London studio · UK & international projects
Bespoke injection moulds and mould inserts, CNC machined from solid aluminium in our London studio: for benchtop presses, for your moulder's mould base, and for runs of plastic parts from the first prototypes to the first few thousand.
Four cavities, one shot
Made around your part
Stranger Hands designs and machines bespoke injection moulds in our London studio. Send the part you want to mould, as a CAD file, a drawing, a sketch or a sample, and tell us the plastic, the number of parts and the press it will run in. We check the part for moulding first: draft, wall thickness, undercuts and where the mould will split, and suggest the small changes that help it fill cleanly and drop out of the tool. Then we design the mould around it, with the parting line, sprue, runners, gates, vents and ejector pins placed for your plastic, and cut the cavity and core from solid aluminium on our CNC machining centre. It takes mould plates up to 400 × 265 mm and 180 mm tall, changes between nine cutters by itself, and repeats its position to ±0.01 mm, so the two halves line up and an insert fits the pocket it was made for. We make complete two-plate moulds for benchtop and desktop injection presses, cavity and core inserts for a moulder's mould base, multi-cavity and family moulds, and new or corrected inserts for a mould you already have. Aluminium tooling suits prototypes, bridge tooling and short runs, from tens of parts to thousands, at a fraction of the cost and lead time of hardened steel. Every mould is checked against the model before it leaves, cavities can be polished or textured, and we adjust the tool after your first shots if the parts need it. We quote before any work starts and post across the UK and abroad.
One design, four coloursWhat we can help with
Before anything is cut, we check your part for draft, even walls, undercuts and sink marks, decide where the mould splits and where the plastic goes in, and suggest the small changes that help it fill cleanly and drop out of the tool.
Cavities and cores are machined from 7075 or 6061 aluminium, which cuts quickly, carries heat away fast so each shot cools sooner, and costs far less than hardened steel. Small inserts in brass, copper or steel can be made by agreement.
Mould plates up to 400 × 265 mm and 180 mm tall are machined in one setup, on a machine that repeats its position to ±0.01 mm, so the cavity meets the core, shut-offs seal and inserts drop into their pockets.
A benchtop or desktop press, or your moulder's production machine: send its make and model, and the mould is sized for its platens and clamping, with the sprue seated to its nozzle and the part and runners within its shot size.
A single cavity to prove the design, several identical cavities to make more parts in every shot, or a family mould with the different parts of one product on the same runner.
Cavities are polished for gloss and clear parts, bead-blasted for an even matt, or left as machined where a face will not show. Lettering, logos, part numbers and date marks are cut into the cavity, mirrored so they read the right way on the part.
A short shot, flash or a part that sticks is usually cured by a small change to a gate, a vent or the polish. Send the mould back with a few of its first parts, and we make the change.
What we make
Tell us the part, the number you need and the press it will run in, and we will suggest the tool: a complete mould, inserts for the mould base your moulder already has, or a change to a mould you own.
1Complete two-plate aluminium moulds for desktop and benchtop injection presses, sized for your machine's platens and clamp, with the sprue seated to its nozzle.
2Cavity and core inserts that drop into your moulder's mould base or master frame, for bridge tooling and short production runs before steel.
3Several copies of one part, or every part of a small product, filled through one runner in each shot, so each shot makes more.
4A corrected cavity, a revised insert, an added vent, lettering or a date mark, machined to fit a mould you already have.
Kinds of mould
Most of our moulds are one of these three. The figures are a guide: tell us the part, the plastic and the number you need, and we quote the tool for it.
One cavity
Proving a design in the real plastic, a first batch for testing, or a product's first customers.
Ask about this mould ↗Two to eight cavities
Small batches for sale, spare parts, kits and launch stock, in identical or family cavities.
Ask about this mould ↗Cavity & core inserts
Bridge tooling before steel, or a moulder who already has the base and the press.
Ask about this mould ↗Not sure which you need? Send the part and the number you want, and we will suggest the tool, or tell you if silicone casting would serve you better.
Ask which mould suits ↗Sizes, tolerances and files
The facts most moulds need before a quote. If your part is close to a limit, send it anyway: there is often a way to mould it.
Faces that slide past the mould as it opens need a slight taper, or the part grips the tool. Allow at least 1° on smooth faces and 2–3° on textured ones. If your model has none, we add it and show you where.
Plastic shrinks as it cools, and thick sections shrink most, leaving sink marks and warping. Keep walls between about 1 and 3 mm, the same thickness throughout, and hollow out thick areas instead of filling them.
Stiffen a part with ribs rather than thickness. Make each rib about half to two-thirds as thick as the wall it stands on, so it does not pull a sink mark into the face behind it.
Sharp inside corners stress the plastic and cannot be cut by a round cutter. Give inside corners a radius of at least half the wall thickness, and the outside corners that radius plus the wall.
