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Posts posted by timgunn

  1. As Jerrod says, it's basically a free-cutting version of 304, which is about the most common (and least-exciting) stainless steel out there.

    For machinability, it's streets ahead of 304 or 316, making it great for fittings. Back when I used to play with a little Myford ML7 lathe, it was pretty much the only stainless worth putting in the chuck.

    I'd keep some of it for stuff that needs machining and try to trade the rest. 

  2. It's only 60W according to the nameplate, so is only rated for 1/50th the current of a 3 kW kettle or heater (under a quarter of an Amp vs 13 Amps for the kettle or heater). Current carrying capacity is largely a function of cross-sectional-area, so skinny wires are not going to be a problem.

    There's a lot of exposed electrical gubbins there. Make sure whatever you build is well Earthed (Grounded) and ensure it's run from an RCD-protected circuit (GFCI?). The RCD won't stop you getting a shock, but it will disconnect the power before it kills you. It's no substitute for common sense: if you drop or hurl a piece of hot steel whilst providing a path for 230VAC, the RCD won't put out the fire. 

    Personally, I use RCD plugs (like the 44855 from Screwfix at under seven quid) on anything I cobble together to ensure that it WILL be RCD-protected. 



  3. It's a long time since I last used it, but Slo-Zap CA used to be very good for positioning/adjustment time. Not silly money either.

    I felt that 20 seconds was about what you safely had to get stuff located, perhaps 30 seconds if the planets aligned, 

    Of course, if you got things positioned quickly, it seemed to take a couple of aeons to stick. 

  4. Looks good Collin. 

    I'm not entirely sure about the firebrick splits for a work support: they look like a lot of thermal mass.

    Whilst the general idea of extra thermal mass to help even out fluctuations is good, the downside is that it slows the response to any adjustments you make to get the temperature right in the first place. You may find it greatly increases the time it takes to get the temperature set.

    You may not: I don't know and the only way to find out is to try it.

    I thought I'd mention it as a possibility now just in case it proves to be a problem: removing the bricks looks like a quick and easy thing to do. It's the head-scratching, posting and waiting for folk in different time zones to respond that usually takes the time if a problem arises.

    I'd certainly keep them in, try it for the first run and then decide whether to keep them permanently.




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  5. The small diameter bands on the rubber drums need to be run fast. Maximum speed for a 25mm x 25mm (1" x 1") Spiraband is 24000 RPM and they seem to like being close to that speed.

    Metal removal rate is tediously slow and their life (in minutes) seems no longer (possibly shorter) when run at drill speeds.

    They are really intended for use in die grinders, though I have used a cheap import trim router to spin them quite successfully.

    Even at the correct speed, they'll never last well compared to a small wheel attachment on a 2 x 72: a 1" Spiraband is about 3" long so there's 18 times the abrasive surface on a 72" belt.

  6. Looking at the first pic in post #2, I think you are going to find the flame runs very rich and probably won't reach anything like welding temperature.

    I do appreciate that there are a ridiculous number of variables and that I could be way off with this, so give it a try and see what actually happens before taking any notice of some random muppet on the interweb.

    Should you find it does run too rich, my thinking is as follows: The end cap looks like it will significantly reduce the area of the mixer throat available for airflow. Restricting the airflow will tend to make the mixture rich and reduce the flame temperature.

    The 58 drill (1.07mm) seems to be on the large side for a (presumably) 3/4" burner. A drilled hole will normally have a lower discharge coefficient than a MIG tip and I think this will actually go some way towards offsetting the larger hole size. My best guess is that you'll have a Cd of around 0.64 vs around 0.8 for a MIG tip, so in terms of gas flow, the 58 drill hole should flow about the same as a 0.91mm actual diameter MIG tip. Mig tips are sized for the nominal wire size they are intended to pass and tend to have a hole about .006" or .15mm bigger than the marked wire size. That would put your hole pretty close to a 0.8mm or .032" MIG tip if my sums are somewhere near.

    With an adjustable-choked burner, I try to get the mixture just a little rich at fully-open for maximum temperature and then use the choke to richen the mixture and reduce the temperature when it doesn't need to be screaming hot.

    If you are intending to get down to Heat-Treating temperatures of around 800 degC (1472 degF), you'll need a VERY rich mixture and I suspect the slot down the middle of your choke plate will allow too much air in. If so, duct tape is your friend.

    If you do find it's way too rich as you currently have it, i'd suggest removing the drilled-cap jet, tapping the stem and fitting a .024" MIG tip. This will eliminate the restriction caused by the cap and the smaller jet will make the mixture leaner. This should get it running and let you see what effect adjusting the choke has. If you find you need to choke down to make it work at all (i.e. it won't run at all with the choke fully open), you can try the next tip size up.

    Using an anaerobic pipe dope instead of tape is good. It lets you clock the fittings then you just need to wait for the sealant to cure and it'll stay put and sealed. Most of the pipe dopes are pretty low-strength and will allow disassembly with normal tools.

