3D WERK
PRINTED WAX · CASTING TREE
CASTING TREE GUIDE
From clean patterns
to a casting tree.
Your patterns are clean and dry. Next they go onto a wax tree, ready for investing. A good tree feeds metal into every pattern and lets each one solidify in the right order. Poor spruing is the leading cause of shrinkage porosity, so take your time with this step.
Before you start
This guide is general information to help you get the most from your WaxJet. It does not replace the Flashforge manuals, the safety data sheets for your materials or your own safety checks. Where they differ, follow the manufacturer's instructions and safety data sheets. Isopropyl alcohol (IPA) is highly flammable, and warm IPA gives off more vapour. Flashforge's manual uses a mix of PPG400, ethanol and IPA at 40 °C, never above 43 °C. Ethanol is also highly flammable. Keep it away from heat, sparks and open flames, heat it only with equipment suited to flammable liquids, use it in a well-ventilated area, and wear suitable PPE such as gloves and eye protection. Investment powder contains crystalline silica, and wax burnout and metal melting give off fumes, so use ventilation and the PPE your safety data sheets list. As a business, you are responsible for work health and safety in your workshop, including risk assessment and how you store, use and dispose of chemicals. See our Terms and Conditions.
THE NUMBERS AT A GLANCE
About 45°
the usual starting angle between sprue and trunk
3 to 5 mm
between patterns, never under 2 mm
6 mm min
from any pattern to the flask wall, 10 mm is safer
19 mm min
of investment above the highest pattern, up to 25 mm on large flasks
Thicker
every sprue a little thicker than the part it feeds
WHAT YOU NEED
Rubber sprue base
sized to your flask
Wax pen
fine tip, adjustable heat
Soft-tipped tweezers
for handling patterns
Casting flask
to check the fit as you build
Sticky wax
for tacking parts in place
Nitrile gloves
no skin oils on the wax
Round wax sprue wire
in a few thicknesses
Digital scale
reading to 0.01 g
Debubblizer
surface tension reducer
Before you start
Fully dry patterns. All IPA must have evaporated. Its vapour is flammable, so keep it away from a hot wax pen.
Inspect under magnification. Only use clean, undamaged patterns. A flaw in the wax becomes a flaw in the metal.
Gloves on, cool room. Skin oils spoil the investment surface, and heat from sun or heaters can distort fine wax.
1
Plan the tree
Pick the flask first and check the tree against it as you build. Keep every pattern at least 6 mm from the wall (10 mm is safer). Leave at least 19 mm of investment above the highest pattern on a small flask, and up to 25 mm on a larger one.
Heavy pieces low, delicate pieces high, which suits most centrifugal and vacuum casting set-ups. Follow your machine maker's advice.
Similar pieces together. Very thick and very thin pieces need different flask temperatures, so put them on separate trees.
Balance the tree. Spiral the patterns evenly around the trunk, and keep them clear of the trunk as well as each other.
Trunk thicker than any sprue. It feeds all of them.
2
Sprue each pattern
Attach at the thickest part. On a plain band that is usually the base of the shank. On a ring with a heavy top, attach at the side of the head or inside the ring, or use two sprues. If a sprue point was printed in, use it.
A little thicker than the thickest part it feeds. Wax wire is sold by B and S gauge: 6 gauge is about 4.1 mm, 8 gauge about 3.3 mm, 10 gauge about 2.6 mm, 12 gauge about 2.1 mm, 14 gauge about 1.6 mm. A thin sprue freezes first and leaves shrinkage porosity. Two thin sprues are no substitute for one of the right size.
Short and round. As short as you can make it while the pattern still sits clear of the flask wall and button. If it has to be longer, make it thicker.
Flared into the piece, not narrowed where it joins. A narrow neck starves the piece of metal.
Away from detail. Never on stone seats, prongs, engraving or texture, so clean-up does not damage them.
Add sprues where needed: one for each heavy area that is cut off by a thin section, and Heavy pieces may need a second sprue. above.
3
Attach the patterns to the trunk
Start at the top of the trunk and work down, so drips cannot land on finished patterns.