Anything that stops the part sliding straight out, such as a hook, a hole through a side wall or a groove round the outside, needs a side action or a loose core. Many can be designed out; tell us which must stay.
Every grade shrinks by its own amount, and every press has a largest shot and a largest mould. Name both, and we size the cavity, the runners and the gates for them.
Not sure your part is ready to mould? Send it anyway. We check every design before quoting, and suggest the changes that make it easier to mould and cheaper to make.
Send us your part ↗What our moulds make
From part to mould
Send a 3D file, a drawing, a sketch or a sample, with the plastic, the number of parts you need, and the make and model of the press the mould will run in.
We check the part for moulding, suggest any changes, and quote the mould with its price and lead time. Nothing is cut until you approve the design.
The mould is designed around your part, its toolpaths simulated with a collision check, and the cavity, core, runners and pin holes cut from solid.
The mould is deburred, polished or textured, assembled and checked against the model, then posted across the UK or abroad, or collected from the studio.
Injection or silicone?
Both make identical copies from one tool, and we make both. An injection mould is machined from metal and filled with molten plastic by a press; a silicone mould is poured around a master and filled with casting resin by hand. How many parts you need decides which.
Three questions, one recommendation
Question 1 of 3
A few useful answers
A metal tool, usually in two halves, with the shape of your part cut into it. An injection moulding press clamps the halves together, forces molten plastic in through the sprue and runners, lets it cool, then opens and pushes the part out. The same mould makes the same part every time, often in under a minute.
It depends on the plastic, the shape of the part and how the mould is run. In unfilled plastics such as polypropylene, polyethylene, ABS and TPE, an aluminium mould usually lasts from a few thousand to tens of thousands of shots. Glass-filled and other abrasive plastics wear it faster. Tell us how many parts you need, and we design the mould for it, or suggest steel inserts for a longer run.
Most thermoplastics: polypropylene (PP), polyethylene (PE), polystyrene, ABS, nylon, acetal (POM), polycarbonate, PETG and TPE. Tell us the exact grade, because each shrinks by its own amount as it cools, and we size the cavity to allow for it. Very hot plastics such as PEEK, and heavily glass-filled grades, need a conversation first.
Yes, if you send its make and model, or its platen size, largest mould size, clamping method, nozzle radius and shot volume. We size the mould to fit, seat the sprue against your nozzle, and check that the part and its runners stay within what the press can inject in one shot.
Yes. Send the drawing of the pocket in their mould base or master frame, or the frame itself, and we machine cavity and core inserts to fit it, with the ejector pin holes and water lines where their tool needs them.
Mould plates up to 400 × 265 mm and 180 mm tall, machined in one setup. That covers most moulds for benchtop presses and inserts for standard mould bases. A larger part can sometimes be moulded from an insert set in a bigger base, or split into pieces that fit together. Send the dimensions and we will tell you what is possible.
Cavities and cores are machined to ±0.05 mm as standard, and shut-offs, pin holes and insert pockets to ±0.02 mm when you name them on a drawing and we agree it in the quote. The machine repeats its position to ±0.01 mm. Plastic shrinks as it cools, so tell us the dimensions that matter on the finished part, and we allow for your plastic's shrinkage in the mould.
Often, with a small change to the part or the mould. A snap fit can usually be designed to release straight out of the mould. An undercut on the outside needs a side action, and one on the inside a lifter or a loose core, each of which adds to the cost. An external thread can be split along the parting line. Send the part and we will suggest the simplest way to mould it.
Yes. Lettering, logos, part numbers, recycling marks and date marks are cut into the cavity, mirrored so they read the right way on the part, and can stand proud or sit recessed. Lettering reads best at 2 mm tall or more, in a clean sans-serif.
We make the mould; you or your moulder run it in your own press. If you have neither, say so in your enquiry: for a handful to a few dozen parts, silicone moulding and resin casting, which we do in the studio, is often the better route, and we can quote both.
Choose an injection mould for hundreds or thousands of identical parts in a thermoplastic, when the cost of each part matters more than the cost of the tool. Choose silicone moulding and resin casting for a handful to a few dozen parts, or when the parts should be cast in epoxy or polyurethane resin.
It depends on the size and shape of the part, the number of cavities, any side actions, the finish and the tolerances. An aluminium mould costs a fraction of hardened steel production tooling and is ready in a fraction of the time. Send your part and we quote the price and the lead time together before any work starts.
Tell us the essentials
Send your part as a 3D file (STEP preferred), a drawing or a sample, with the plastic you will mould, the number of parts you need, the press it will run in (make and model), the finish you want and the date you need the mould by.
Some photographs are from Unsplash, by hosein fayton, mastars MT, Mastars and Defrino Maasy.
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