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timgunn

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Everything posted by timgunn

  1. I'd be inclined to build from scratch, rather than substantially modify an existing unit, unless it is very clear from the outset that modifying will be cheaper and/or easier. I've built 5 electric HT ovens from scratch, 4 of them for work up to 18" long and one for work up to 42" long. All will work vertically or horizontally. I think the long one would probably work best at about 45 degrees; vertically, it's a long way to have to lift out a full-length workpiece. For your questions: First: Maybe, but it's fun. Second: You can buy elements from many places. As a general rule,
  2. I took a punt on a far eastern diamond indenter off ebay a year or so back. Mine shipped from Hong Kong. I tried it in a friends tester and was getting readings 3 RC points below the ones he got with the indenter that came with his tester, on the same test block. As far as the weights go, the weight is the important thing. If you can weigh the weights from another machine of the same model, and make another weight that weighs the same, it'll work. A bag of lead shot would get the job done so long as the weight is right. If you are only going to be testing blades and are not going to be us
  3. I've only seen 2 of the 55-gallon drum HT forges. Both worked very well. The first one was all-manual and had a surprisingly small burner; about 1/2" from memory. The other used two cheap Chinese propane torches and a PID controller; the (very) small torch was the continuous pilot, with the larger torch switched on and off by the controller. I'm pretty sure the gas jet in the big torch was 0.35mm/.014", which should give a fair idea of the heat input needed; I normally fit a 0.6mm (0.024") MIG tip, which actually measures about 0.7mm (.028"), in a 1" burner. Half the gas jet diameter
  4. Yes, look for Sodium Borate Pentahydrate. The active part is the Sodium Tetraborate. Ideally, you'd use anhydrous Sodium Tetraborate, but this is not usually as easy to obtain as the hydrated forms. The hydrated forms are the Pentahydrate, which has 5 water molecules associated with each molecule of Sodium Tetraborate, and the Decahydrate, which has 10 water molecules associated with each molecule of Sodium Tetraborate. Given that what we want is the Borax part, and that the water is undesirable, the Pentahydrate is better for our purposes than the Decahydrate. Both hydrated for
  5. You can buy ready-wound elements. Many pottery equipment suppliers will wind them to your spec, albeit at a price. I got the coils for my ovens from ebay seller jrider12 in Portland, Oregon. He seems to have dropped off the radar lately, but ebay seller pmtoolco, also in Portland, seems to offer similar coils. Prices, shipped USPS flat-rate to the UK, were less than I could buy the Kanthal wire for from anywhere else. The coils I have are wound from 16ga (AWG?) wire. There are a number of far-East ebay sellers offering kiln elements very cheaply now, but these appear to be of ver
  6. There are a few pretty close UK equivalents to the AISI 10xx steels. CS70 is equivalent to 1070, CS80 to 1080 and CS95 to 1095. EN9 is a pretty close match for 1055. As Jake and others have said, a good starter steel if you want to make things that will cut, is BS1407 silver steel. Downsides are that it's prone to grain growth and benefits from careful attention to normalizing. It only tends to come as precision ground rod, so is expensive by weight. On the other hand, it's widely available in a good range of sizes. You can buy the diameter you need and immediately make stuff, rat
  7. I just cut the grooves straight in and pinned the elements fairly closely using little U-shaped staples pushed into the bricks. The staples were bent from 1mm Kanthal wire. The outside diameter of the coiled elements was only just under 10mm, so they were a pretty good fit in the grooves. They did feel a bit springy as I was fitting them in the first one, and I wasn't sure the staples would be enough to hold them in use. Everything seemed to stress-relieve on the first firing and I've not worried about it since. The element seems to sit quite happily in the groove. Not the best photo
  8. Salem I'm no expert, but I've built 5 electric HT ovens so far and I've found out a few things on the way. The soft bricks tend to suck all of the moisture out of whatever jointing compound you use, so it's quite easy to stick the bricks together with a thick layer of the compound, but it gets more difficult as the joint gets thinner. Because I want a close joint, I've tended to fit them dry. Where I've been concerned about gaps, I've just slathered the outside of the joint with watered-down fire cement (Satanite and AP Green seem to be unavailable here, so I can't comment on them). If
  9. Sounds like you've got it covered, so I'll just sit back and wait. I'm told patience is a virtue. Any information you can provide on the control system you mentioned would be gratefully received. My last 4 builds have used the AutomationDirect Solo controllers (They seem to be the same as the Omega CN 7200, 7500, 7600, 7800 series controllers). It's a good controller, but doesn't seem very user-friendly when it comes to the profile programming, especially for non-geeks. I need to get something pretty soon for my next build and if there's something that may be better available, I'd like to
