timgunn1962

Almost certainly "WARRANTED"? Probably not much help with identifying the maker though.

It is certainly possible on a technical level, though the only realistic reason I could see for doing it would be a pretty extreme lack of space. In general, tools that are built to do multiple tasks do them all rather less well than individual designed-for-purpose tools do each separate task. I would recommend you build the forge for the task you want it to do. Research the burner carefully and buy or build the best you can with versatility high on the priority list (hints: all the hype and BS about welding temperatures is completely irrelevant if you are not intending to weld. Also "Temperature" and "Heat" are not the same thing at all; make sure you understand the concepts before you make any buying/building decisions). That way, the burner will be transferable between the forge and the melting furnace. Do a web search for "Jeff Pringle Kaowool" to see how simple a basic melting furnace can be. You can, of course, make a more permanent shell than the couple of turns of wire Jeff uses and coat it internally. It's probably wise to do so if you have somewhere to store it between uses.

Given that Vulcan was the Roman God of Fire and therefore very closely associated with Smithing, coupled with the fact that anvil making has been going for much longer than trademark registration (which only started in the 1870s), it would seem somewhat presumptious to suppose that there could only ever have been a single anvil manufacturer associated with the name. There was an Ebenezer Burdekin, anvil maker, at Vulcan Works, South Street, Sheffield in 1828. http://www.gracesguide.co.uk/Ebenezer_Burdekin

I'm also very impressed indeed. I've not tried ITC100 myself as it's very hard to find over here and the price in the UK is way over the US price. If you do try it, could you be persuaded to tune and run the forge without it first, then apply it and try to get some quantitative data relating to any improvement? Could you also let us know the dimensions and what burners you are intending to try?

I'm not a blacksmith. I don't have a high level of skill. I certainly don't have a good eye for judging temperature by colour. I am relatively easily distracted. There are definite advantages, at least to me, of being able to set the forge temperature/atmosphere at the temperature I want the steel to reach. I'd expect the same to apply to many beginners. If I run the forge at, for example, the maximum recommended forging temperature for the particular steel being worked, I will have the most reducing forge atmosphere consistent with reaching that temperature. If I get distracted and leave the work in for longer than intended, it will not overheat, because it cannot exceed the forge temperature, and it will suffer relatively little Oxidation because the atmosphere is strongly reducing. For bladesmithing, which is more in line with my interest than blacksmithing, the ability to set the forge temperature low with a very reducing atmosphere and hold it more-or-less indefinitely is very useful when heat-treating steels that require a soak at temperature. Tuning a burner with a well-implemented adjustable choke is easy: start with a jet that will give a neutral-to-slightly-lean burn and do the fine-tuning on the choke: no need to shut down and change or trim jets. Once tuned, it can be run as a normal fixed-choke burner (it's easy enough to mark the choke so that you can return to that adjustment). The choke adjustment does not replace pressure adjustment. It is in addition to it.

If you only use your choke to maintain a neutral flame, you are missing out on a huge amount of the burners capability. By adjusting the choke, you adjust the air:fuel ratio, simultaneously adjusting the flame temperature and the atmosphere (reducing-less reducing in most cases, but if the gas jet is small enough to run lean at fully-open choke, reducing-neutral-oxidizing as you open the choke. Maximum temperature is usually around Neutral). A lousy quality video showing the effect of adjusting the choke on a miniforge I built for bladesmithing. The choke adjustment is screwed on mine and by a sliding sleeve on the T-Rex, but the principle still holds. https://www.youtube.com/watch?v=Rp73eBS4LTk The HybridBurners website shows a 14-35 jet as standard for a T-Rex, Frosty.

As RobbieG says, type 304 stainless melts by about 1450 degC (It's a non-eutectic alloy, so doesn't have a melting "point" as such). It will go pasty and become progressively more liquid as the temperature rises between about 1400 degC and 1450 degC. The brake drum itself is likely to be a gray cast iron, with a melting point or range somewhere closer to 1200 degC, perhaps as high as 1250 degC. Pure metals and eutectic alloys have definite melting points. Non-eutectic alloys have melting ranges.

