Make a spot welder

[Steven Sesselmann]

Hi Guys,

Yesterday I made a spot welder, it only takes a couple of hours and works perfectly for welding thin parts, such as your grid wires etc..

Firstly let me credit RF technologies for giving me the idea to use a MOT and Gabriel Mendez for suggesting the drill press.

STEP 1
Take an old microwave oven transformer and carefully remove the secondary coil (the one with the thinner wire).

STEP 2
Find a thick insulated copper cable and wind it three times around the iron core, where the primary was. (an old start cable works well).

STEP 3
Fit a switch and a 10 amp fuse in front of the primary

STEP 4
Make a couple of copper electrodes and solder these to either end of the cable.

STEP 5
Make up some insulators for the copper electrodes, I used nylon, but wood is okay too, as we are only dealing with 3 volts.

STEP 6
Rig up some kind of press, or if you have a drill press, then you have all you need

Have fun sticking bits of metal together..

Steven

http://www.beeresearch.com.au

[gabrielArgentina]

Very simple and nice work!! congratulations!!!.
Gabriel.

[ScottC]

I made something similar a few years ago. You may have trouble with the copper electrodes sticking to what you're welding. I made mine from brass with a tungsten insert in the center that I could change out. It worked well with small SS wire also. I like the drill press idea, I'll have to set something up like that for my mill.

Nice work.

Scott

[MarkS]

funny story... it is what we used to make our grid

happy new years!

[George Schmermund]

http://www.harborfreight.com/cpi/ctaf/d ... mber=45689

[Richard Hull]

Nice job! that sort of thing was what I used for my first spot welder, until I found the super Raytheon electron tube element spot welder at a hamfest for $2.00! It weighed about 60 lbs.

The Raytheon uses the classic variable joule setting heat control of a capacitive discharge type and uses large thyratron tube switching to pulse the internal transformer with 600 volts stored in large capacitors. About all this gives you over your operation is a highly accurate, repeatable energy delivery so that once you "dial in" of find "your heat" you can replicate every weld for thousands of welds.

The one thing I had to get was the proper electrodes. Those I obtained at a local welding shop. The pro's use a special high phosphorus copper. Pure copper will stick at certain energies with certain materials. The proper electrodes never, ever, stick.

Richard Hull

[Eldarion]

does anyone know how to build a TiG welder from similar stuff?

[tligon]

I agree with Richard ... slip on down to the local welding supplier and see what they have in the way of welding electrodes. You can also order them on-line, or buy the stock material from some place like McMaster Carr.

In my case, I bartered for a beat-up, broken-down, real spot welder with an 80 joule capacity from my former employer. They owed me for a consulting job and were about to go bankrupt, so I saved somebody the cost of disposing of the thing. The thyratron-based charging circuit was shot (Richard probably has a tube for it in the drawer somewhere). I simply bypassed the fancy part and adjusted the primary voltage using an autotransformer. The real key was the selection of electrodes I found in a box in its accessory drawer, the mechanism for pressing them together, and the ability to adjust the electrode force at which the unit fired.

I grew spoiled using it. I left it with EMC2 when I came home, and saw it last summer, still in use in Dr. Nebel's lab out in Santa Fe.

Dog and Pony 2 is seriously in need of a new outer grid, and is not making a good star mode due to the present mismatch of the inner and outer grids. I have not taken the time to build a good new spot welder, so have been putting off building the replacements. I'd like to try the tantalum wire Richard gave me for a new inner grid. I really like the drill press approach.

[tligon]

Man, I was shopping e-bay last night and spotted a Weldmatic like the one I donated to EMC2, listed for about $1k.

I've been asked to drag Dog and Pony II to at least one SF convention this summer, and the grids are a wreck. It is time to get off my fanny and do something about it.

E-bay has a number of hand-held spot welders available, all grossly overpowered welding 0.020" wire, but evidently containing a beefy step-down transformer and with a set of arms and electrodes that can be adjusted in force, with a triggering system driven by a hand grip. The more advanced ones use cycle-counting to adjust energy delivered. I suspect the cheaper ones may just run on a pressure switch.

I expect even the smallest of these would vaporize grid wire, but I'm intrigued by the mechanism. Has anyone here tried building a capacitor discharge system for one of these? Or just running one on an autotransformer at really low voltage (I have a 20A Variac). I could get a photoflash cap capable of storing aroung 60 joules at 160 V for about $40, and discharge it thru the primary.

