Living with a PUK welder:
An Ongoing Review of PUK 3 Pro Plus welder

© Brian Meek, all rights reserved. V2.0

The PUK 3 in its original setup on a spare table. Note the improvised handpiece clamp and the microscope setup.

The PUK series of welders call themselves “Pulse Arc” welders. In practice, they function like desktop micro-TIG spot welders. TIG standing for “Tungsten Inert Gas” welding. Essentially what happens is that there are a set of large capacitors inside the PUK that charge up, and then release all their energy in a single pulse when the welder fires. This produces an arc of plasma between the tip of the tungsten electrode in the PUK handpiece, and whatever workpiece is being welded. The heat of the plasma melts a small spot of the target metal, which ideally fuses something together. The PUKs use high-purity argon to both shield the melted puddle from atmospheric oxygen, and to give the arc a pure gas to turn into plasma. With the inert gas shielding, the PUK welders can handle any jewelry metal, as well as exotics such as titanium & niobium. Silver and copper cause some issues because of their conductivity, but can be successfully welded with patience.

A word about silver (and copper): Silver is challenging for electric arc welders (like the PUK and others) because it’s so conductive. This conductivity makes it hard to get enough energy concentrated in one spot to make a decent weld. Silver takes substantially more power than gold or other jewelry metals. It also leaves black soot on the surface when it welds. This is apparently normal, and it cleans right off. After talking with other PUK users online, I found it is possible to get a good weld bead in silver with a PUK, but it takes patience and practice. I’ve only recently managed it.

The differences between the various versions of the PUK are largely ones of power and sophistication. The original PUK 111 welder didn’t have a whole lot of power, and the capacitors took a second or more to recharge between shots. The PUK 2 and 3 improved on this, but were (and are) still essentially tack welders. The PUK 3 Pro added electronic controls and a pair of “other” modes, one for micro-welding, and a ‘super high power’ mode (“gap mode”) to generate maximum power for hard to weld metals like silver.
The PUK 3 Pro Plus has several other features. The most important being even bigger capacitors for 30% more power and faster recharges, as well as 5 memory settings for common setups.
The newer PUK 3S was essentially the same as my PUK 3 Pro+, with the exception that Lampert unhitched the high-frequency start setting (helpful for silver) from the high power setting (gap mode). So the S model could do a better job with thin silver than my 3+. The 3S also switched to LED lights in the microscope, powered from an aux power supply built into the PUK itself. (meaning that Halogen lit microscopes from previous PUK models didn’t have the right power setup to run with the new version. Not a problem if you bought the scope/PUK together.)
The next PUK was/is the PUK4. The main obvious difference was that the 4 has a touch screen, more “saved” memory setting spots, as well as a bunch of “start here” recommended settings for basic sorts of jobs. Other than playing with a 4 at shows, I haven’t use one, so I welcome feedback from those who have used it.

Front and rear panels of the PUK 3 Pro Plus

This review will be of my machine, bought for my purposes, so let me explain what those were, and what I use it for.
I bought it from Otto Frei in December of 2007. I do a lot of work with reactive metals, such as titanium, niobium and tantalum. Without an inert-gas welder of some sort, there’s absolutely no way to join those materials. You can’t solder them, all you can do are cold connections of one type or another. To do large-scale holloware, that wasn’t enough, so I bought the PUK. I did not buy it for gold or silver jewelry repair. I’ve used it for that since, but that wasn’t the primary purpose, and it isn’t the majority of what I use it for.
I already had a spare binocular microscope, so I opted to save some money and just get the electronic shutter, rather than their full-on microscope setup. I also had an existing argon rig, so I decided not to get their argon regulator, and use my own, saving $150. Neither of these were wise decisions, for reasons I’ll go into at more length later. For now, just trust me: get their microscope, and their regulator.

