Here’s something that may be of interest to all the reprappers, vacuum formers, and other plastic fabbers out there: ultrasonic welding of plastics. If you’ve ever wanted to join two pieces of plastic without melting them together with acetone or screwing them together, [circuitguru] is your guy.

Ultrasonic welder setups are usually reserved for companies that don’t mind spending tens of thousands of dollars on a piece equipment. There are smaller versions made for heat staking - melting plastic pillars into rivets on the work piece – and [circuitguru] was lucky enough a somewhat reasonable price.

Because the heat staking gun was a handheld unit, a rotary tool drill press was put to work. The end result is a relatively inexpensive way to join two plastic parts without screws, glue, or solvents. The bond is pretty strong, too. Check out the video after the break to see [circuitguru] join two pieces of a plastic enclosure and try to tear them apart.

This project really puts an end to arguing over who has to ride in the back of the tandem bicycle. We challenge you not to smile while viewing the maiden voyage that [Carlos] and his daughter take on this side-by-side bicycle. The video can be found after the break.

It certainly makes a bit more sense than an over-under tandem, and the fabrication process is really quite manageable. This requires alterations to the seat, handle bars, and pedals, but the majority of the bike (frame, gearing, fork, wheels) is unaltered.

The cranks have been replaced by a custom welded cam mechanism that reminds us of how the pedals on a paddle boat work. Both riders must pedal at the same time and rate. To give each a place to sit the seat post was converted into a T bar to host saddles to the right and left of the frame. Finally, the handle bars are the most complicated of all. Extra framing was welded onto both sides for the front tube to provide a place to mount two pair of handle bars. One of them is fixed in place, the other can be turned, using a lever mechanism to steer the front fork.

It looks a bit awkward to get started, but once both riders are up it seems quite stable.

Someone let [Tane] play around with welding equipment and bicycle parts and look what happened! He built a diminutive velocipede. Now that’s just a term for a human-powered land vehicle, but the term fits a bit better as this is missing most of the stuff you’d expect to see on a bicycle.

He started with a mountain bike and a kick scooter, then went to work on both with a hack saw. A bit of welding and angle grinding left him with what you see above. It’s still steerable, but missing are the cranks, chain, and brakes. That’s okay though, the bike is low enough for your legs to reach the ground – you start it up and come to a stop Fred-Flintstone-Style.

[Tane] originally meant to add electric propulsion but didn’t quite get around to it. There’s always the option to add a hub motor to the rear wheel if he has the time and motivation.

So you fancy yourself as an amateur engineer? Been working on those welding skills for a while? The real test is to trust your children’s lives on a roller coaster you’ve designed and built (translated).

Now we’re not talking some tired old carnival ride like the teacups. This is a full-blown roller coaster, complete with an upside-down loop. The ride starts off with a chain-lift to the top of the garage/barn roof. From there it’s off and away on the single-rider train. We’d recommend keeping your hands and feet inside the car… if there was a car. The ride utilizes an automobile seat, but you’ll have to settle for a lap-belt as there’s no shoulder restraint here. We’re a bit wary of the track footings – we’d bet they’re not well anchored in the ground – but the fact that the entire length of track has been painted makes us think that [John Ivers] might have known at least a little bit about what he was doing. Don’t forget to catch the video below the fold.

Update: Much better video now embedded after the break thanks to [Tom 101's] link in the comments.

Update: Source link changes to the original thanks to [Mike's] comment.

Well produced overview of the coaster:

Quick and dirty demo:

[Thanks Andrew]

[Andrew] built himself a stoplight that flashes along with the music. Unlike the traffic signal we checked in on a year ago, this one’s not a reused municipal fixture. [Andrew] imported a 3D model into Sketchup, printed out the results, and traced them onto Bristol board to make his templates. He cut out the parts, used a brake for the bending, then a combination of spot and MIG welding to complete the housing. Off to his school’s spray booth for priming, baking, and painting for a perfect finish.

