Rotocast #17 | How to use metal inserts without losing parts feat. Rafael Renis | LIVE

What you gain by watching

• You gain criteria to specify metal inserts by torque, corrosion and application — not by catalog price.
• You see how to avoid a batch rejected abroad, a thread that won't start and rework with decisions made still in the design phase.
• You understand when a simple positioner, an automatic lathe or a real CNC makes sense in your process.

Episode chapters

1. 1

   Thirty years of inserts: Renis Usinagem and the art of molding metal into plastic

   We opened episode 17 of Rotocast with Rafael, from Renis Usinagem, a family business that has been producing inserts for rotomolding for nearly thirty years — and he takes us from its founding by his father, Mr. Ovidio, to the creation of Haro Usinagem during the pandemic. Along the way, we understand the fundamental division between assembled inserts, placed after the part is manufactured, and molded inserts, which go into the process already, varying in brass, stainless steel, aluminum, or carbon steel according to the customer's application. It is the story of a family business that turned metal into an inseparable part of rotomolded plastic.

   ▶ Watch at approximately 2:43
2. 2

   The right insert is not the cheapest one, it is the one that withstands the torque

   The question that got the conversation going was simple and direct: after all, what is this insert that everyone talks about and no one explains to those just getting started in rotomolding? We explained that there are two paths — the insert applied after the part is ready and the one that goes inside the mold, coming out already encapsulated by the plastic, protected against cracks and contamination — and that the decision between one and the other comes from the real need of the project: torque, corrosion resistance, type of fastening.

   ▶ Watch at approximately 7:51
3. 3

   Without the right part, the entire batch comes back from abroad

   Problem-solving over thirty years became accumulated knowledge that we now try to apply to avoid part loss and mold defects — and one of the clearest cases was that of a customer who exported to the United States and saw the batch rejected abroad because of an out-of-spec insert. We pursued the project and showed that the solution was not to adapt any random nut into the middle of the plastic, but to specify the right insert for each application: "You're going to put an insert like this here in a dumpster, it's the smallest one," but as long as it is well specified, because oversizing generates cost and less result in the end.

   ▶ Watch at approximately 13:12
4. 4

   When the Little Insert Becomes a Nightmare on the Rotomolding Line

   A partnership of nearly three decades with Resi Plastic taught us that the insert ready in the drawing looks like the fastest path, until the standard thread doesn't fit because of plastic shrinkage and the fit becomes exclusive to that part. What we advocate is bringing the supplier to the table during the design, because standardization and quality in the insert prevent rework, a client turning up their nose, and that emergency technical solution everyone knows as a hack job.

   It's that famous technical solution, you know, better known as a hack job.

   ▶ Watch at approximately 18:13
5. 5

   The poorly specified insert that consumes two employees per part

   We've seen the inadequate insert delay production in a way that the cost doesn't even tell the whole story: while one employee placed the insert in the mold, the other removed and carried the part, which is absurd when there's a shortage of people on the line. The solution we brought was to show, with hands-on examples, how an insert positioner welded to the ring simplifies assembly inside the mold and gives time back to production; the same logic of experience that makes the difference between the mechanical lathe and the CNC, where one machine doesn't always solve what the other solves.

   He spent more time placing four inserts inside the mold than he did loading, removing, and loading the part.

   ▶ Watch at approximately 24:40
6. 6

   What to do when one director wants a R$ 1 million CNC and the other advocates a R$ 5 thousand lathe

   When a newly arrived director proposed a R$ 5 thousand turret lathe to solve the machining, the old director resisted: "let's buy two more lathes, buy another milling machine", fighting for a CNC costing more than R$ 1 million. In the end, we showed that the decision isn't about having the most modern machine, it's about analyzing cost-benefit — like a tiny insert that would be unfeasible on the CNC but delivers a productivity gain on the automatic lathe.

   Oh no, they bought the machine, it didn't solve it.

   ▶ Watch at approximately 29:42
7. 7

   When the insert comes loose in the middle of the river: the joint of two parts that solved the torque problem

   A customer thought that switching to chrome would solve everything, but we know that in the food-grade line the base has to be stainless steel, otherwise there will be flaking and contamination — and the mindset of those who demand results without letting things get solved blocks any progress. It was exactly in a partnership like that that we turned things around: in solar energy floaters in constant motion, the aluminum insert came loose on its own during the panel assembly, so we developed a second part with the same flat that goes in under pressure, without welding, letting the plastic adhere and ensuring much more resistant torque.

   ▶ Watch at approximately 34:46
8. 8

   Bits, 304 stainless steel and the lathe operator who made ten parts while the other made one

   In the Minas Gerais city known for dairy, the people there dealt with 304 stainless steel using bits, taking half a step at a time and stopping to sharpen the tool — a struggle that even compromised the quality of the BSP threads. When we arrived to work as a lathe operator, we started buying inserts, welding and assembling our own tools; in the first week, while the colleague produced one part, we had already made ten on the lathe next to him. The insight that remains is that many people only see the cost of the holder and the insert, but they work their whole lives the way they learned — and never knew another way.

   While he produced one part, I had already made ten on the lathe next to him.

   ▶ Watch at approximately 39:48
9. 9

   The right tool for each metal and insert: when the problem isn't the machine, it's the partner

   From cast iron to graphited bronze, each material requires a type of tool — and anyone who has ever broken a part on the lathe knows the cost of getting the angle wrong. That's what we talked about when we opened the little bag of metal inserts and showed, in practice, that a metal core in a rotomolded part goes far beyond threading: it's reinforcement, positioning and torque, and only a partner company develops your project together instead of just delivering the product.