Note from the future: Lampert stopped making the secondary shutter that I used for my scope. Apparently, I have one of only 20 ever made! Collector’s item! Make me an offer! So now you have to buy their scope. Trust me on this: you really want to anyway. Since the aux shutter is no longer available, and only 19 other people on the whole planet were nuts enough to buy one, I’m removing my ranting about it. For those of you coming later, be aware that the ranting wasn’t Lampert’s fault. The aux shutter was an idea whose time should never have come. The only reason they built one was to accommodate idiots like me. That said, I did eventually pony up for one of their scopes, and am quite happy with it.

The machine arrived in one big box, very well packed. Being a German company, Lampert are fastidious about such things, and the fit-and-finish of the machine are top notch. It’s a $4,000 hunk of hardware, and when you hold the handpiece, you feel it. It comes with a variety of widgets: three different grounding clips. (a set of pliers, a set of crosslock tweezers, and an alligator clip, all wired up to be the positive connection point for the arc.), a set of 10 electrodes with a diamond regrinding wheel, a small rotary hammer burr for the flex shaft, to allow you to burnish down porosity, as well as a very nice little fiberglass scratch brush. (Watch out for the slivers!) And a small bit of fiberglass cloth with no real explanation, but I surmise that it’s intended to be a spark-catcher. Since I didn’t get the microscope or regulator, mine just came with the auxiliary shutter fitting that clamps onto the bottom of my microscope. (In this case, a Nikon SMZ-10 — Oddball estate auctions are always worth the time...) The Mezzo microscope comes with a built-in clamp for the handpiece. Since I didn’t get that, I had to improvise one out of a test-tube clamp.

The bags of goodies that came with the PUK 3. The handpiece is in the bag on the left.

Setup was simple and straightforward. Plug this here, plug that there, and away you go. The only fun part was that the hose included for the argon is metric. To fit the metric barb fitting on the back of the machine, and the metric barb fitting on the metric argon regulator I didn’t buy. So it took some improvising to get their hose to attach to my (english) regulator. I did eventually manage it, but that’s not the only problem: the PUK 3 requires at least a little argon pressure before it’ll fire. It seems to do best with very low (1-2 Liter/min) flow rates. Most lab regulators get pretty flaky down in those low-flow situations. Not to mention that all the information from Lampert is in LPM, rather than PSI. The PUK regulator is specifically a low-flow regulator, and does a very good job in those ranges. I eventually decided it wasn’t worth the hassle of fussing with my normal argon regulator, and ordered one of the PUK regulators. Much easier now, and I’m chewing through much less argon. This is also a factor. The PUK documentation says that the PUK likes “Argon 4.6”. That’s a European designation. What you want to get from an American gas house is “Ultra-high purity” argon, or “5 nines” argon. (99.999 pure) Sometimes also known as argon 5.0. Since I have an inert-gas oven, I already had a bottle of welding grade argon. The PUK really didn’t like that for welding on titanium. The reason this matters is that a smallish bottle of welding argon (a “Q” bottle) runs me about $50. The same bottle in .99999 is $200. This is definitely a thing to consider, but lasers require high-test argon as well, so it’s pretty much a wash between the two systems.

My PUK is a 2007 model. Sometime in late 2008, Lampert introduced a new tip for the handpiece with a ceramic extension nose on it that restricts and focuses the argon flow, meaning that you use much less argon for most things. New machines come with this automatically, and older machines can be updated with a new nose for about $50. Otto Frei and Rio can both get the new noses. I improvised something similar by chopping up small sections of fast-food soda straws and using those to extend the nose of the handpiece. Mine burn eventually, but on the other hand, they’re free, and can be customized for any particular space or task that I need, in seconds. Specifically because I do reactive metals which need more shield gas, I like having the old-style wide nozzle. It gives me a larger area of protection. Reactives are so sensitive to atmospheric contamination of the weld that I built a secondary argon nozzle to flood the back sides of large reactive pieces with argon to prevent discoloration and weld embrittlement from atmospheric contamination. It would be nice if the PUK had a secondary argon port for this purpose. It would be even nicer if you could control the pre-and-post weld cycling of this secondary argon port. As it is, I just turn mine on, shoot my welds, and turn it off. So it just sits there, flooding $200/bottle argon into the room while I weld. Not the most efficient, but it does work, and I get great welds. I keep thinking about building a foot-pedal trigger for it, but I haven’t gotten there yet. If you’re not doing lots of reactives, you don’t need to bother with that sort of tweaking. (5 years later, I still haven’t built that foot pedal….)