Hard to find though, and usually horrendously expensive if you do find it. It's pretty good for cycling up to around 1100 degC, 2012 degF, but if you take it higher, it tends to lose a layer to Oxide every time it cycles through that temperature. In a welding forge, it would definitely be a consumable. If someone is in an industry where scrap/surplus type 310 S/S is available, it's quite likely to be an industry where other scrap/surplus refractory materials are also available. If it comes my way, I'll use it, but in a smithing context, the only application for which I'll actively seek it out is burner nozzles, where it lasts much better than 304 or 316. As for using an unknown grade of found S/S, why not? It will be consumed. At 3/8" thick, it'll probably take a while. I'd be looking to introduce some fall to direct the flux run-off to where it can do no harm. It will probably need clearance all round, since most of the Stainless Steels seem to have high expansion coefficients and you don't want to crack the Kast-o-lite.

My advice is as follows: 1/ Work out exactly what you want to do in your first forge. 2/ Find a well-documented forge-and-burner design that has a proven track record of doing the result of 1/ above. 3/ Build EXACTLY to that design. Note that you want a "forge and burner" design, not a separate "forge" design and "burner" design. 4/ Use it. Take notes. Look at other designs. Try to understand what is going on. Don't expect it to be easy: it's not particle physics, but it does have a fair bit in common with rocket science. 5/ When you are confident that you understand how all the many variables interact, reassess what you want to do and what changes need to be made to enable you to it. 6/ Only ever make one change at a time. Make notes. Photos and Videos can be useful too, but a notebook is indispensible. Since you seem to be strongly attached to the box, I suggest you keep your forge, burner, etc. in it when it is not in use. A 2"-Kaowool-insulated knifemaking forge is unlikely to need a shell much above 8" diameter, so the box should be plenty big enough. My experience to date is that the most difficult thing to get a forge to do well is the heat-treat. All the hype is usually about achieving welding temperature and there seems to be an unspoken presumption that a forge/burner setup that will weld can do anything involving lower temperatures with ease. I am pretty sure it just ain't so, though others may have different experiences.

A couple of questions. Does the huffing seem to be the flame running back down the burner tube from the forge chamber, or the flame running back through the forge chamber from the forge mouth? Usually, the flame running back down the burner tube is due to too low a gas pressure and it tends to be more likely when the mixture is closer to neutral. It happens when the mixture speed along the burner tube is less than the flame speed through the mixture. The flame aceelerates down the tube until it runs out of mixture and goes out. Then the gas and air mixture reaches the hot forge chamber, ignites and repeats. At lower pressure, the flow is less and it takes longer for the fresh mixture to reach the hot chamber. I can sort-of-visualise a similar thing happening in the forge chamber, but I think it would need some pretty specific conditions and does not seem particularly likely. One of the conditions in my mental model is high back-pressure, so a photo of the inside of the forge showing the burner placement would be useful. Are you getting the forge chamber hot before you try to choke the burner down? Burning at the rich mixtures that give flame temperatures in the Heat-Treat range is getting pretty close to the edge of what is normally considered to be the flammable range, perhaps even beyond it. The text-book vales for Upper-and Lower Explosive Limits seem to be based on room temperature gas/air mixtures. At higher temperatures the range certainly seems to be wider, but I've not seen any rigorous test data either way. I find I need to start my HT forge with a fairly wide-open choke (probably around the setting used for your first pic, perhaps even a little more air) and get the forge stable at a higher temperature than I want, then take the temperature down by choking the burner in small steps, leaving it to stabilise after each step. On my forge, there is no chance of starting with the final mixture and getting the flame to stay alight long enough to bring the forge temperature up from cold. What gas pressure range is your burner intended to operate with? And what gas pressure are you running? I tend to run my burners to 60 PSI/4 bar max for welding and usually run around 20 PSI/1.3 bar for HT. Forging is done with the burner in a fairly conventional forge, but I transfer the burner to a purpose-designed HT forge for Heat Treating. With the finely-adjustable air:fuel ratio provided by the commercial Venturi, you have control over the flame temperature in a way that most NA burners do not. Where most people would just think in terms of turning down the pressure to reduce the amount of gas being burned and therby reduce the forge temperature, you can think in terms of reducing the airflow but leaving the gas flow/pressure fairly high and reducing the flame temperature. https://www.youtube.com/watch?v=1xvWkXBXY6U&feature=youtu.be It's not my video, but it's one of my HT forges with a burner built on an Amal atmospheric injector.