The going price for a Pitbull DN-100S is about $120, shipped. There's another popular model by Harbor Freight for a bit more (which probably means the Pitbull is lower quality than HF carries!).

[Doug Coulter]

Here's the one I built and use for grids and type C thermocouple wire (which is tungsten/rhenium).
I also have the harbor freight one, which works well with some custom electrode tips (to reach into funny places) on a large variac so it does skinny stuff.

But the cap discharge one is far more repeatable for tiny things, controlled jaw pressure, energy, etc.

This is a couple old computer caps (from the mainframe days), a variable volt regulator, and a big SCR from an old X ray machine.

Most should be obvious from the pic. I was planning to write it up someday....

Wire welder (MIG) tips work well for this and don't weld to the work. Special alloy used (just try to do anything with them other than grinding -- warned you ;~).

Buying a tap for the MIG tips is both easier and cheaper than making a big copper electrode set, they're cheap enough to grind them to custom shapes, and they work better.

[tligon]

Doug,

I was figuring the physical form of the hand spotwelder might adapt well to a homebrew cap discharge system, but I've never messed with one. Since you have the Harbor Freight, can you tell me if it has electronics driving the primary? Evidently the better ones in the $500 range count out a number of cycles at 60 Hz to control energy.

Do the economy models just respond to pressure on the lever to switch current? If so I would think I could rig a capacitor, rectifier, and autotransformer to charge the thing up to the desired joules, and just plug it in. Or bypass the electronics and do the same thing.

I like the fact that for $120 you get replacable (hopefully standardized) electrodes on arms, plus the transformer, plus apparently some abiity to adjust force.

[Doug Coulter]

The Harbor Freight one is as dirt-simple as it can possibly be. It's just a switch on the primary. Weld pressure is by feel on the handle, which is a toggle type so if work thickness changes it's hard to get the new feel, and no, I've not seen where to get new tips for these yet -- probably such a good copy of the original (have to find that) that the same spares would work.
They are that same "special" alloy of Cu that a file simply skids across, cool stuff, but can be nasty to reshape and clean gunk welded on to them -- they are hard to remove to hold on a grinder.
I've had good luck getting spares from Grizzly and from McMaster on the Chinese stuff, but H-F, forget it.

So what I did there is buy a copper rod the right diameter (5/8" IIRC), bend it as desired, thread end for one of those MIG tips, which was also ground as desired...and now it's nice. This made the lower electrode more or less horizontal and skinnier at the end so it could reach inside things like grids. It's rare I turn the variac above 60 or 70v (it's a big variac that can take this and not sag).

Anyway, it's not fancy enough to count cycles, and one Bill brought over the other day didn't either, it just had a variable one-shot driving the SCR bridge. So, even it needed a variac, but didn't have provisions for it (but it wouldn't take much to fix that part).

Given the lack of control (even with a variac, which does help a lot) and the still inability of the thing to do type C wire reliably, I built the other thing. I use both, it depends on the job.

You really need all of pressure control, voltage control, and time -- and to really do it right on some materials, time-variable power so you anneal the weld while still clamped -- else you can make some things so brittle they go bang when removed. The fancy stuff can give a current profile of X cycles to max, controlled time at a settable max, then a controlled ramp back down, and having tried one, it's really nice. But very expensive and mostly not needed.

Good eye hand coordination and a little mental focus (things happen fast) can overcome most of that. Practice first...you can flip the switch just so for only a few cycles...kind of a wipe your fingertip across it motion.

I'm going by the American Welding society books here a lot, which I lucked into (the entire series for a few bucks, used). That's been a godsend -- if you want to know how to stick Ti to unobtainium, cladded with bizzarium that's been brazed with irridium, this will tell you how to get it right on the first try more often than not, including the type of every filler and flux and how to do it technique wise. Good stuff (9 volumes @ about $100 ea if bought new).

So I made an adjustable spring loaded jaw on the variable energy pulsed one, and that really does the deal on small delicate stuff, much less skill needed. Basically, there's a pot on there to set cap charge volts, and a switch to fire it. It holds the work in there by the adjustable jaw pressure. Very repeatable. Oh, and a heck of a lot lighter in weight so it's easy to move and to stash when not in use. About 30-40 lbs lighter...a fairly big deal if you sometimes have arthritis. The other one only looks portable!

