26 Oct How it’s made: Large security cabinet and safe
This month’s ‘How it’s made’ details the complex nature of projects we undertake at Constant. This large security cabinet, primarily a money safe, is designed for a leading high-street chain of stores to allow easy depositing of cash from the shop floor. Our client briefed us with the requirements of the security cabinet, provided the preferred locks for us to integrate into the design and provided the general specifications to follow.
This case study follows the initial prototype in the factory.
Before you read on, here’s a snapshot of the complexity of the metalwork of the 5 main units making up this cabinet:
- Measures height 1500mm, depth 600mm and width 600mm
- 7 sheets of mild steel, at 2.5m x 1.25m in varying thicknesses
- 301 ancillary fixings including hinges, nuts, rivets, screws and washers
- 160kg in weight
- Over 34 metal component parts
- 7 key operated locks
- 2 digital keypad locks
- 5 metal doors
- 1 metal drawer with shoot
- 1 internal cabinet housing 3 tier shelving unit with individual self closing and locking doors
How it’s Made Stages and Processes
1: CAD Phase
Our CAD designers spent in excess of four days drawing up the cabinet in Solidworks for production. To give a comparison, an average part we design for an air conditioning unit may take up to 2 hours to program. The complex nature of the project, and the security aspect, meant extra detail and attention had to be paid on the joins, hinges, and any other element prone to attack. As we already have designed and manufactured a range of security chests and cabinets, this was familiar territory for us.
The unit can be seen here in closed view, open view and section view. Each drawing by the CAD team details the parts, assembly elements, bends, rivet placements, welding marks and of course, the shape to cut on the machines. The CAD drawings (with elements blurred for confidentially agreement) detail the complex nature of just two metal parts of the 34 this unit entails.
2: Metal to Laser Cutting
The first manufacturing step is to take the pieces of mild steel and cut them on our Trumpf laser cutting machine. The steel measures 2.5m x 1.25m in size, and varying thicknesses from 1.5mm to 2mm. Our prototypes like this cabinet typically get cut on our laser, and then transferred to our CNC punch machines once they go into mass production. The laser cutter gives us more flexibility if we need to potentially re-program and re-cut parts or components during the prototype phase.
You can see one of the seven sheets of metal being laser cut on our Trumpf TruLaser 3030 in this video.
3: Over 150 expert bends
These photos highlight the complex nature of the cabinet and the bends involved in the design. To make a cabinet secure from attack, edges are bent in on themselves to prevent devices prying joints apart or open.
Here you can see our machine operator bending one of the internal enclosures, using a combination of his time-served experience and the pre-programmed instructions to create expertly bent and sturdy metal work.
4: Castellated marks
These small nicks out of the metalwork are not flaws or cutting errors, they are in fact called castellated marks to indicate where to weld when welding parts together.
5: Riveting the enclosure
Once bent, our team of welders rivet various parts together before welding. This speeds up the assembly of the main units, and reduces the quantity of tack welding required when joining the parts securely together. Rivets also hold the unit in shape, reducing the need for several jigs.
The rivet holes are pre-programmed in during the CAD and laser cutting steps, so there is no guess work to as where the holes are, and alignment of the cabinet. It is much like slotting together a large jigsaw with the rivets as guide marks.
6: Tack welding
The welding team then took the riveted enclosure, and tack welded the inside seams before MIG welding them together. All the joins are secured by two methods when finished; rivets and welds.
Tack welding is the same concept as pinning and sewing. Tacks (pins) are dotted along a join to secure it in place tightly before the MIG welding (sewing) welds along the entire length sealing the join.
To give extra strength to the sides of the cabinets we insert metal bridges, described as ‘top-hats’ in the industry. These top hats are put along the walls of the external cabinets, but also help locate the internal cabinets into place.
In the time-lapse video you will see the welder tack welding the top-hat into place.
8: Making of the drawer with hidden shoot
The drawer within the bottom metal cabinet isn’t as simple as it initially looks. It holds a drop flap to allow the contents of the drawer to drop into the locked cabinet below. The flap has to be strong enough to hold large volumes of coins without buckling, so it is reinforced with metal strips seen in the photos as the ‘E’ shape.