If you can get the cover off the connection box and get a photo with a phone, it might be clear from the terminal configuration: 2 windings connected in parallel for 110V that can be connected in series for 220V. Smartphone pics are pretty much my default way of reading rating plates, etc. nowadays. They'll get into spaces far tighter than I could ever get my head into and they'll focus close in. Otherwise, I need at least 18" of extra clearance now to accommodate my ageing eyes. Pretty much the only thing good about getting older seems to be that it's better than the alternative.

Sodium Silicate comes in various densities. I think the units normally quoted are degrees Twaddle and my supplier sells both 140 and 75 and other sources may be different again. It means that it's difficult to come up with a simple dilution ratio in the form X Sodium Silicate to Y water. I have found that diluting with tapwater to give a solution density of between 1100 and 1150 grams/litre gives a rigidizing solution that seems to work about the same as the commercial colloidal silica rigidizer in a forge application: I think it works out to around 17 1/2 to 18 1/2 Ounces per US Pint, but I'm not really familiar with the US units.

Hard fire brick is a lousy insulator. It has its place, but I don't think it's very likely to be appropriate for you. That said, you don't actually seem to have told us what you are intending to do in the forge and it makes a big difference to the appropriate design and materials selection. I've tried googling Urutsz burner without success. Do you have a link to any online information, or maybe a book to look for? It sounds interesting. "Based off" and similar phrases are always rather worrying when discussing burners, given the number of folk that seem able to louse up even relatively simple Propane burners by not following well-documented plans accurately. Where in North West England are you, and do you drive? An advantage of living on a little island is that, if it can be got here, it's not likely to be very far away. ANH Refractories have a place on the Wirral, for example. They don't sell direct, but IMS do. They are on the same site and are an ANH distributor.

I've not watched any of his other stuff and I am not at all keen on what seems to pass for his style, but I've just watched the one where he built a 3/4" burner with a .025" mig tip jet and it looked pretty much ok to me. The use of an adjustable choke plate (which he repeatedly and rather irritatingly refers to as a regulator) seems to deal quite effectively with many of the build accuracy and tuning issues of chokeless NA burners: size the jet to burn leaner (and hotter) with the choke fully open than you are ever likely to want to run in anger, then adjust the choke in use, along with the gas pressure, to get the mixture and flame temperature you want for the job in hand. It seems to me to fall somewhere between the Frosty T and Mikey burners in concept: not as simple as the Frosty T, but with some of the user adjustability of the Mikey burner. Output for the nominal pipe size looks to be less than the full-on Mikey burner, but it should be pretty much the same as any other burner using the same .025" mig tip for a gas jet and running at similar gas pressure. Am I missing something?