The only other way I've been able to weld type C thermocouple wire (W/Re alloy) or W is with a jig I made for the TIG welder that holds the torch end, and a grounded fat W electrode adjustable in a 2" sq iron pipe (both facing inward across the pipe at one end, so the inert gas stays in there a bit). You just get an arc going (push the button) and it will sit there and you can use it like a very very hot flame....nice and cheap and easy, once you have the welder. Which by the way, I got the HF cheap inverter TIG and it stinks roundly -- anyone want a cheap TIG that kinda almost works if you're a real pro on only some things? But the more expensive Grizzly one is a complete joy -- every automatic ramp you could want, current waveform, duty cycles, AC/DC....the works, and it makes perfect welds of course, even for me. Don't get a cheap TIG, they are not worth it. Especially not without a high voltage, high frequency starter.

I *really* liked the transformer in the H-F spot welder, though, so I bought another (ouch) and took it apart. There's one big U of copper for the secondary, about 1/4" by 1.5" by maybe a foot leg all in the core -- look at the picture, that's all transformer with tips hung on it, a real beast.

So for a truly overkill, very stiff voltage source for my evaporation stuff, I wound a new secondary on it with #6 wire, 8 turns with enough welded-on 1/4" brass bolts to have taps at 0, .5 turn, 1 turn, and so on up. I run 6-8v nominal heaters off the 4 turn tap for Al deposition. I added a *big* SS relay and a button for use with my vacuum system for that. This would have been a good job for a MOT -- this is way overkill, but nice..,
For evaporation, you almost cannot have a stiff enough voltage source to make things run smooth in the presence of a 10::1 change in load as the heater heats up. Trying too small a transformer in "overload" for that means it sits there for all too long, then gets way too hot way too fast as the heater resistance suddenly goes up 5-10x with temperature. With a stiff source, you can just push the button until the material has deposited almost enough (takes awhile to quit), let go, and wait, you're done.

The H-F spot welder welds .030 Ti wire just fine on the variac but takes a "touch" to do really nice work. (and a lot of other things less critical, it's a good tool). Spot welders are way good things to have.

I'll have to write all these up for my website, and post here when I do so y'all can see what I use.

[tligon]

Thanks! Hard to see how I can go too far wrong with that thing, cheap as it is. If I can adapt it to low power or capacitive discharge, so much the better.

Worst that happens, I'll use it to fix the tractor. A guy can never have too much welding equipment.

I remember all the skills I had to learn using the Weldmatic ... keep in mind, I was the one who introduced Richard to Hirsch Farnsworth machines, so I've been building lopsided grids for longer than most of you, just not since I gave up that beat up old Weldmatic, which is similar in a lot of ways to Richard's,and almost as old.

But knowing some of the people here have successfully welded tungsten is really impressive ... I never could do it without making such a brittle weld the thing snapped before I could finish the grid. I have some tantalum Richard gave me years ago that I always wanted to try. The C thermocouple wire sounds interesting, too.

[Doug Coulter]

You're welcome of course. I wouldn't buy it just for the mechanicals, which aren't that great, but it's usable indeed. Making a new lower electrode wasn't that easy (machining OFHC copper is always fun) but way worth it. The main thing it needs is better control over the input power, for which lamp dimmer types of thing don't work well -- A variac is better. A timer would be better yet. As it is, it will definately fix your tractor -- I agree you can't have too much welding gear. Here we have TIG, MIG, regular arc, oxy-acet, oxy propane, and spot, at least two of each. The right tools make things easy.

When I can, I use TIG for W and Ti. Works better if you can get the power down low enough (the grizzly machine does). My main welding of tungsten is wires, as I haven't found a good source of sheet tungsten.

Speaking of lopsided grids, I'm the cylinder grid guy here at the moment -- I like the way they work in both theory and practice. Here's one I did without any welding -- graphite end caps and all done by precise, tight fits. The camera gives it more of a twisted look that it really has, perspective and all that.
Those are tungsten rods (.040" tig rods, pure), graphite end caps, and Ti bolt and bottom washer.
This one makes record neutrons (for me, with the possible measurement errors both here and elsewhere, it may or may not be an amateur fusor record). Next time I make sure there's no dirt under the circle table when I drill the holes for the rods! All those materials were from McMaster.