About 45° to the trunk, pointing up and away from the base. If your caster specifies an angle, use theirs.
Wax pen on low heat. Melt the sprue wax and let it join the pattern with the least heat you can. Keep the hot tip off thin detail.
Smooth fillet at every join. No gaps, pinholes or sharp corners. A sharp corner of investment can break off and end up in the casting.
At least 2 mm between patterns, and 3 to 5 mm is a good working gap. Leave more for resin., and nothing touching.
Check every join. Tap the base gently and reweld anything that moves.
4
Final check and weigh
Look over the whole tree. No drips on patterns, no wax bridges between them, every join smooth.
Weigh. Weigh the printed patterns before spruing. Weigh the empty rubber base, then the finished tree. The difference, minus the patterns, is your sprue wax.
Work out the metal with the formula below, then add a button, about 15 g or about 10% of the metal weight as a starting point. Adjust it for your flask, machine and alloy.
Debubblizer. It helps stop air bubbles clinging to the wax. Recommended with a bell jar setup, optional only if an investing machine mixes and pours under vacuum. Follow the debubblizer maker's instructions for drying time.
Keep the tree clean until you invest: covered, cool and out of the sun.
Metal needed
patterns × (metal density ÷ printed wax density)
+ sprue wax × (metal density ÷ sprue wax density)
+ button
Take the sprue wax density from its data sheet, and measure your printed wax once with a 20 mm test cube, as our metal weight calculator shows. Printed wax and sprue wax are not the same density, so one standard ratio for the whole tree will be off.
COMMON MISTAKES
Sprue too thin, on a thin section, or two thin sprues instead of one proper one
WHAT IT CAUSES
Shrinkage porosity, incomplete fill
DO THIS INSTEAD
A sprue a little thicker than the thickest part, attached there. Extra sprues only where needed
Narrow neck where the sprue meets the piece
WHAT IT CAUSES
Feed metal cut off, porosity
DO THIS INSTEAD
Flare the sprue into the piece
Sharp corners or gaps at joins
WHAT IT CAUSES
DO THIS INSTEAD
Investment breaks off and ends up in the metal
Smooth fillet at every join
Patterns too close or touching
WHAT IT CAUSES
Thin investment between them breaks, leaving fins or joined castings
DO THIS INSTEAD
3 to 5 mm apart, never under 2 mm
Too close to the flask wall or top
WHAT IT CAUSES
Thin investment cracks or metal breaks through
DO THIS INSTEAD
At least 6 mm to the wall, 19 mm of investment above the highest pattern
Wax pen too hot
WHAT IT CAUSES
DO THIS INSTEAD
Melted or distorted detail
Low heat, touch the sprue wax only
Sprue on a setting or fine detail
WHAT IT CAUSES
DO THIS INSTEAD
Detail lost during clean-up
Sprue where clean-up is easy
Thick and thin pieces on one tree
WHAT IT CAUSES
Thin pieces fail to fill, or thick ones shrink
DO THIS INSTEAD
Similar pieces on the same tree
Guessing the metal
WHAT IT CAUSES
DO THIS INSTEAD
Short pour, or wasted metal
Weigh and calculate every tree
BEFORE IT GOES INTO THE FLASK: CHECKLIST
Every pattern clean, dry and inspected
Heavy pieces low, delicate pieces high
Each sprue on the thickest part, and a little thicker
Every sprue flared, every join filleted
3 to 5 mm between patterns, clear of the trunk
6 mm min to the wall, 19 mm min of investment above the highest pattern
No drips or bridges, every join checked
Tree weighed, metal calculated
Debubblizer fully dry, if used
Make it easier in the design file
Add a sprue point to the model, such as a small post at the thickest part. Attaching is quicker and the join stays off your detail.
Print similar pieces together, so each print run makes one well matched tree. Our design for casting guide goes further, and the investing and burnout guide takes the finished tree into the flask.
GUIDE 8 OF 13 · CASTING
THE BIG PICTURE
1 · DESIGN
2 · PATTERNS
3 · CASTING
4 · AFTER CASTING