Here in the UK, single-phase motors over about 3HP (2.2 kW) are unusual. Anything in the 10 HP range and up is likely to be a special and horribly expensive. I've seen a few 2-pole 4HP- (3 kW-) single phase motors on reciprocating compressors to try to maximise their output on single-phase power, but I don't recall seeing anything any bigger on single-phase. Most (all?) of the 3-phase motors I've seen above about 7.5 HP ( 5.5 kW) are wound for 400V Delta/690V Star to allow Star-Delta (Wye-Delta) starting on 400V 3-phase supplies. This is intended to keep the starting current down. Direct-On-Line (Across-The-Line) starting often pulls between 6 and 7 times the rated current, where Star-Delta starting "only" pulls about 2 1/2 times rated current. Almost all of the 3-phase motors I've seen of less than about 4 HP (3 kW) have been wound 230V Delta/400V Star and these can be run from a 230V-in VFD or a transformerless Phase Converter. Between 3 kW and 7.5 kW, things are less clear-cut: some motors are wound 230V/400V and others are wound 400V/690V, making it a case of check before buying. The 400V/690V motors need a step-up transformer in the system to get the Voltage up to 400V before either the Phase Converter or the VFD does its thing. VFDs are available, albeit at a cost, with the transformer built in. These are often described as "Digital Phase Converters". Both Static and Rotary Phase Converters here have the transformer in. Of course you can buy a transformer and a 400V-in VFD and effectively make your own DPC, but you'll need a VFD that will actually run on a single-phase 400V supply. The thresholds on motor sizes and Voltage may be quite different in the States, as the power distribution system is completely different. I think small industrial 3-phase is usually around 230V and the big stuff runs 460V, but I'm not 100% sure.

I know it's contrary to most of the advice you'll get, but I'd go with one of the cheap Chinese HuanYang drives in the OPs position. There are a couple of reasons for this. I have yet to encounter a large (4 kW and up) VFD from any of the major manufacturers that will actually run off a single input phase. I have seen all the stuff on the web about needing to derate if you do run on single phase, but all of the drives I've actually played with give a fault message and refuse to run if there are not 3 phases present. I'm in the UK so things may be a bit different in the States, but please check carefully before buying. The HuanYang drives up to 10 HP, 7.5 kW will run on a single input phase without derate and without showing a fault. Most of the RPC specs I've seen seem to give a maximum single motor start of roughly 2/3rds the RPC motor size, so I'm guessing the 15 HP rotary mentioned in the OP is to start a 10 HP motor. I get the impression that the manufacturer has taken a pragmatic approach to things and massively oversized the input stage compared to western drives, hence the zero derate on single phase. I certainly find I can run a 3 HP, 2.2 kW HuanYang drive on a small gasoline-powered generator, where a 2.2 kW ABB drive simply refuses to run. KBAC drives seem popular in the US and are widely recommended on the knifemaking & smithing forums, mainly because they are sealed drives. I don't think there is a bigger single-phase-input KBAC drive than the 29 (3 HP, 2.2 kW), so the choices seem to be another manufacturer's sealed drive (if you can find one that runs on single-phase), or box up an unsealed drive. The box cost is likely to be about the same regardless of manufacturer, making the cheapest drive the cheapest option. I tend to tinker around with stuff a lot and the VFDs in my shop are mounted in boxes with 3-phase sockets and remote control pendants so that I can plug in whatever machine I want to power at the time. The protection settings in the drive therefore tend to be left at factory default (invariably set for the biggest motor that the drive will run). I always assume that, at some point, I'll try running some machine I've found, built or am trying to fix and there will be a fault that will kill the drive. It's much easier to accept this if the drive you are going to kill is a $120 unit than if it's a $500 unit. A HuanYang drive to fit plus a spare to keep on a shelf against the day the first one dies still works out cheaper than a big-name drive over here. Where I would go for a big-name drive is if I needed a particularly low minimum speed, in which case I'd buy an SV drive. In my experience, Sensorless Vector drives will drive smoothly down to under 3 Hz, where V/Hz drives seem to start feeling "coggy" somewhere between 10 Hz and 7 Hz. I would not buy a used VFD. Period. For the grinder, the choices are KBAC for minimal hassle at not-ridiculous cost, cheap Chinese and box it yourself (more hassle and usually significantly cheaper than a KBAC) or "known brand" and box it yourself (more hassle and usually more expensive than a KBAC).