My one complaint is the manual. Clearly it was written in German originally, and translated into English by a German speaker. It’s reasonably clear, but a little stilted. Having spoken German as a child, I can figure out what they mean, but some of their phrasing, especially of jeweler’s terms, is a little odd. The manual could certainly stand being reviewed by an English speaking jeweler. All of the technical information is still Eurocentric. Meaning that when they talk about what kind of argon the PUK needs, for example, they give you a European designation that an American gas house may or may not be familiar with. Equally, they talk about the regulator settings in liters per minute, rather than the PSI ratings that American regulators use. They don’t discuss electrode sharpening angles at all, other than to say you want a 15˚ tip, and that changes in the tip angle will change the weld size and penetration. If I didn’t already know about the relationships between tip angle and penetration from TIG welding, I’d be totally lost. Lampert also puts out electronic “how to” flyers every so often. These are useful, but not very detailed. They could certainly do a better job of user education.

On the other hand, having bumped into them at shows since I wrote this the first time, I can say that they’ll go out of their way to be helpful if you have problems or questions.

The left view is a rough idea what you see through their scope, except it’s colored yellow, and better lit.
This image was part of my rant about the now blessedly un-available aux shutter, so ignore the green image on the right.

Now that I’ve actually ponied up for a real Mezzo scope, I can say that they’re very nice. The view is good, and with the built-in LED (Halogen on older models) lighting, you can see clearly. The view’s yellow, because of the shutter, but this isn’t the scope to use for judging stones anyway. It’s more than clear enough for targeting a welder.

Now for actually using the PUK 3+
It’s a great little welder, so long as you understand what it does. It’s not exactly a spot welder, but it does fire individual welding pulses. In order to get a running seam, you have to take a shot, move the workpiece, take another shot, and so on. The biggest advantage to the PUK 3 Pro Plus is the bigger capacitors. They let it cycle much more quickly than any of the other models. Its cycle rate is about three shots every two seconds. (I understand that the PUK4 is about twice this fast.) In practice, that’s as fast, or faster than I can shift my hands, and retarget the tip. I never find myself waiting for it to cycle. As soon as I get the tip on target, it’s ready for me. If you’re used to normal TIG welding, it’s very much like a TIG in spot mode. Unlike a TIG, however, the PUK requires the tip be in contact with the target piece at the start of the welding cycle. The contact between the tip and the piece is the PUK’s signal to start the firing sequence. The handpiece has an internal actuator that pulls the electrode away from the target metal at the exact moment the welder fires. Sounds weird, but it works. Speaking of sound, in the high-powered mode, the handpiece squeaks when it fires. Turns out that this is an artifact of the high-frequency start system that aids in starting difficult welds. All the pulse-arc welders make the same squeak in HF-Start mode. (The Orions do too, I’ve tried them.) The squeak is the arc itself vibrating like a speaker drum. (Want your mind blown? Check out Plasma Speakers. Same effect.)

The big difference between my 3+ model, and the later 3S, was that Lampert broke the HF start out from the high power (gap) mode, so you could have HF start in lower power settings, which was good for delicate items, especially in silver.
My understanding of HF start is that the high speed vibration of the arc cause mixing of the weld puddle, which makes it easier to get a solid bond, especially in metals like silver that don’t really want to.