  10. Looks the business, Dan. Nice use of the TIG shrouds. I just might have to steal that idea for a future build. Any chance, as you write it all up, you can major on the control/electrical side of things? Most of the oven/furnace write-ups I've seen have tended to gloss over all the boring-looking technical bits. Whereas most of the guys I've spoken to, who are considering building one, are happy enough about the physical build, but rather nervous about the electrics and control. Hopefully, all the questions will be answered anyway during the WIP, but there are one or two that s
  11. If you really need to contiuously measure welding temperature, you'll almost certainly need to go for a Platinum-based thermocouple with a ceramic sheath. The Omega thermocouple John uses is really about the upper limit for base-metal thermocouples. Where I feel it is most useful for the novice forge-welder is in establishing whether the (gas) forge is hot enough to weld high(-ish?) carbon steels. My feeling is that it's unlikely to help the experienced guys much, if at all. I originally recommended it because I feel that it offers the most bang for the buck. Over here, the additiona
  12. There are a lot of things involved in putting together a PID controlled gas forge that works reasonably well. Few of them are immediately obvious to most people. Not all are immediately obvious to me, and I'm a seriously geeky type who deals with PID-controlled gas equipment for a living. The Don Fogg oil drum HT furnace lends itself well to simple PID control, but is about the only design I've seen that does (without going to analog control, which is getting rather specialized ). For the Don Fogg setup I've played with, a separate pilot burner was used and ran continuously. The main b
  13. http://i1138.photobucket.com/albums/n537/HeathBesch/IMG_0090.jpg shows the photo for me Looks pretty good in the photo. What are you using for the burner? It's not clear from the photo, but I can't see a blower so assume it's some sort of atmospheric mixer, either with or without a Venturi. Photos never seem to give a true picture of either the temperature or the flame from the mouth. I suspect most digital cameras do something strange with auto white balance, so the colour is almost always misleading. Subject to the uncertainty in the photo though, it looks like you are runnin
  14. I can't help on brands, but a couple of suggestions on things to look for: I don't know how it is on your side of the pond, but over here, a lot of the newer drills have a male chuck taper machined directly onto the end of the spindle. It's obviously cheaper to make than having a female Morse Taper and an MT-to-chuck-taper arbor, but it drastically reduces versatility. The long MT is designed to allow rapid tooling changes, whilst the short chuck tapers are effectively a permanent thing. With an MT spindle, you can change chuck/arbor assemblies easily, so you can have a big chuck
  15. There are several ways of doing the heating part, but the easiest, most accurate and often cheapest is to use electric heating coils. The Solo controller I linked to has a low-voltage DC output to switch a Solid State Relay. The SSR switches the mains power to the heating coils. The SSR is switched on and off on a cycle. I use a 2-second output cycle on my electric HT oven/furnace. For half power, it is on for 1 second, off for 1 second. For one quarter power, on for half a second, off for one-and-a-half seconds. You get the idea. When powerful heating elements are used at low tempera
  16. Looks pretty good to to me, with the caveat that flame color is always different in photos. I'd strongly recommend you get a couple of MIG tips in the next 2 sizes down and rig up some form of adjustable air restrictor on the air inlet, though. The central cone is where the primary air (the air that gets drawn in at the Venturi) is burning with the gas. The outer, bushy, flame is where the excess gas mixes with secondary (ambient) air and completes the burn. When you stick it in a forge, with nowhere for the secondary air to get in, the bushy part of the flame will become the Drago
  17. It all depends on what you are doing. If you are setting the fuel:air mix on a forge, it's usually best to take it out once things are stable, just to save it getting damaged when you stick stuff in and out. Heat will tend to soak back along the thrmocouple, so you need to be careful of overheating the "cold" end. Handheld probes usually have a plastic handle. Mostly it's just common sense. Type K thermocouples tend to suffer "drift" above about 1000 degC. Type N was developed to overcome this, but all the really cheap readouts, like the TM902C, only take type K inputs. From that
  18. Thermocouples basically measure at the junction where the 2 different materials join, so broadly speaking, at the tip. For Mineral-Insulated thermocouples, there are 3 options. Exposed junctions have the outer sheath and insulating powder removed to expose the junction. This gives the fastest possible response but gives no tip protection. Insulated junctions have the end of the sheath closed and the insulating powder all around the junction. Slow response, as the temperature has to equalize across the insulation, but good protection and fine for slow-changing processes. Because of the
  19. As the OP appreciates, there are 2 things needed for temperature measurement. One is the thermocouple, the other is the display. Realistically, you only need a simple handheld readout for checking temperatures. I use a TM902C bought off ebay. It's dirt cheap and accuracy seems good; the readings compare well with much more expensive big-name instruments. Downside is a Celsius-only readout. I'm in the UK and don't think in Farenheit, so it's not a problem for me, but it may be for some. It reads to 1300 degC, which is 2372 degF. If you need Farenheit, it's a safe bet that even the
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