If you want replaceable tips, the cool tip (!) is really to use the MIG tips you can get for a buck each at any hardware store -- same alloy, the little hole is not really a problem if you use them off axis, and in the bargain they make great torch tips for my glass blowing torch too...They have a weird thread, but you can get a tap for that...

[Richard Hull]

I picked up my Raytheon tube element spot welder about 4 miles from Tom's home at the Manassas hamfest back in 2000. It has several smoothly adjustable ranges but the the max impulse is 60 joules. There are 8 vacuum tubes in the thing and a large mercury thyratron blasts about 1000 volts from a capacitor bank into a large iron core transformer whose secondary is about 5 turns of 3/8" copper pipe. I had to make up my own cables and points from the proper allyed point purchased from a welding shop.

When I got the welder at the fest, it was $1.00 and was missing a couple of tubes, which I ultimately found and once cleaned up has been my tube element and grid welder for all these years.

Tom, you are always welcome to visit and use mine if you get in a lurch.

Richard Hull

[tligon]

Richard,

Thanks for the offer, but if I don't build my own spot-welder I will find ways to put off doing what I ought to be doing on my fusor, as I have for about 9 years now.

Years ago I started a write-up on what it would take to build one for making grids, and never finished the project ... largely because I knew I needed to build the thing before I published the article. A couple of things that stopped me:

1. I wanted to find caps intended for high discharge.

2. I needed to specify a step-down transformer anyone could get.

3. I needed to come up with functional electrodes handy for making grids.

The excuse kept coming back to the transformer. I kept meaning to get a Radio Shack 4A 12V to see if that would do the job, but never did because I had enough doubts that it would do squat to demotivate me to get a round tuit.

The welder shipped yesterday. I can be absolutely certain that the transformer therein is capable of spot welding. Even if the electrodes prove useless, I can still stick an insulator between them, u-bolt a couple of cables to the electrode arms, and route power over to electrodes of more suitable design (I have something in mind based on needle-nosed pliers and some copper-chrome rod from McMaster-Carr).

And I believe it won't take much effort to attach this unit to a capacitor discharge system to drive it. I found a large photoflash cap on a surplus site a few days ago that should work, resulting in a unit of about the power of yours. I don't think I've ever used more than about 20 joules making grids before, and 60-ish should be plenty. If I need more I would just use the unit on a conventional supply.

[DaveC]

At work we use an old Hughes cap discharge welder. 50 w-sec. single pulse and a 25 w-sec anneal ( possibly unnecessary ) does a good job on 0.063 SS wire, that we use for cathode structures and such. From my experience, the clamp pressure has a lot to do with the energy needed and the weld quality. No surprise there, eh?

FWIW.


Dave Cooper

[Richard Hull]

I have a couple of good transformers for the job. I used one to make an early crude system prior to falling into the Raytheon unit.

Look at hamfests...........

I found a 120/240 primary to 2.5 volt 80 amp filament xfrmr for an old transmitter. Another I have is a 120v to 5 volt 100amp filament xfrmr. I am reasonably sure a modified or rewound M.O.T. might be turned to this discharge service, albeit rather weakly.

Richard Hull

[tligon]

I used to routinely fire annealing pulses using the Weldmatic.

Yes, force on the electrodes when the thing fires is the secret to happiness. I presently have a kludge setup involving an old lead acid battery and electrodes pulled together using rubber bands. The force applied is OK, but slapping a lead against a lead acid battery just is not cutting it for consistent energy delivery. I managed to stick my inner grid back on its lead that way about a year ago, but it involved a lot of very bad language, and I'm not going to build replacements that way.

I came across this outfit when looking for suitable high-discharge capacitors. From the looks of the product line I have to believe people here have discovered them as well.

http://www.amazing1.com/capacitors.htm

The 1500 mfd photoflash cap, charged to 170 V using 120 V and a FWBR rectifier, should hold 21.6 joules. The 6300 mfd cap they list ought to do around 91 joules at 170 V. Taking better advantage of the voltage ratings would kick butt, but there is no reason to be greedy.

But with the current capability of the spot welder (did I see 2500 A?), I might even consider a bank of the 6300 mfd caps. They point out that 10 in parallel is 5000 joules ... picture discharging that into a small rail gun? What does it take to build a plasmoid generator? All kinds of high energy mischief could ensue!

