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Everything posted by timgunn

  1. The "rules of thumb" near the bottom of the page at https://www.abana.org/ronreil/design1.shtml#rulesgive 450 BTU/cu.in. I'm not sure how the rules were arrived at though.
  2. First thing to say is that I've built a few forges and they seem to work ok. I've spent most of my working life dealing with gas burners and temperature control and I think I understand it fairly well. However, I'm no smith and there are plenty of guys out there with more experience than me. That said, my take on it is this: There are a number of factors that determine how much gas you really need and those rules of thumb are just rules of thumb. Most of the stuff that is out there on BTUs and forges is aimed more at blacksmithing than at bladesmithing. Welding temperatures for mil
  3. I'm guessing the burner throat is (maybe) too big, or you are not putting enough fuel/air through it. Does the following make sense and/or sound like it could explain things? In the burner tube, the mixture needs to be moving towards the forge faster than the flame-front travels through the mixture in the opposite direction. The speed of the flame-front is not a constant. It depends on the air:fuel ratio, the pressure and the temperature. As the forge heats up, the temperature of the burner tube tends to rise a little and the speed of the flame-front increases. At some poin
  4. Kaowool looks fine. Burner looks like it should be OK. Meter looks fine. Personally, I search for TM902C on ebay, filter by shipped price and buy the cheapest. The TM902C reads in degC only but that's not a problem when you are aiming for a target temperature you've decided on beforehand. I've had 20 or so and they've all worked to 1368 degC (just under 2500 degF), regardless of the range marked on the front. I've had them on the calibrator at work and accuracy has been just as good as brand-name instruments at 20 times the price. At around 5 bucks delivered, they are a bargain. Th
  5. I've not tried 3/4" kaowool (or even seen it). If it's the high-density stuff (128 kg/m3, 8 lb/cu ft) I think it "should" work, but will give you a bit less headroom for getting the rest right than the thicker stuff. I'd rather expect the lower densities to give marginal insulation at 3/4", though if you get everything else pretty much perfect, it should still work OK. I'd recommend a long type K mineral insulated thermocouple with a 1/4" sheath in type 310 stainless, Inconel or Super Omegaclad XL. That way you can put the tip anywhere you want it and can move it about to profile the tempe
  6. Depends on the stainless and the the temperature you are working, but tentatively yes. What kills stainless in heat cycling is loss of the Oxide layer. When it gets hot, an oxide layer forms. When it cools, the mismatch between the expansion coefficients of the Oxide layer and the underlying Stainless Steel causes the Oxide to spall off. After a number of cycles, depending on thickness, there's nothing left. Different stainless steels will hang onto the Oxide layer through different temperatures. 316 keeps the Oxide layer intact through around 850 degC/1560 degF, so is good enough for most
  7. There are many more things going on in a gas forge than there are in a gas cooker and it is very dangerous to assume that a forge will be as safe as a cooker simply because both burn gas. The "well-tuned" part is where most of the complexity comes in when referring to a gas forge. For heating things with flames, the flame needs to be hotter than the thing that it is heating because heat transfers from areas of high temperature to areas of low temperature. For cooking, the thing being heated (the food) tends not to need to reach a temperature much above about a couple of hundred deg
  8. I have a 2' diameter factory-motorized natural wheel, running in a water bath. I think it probably dates from the 1950s and it turns at a heady 42RPM thanks to a reduction gear on the motor and a reduction v-belt drive. That's so close to a surface speed of 3 MPH that I'm sure it was the target speed when they specified the drive. It works a lot better wet than it does dry, but it is very, very slow going. It always seemed pretty good for recovering badly-abused cutting edges but was no good at all for removing stock. At that speed, the water doesn't get thrown off. However, it does ge
  9. Unless you are pretty good at scrounging, electric is probably out of your budget. A Don Fogg style 55 gallon drum HT forge is cheap, about as simple as it gets and sounds very much like Jesus' suggestion. Basically, it is a 55-gallon drum, mounted horizontally and lined with a single layer of 1" Kaowool blanket, with a small burner mounted into the original 2" bung hole low down at one end. High up at the other end, a fairly small (maybe 2" wide and 3-4" high) opening is cut for workpiece access and exhaust gas egress. In the two I've seen, the workpiece is hung in wire loops which a
  10. Whereabouts are you? As Alan says, some stuff is harder to find in the UK. Other stuff is easy and, on a little island, pretty close. What is the forge? Pics or a good description would help. Pics are usually better: since you are asking the question, there's a fair chance you are new enough to this that you don't yet know the right questions to ask. What do you use it for? The temperature makes a difference and if it involves flux, the answer will be very different to if it doesn't involve flux.