   I think what's more important is for you to know what Renes or Haro is today, a partner company that will come and develop your need.

   ▶ Watch at approximately 44:55
10. 10

    The weld nobody sees and the test that guarantees everything

    We went through it piece by piece and got to a fuel strainer from the agricultural line, all in stainless steel — and then came the detail that almost nobody outside the factory sees: the alignment between different diameters, which only those who work with stainless steel know how much it weighs on the weld. To make sure the machine doesn't draw air into the diesel and cause equipment failure, every part goes through a leak test submerged in a tank, with air injection, one hundred percent at Rennes. And it was in that vein that a comment in the chat raised the alert: there are a lot of engineers specifying material and tolerance without knowing the application — on screen it works, in production it doesn't fit.

    ▶ Watch at approximately 49:59
11. 11

    A bricklayer, a strand of hair and the hundredth that brings down the project

    The question that opened the conversation was simple and uncomfortable: does the engineer know what a hundredth is in practice — or only on paper? To show the size of the damage, we told the case of the bricklayer who delivers nine meters of wall and leaves one meter 'that nobody will see', and we used the image of a strand of hair divided by ten to give scale to the problem. The twist is that the more the designer knows the factory floor — engineering plastics, mold, temperature, insert, machining — the less he asks for what he doesn't need, avoids unnecessary regrinding and EDM, and in the end, what wins is the part and the client's cost.

    ▶ Watch at approximately 55:05
12. 12

    A metal insert can put an end to the leachate in the condominium

    Ever imagined delivering a part that pierces or cracks on the first impact and seeing the client having to replace the entire tank? That was exactly the case we remembered from condominiums, where the thread would break and the leachate would leak — and the solution we defend is simple: putting a metal insert with a large base, with a reinforcement plate on the feet, so the part can withstand hits and last much longer. In the end, the message that remains is that it's not price, it's the cost of your sleep — and seeking a partner specialized in molds with that experience makes all the difference in the cost-benefit that the client sees.

    It's not price, it's the cost of your sleep.

    ▶ Watch at approximately 1:01:15
13. 13

    The bolt that threads all the way in and the other one that doesn't even start

    The pain that shows up most on the workbench is thread depth variation: when assembling the mating part, one bolt goes all the way in and the other doesn't even start threading, because the part came out without threads. That's why we showed the complete path of the insert, from design and raw material to the lathe, with strict process control, the recently earned ISO 9000 certification, final inspection, degreaser cleaning, and air injection on practically 100% of the parts so no chips are left at the bottom of the thread.

    So when you go to assemble the mating part, the bolt threads all the way in, the other one doesn't thread. Damn. The other one doesn't even start the thread because the part has no thread.

    ▶ Watch at approximately 1:06:39
14. 14

    Blind inserts, rolled threads, and the care that avoids rework in machining

    When the insert is blind, dirt and chips stay hidden deep inside – and that's where cleaning with compressed air and degreaser comes in, along with final inspection and packaging before sending a little kiss to the box and delivering it to the customer. That's exactly the kind of care almost no one maintains: rework costs more than production, and when the customer already has the product on the machine and the inserts come with variation or dirt, the bill gets even worse.

    Send a little kiss to the box and deliver it to the customer.

    ▶ Watch at approximately 1:11:59
15. 15

    Stainless steel isn't all the same: the mistake that rusts tanks, bids, and the reputation of whoever sells

    Not every stainless steel suits every product – milk attacks the steel's protective layer and gradually weakens it, salt air and chemicals require the right specification of 304, 316, or 316L, and in a bid the cheap option can turn into a headache. From public gym stainless steel that oxidized to the tank that got rust spots because carbon steel sparks stuck to the stainless steel from a distance, the lesson is that technical information and attention to after-sales, with support that arrives the same day or within twenty-four hours, is what separates those who deliver a lock nut from those who build thirty years of trust – because everyone makes mistakes, what matters is how they're resolved.

    Milk gradually attacks that protective layer of the stainless steel, right. So it ends up, it doesn't oxidize, but it starts to weaken, it keeps breaking down.

    ▶ Watch at approximately 1:17:01
16. 16

    A rotomolding group that refuses to settle for just 'I've been through that'

    We want to break the paradigm of keeping information within a small group and create a space where the real pains of the factory floor are addressed live, every month, with those facing the same problem. That's how our rotomolding group was born: virtual meetings with partner companies, cases like metal inserts brought to the table, and the certainty that sharing experience without fear makes the market move faster. Anyone who wants to join or sponsor the Rotocast will find open doors via WhatsApp, and in our marketplace there's already a line set up waiting for those who need used equipment with a short deadline.

    We want to break the paradigm of information exchange. Oh, man, I'm not going to send this here in the group because there are people who won't like it. No.

    ▶ Watch at approximately 1:22:07
17. 17

    An invitation to see machining from the inside

    We closed the episode by opening our doors: anyone with any difficulty, not only in rotomolding but in machining in general, is welcome to exchange experience with us and add value along with the client. Our heartfelt thanks to the whole team, employees, suppliers, partners, and clients — and here's the invitation to visit Renis Usinagem in São Caetano do Sul, have a coffee, and follow our videos on Instagram.

    Lots of experience, lots of information exchange to add value, yeah, add value to the client, right?

    ▶ Watch at approximately 1:27:19