I appreciate that Wikipedia is far from being an authoritative source of information. However, it does have the big advantage of being accessible by everyone and I'd much rather give anyone who might be interested the opportunity to check whether I'm spouting complete drivel or not, than take values from a more authoritative text. I did check that the Wikipedia values agreed pretty closely with the values in the books I've been using for the last 25 years or so before posting. Those values are for adiabatic combustion with air. With Oxygen, the values are obviously higher. Wikipedia gives an adiabatic flame temperature of 2526 degC/4579 degF for Propane/Oxygen, almost 1000 degF higher than Propane/Air at 1980 degC/3596 degF, but does not give values for Methane or NG with Oxygen. I am not sure what you mean by "slash those figures in half and it will actually work there". Can you provide any further information or references? Using a type S thermocouple and pyrometer, I have measured forge temperatures in a couple of forges with Propane burners built to the designs in "Gas Burners for Forges, Furnaces and Kilns". One had been running at a nice forge welding temperature (making Damascus for blades) of about 1300 degC/2372 degF while in use and reached 1470 degC/2678 degF when we wound it up to maximum. That certainly seems to be considerably more than half the adiabatic flame temperature by any criteria most of us might use. Do you have any references for the partial recombination phenomenon? I have been unable to find anything online and I'm very interested. Methane is much less dense than Propane, so its energy per unit volume is indeed about half that of Propane (measured as BTU/cuft, MJ/m3, etc). However, when measured as energy per unit mass (BTU/lb, MJ/kg, etc), Methane has a slightly higher value than Propane. I've been unable to find anything useful by googling "practical heat output", so it does not seem to be a recognized technical term. Pretty much every NG burner I've seen has, as you say, been utterly puny, at least in forge burner terms. However, they have all been fed with low-pressure NG, where pressure is measured in inches of water column. If we are going to compare Methane/NG with Propane, we really should at least compare the 2 gases at broadly similar pressures. Here in the UK, regulators for use with Propane BBQs have an outlet pressure of 28 mbar, or about 11" WC. Mains NG supply pressure to domestic uses is nominally 8" WC, so I think it's fair to say that the pressures are broadly similar. I gather the pressures are also broadly similar in the US. A forge burner running on propane supplied by a BBQ regulator also seems pretty puny. The OP was specifically asking about running a burner on Compressed Natural Gas, not domestic NG supply, so there seemed a good chance that low pressure would not be an issue.

There seems to be no technical reason why not. It will get hot enough for anything you are realistically going to want to do with it: Wikipedia gives adiabatic flame temperature as 1960 degC/3562 degF for Natural Gas and 1963 cegC/3565 degF for Methane vs 1980 degC/3596 degF for Propane. NG composition is actually pretty variable, depending on the source, and it might be worth getting hold of the specs from your suppliers to see what sort of range you might expect to see. Be warned though, the specs they'll provide are usually little more than a heat value per unit volume. The biggest problem with using Natural Gas in a forge is usually down the low pressure available on the mains gas supply and that simply isn't a problem with CNG. You'd need to see what sort of hoops you'd be expected to jump through to meet local safety codes though. I get the impression that, where a lot of stuff on LPG got grandfathered into safety legislation worldwide because it was already widespread, CNG seems to have been pretty unusual until quite recently and therefore got the latest gold-plated safety standards applied in many jurisdictions.

I looked into Saffil and Maftec blankets at work a few years back. Both are high Alumina, rather than Alumina/Silica, IIRC and the cost was eyewatering. In the end it was much cheaper for us to improve the control, eliminate hot-spots and keep using Alumina/Zirconia/Silica modules than to change the material to something that would not be damaged by the hotspots.