  11. I've not often seen it with torches, but it's a fairly common effect with Naturally Aspirated burners that draw primary air. Normally, the speed of the mixture moving away from the nozzle is higher than the speed the flame can move through the mixture all the way to the burner exit. After the exit, the mixture can spread out over a larger area, slowing down as it does so, to give a narrow band somewhere near the burner exit where the flame speed matches the mixture speed and you get a stable flame. Rather unhelpfully, the flame speed changes with the air:fuel ratio, temperature and pre
  12. My thoughts on a dedicated tempering setup are as follows: A length of reasonably thick-walled box section, big enough to take the anticipated work (say 4" x 4" x 1/4"+ wall). A length of reasonably thick steel flat on the bottom of it (say 4" x 3/4"). This needs to have a hole drilled in it to take the thermocouple, but it can be drilled from the side so it's not a big deal. A rod-type electrical heating element on the bottom of that. Diameter seems to be around 8mm or 5/16" for the ones I've looked at. Two strips of steel flat, whose thickness is the same as the diameter of the
  13. Looking good. What burner are you using?
  14. OK. A couple of things jump out. First is the Propane cylinder. It's a Patio Gas cylinder inended for patio heaters and, as far as I can tell, only takes a 37mbar clip-on regulator. Second is the amount of Carbon on and in the forge. This shows a very rich burn: you are not getting enough air in to burn the gas. You may not be getting enough gas in to make temperature either, but the lack of air is the first thing to address. You don't show the burners you have tried. I'm guessing they were atmospheric burners. If you are going to use the Patio gas, I'd expect you to have to go
  15. Borax is very viscous at Carbon Steel HT temperatures. I tried it once in a mini salt pot and it was just too thick to use for O1. I tried low-sodium salt next (Class 5 HT salt, but from my local supermarket) and it was much better. Borax might be usable at higher temperatures, but I'm not sure. In the forge, it seems to go properly runny at about welding temperature and I think that might be too hot. It does have a tendency to dissolve refractories too, which can be something of a nuisance. I'm sure there are other good reasons Borax is not used, but the viscosity was enough fo
  16. The C706 and C715 actually look to be CuproNickels; Copper/Nickel alloys with no Zinc. As I understand it, the Nickel Silvers are Copper/Nickel/Zinc alloys. I gather the 18% Nickel C752 is the one to use for the "silver" colour. The 10% Nickel stuff tends to look a bit brassy, with a definite yellow tinge.
  17. I cannot be sure; do you have a link to the one you can get? The ones we use are a 3/8 brass valve with coil to suit the supply and an asymmetric timer that fits between the DIN connector and the coil. The timer is universal supply. Price here is 30-35 GBP, so I'm guessing it's basically the same thing. They look a lot like this: http://www.cccme.org.cn/products/detail-8063679.aspx
  18. We use them at work a lot; usually on 3 HP piston compressors with around 40-gallon tanks running 24/365 to provide control air on remote sites. The motor/pump duty cycles are usually in the 10-25% range. The drains are unbranded, made in the Far East and are pretty reliable as a rule. The most common failure mode we see is little tiny balls of steel from when the tank was welded, getting trapped in the valve and stopping it from closing properly. It tends to be more of a problem with new compressors. Timer failures and coil failures are much rarer. We see perhaps one every year
  19. Using a Propane forge indoors is a fairly high-risk activity. Carbon Monoxide is produced in quantity and is a very poisonous gas. It can be managed safely, but there are a few things to consider and they may not be obvious until you've got some experience and done some research. Stick with plan A for now. Whatever forge you build, you'll find that you reach some limit at some point and need to build another.
  20. Are you getting Dragons breath? There seem to be 2 possibilities: First is that you are not getting enough gas in. This condition is likely to give the same effect as the forge just being run at lower pressure than you want and whether or not there is any Dragons breath depends on the normal burner mixture. Second possibility is that you are not getting enough air in. If there is a restriction to the air supply, there will be a lot of Dragons breath. The dragons breath should narrow down where to start looking.
  21. Search for "TM902C" on the well-known auction site. If you think in Farenheit, find an conversion table and print it out as the TM902C reads in degC and only works with type K thermocouples. It's around 5-6 bucks, delivered. It's cheap, accurate and battery-powered You'll still need to get a suitable type K thermocouple with cable and a miniature plug, but you'd need that for the PID controller as well (though not the plug). The one that comes with the TM902C is only good to 400 degC/752 degF Type K tops out at 1370 degC/2500 degF (as do all of the TM902Cs in my experience, though I ha
  22. I have done a few remote boxes like this. It works for most drives I've come across, but one or two need separate start and forward/reverse inputs. It's just a wire to move in the remote box to make it work on these. The cable needs to be at least 7-core. I make mine long so that I can use the same drive for different machines by moving the box to the appropriate machine and plugging its motor into the drive. For the same reason, the forward/reverse switch is keyed; If the machine is not reversible, I can take the key out. I lucked into a bunch of multiturn pots. The one on this bo
  23. That doesn't look like a sealed VFD in the pic, though it's not one I recognize. I guess you were controlling the speed from the front panel in the vid. If it's not sealed, I'd strongly advise a remote control box at the grinder and a sealed enclosure round the VFD. Conductive steel dust in the power electronics tends to get exciting. Briefly. And irreversibly.
  24. Not using PID control means you have to do all the control manually. As one of the advantages of salts is the huge thermal mass involved and it's ability to damp out temperature fluctuations, things tend to happen slowly. The intention is to control over a very narrow temperature band. The PID controller, if correctly set-up, can see the small temperature changes occuring over relatively long timescales and respond appropriately. If you do the control manually, you need to see the temperature readout change, usually by whole degrees, before you can respond. Even if you are good at
  25. Formula is SFM = (Shaft RPM x Wheel dia in inches x 3.14159)/12 For a 5" wheel 2258 ft/min For a 6" wheel 2710 ft/min
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