The cope is the upper section of a sand mold and the drag is the lower one — the two halves of the flask, rammed separately, then closed on each other to form a single cavity. The mold is split because a one-piece mold cannot release the pattern, and the joint where the halves meet is the parting line.
What Goes in the Cope and What Goes in the Drag
The drag carries most of the casting and all of the cores, the cope carries the feeding system — sprue, risers and vents — and the parting plane between them sits where the pattern can be drawn out of both halves.
A published SFSA design study states the rule for the designer: critical surfaces should be molded in the drag.
That study’s example is a 3,676-lb low-carbon steel pintle socket. With the bowl rim up in the cope, inclusions would have been trapped in the rim and the interior surface that had to be machined, so the bowl was turned rim down into the drag.
Mark the drawing accordingly: machined faces, sealing faces and anything the print calls critical belong on the drag side of the parting line.
How a Cope and Drag Mold Is Made
The drag is rammed first, with the pattern lying face down on a mold board; the half mold and the board are rolled over together, the joint face is dusted with parting compound, and the cope is then rammed on top with the sprue and riser pins standing in place.
The halves come apart again to rap and draw the pattern, the sprue and gates are cut, the cores are set into their prints in the open drag, and the mold is closed back down on its pins and clamped for pouring.
Some shapes need a third section: where more than one parting plane is required, a cheek goes between the cope and the drag. The split changes the mold-making steps only — pattern making, pouring and shakeout run as they do on any sand casting job.
The Parting Line Between Cope and Drag
The parting line is the plane where the cope meets the drag, and it shows on the finished casting as a seam: a fine step where the halves did not register exactly, and a band of flash where metal pushed into the joint.
The plane goes at the largest cross-section in the draw direction, so both halves pull away from the pattern, and it should be straight.
A dimension formed across the joint is more variable than the same dimension formed inside one half, and published capability data sizes the penalty: no-bake molding adds 0.040 in. (1 mm) of 6-sigma variability to a feature that crosses the parting line, where green sand shows no significant addition. Keep close-tolerance features and the datums they are measured from inside one half.
Every vertical face either side of the joint has to carry draft so the pattern releases. The seam itself is ground flush, machined off or left as-cast — say which on the drawing, and keep gasket and bearing faces away from it.
Alignment Pins, Mismatch and Cope Lift
The cope locates on the drag through pins and bushings on the flask, and it has to be held down — by weights, clamps or bolted flasks — because the metal standing in the sprue and risers presses up on it across the whole projected area of the casting.
A mold that closes slightly off its pins gives mismatch: the step you can feel at the parting line, measured as the displacement between the two halves. Under ISO 8062 that step is bounded only by the casting’s general tolerance grade unless the drawing says otherwise, so a part that needs it tighter has to carry a maximum mismatch value on the print.
If the cope lifts, the casting comes out oversize across the joint with thick flash at the seam — what a foundry calls a strained casting.
Weighted molds run 0.02 in. (0.5 mm) more 6-sigma dimensional variability than clamped ones, so on a close-tolerance part it is worth asking how the mold will be held.
Cope and Drag Patterns vs Match Plate Patterns
On a tooling quote, a cope and drag pattern means the two pattern halves are mounted on two separate plates, one for each half of the mold, rather than back to back on the two faces of a single match plate.
One match plate makes both halves of the mold at a single molding station; separate plates run at their own stations, and each is rammed, rolled and drawn on its own. Both are mounted tooling, doweled to the plate and located to the flask pins, unlike a loose split pattern the molder beds in the sand by hand.
The trigger is size. For parts in the range this plant pours, the pattern halves are too large and heavy to sit back to back on one plate, whatever the run length. The pintle socket above was tooled that way for a run of four castings, and so was a pattern set running six small steel castings to a mold, so the phrase on a quote says nothing about the volume the tooling is good for.
At that size the halves are CNC machined in hardwood or urethane and screwed to their plates.