Then the hinge on the flap is fixed to the drawer’s back panel. The welder clamps the two pieces together with a small hand clamp, and then the hinge is spot welded using a spot welding machine. The welder knows where to place the spot welds as there are small engraving marks in the metal work designed by the CAD team and laser cutter. The spot welds went in repetition in-between the knuckles of the hinge.
When the shoot flap is attached to the main drawer body, the team attached a set of rollers to guide the drop flap back and forth when the drawer is in motion, making it easier to operate.
Testing the drawer
The drawer is then placed into the unit to test it fits snugly, and also the rollers work as intended.
The drawers then have runners attached, and then fitted permanently into the bottom cabinet.
9: Forming the top cabinet
The top unit consists of a three shelved unit, which is transformed into a three tier secure cabinet, with doors, self closing studs and locks.
Testing doors and alignment
Before the internal unit is fitted into place, the welder checks that the doors align and fit snug enough to deter attack.
Fixing the snap lock in place
The client provided specialist internal locking mechanisms for us to fit. These were bolted into place and then the locking unit was welded to secure it further.
Internal shelving cabinet
The team place the internal shelving unit into the main top cabinet. It is riveted into place at the bottom and top. This unit doesn’t need to be welded as it won’t be vulnerable to attack from external forces as it sits within the main external cabinet.
Hinging all the doors
Now the top cabinet has its internal section in place, all the doors, which there are four of, are attached to the main body of the enclosure, and to the internal unit. We’ve used specialist piano style hinges, which means they only need to be riveted into place with minimal welding.
The welder and assembly teams test the doors close properly, align correctly, and the locks align and work. He does this for each door before he moves to the next one completing the top unit.
Completed top cabinet
As per the client’s request, small studs, ended with a rubber cap, are affixed to the main external door. This means when the external door is closed, if any internal doors are open they will be pushed shut, and due to the lock mechanism on the doors, it will auto lock. Making the cabinet, in a manner, self securing as the main external door closes.
10: Bottom casing, smoothing edges
The bottom cabinet also has an internal cabinet. This one holds the contents deposited from the drawer above. This internal cabinet was riveted together initially during the first stages, however it then has a jig placed inside, which can be seen as the square shaped ‘O’ in the photo, as this allows the welder to guarantee the welds will be at the correct angles, reducing the movement of the cabinet when welding.
Once the cabinet is welded, he grinds down the welds to make them smooth. This isn’t just for aesthetics, it also helps prevent the internal cabinet from sticking or not fitting into the external cabinet.
11: Finished metal security cabinet
The three main sections of the large metal secure cabinet: Top shelving unit, middle drawer and bottom cabinet.
Keypad locking mechanisms are fitted onto the two external cabinet doors, alongside a traditional key operated lock.
Drawer and shoot
Here is an example of how the drop shoot drawer works.
- The drawer is opened. The drawer is quiet heavy, and this is by design. Once the drawer is closed, one doesn’t want an opportunist to pull it open a split second later before the shoot empties into the bottom cabinet.
- Contents are placed in. For our example we’ve used Mr Badger. He is a favourite toy of Rosie, one of our office dogs. What better way to demonstrate a secure money cabinet than making sure one of our mascot’s toys are kept safe!
- The drawer is then closed.
- Empty drawer remains. If you open the drawer again the contents have disappeared. The shoot flap can’t be pushed or forced down due to the design. It has a hidden shelf making the shoot flap, when open, double strength and ridged. Again, another measure to prevent opportunist theft.
- The safe contents. Opening the bottom cabinet reveals Mr Badger, safe and sound. Sent down there by the automatic shoot built into the drawer above. You can see the shoot’s flap in the top half of the photo.
- We’ve filmed a short video of Mr Badger demonstrating the shoot drawer mechanism.
12: Final cabinet in various situations
13: Production Edition of the Cabinet
The end unit has been signed off, and now in full production at Constant. Here’s the unit in its powder coated glory.