U.S. Heatstake · Design Reference
Design the joint before the boss.
Five decisions, made in the order you'll actually face them. Get the five right and the press does the easy part. This guide is a set of tools, not a lecture: put your numbers in, get your geometry out.
Decision 1 of 5
What does this joint have to survive?
Not "what should the boss look like." That comes last. Start with the job the joint has to do, because one answer below changes everything downstream.
When not to heat stake
A stake is a plastic rivet. It is permanent, it loads best in shear, and it does not come back off nicely. Walk away from staking when:
| The joint sees sustained tension | A formed head holds parts together; it is not a tie rod. Sustained pull-off load wants a screw in a brass insert. |
| Service happens more than once | A hollow stake survives one careful re-form. Anything beyond that, use an insert. Your service techs will say thank you, quietly. |
| The material is a thermoset or silicone | If it cures instead of melts, there is nothing to form. No heat process will fix chemistry. |
| You need adjustability | Staked parts do not shim, slide, or reposition. Decide the position first, stake it second. |
Decision 2 of 5
Your plastic decides more than you do.
Amorphous resins soften over a wide band, like butter on a warm bench. Semi-crystalline resins hold their shape right up until they don't. That one difference sets the temperature, the process window, and how much forgiveness you get.
Your pick carries through the calculator and the head selector below.
Show the numbers — tip temperature by resin
| Resin | Behaviour | Tip window, °C | Tip window, °F |
|---|
Filled grades: add about 20 °C (36 °F) and read the glass-fill warning in the calculator. Windows are starting points for a contact tip; confirm on your part, not ours.
Decision 3 of 5
Size the stud, and the rest follows.
Every dimension in a staked joint hangs off one number: the stud diameter. The head has to come from somewhere, and conservation of mass is strict about it. Type your diameter in; the drawing and every number update as you go.
0.118 in
Show the numbers — the whole guide in seven ratios
| Feature | Rule | Why |
|---|---|---|
| Stud protrusion | 1.5–2.0 × D | Exactly enough material to fill the head, plus a little for the corners. |
| Formed head | 2 × D wide, 0.5 × D tall | The proportion that grips without starving the stud. |
| Boss at the base | 2–3 × D | Spreads the working load into the wall instead of a point. |
| Clearance hole | D + 10–25% | Room to locate; small enough that the head still bridges it. |
| Root radius | 0.4 mm minimum | Sharp inside corners are where cracks are born. This is the cheapest strength you will ever buy. |
| Edge distance | 2 × D minimum | Keeps the melt zone out of thin, fast-cooling territory. |
| Solid or hollow | Hollow above 4 mm | Big solid studs heat slow and sink the base. Hollow forms fast and pulls harder. |
Decision 4 of 5
Pick the head that matches the job.
Six head profiles cover nearly every joint we've ever tooled. Answer the questions, then grab the model and spin it — the cutaway shows what the formed head actually does inside the joint.
drag to rotate · scroll to zoom
Decision 5 of 5
Now make it moldable — and stake-able.
Five details separate a drawing that molds clean and stakes clean from one that fights you for a year. None of them cost anything while the tool is still being cut. All of them are expensive the week after.
Draft: 0.5–1° per side
On the stud and the boss. The part has to leave the mold before it can meet the press.
Root radius: 0.4 mm minimum
At the stud base and the boss base. Nearly every "process problem" we get sent starts as a sharp corner on a print.
Lead-in on the hole: 0.5 mm
A small chamfer on the mating hole finds the stud for you. Robots appreciate it; operators appreciate it more.
Stud tolerance: ±0.05 mm
The stud sets every other number, so hold it tighter than the parts around it.
Keep the gate away
A weld line through a boss is a crack with a head start. Ask your molder where the flow fronts meet.
The cycle that forms the head
Impulse staking heats, forms, cools under pressure, and only then lets go. Cooling under load is the difference between a head that stays tight and one that springs back loose on the bench.
After the fact
When the head looks wrong, start here.
Nine times out of ten the machine is innocent. Find the symptom you're holding in your hand; the cause and the fix come as a pair.
Take it with you
The one-pager.
Everything above, boiled down to one card. If you've used the calculator, your numbers are already on it. Print it, pin it above the monitor. We've seen shops laminate it; we respect that.
Send us the part. We'll tell you if it works before you cut steel.
Quotes in 24 hours, tooling in about 4 weeks, 12-month warranty on the press. A real person answers the phone — usually the one who set up a press that morning.
U.S. Heatstake · Roanoke, Indiana · Benchtop and integrated impulse presses, up to 8 bosses per cycle · usheatstake.com