# Name Cost 1. Giberson Ceramic Burner Head $175.00 2. Dayton Blower #1TDP5 $95.00 3. 1-1/2" pipe (various lengths 6"-8") (for 2 pcs.) $15.00 4. Standard 1-1/2" Steel Coupling with hole drilled to fit gas pipe $4.00 5. Gas cock $15.00 6. Gas Gauge (inches water col.) $75.00 7. Assorted gas pipe 1/4" black iron $10.00 8. Orifice cap (hole drilled into iron cap) $2.00 9. Floor flange 1-1/2", bolted to blower $6.00 Total Cost (Priced at WW Grainger and local hardware store, 11/5/2015) $397.00 Parts list for the burner setup in the previous post. Added to keep it all together should the link from Latticino's post be lost in the future. With burner designs, it's a case of follow someone else's design EXACTLY, or accept that you'll be developing your own design with all that entails. "Exactly" includes using the same parts.

If you are blowing off the excess air, it's a really good idea to do it through an air curtain along the lines of the one that Wayne uses and Frosty recently started a thread about.

Huge caveat to start: I've yet to try a ribbon burner. The following is based on my understanding of burners, fans, compressors, etc and I am sadly not infallible. 1/ Altitude affects blower pressure and the density of the forge atmosphere. I think this will mean that a given forge heating a given workpiece at different altitudes will heat it slower, higher up. The maximum temperature should not be greatly different though. I don't think the effect will be significantly different between N.A. burners, blown burners and ribbon burners. 2/ An air compressor probably can be used but is a poor choice. A good compressor will usually give somewhere in the region of 4 CFM per HP on a good day. Compressing up to maybe 80 PSI to drop the pressure to perhaps 10" WC is very wasteful of energy. 3/ Suppliers CFM figures tend to be very misleading. Where given for a fan or blower, they are usually the maximum flow at zero pressure. Where given, pressures are usually the maximum pressure at zero flow. We tend to need some value of flow (CFM) at some pressure and unless the graph showing the relationship between flow and pressure (the curve) is available, we have no idea whether the fan in question can meet the duty. Burning Propane with air, I calculated that each CFM of air will burn with between 0.3 lb/hr (to CO2) and 0.44 lb/hr (to CO) of Propane. I did the same sort of calculation for Carbon (coal/charcoal) and Methane (Natural Gas). If anyone wants to check the calculation, it is attached. If I've loused it up, please feel free to tell me so (I'm not sure I believe the numbers I'm getting TBH). Calculation of heat produced and fuel used by burning with air.ods