The internals are what you’d expect. Each light source is made up of a cluster of LEDs controlled by an Arduino. Music synchronization is handled by a Processing script that [Andrew] wrote, which you can see in action after the break.

This recumbent trike was built using parts from three salvaged bikes and without welding. These bikes are a bit easier on the back and neck than the traditional riding position. This one also allows for a shorter pedal crank which was a concern for the creator, [Barry Millman]. Not only did he do a fantastic job of making the thing, but he shared the project in verbose detail.

It’s a good build. It won’t win a prize for light-weight design as it includes a big chunk of plywood. But it is worth the weight hit if welding is not an option. For your viewing pleasure you’ll find a short parking lot test-drive of the finished recumbent after the break.

Oh, and if you want a more dangerous cycling build, try this over-under tandem.

[Rob] just finished reinforcing a cheap drill motor. He picked up the tool at Harbor Freight and ditched the case. The plastic retaining ring was replaced with a thick metal washer which he machine The washer uses three bolts to attach to the mounting plate that he welded together. We’re not exactly sure what he’s got in mind as he only mentioned that this will be used with a robot. We wouldn’t mind having one of these as a bench motor but there must be hundreds of uses now that it can be attached to just about anything. It seems Harbor Freight has become popular as hacking’s raw material source. The last example we saw of this was a welding table made from a utility cart.

[Todd Harrison] put together a welding cart that has all kinds of tricks built-in. The carcass is a cheap rolling cart that has been reinforced with steel plate and beefier wheels. The top tray can be loaded up with fire brick for oxygen-acetylene welding or with a grate for cutting. That grate lets the slag fall through and into the red-rimmed fire-box below. Finally, there’s a steel plate to the right of the cart that rotates and slides over the top of the unit to prepare it for MIG welding. Todd walks us through his versatile invention in the video after the break. This will nicely augment your other welding hacks.

[Rob] sent us some information on how he converted his flux-cored welder to a metal inert gas welder. He used a piece of DOM tubing as a collet with a side inlet tube that he uses to inject carbon dioxide. The gas is sourced from a 12 ounce paint ball CO2 tank and it looks like there’s a valve right at the junction with the collet. We wonder how long it would take to tear through one of those tanks, but if you’re not doing a lot of MIG welding this saves on the upfront cost of buying a separate setup.

[Joel] wanted to use his newly acquired welding skills to make something useful. With tasty flesh in mind he put together this meat smoker. What resulted is incredible, but the fact that he then gave it away as a gift is just amazing.

A curved joint between two pipes is known as a ‘fish mouth’. They can be a hassle, as with the pirate wheel project, but [Joel] used his noggin to make things easier. He first modeled two 55 gallon drums in CAD. The intersecting curve was then generated by the software, printed out on paper, and stenciled on the drum to be cut out with a jigsaw.

[Joel's] writeup is greatly detailed and shares many pictures. He makes every part of this smoker, including the wood handles and the stainless steel grates. The guy really knows how to build stuff, but we should have known that after seeing the Crushtoberfest.

If you’re marooned on a desert island, you want to have a Professor who can build useful items out of coconuts. [LostMachine] is one of those guys, and he’s currently building a land-loving pirate ship. The wacky vehicle will use the giant wheel above to propel the vessel while the captain sits comfortably in the lofty crow’s nest. A crack-pot concept? Not really, he plans to take this to Burning Man where it will be a fairly useful build compared to the folks who have really gone off the deep end.

The story here is the build quality. Take some time to watch his videos which we’ve embedded after the break. In the first, he details his method for creating a precisely level building surface on top of his uneven driveway. This is accomplished by welding supports in a circle that are level compared to the center point. He goes on to share his liquid-cooling system for cutting the pipe supports with a custom-built jig and an old windshield washer water system pump from an RV (second video). The final video shows the construction of the wheel which came in with 2000 welds and about 250-300 hours of construction time.

If you hadn’t guessed, [LostMachine] is a structural engineer. Unfortunately he was laid-off this spring which has put a damper in his building schedule. We hope that with a quality project like this in his portfolio a new job is just around the corner for him.