The handpiece itself is a beautifully machined piece of stainless steel. As I mentioned, the PUK is very much like a micro-TIG. So much so that it can even use small TIG electrodes. The PUK comes with a set of 10 ‘non-thoriated’ electrodes. You can get another box of 10 for a little more than $50. You use both ends, and you can re-sharpen them until they’re ground down to almost nothing, so they’re not too horribly expensive in the long run. Alternately, you can get .020” 2% ceriated tungsten TIG electrodes for about $20 for a pack of 10 (Here), and these are 7” long, unlike the 3” PUK electrodes. Cut them in half, and you have 20 electrodes for $20. I’ve been using ceriated electrodes on my PUK for years, and haven’t noticed any difference in performance. I suspect the ‘official’ PUK electrodes are actually also ceriated tungsten because they say they’re not thoriated (and thus radioactive) and they’re not as brittle as pure tungsten electrodes would be, which leaves not much else they could be. (There’s no way Lampert’s making a custom blended tungsten electrode.) This matters because you do chew them up pretty quickly, especially when running a long seam. Electrode changes are quick and easy. Just dismount the handpiece, pull the nose off, twist a little collet nut, pull the tungsten rod out, slap another one in to the right length, tighten the nut, replace the nose and handpiece, and you’re back. Takes about 30 seconds to do. The recommended 15˚ angle will give you the shallowest penetration, and the widest weld bead. As the tip blunts, your penetration will go up slightly, and your bead will grow narrower. In some instances, you may actually want a narrower weld puddle, so blunting the point may not always be a problem. In other instances such as tacking a piece together before soldering, you may not care at all, so long as the piece holds together long enough to solder. So in practice, the fact that it blunts points quickly may not be as much of an issue as you’d think. My procedure with the electrodes is to sharpen up the whole batch on my power-hone, use them all, then resharpen the batch. I’ve got a little pin-vise that I rigged to fit into the sharpening fixture for the power hone. It’s rigged to spin, which allows me to load it, sharpen each tip quickly, and then change out in a hurry. About 45 seconds to do both ends. The PUK electrode packs come with a little diamond disk that’s intended to be used in the flex shaft to free-hand sharpen the electrodes. That’ll probably work almost as well, I just already happened to have the power-hone etc. However you do it, tungsten electrodes are hard enough to require diamond abrasives to sharpen them effectively.

The later PUK models, like the 3S, and possibly the 4, came with a little micro-motor that hangs on the side of the machine, and is used for quick hand sharpening of electrodes, powered from the onboard aux power supply. I’ve used the powered sharpener. It’s definitely a widget, but it does work, and it’s a lot handier than trying to wing it with a flex shaft. Not having one myself, I don’t miss it, but it is a handy little toy.

First weld. .050” titanium. Note the brown & blue discolorations in the weld bead. This was due to using industrial argon initially, rather than the high-purity argon the PUK prefers.
This is the same sample as under the microscope above.

First weld, snapped open. I only welded one side, and cracked it open to test penetration.
At 80% power on gap mode, it got about 1/3 depth on a piece of .050” titanium.
Another sample welded on both sides could not be broken apart.

One of the advantages to the PUKs in general is that while I use mine under the microscope 99% of the time, if I get some large thing that just won’t fit under there, I can dismount the handpiece, and weld bare-handed, anywhere I can get the handpiece to fit into. Tempus Fugitive, the first large titanium goblet I did with the PUK had its legs welded together while I hand-held the PUK handpiece. There were some angles on those internal struts where I simply couldn’t get it to fit under the scope. The only trick to doing it bare-handed is to have very steady hands, and to remember to close your eyes after you hear the PUK beep. (You’ll only forget once...) Having previously worked with a laser that could only target through its microscope, and only handle things that would fit into the cabinet, this was a very handy feature for me and my larger pieces. The one feature of the laser that I do miss, and that you can’t fake with a PUK, is the ability to widen out the beam and go back over the weld a second time to smooth it out. Simply not something the PUK can do. On the other hand, even at $5000, the PUK is still 20% of the price of a small laser. For a difference of $20,000, I’ll deal with not being able to planish my welds with a hammer of coherent photons.

In conclusion, I’m quite happy with it. I’ve been using it for about five years, and haven’t had a moment’s trouble. It does exactly what I wanted, and does it at a reasonable price.
As I get time, I’ll add examples of welding different metals with it, specifically silver, so you can see what it can do.