It looks fine to me, at least for a forging forge or, if you are into knives/swords, a HT forge. I've not found any discernable performance or handling difference between blankets of the same density and temperature rating from different manufacturers from my hairyarse-with-hammer perspective (this is completely unlike my experience with IFB). There are so many other variables involved with forge building that few of us are ever likely to build to a standard design that allows the differences between blankets to become apparent. I have found that the higher-density stuff seems to be more able to tolerate the prodding and poking it gets from the workpiece and the erosion it gets from the hot, high-speed gases near the burner. I would normally go for the 8 Lb/cuft version, not the 6 Lb/cuft, primarily for this reason, together with its better insulation properties. However, in this case the R values are looking pretty odd to me. I'm used to seeing thermal conductivity drop as blanket density increases http://www.unifrax.eu.com/web/Audit.nsf/ByUNID/6CCA5961F2AEEBCC85257F950069198C/$File/Fiberfrax%20Durablanket%20S%20EN.pdf The R-value is a measure of thermal resistance, so I'd expect it to increase as blanket density increases and thermal conductivity drops. For the Unitherm, it does the opposite, based on the 1.06 R value for the 6Lb/cuft and .75 for the 8 lb/cuft. https://www.zoro.com/unitherm-ceramic-insulation-24-in-w-25-ft-cf8-1-24x25/i/G8489634/ I suspect that the quoted R value is based on a temperature difference of around 70 degF and that the heat transfer mechanism is probably very different at typical forge temperatures. I don't know how great the cost saving is with the Unitherm blanket where you are, but I suspect the overall cost saving will be smaller once you look at the various other things you'll need to build a forge and take shipping into account. It is entirely possible to simply line a shell with a double layer of 1" blanket and fit a burner to get a usable starter forge, but it makes for a fragile lining and you need to be very careful about airborne fibers. Some sort of coating and/or rigidizer is definitely a good idea and it gets much easier if you can one-stop-shop for everything. Frosty has done some playing around with homebrewed coatings and I've tried some myself with moderate success. The best I've found to date is about a 2:1 mixture by volume of Zirconium Silicate (Zircopax) and powdered porcelain clay, mixed to a single-cream-like consistency with a solution of Sodium Silicate in water. Sodium Silicate is sold in varying concentrations and this makes it difficult to give dilution rates on a volume basis. My best results so far have been with a Sodium Silicate solution density of 1100-1150 grams/litre. Liberally sloshing on the mixture lets it soak into the surface with the Sodium Silicate penetrating perhaps an inch, The clay/Zircopax only penetrates perhaps 1/8" into the blanket and most of it stays on the surface. You only get one attempt at it so too much is better than too little: once the clay has formed a continuous top layer, it's pretty impermeable and a second coat just will not soak in. It needs to be dried well before heat is applied, otherwise it balloons. Once fired, it seems to be reasonably durable (I give it a couple of hours at a temperature I'd consider a good bladesmiths welding temperature; around 1300 degC (2350-2400 degF)). I've not tried its flux resistance yet and I don't expect it to be great. It's certainly not suitable for a heavy-use forge, but seems pretty good for a hobby forge. I'll only really know if it holds up ok in a couple of years. Zircopax, Porcelain powder and Sodium Silicate are all readily available from pottery suppliers, usually in reasonably small quantities.

I'm sorry to be a pedant because Kozzy's point is well made. Comparing orifices, a .035" diameter orifice does indeed have have 2.3 times the area of a .023" diameter orifice. However, when comparing MIG tips, they are sized on the nominal welding wire diameter they are intended to be used with. When I've measured MIG tips, all have tended to have a hole size about .006" larger than the nominal wire diameter. A .023" MIG tip will therefore have a hole diameter of .029" and a .035" MIG tip will have a hole size of .041". Comparing the hole areas, the .035" tip has almost exactly double the area of the .023" tip and will flow twice as much gas at the same pressure. If you wanted to turn down the pressure to get the same flow from the .035" as from the .023", you would need one quarter of the pressure: flow through an orifice varies with the square root of the pressure difference. It's not just about gas flow though. You also need to get enough air in to burn the gas. Going to a smaller gas jet reduces the gas flow in direct proportion to the area, but has a much smaller effect on the air flow and therefore effectively leans off the mixture. The air:fuel ratio affects the flame temperature and I've seen more forges that will not make temperature because they are running too rich than because they are running too lean. If you have Dragons Breath (a sign that the burner is running rich) and are not reaching welding temperature, it's almost always worth trying a smaller gas jet.

The Mitsi's are certainly nice, as are many other of the big-name drives if the budget will stretch to them. I rather like the Telemecanique Altivar 31 with Sensorless Vector control. I bought one of the 2.2 kW HuanYangs just to see if they were actually usable and was impressed enough to have used another seven of them for various things. I get the impression that they have been oversized on the input side, by comparison with the big-name Western drives, presumably to make them less sensitive to problems on the power network. They are the only drives I have been able to get to work reliably running on a small gasoline generator (3.5 kVA). Most of the big names will not work at all on a generator IME. The HuanYang drives that say they'll accept either a single-phase or 3-phase input do so without derating when connected to a single-phase supply. It means I should be able to use a 230-400V autotransformer to step up a single-phase supply and run a 400V HuanYang VFD to get the 3 phases. Even though I'll need a Sine-wave filter to get a clean waveform that'll run old motors without problems, it should still come in much cheaper than an RPC.