Fittings and threaded parts made to drawing

We cast fittings to the customer’s drawing, in zinc or aluminium, and thread and machine them in house, so the part can go straight into your assembly. Two of our product examples show exactly this: a zinc bracket threaded and finished here and a zinc furniture bracket.

What characterises a fitting

A fitting has no function of its own. It exists only to hold two other things together. All its value therefore sits in the interfaces, and this type of part tolerates less slop than any of the other three.

The practical consequence is that dimensions should be set from the seating face, not from the outer edge of the part. A casting has draft on every external face. Measure the hole from the outer edge and you are measuring from a face that is not perpendicular to anything. Measure from the seating face and you are measuring from the face that actually meets the part it is fixed to.

Threads: cast, cut or insert

Cast thread. Possible, but only coarse threads and only where the parting line allows it. The tolerance is a casting tolerance, not a thread tolerance. It rarely suits anything that will be unscrewed again.

Cut or formed thread. The standard choice. The hole is cast with a core, and the thread is cut or formed in the CNC machine afterwards. That gives the correct thread class and a position that repeats from part to part. Zinc takes threads well: soft enough to form cleanly, hard enough to hold.

Threaded insert. When the thread must survive many disassembly cycles, or when a steel bolt in soft metal is a problem. It costs one extra operation.

Which of the three fits depends on how many times the screw comes out again, and on the tightening torque. Send us both figures and you get a concrete answer. There is more on the choice in threads in cast parts.

When casting fits

• Complex interface geometry. A fitting that meets a profile at one angle and a plate at another can be cast in one piece.
• Holes are cored in. That removes most of the drilling and cuts machining time per part.
• Casting and machining in house. The part does not travel between foundry and machine shop. You have one point of responsibility when a thread is out of tolerance, and no transport leg adding days to the lead time. See CNC machining.

When casting does not fit

• A standard part does the job. Buy it.
• The fitting is a flat plate with four holes. Laser cut it.
• The quantity is small and the part simple. Machine it from billet.
• The thread must carry high preload in a safety-critical joint. Then steel is the right material, not aluminium or zinc.

From drawing to finished fitting

We review the drawing before the tool is ordered: which threads are to be cut, where the machining allowance goes, and which faces the dimensions are taken from. We procure the tool, and you own it. Casting, threading, machining and blasting happen here. If the fitting is to be coated, a sub-supplier does it, and we order and follow up that step. The whole chain is described in from drawing to assembly-ready part.

What customers usually ask

What do you need to quote? The drawing with thread sizes, quantities per order and per year, and how many times the part has to be taken apart. Request a quote.