heat, and it does need stirring up to release the solid waste.
Once the molten shot is all liquid, it's ready for casting.


Just poured
Cooling and part of
the mold removed.

The bismuth expands as it cools, compare the surface of the molten bismuth (left) to the cooling block (right)... about 15 minutes elapsed between pictures.


B & Q Poly power glue and bismuth blocks.
Bush glued to magnet with contact adhesive.

The last stage in preperation is too glue some Lego Technic Bushes to the bismuth and a bush to the magnet.
The surface of the bismuth may have to be filed flat, and I used a Lego frame to hold the bushes in the right place as the glue set.
I used the poly power glue on the bismuth, as both the contact adhesive and bismuth are fairly brittle and can break away by an impact... the poly glue 'gives' a bit.

Preparation complete, time for construction.

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