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timgunn

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timgunn last won the day on August 29

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About timgunn

  • Birthday 03/15/1962

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    Lancashire, UK
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    Tools, science, food, wine. Making things that "just work".

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  1. The 37 mbar delivery pressure may well be sufficient on its own to explain the poor performance. Things could be looking up. There may be some deviation from normal Gas-Safe practice needed: I don't think LPG necessarily falls within the same regs as mains gas (for anyone reading this outside the UK, "Gas-Safe" is the registration body with which anyone working with mains gas in the UK must be registered). Naturally Aspirated burners use the momentum of gas emerging from a jet to entrain air and mix it with the gas. This means we need a high speed through the gas jet. T
  2. I'd say that looks just enough like a forge to fool the beginner into hitting the buy button: Prepare for a precipitously steep learning curve. First off, can you get some photos of the whole lot? Something is obviously wrong. We can see that from the photos of the flame, but we have no information with which to diagnose the cause. The flame looks horribly rich and therefore cool. There's either too much gas for the amount of air, or not enough air for the amount of gas. Same thing, but not everyone sees this. My first impression is that the mixture is pants
  3. I usually use 2.5 mm 3-core from the 13A plug to the VFD and 1.5 mm 4-core from the VFD to the motor. I usually use H07RN-F cable if I can (it has a tough rubber sheath and is nice and flexible). I don't know whether it's in accordance with the current wiring regs though. When I build a VFD into an IP66 enclosure, I do like to fit a socket for the 3-phase out, mainly so that I can use the VFD for running different machines, just by plugging in the one I want to run. A few years back, it was relatively cheap and easy to use the blue 230V 3-phase and earth IEC60309 plugs
  4. Something that is quite likely to happen at some point is that you'll get the flame running back up the burner tube. It can be pretty worrying if you are not expecting it. The air/fuel mixture needs to be moving towards the forge faster than the flame-front can move through the mixture in the opposite direction. The flame-front speed is not a constant. It varies with temperature, pressure and air:fuel ratio. With your burner (which is a Naturally Aspirated design without an adjustable choke), the air: fuel ratio is effectively fixed. The mixture pressure (
  5. Kast-O-Lite 30: The number needs specifying. Kast-O-Lite is the trade name of a range of insulating castables. The number that follows is the rated temperature in hundreds of degF. Kast-O-Lite 30 is rated for 3000 degF. As a general rule, the higher the temperature rating, the higher the Alumina content (Alumina content is a big factor in flux-resistance) and the higher the thermal conductivity (higher conductivity = poorer insulator). There are certainly a Kast-o-lite 23 and a 25, probably others too. I'd hate for someone to search for Kast-O-Lite, buy 23
  6. The length of the burner tube matters. There is a pressure loss (resistance to flow) associated with the length of the pipe and the flowrate. The maths gets pretty complex pretty quickly. The gas issuing from the jet generates a low-pressure zone around the gas stream that draws air in. The gas and air mix with the gas slowing down and the overall gas/air mixture retaining the momentum of the original gas flow. This effectively results in a (very) small overpressure that drives the turbulent mixture along the burner tube towards the forge. "Some" length of burner tube is necessar
  7. It would be nice to see the position of the gas jet relative to the end of the long threaded nipple with everything assembled. Looking at the photo, it seems that with the brass sleeve-thing inserted into the threaded nipple with enough sticking out at the back end to get the hose on, the jet will be somewhere close to flush with the end of the threaded nipple? I suspect that'll cause all kinds of turbulence right where you don't want it. I think you probably want the full length of the mig tip exposed to allow air to be drawn relatively smoothly into the low-pressure
  8. There was a group buy of 2" x 36" Multitool attachments on the now-defunct British Blades forum a few years ago. I think it was an importers stock clearance, but the price was a fraction of list (I think they were about 60 quid each). I bought 3 of them, and a 4" x 36. One of the guys on the forum came up with a kit to fit the MT to an IEC metric 80-frame foot-and-face-mount motor. It was a pretty simple kit: basically a few bits of plasma-cut 6mm plate, a few fasteners and a bit of 1mm shim stock to wrap round the 19mm motor shaft and adapt it to the 3/4" bore of the wheel. I boug
  9. As mentioned, some systems have a built-in flow-limiting valve. It is broadly similar to the "air fuse" sometimes fitted to pneumatic systems before a hose. The idea being that if the hose gets cut, the air fuse will close and limit the airflow, so you are not having to deal with several yards of angry hose thrashing about and trying to beat you to death. It will limit the flow to some (fairly small) fraction of the maximum design flow and will automatically reset when the flow drops to zero (or near-zero). With a gas system, the potential is for several yards of angry hose with several feet o
  10. The "Inverter duty and TENV motors" curve in Cody's second graph will almost certainly be for Non-Ventilated motors and for fan-cooled motors with a separately-powered cooling fan: effectively a mains-powered, fixed-speed fan which maintains the cooling airflow regardless of the motor speed.
  11. The VFD will effectively vary the Voltage and the Frequency together from minimum speed up to the rated speed of the motor. The maximum Current (in Amps) is whatever the motor is rated at, regardless of speed. Power can be thought of (in slighly oversimplified terms) as Volts times Amps. As the Volts go up, and the Amps stay the same, the power goes up. This is the "constant torque" part of the torque/speed/power diagram: Power is also Torque times RPM. Once the rated motor speed is reached, the rated Voltage is also reached. The VFD cannot increase Voltage beyond this, but can sti
  12. I think the consensus view on the internet (insofar as such a thing is possible) is 7 times the burner port area as the minimum for the combined openings. In most cases, the need to have an opening big enough to get the workpiece in and out will mean that the area of the openings comfortably exceeds this. Taking a worst-case scenario with a 3/4" burner: the thinnest wall, largest inside-diameter pipe anyone is likely to use is Schedule 5, which has 1.050" OD and .065" wall thickness for an ID of 0.92" and an area of 0.66 sq in. Multiply by 7 to get 4.7 sq in. A 2 1/2" x 2" opening
  13. What sort of burner(s) are you thinking of? Naturally Aspirated, I'd go one (bigger) burner every day. It is much easier (and cheaper) to build a single adequate burner than it is to build two identical burners. I don't know what size your forge will be (I'm in the UK so "propane tank" is not a size I am necessarily familiar with), but for bladesmithing I'd guess you are looking at two 3/4" burners or one 1" burner. If you are going for blown, either one or two ports will work fine, so long as you keep everything downstream of the mixing point perfectly sy
  14. When you “increased the pressure a little bit”, what was the proportion? It will need a big change in pressure to make a significant change in flow/mixture speed. If you poke out the gas jet, be very careful. The diameter, shape and surface finish of the jet are all important. If you change anything by poking it through with something inappropriate, you will alter the air:fuel ratio of the burner. I usually end up using Copper wire to poke out gas jets because it is soft enough not to scratch the bore but stiff enough to work.
  15. If you get the same with no wind, one thing you might try is increasing the gas pressure. Burnback is usually because the flamefront travels through the mixture faster than the mixture is moving through the burner tube in the opposite direction. Flame speed depends on several things: air:fuel ratio, pressure, temperature. Pressure in the burner tube is about atmospheric and you don't want to be messing with the air:fuel ratio if it's right. Initially, things are cold and the flame speed is slow. As the forge heats up, the flame speed increases. If the flame speed gets fast enough, it will trav
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