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timgunn last won the day on August 29 2020

timgunn had the most liked content!

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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. On a single burner forge, a small leak is not usually a significant problem. On a double-burner, it may be. The gas leaving the jet at high speed is what causes the air to be entrained. Gas from the leak is relatively slow and effectively non-directional, so doesn't help to induce air itself and just mixes with the air going past. This means that the "air", induced by the gas leaving the jet as intended, is actually a (lean) gas/air mixture and the overall mixture will be richer than that from an otherwise identical, but leak-free, burner. Flame temperature
  2. When I built my first HT oven, I made an angle-iron frame, put everything together and test-ran it. I was intending to clad the outside in sheet metal, but had no idea how hot it would get until I tested it. The available choices seemed to be plastic-coated steel, Aluminium or Stainless Steel, in increasing order of cost. In the event, I found the surface temperature reached about 135 degC, 275 degF, but that the IFB provided such poor heat transfer to human skin that it seemed safer without a metal cladding. I am aware that knifemakers in general tend to cluster towa
  3. What size are the gas jets in your "Venturi" burners? Can you change them fairly readily? If you are using mig tips as gas jets, try a smaller size. It may seem counter-intuitive at first, but there is a very high probability it will increase your temperature and dramatically reduce the Dragons Breath. I would aim for about half the area at first; 0.707 times the diameter and see where you need to go from there. Ideally, you want to get to, or just above, the maximum (welding) temperature you'll ever want with the choke slides fully open. Then you can reduce airflow wi
  4. I wouldn't. I'd put the fuel inlet out to the right of your picture and I'd definitely only have the one. Having a gas inlet per burner means you are going to have to adjust both to the same mixture to get the same air:fuel ratio and flame temperature from each burner. That simply ain't gonna happen, at least not regularly. If you inject the fuel and mix thoroughly before the burner feeds separate, both burners will always get the same mixture without any faffing about on your part. I might also look at redesigning the manifold. I think the left-hand burner
  5. What is the actual time from start to stop? Is it 105 minutes? It may be that you have put in too simple a program. If you have a system that will reach 1825 degrees from a starting temperature of 50 degrees in 90 minutes under full power, the first part of the Temperature/time curve will be very steep. It will tail off as the temperature gets higher. 937.5 degrees (the half-way temperature) might well be reached within 5-10 minutes, leaving 80-85 minutes to achieve the other 887.5 degrees. If you slow down the time to 937 degrees with the first
  6. I'm not familiar with that controller. Looking at the manual online, it appears times are in minutes? From 50 to 1825 degrees is 1775 degrees of temperature change. 90 minutes is 5400 seconds. 1775/5400 is 0.33 degrees/second 1.65 degrees every 5 seconds, so your 1-2 deg per 5 sec seems about right to me? I'll try to look at it again when there's a higher concentration of blood in my alcohol stream, and see if I can work out why it's going to "stop".
  7. 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
  8. 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
  9. 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
  10. 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 (
  11. 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
  12. 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
  13. 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
  14. 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
  15. 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
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