[George Schmermund]

Dave - You're right about the pressure being important for a good weld when using a CD type welder. I have several of both Hughes and Unitek supplies. I also have several of the assorted weld heads for them. The weld head and electrodes are as important in choice as the PS itself. A good weld head will allow adjustment of the electrode pressure by using a variable spring load setting. This arrangement sets a repeatable pre-load to the work before the discharge is triggered. The spring loading will also determine the amount of follow-up pressure that is applied to the weld "nugget" that is formed at the interface of the parts being welded. If the follow-up pressure is not fast and adequate, an unsatisfactory weld results.

I use a pull tester to check things like filament to post welds. Pull testing is also mandatory for assuring good welds when making platinum RTDs. These wires are only 3 mils in diameter and the weld must be able to handle thermal excursions from -50 deg.C to +450 deg.C repeatedly and forever (?).

My workhorse right now is a Hughes dual range 0 - 20 Ws / 0 - 100 Ws. It offers a choice of 3 pulse shape settings. The 0 -20 range allows me to make repeatable fractional Ws welds. I use a Unitek Weldmatic miniature welding head with it. This is a foot operated head which allows use of both hands for positioning the work.The range of position adjustment is wide and it accepts a large array of electrodes for welding together just about any metal or alloy. Copper to copper? Just slide a small piece of nickel foil in-between.

[tligon]

You're breaking my heart! All those wonderful features on my old Weldmatic! Foot pedal operation ... adjustable electrode holders ... rigid mechanism to move the electrodes together ... adjustment of firing pressure ... meter calibrated in Watt-Seconds ... and a drawer full of electrodes of various shapes. Sigh!

Hopefully it will help EMC2 make fusion one day. Dr. Nebel said it was getting a little erratic ... maybe the relay is going bad (I paralleled an SCR on its mate where I used to work, really cleaned up the pulses), or possibly the caps are failing (the poor thing was built around 1961, was used on Project Mercury).

I'll probably wind up with rubber bands for electrode tension. Maybe a weight. Position the electrodes and work, apply tension, then go over and fire the system.

[tligon]

The handheld spot welder arrived, and the thing is exactly what I hoped it would be, a big honking step-down transformer powered straight off 120 VAC with a simple momentary contact switch on the primary.

The first thing I did was weld a fender washer to a piece of angle iron, and my first attempt produced a solid weld.

That simple no-electronics circuit should mean I can just build up a box with a photoflash cap in it, a rectifier, and some simple switch to control charging, plus probably some means of bleeding it when done. Plug the welder in to the cap, plug the cap box into my variac set to the desired voltage, swat the switch, and bingo, a precise pulse of energy delivered according to V^2*C/2. The same design would probably work just fine with a modification of a microwave oven transformer (for you newbies needing a cheap spotwelder, that's MOT above ... do your part for the environment and recycle microwave ovens into fusion equipment).

I am working on a design for a specialized set of electrodes for making grids. I did pick up some MIG electrodes at Harbor Freight which look fine for the "top" electrode, but I think they are too bulky for inside of an inner grid of the 6-ring geodesic I normally use. I'll probably use a bent piece of copper-chrome rod of about 3/16 or 1/4 in diameter, rounded on the end and with a groove in it to seat the grid wire. The lower electrode will be rigid, the upper mounted to a hinge from the common support, probably Garolite LE. But hard wood would work, too.

That's my theory. Of course, in theory, theory and practice are the same. In practice, they aren't. So I guess now I have to build it and post the results here.

[Doug Coulter]

Tom,
for my mods on the HF welder, what I did was replace the fat rods (they are just clamped in) with some Cu stock from McMaster. For the bottom one, I simply didn't bend it 90 degrees as they did, but only about 15 degrees -- so it's nearly straight, just bent enough so that the tips can meet. I then mounted one of the MIG tips in that, tilted up only slightly, perhaps another 15 degrees. That makes it fit inside grids pretty well. They have to be bigger inside than 5/8" or so, not a big problem. The top electrode could just as well have been left stock as it doesn't have to fit inside anything.

I'll be interested in hearing about results dumping a capacitor into one of these -- haven't tried that yet. The CD one I built just uses the cap and an SCR -- no need for a big transformer in that one, just need a little one to get the caps charged. In my case I added an LM317 and a pot to control the cap voltage.
The tricks there were making the jaws, and finding an SCR that would take the peak currents -- I used Be copper for the "hinge" on the top one, and added an adjustable spring for consistent (but light) pressure. I got lucky on the SCR from an old X ray controller. Seems the peak ratings of SCR's can't be inferred from the normal ratings -- some will hack huge peaks, some won't, and size isn't a terribly good indicator of that -- you just have to hit the data sheets.