Creating a level surface on an uneven driveway.

Cooling jig to cut fish mouthed joints in pipes.

Building the big wheel.

[Thanks Rebecca]

Spot welders are used in the fabrication of automobiles, PC cases, power supplies, microwave ovens, electrical junction boxes, Faraday cages, and various electronics. A spot welder is used because it produces a highly defined point of contact weld. The materials are welded without excessive heating, so working pieces are handled easily. The weld is also highly controlled and repeatable. In this how-to we cover the basics of a spot welder, and then show you how to build one from a microwave oven transformer.

A spot welder’s electrodes serve at least three functions. They transfer electrical energy to the material while also holding it together; this also controls resistance. The greater the pinch force the less the resistance, which results in decreased resistive heating. A lesser pinch force results in increased resistive heating. The electrodes also conduct heat away from the material, while in the off cycles, helping to cool and temper the weld. A resistive spot weld is commonly referred to as a ‘nugget’. Spot welders are generally confined to ferrous materials which somewhat limits their application range. Most produce a weld with low voltage and high current. The welder in this How-to operates from a secondary of 3vac. The primary is 120vac line voltage that should be treated with respect. The low voltage secondary makes the welder very safe, so the electrical shock hazard from the electrode is virtually non-existent. There is however the risk of burn due to the high temperatures as with any welder.

This particular welder is not intended to weld a body panel on your 1966 Jeep; it will not work well on material heavier than 20gauge sheet metal. The intended use is for small projects, for it is not capable of continuous operation. Possible uses are as follows: Welding electrode material for electrolysis cells. Working with the fine components of a vacuum tube. Building a light weight frame for a small robotic platform. Most of us have enough parts laying around to build a spot welder. If you have a microwave oven transformer (MOT) laying around, then you are half way there. On a related note, we had covered a microwave oven arc welder in 2006.

We also needed some heavy gauge copper wire. We used about four feet of 4AWG wire to build the spot welder in the photo. Other materials included scrap 2×6, 2×2, two copper screw type lugs, two copper welding cable lugs, two MIG welder tips, two 4″ x 3/4″ zinc plated corner braces, drywall screws, and three washers.

Pictured above is a working MOT. The first thing we had to do was remove the secondary coils. Namely the high voltage winding, and the low voltage winding. We used an angle grinder with cut off wheel while being careful not to cut the primary winding.

We cut the secondary flush with the MOT laminate core. Both sides of the MOT should be cut. Inspect the MOT for signs that the laminate has been welded. We have found that welded MOTs can handle a little more abuse than their sealed only counter parts. If possible try to keep the core insulation intact, where the secondary will be wound. Though it is not a show stopper if the insulation becomes damaged. The insulation makes it a little easier to wrap the heavy gauge secondary.

After removal of the secondary we had something that resembles the above photo. If the magnetic shunt material falls out be sure to replace it as it was before. The shunt keeps the core from transferring too much power to the secondary. A magnetic ballast if you will. The shunt acts to control the saturation of the core. A brute force project like this relies on such a shunt for proper operation.

Rewinding a MOT with 4AWG is no walk in the park. If you’ve damaged the core insulators, we suggest wrapping a layer of electrical tape in their place. This will help to avoid damaging the insulation on the wire as it is pulled through the core.  Our experience is that 3-4 windings is plenty. After all, this spot welder relies on high current and marginal resistance. Not high voltage.

We were careful to ensure that the secondary coil was wrapped in a helical manner to complete the secondary.

We mounted the MOT and 2×2 to the 2×6 base. This particular build used 12″ 2×6 with two 7″ 2×2. These dimensions may or may not work depending on the physical size of your MOT. The only critical part here is keeping the wire length as short as possible.

After the lower jaw was mounted, we also attached the corner braces. It was found that a spare piece of 2×2 as a shim worked well to align the upper and lower jaw. After the upper jaw was aligned we attached it to the corner braces with screws. This formed the hinged portion of the jaw.

