Modding the beast
This is the ultra nerdy part about using a Saunders spin casting machine. It will get absolutely the best results and allow easy setting up for different moulds while running a typical cycle of five or more moulds at a time.
The key to getting the most mould-line free castings on a Saunders is where the arm adjustment bolt falls on the top plate. It needs to fall over the centre of the pillar that both separates the two casting machine plates and locks the top plate into position to stop it spinning off when the machine starts up.
What you need is three 15mm turntable spirit levels, typically available from eBay. These are intended to get a turntable and turntable arm set up on a record deck, which will mean nothing to anyone under the age of 30… apart from hipsters with new vinyl record collections. Plus you’ll need some green stuff (epoxy putty) or five-minute epoxy adhesive – green stuff takes longer to set but will allow the spirit levels to be seated better.
First, ensure the casting machine is level. Use a conventional spirit level on the wooden base and if necessary pack under each foot of the machine’s tubular frame until the casting machine is level.
Take off the top platter. For each weight arm and pillar, turn the adjusting bolt in the top of the weight arm and raise the pillar until they touch and by eye align centre to centre. It doesn’t matter about how high the pillar is or how much through the top of the arm the adjusting bolt projects – it simply matters that they align. Link all the arms using rubber bands to pull them together and keep them in place for the next step.
Mix up some epoxy putty and put enough into the base of each spirit level so that any cavity is filled and there is some surplus to provide a bed into which the level can, if necessary, be pushed. Stick one level to the top of each weight arm, being sure to leave enough space between the level and the nut on the adjusting bolt. Carefully press the level into its bed of epoxy putty so that the bubble in the spirit level is centred. Leave to set. (You can use five-minute epoxy adhesive instead, which sets quickly but is fluid and needs continuous adjustment of the level until the epoxy sets firm.)
If you’re thinking why not attach the level to the top of the adjusting bolt, which will be horizontal, it’s because there may not be enough clearance between a level on top of the bolt and the lid of the machine when in use.
When the epoxy has set, remove the bands and wind the adjusting bolts and pillars to approximately their usual positions.
Place a mould on the bottom plate, and then put the top plate on, locating the tops of the pillars in the appropriate holes to hold it in position. Adjust the pillar height so there is a gap between the shoulder of the pillar and the top plate even when the assembly is compressed slightly.
While holding the weight arm so that the adjusting bolt is lightly in contact with the top plate, turn each adjusting bolt so that the bubble is the spirit level shows that the arm is level.
This adjustment is the key to good castings. It ensures that each weight arm applies the same pressure at the same distance from the edge of the top plate, without tipping the top plate in any one direction. Combined with correctly positioned weights on the weight arm to give enough pressure to seal a mould, this will minimise mould lines.
Update: Using this arm position on the top plate is a starting point. Moulds may benefit from having the arm shown slightly off-level – provided that all arms are the same degree off-level. I get better results on some moulds by having the contact point slightly towards the edge of the top plate, and adjust the bolt so that the bubble in the level is up on the top of the marked circle in the level – i.e. nearer the bolt (bubble nearer the bolt equals contact point nearer the edge; bubble nearer the edge equals contact point nearer the centre).
Weights can be positioned evenly down the weight arms simply by measuring from a fixed point. When setting up for the first time, I take the weight arm off a machine and measure using a ruler from the pivot point (actually the top of the hole in the weight arm) to the top securing nut of the weight. When in use, I typically use an item of fixed width, such as a metal bracket, to set each weight the same distance along each arm. I then fine-tune the distance by making test castings and increasing or reducing the pressure by moving each weight the same number of turns respectively down or up the arm until the mould stops flashing or starts filling all the cavities. Once I’ve identified the right setting for, say, a 15mm infantry mould, I note which gauge I’ve used and the number of adjusting turns, and then use that setup as the basis for all other 15mm infantry moulds.
Importantly, this is just a starting point. Individual arm weights may vary very slightly in weight thanks to the accumulation of casting metal from inside the machine (hence it is important to clean them). And the three threads making up the weight arms may vary very slightly in length, adding marginally to the mass and therefore causing a slight difference in pressure on the mould. Even after careful setting up, you may find that one weight may need a quarter or half turn up or down the arm to balance the machine: exactly what adjustment is needed is part of the black art that is spin casting.
The spirit levels allow minor adjustments to account for small differences in mould thickness to be made very quickly. If you make sure a casting session involves only moulds of about the same thickness – there is a natural variation in thickness caused by differences in the original mould blanks and by the volume of the originally moulded figures (big figures displace more rubber!) – then each mould may take only a quarter or half turn of the adjusting bolt to set the machine up optimally.
Also, it is important to bear in mind that moulds may be uneven, sloping to a lesser or great degree, because the vulcanising press is not even. What I do is work out the thickest point of the mould (it is, by and large directly opposite the thinnest point) by running the jaws of adjustable wrench round the outside of the mould until the wrench stops (closing up the wrench if necessary!). I mark the point and then run the wrench round the other way until it stops again, and mark that point. Halfway between those two points is usually the thickest point. I mark that point on the mould with paint or a marker pen. I then always align that point with the same pillar on the mould, so that all moulds always have the thickest point aligned with that pillar, meaning I have the fewest turns to make on the adjusting bolts.
Sometimes I just set up the machine perfectly for one mould, securing the adjustment bolts in place by tightening their locking nuts. I then cast only from that mould, leaving slightly longer between spins before opening the mould (i.e. so that the central core is set) compared with operating using a stack of moulds. This keeps the mould hotter, helping the flow of metal – handy for lower density casting metals such as pewter.
I’ll run another blog entry sometime soon on my casting tips, covering metal temperature, mould temperature and talcing.
Next: Cleaning, repairing and refurbishing an old Saunders