I found repeatable, light pressure more important the smaller the thing I was trying to weld.

[tligon]

Doug,

Actually, this is more for the newbies trying to figure which one of us to copy ...

Long ago I had one of those big computer caps, maybe a quarter of a Farad or so. I have no idea what became of it. It was great fun to make big sparks with it, and it most certainly could have spot welded.

I have used low-voltage electrolytics to spot-weld (typically fusing thermocouple ends), and obviously they will work. What makes me steer clear of them is stories about damaging them with high-currrent discharges. If you can find caps intended for this they may hold up OK. By the same token, if they are cheap and easy to replace, they may be just fine for making the occasional fusor grid. Controlling the charge voltage with an LM 317 or a good bench supply should make setting precise energy a snap.

These days it seems caps intended for rapid discharge are more easily found in the higher voltages. Since working with a couple of Weldmatics, that has always been my preference for spot welder configuration. My Weldmatic used a simple relay to discharge the caps, which also disconnected the charging circuit. Its stablemate originally had just a relay, but we noticed it was becoming erratic, so I paralleled an SCR (a simple driver circuit had to be rigged for the gate, which nowadays I might do with an opto-isolator or use an SCR with some sort of built-in opto-isolated gate). It is probably a lot easier to find a suitable SCR for higher voltage, lower current.

The choice most likely comes down to what the options cost and what you have on-hand to do the work. If you happen to have a big low-voltage computer cap, especially if you have a good low-voltage bench supply to charge it, this route is a no-brainer. You could even forego the big SCR and just use some likely-looking switch, maybe a battery disconnect switch, or similar high-current knife switch. We used these a lot at EMC2, even taking them apart and turning them into high voltage disconnects.

http://www.jcwhitney.com/surface-mounte ... map=19486G

[Doug Coulter]

Tom,

I get it -- and whoever they copy, it's probably going to work -- bonus! I notice this thread is getting a real high hit count, evidently a lot of people have interest, which I think is a good thing, because spot welders *are* very good for a lot of this work.

Yes, the transformer means you don't need as much peak current in the cap and switch, which can be a big advantage, as long as any energy that gets stored in the transformer leakage inductance doesn't make a killer flyback voltage pulse that kills your switch at turnoff. I would for sure have a diode or ZNR high power flyback catcher in there...Especially if the transformer I was using was a re wound MOT -- they have lots of leakage inductance. The xfrmr on the Harbor Freight one is not so bad that way.

So far, I've not messed up any of these big old-school computer caps doing this, and if I did, they're around surplus all the time FWIW. They have so much ESR they kind of self limit (which also helps the SCR live). Newer tech, you might get in trouble with -- there has to be some limit due to the simple fact the new ones are ten times smaller for the same ratings.

I tried a big 3 phase contactor for 20 hp motors on my first try with one of these big caps and roughly 60v and the contactor welded on every try -- had to pry the contacts apart each time. Knife switch would likely be a lot better.

Here's a pic of how I modified the Harbor Freight lower tip. I just ground the MIG tip to have a flat.
The lower electrode will easily reach inside most grids. I simply put the thing on a (big!) variac, which makes the time on the switch a lot less critical. I only use the CD one for where total energy is the most important factor, as I find that a bit longer dwell at heat makes better welds -- so I just cut the power down a bit so I can have that dwell, and ease of use.

What I finally found with type C thermocouple wires is that spot welding just doesn't work very well at all -- possible, as I made a couple of successful welds between them and W evaporation boats, but it took more than a couple tries too. They want to weld to the tips, haven't found any material they don't stick to better than one another, yet. So you often break them getting them free of the welder.

For just welding the tips of the wires, nothing for me has beat a little jig for my TIG welder that just holds the head and a grounded W electrode spaced a little apart so that you can have a hands free arc going, then poke the wires into it -- perfect every time. Type K is no problem with just about any technology, it just won't go high enough in temperature to suit me. Type C is another whole world.
(FYI out there, type C is W+5%Re and W+26%Re, it's real refractory stuff)