The picture above shows the MIG welder tip and the screw type copper lug. This is an improvement from an earlier model we had built. Initially, we used copper tubing with a hole and a piece of 6AWG grounding wire serving as the welding electrode. The grounding wire was held in place by a screw that threaded inside the copper tube perpendicular to the electrode. It was very crude, but it worked. This new method is much more practical.

Here are the two electrodes ready to be fixed to the lower and upper jaws. We double checked the MIG electrodes to make sure they were tight. A loose connection will take heat away from the weld nugget.

Evenly aligning the welding electrodes, we were careful to keep the upper jaw in the natural position where it was mounted. This maintained a flat contact area for the welding electrodes. After we were sure that the electrodes had been properly aligned, the jaws were marked. We then drilled a small hole. Since we mounted with the grain of the 2×2 the holes helped to protect from splitting the 2×2.

With the electrodes mounted, we cut the wire to proper length. We never cut the exact amount we need. We always cut more than we need. This rule of thumb should apply to all electrical wiring. After all it is much easier to cut off excess than wrap a new secondary.

We bent the wires in to the approximate positions in which they were to be assembled and stripped the wire in preparation for the crimp type welding lugs. It is a good idea to strip more than is needed here as well. Simply cut off excess after sizing up the lugs depth. Never crimp insulation with the lug. This will create a potential problem area due to the loss of conduction.

Using a good non insulation crimp tool to secure the wire. We inspected the crimp and gave it the tug test. Simply tug on the wire if it is loose it will pull out. It if doesn’t pull out then an adequate crimp suitable for high current has been made.

The crimped wires were attached to the welding electrodes with screws. We were careful not to over tighten the screws. If a drywall screw had stripped out of the wood, we would have had to use a larger wood screw in its place. After both welding electrodes were fixed to the jaws, we aligned the electrodes. Using pliers we bent the electrodes so that they contacted each other evenly. The electrodes should be fairly close already since they were aligned before drilling.

We opened the jaws and wired the primary to an electrical cord and then tested the secondary. If the breaker trips, check for the following:

1. The secondary is  shorted (the jaws are closed)
2. The magnetic shunts are missing or not properly reinstalled
3. Faulty line wiring to primary or shorted primary
4. Too much load on the circuit of test or undersized breaker

We observed proper electrical wiring practices. It is also stressed that this is a welder and it should have a dedicated circuit as any other welder would have.

With the power physically disconnected we verified the welding electrode alignment with the material we intended to work on. Before connecting the power and performing an initial weld, we observed a few safety guidelines. This is a welder and will produce very high temperatures. Keep fingers away from the welding electrodes. Allow the material to cool prior to handling. Always wear eye protection. You may be interested in reading about spot welder parameters. There’s also the problem of combustible materials…

This Compaq used very thin aluminum to support the screen and connect the hinges. The metal broke and destroyed most of the lower plastic. We were able to make new supports from 22AWG stainless steel sheet metal. All the welds were made using the spot welder with a special power controller. The power controller will be covered in another how-to.

When welding with an AC arc welder, it is often necessary to “scratch start” them to get the arc going. For those unfamiliar, it is just like it sounds. You drag the head across something just like a giant match. There are some that come with an arc stabilizer or “high frequency starter”. This is preferred, but they can be hard to find. [Bill] shows us how to make one of our own. Though you may have an easy enough time finding a big transformer, you might run into some difficulty finding the capacitors, and tungsten spark gaps. If you manage to get your hands on them, you can follow [Bill]‘s schematic and build one of these starters for yourself.

Wow, Caribbean Conquest Day is such a dull holiday. If it’s a holiday at all: we’re at work today and you probably are too. We decided to post what we’re working on in hopes of breaking out of our holiday slump. Pictured above are two IR illuminator boards we assembled this weekend. We bought the kits from BG Micro. We’re planning on testing their camera blocking ability once we come up with a ~13V portable power source.

That’s what we’re doing. What have you been working on lately?

(If anyone can find a source for the welding goggles in the picture, we’d love to hear it.)