  7. The appropriate paint will depend on the temperature it will be exposed to. That will depend largely on the insulation provided by the materials used in the build and the temperature you run the forge at.

    There's also a potential compatibility issue with the Hi Heat paint you have on it already. Some paints don't play well with others. Hi Heat paints "cure" and this can affect things.  

    Safest is probably to use Rustoleum Hi Heat and complete the paint job before curing. 


  8. You certainly got something of a bargain there.

    As Alan noted, the only Tractor Supply fire brick I could find online was the 1 1/4" hard brick from US Stove. There's not much spec on it, either.

    Easiest thing to do is probably measure and weigh one of yours to see what you've got. Maybe post pics?

    Do you have any details on the board? The temperature rating is the main thing. If there's no spec or ID, the color can often give some clues. If the board looks like compressed HPS blanket and/or has a similar temperature rating, board ends on a 10" diameter cylinder, 18"-24" long and lined with 1" of blanket makes a good HT setup when paired with a properly-controllable burner.

  9. The 1/2" should be OK in a small chamber, but it'll probably be a PITA in a big one where it's not stiff enough to hold the curve of the top of the chamber without sagging, particularly when wet with whatever rigidizer/coating you use..

    If building a biggish forge, I'd be inclined to find a suitably-sized former and get a couple of wraps well rigidized onto the outside of it before wrapping with more layers of unrigidized blanket and inserting into the shell. My first attempt at doing this was a dismal failure because I couldn't get it off the PVC pipe former. For the second attempt, I wrapped the PVC pipe with a layer of an old sleeping mat (10mm, 3/8", closed cell foam), allowing me to pull the pipe from inside the foam and then remove the foam. This worked pretty well.

    What is the fire brick: Hard or insulating?



  10. I'm pretty sure I picked up a roll of the HTZ for cheap a while ago: 128 kg/M3, 25mm thick (8 lb/cu.ft, 1"). It was pretty much indistinguishable from the Unifrax stuff I usually use, both to build with and, as far as I can tell, in terms of durability.

    If welding is anything like a possibility, I'd urge you to consider the HTZ rather than the HPS, though HPS should be fine if you are simply forging and are not just using a burner tuned for welding (high flame temperature) with the pressure turned down (low heat input). 

    Refractory Ceramic Fiber is well established technology and there are many factors that will have a much greater impact on how well a forge works and lasts than the name on the box of blanket.

  11. I've not seen a Devil Forge forge up close and have some reservations about them, much as with anything built down to a price.

    I recently bought one of their DFP burners to play with and have not had the chance to do so yet. It does have a screwed choke adjustment which seems nicely progressive and, assuming it draws enough air fully open for a near-neutral flame, looks to offer good control of atmosphere and flame temperature.

    I got the standard DFP because the choke adjustment on the more expensive DFPprof does not look as sensitive in the pictures. I usually use burners based on Amal atmospheric injectors, which have very fine control. 

  12. The idea that there is a sharp transition from Oxidizing to Reducing is one of those oversimplifications that are very useful when trying to explain broad general principles, but which can get you into deep trouble if you take them as gospel.


    If you try to think in terms of there being a range over which the atmosphere varies between strongly Oxidizing and strongly Reducing, then factor in the position of the workpiece within the flame itself (within the flame, the Oxygen and fuel gas have not yet finished combining, so there will be more free Oxygen available to react with the steel in the early part of the flame), you may find it easier to work out what is going on.


    If you richen up the flame a little more (more gas for the same air or less air for the same gas), there's a good chance you'll see an improvement. You may see the forge temperature drop when you do this, so may then have to increase both gas and air in the same proportion to get the forge temperature back up to where you want it.


    There are 2 factors at play here: the temperature of the flame and the amount of flame.


    The amount of flame is quite easily understood.


    The temperature of the flame is dependent on the air:fuel ratio and will be highest at the stoichiometric ratio. This is the point at which all the Oxygen and all the fuel combine, leaving neither excess fuel nor excess Oxygen behind. It corresponds to the sharp transition point in the oversimplified model.


    We do not want excess Oxygen so we are always going to run on the fuel-rich side of stoichiometric. The heat produced will therefore be limited by the amount of Oxygen present. If we richen the mixture by adding more gas, the amount of heat energy released cannot increase because there is no Oxygen for the extra gas to react with. The extra gas will absorb some of the heat energy released by the original fuel burning and this will lower the overall flame temperature.


    We can turn up the gas-and-air flow to increase the amount of flame to compensate, but we can never get the forge temperature above the flame temperature. This means that the forge cannot be run as highly-reducing at high temperatures as it can at low temperatures.


    Part of the skill involved in using a gas forge with variable mixture is achieving an effective compromise between gas usage and oxidation of the workpiece. In my very limited experience, gas is a whole lot easier than using solid fuel, but it still involves a bit of a learning curve.

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  13. Just a heads-up on the TM902C pyrometers: I'd had about 30 or so that were boringly reliable and as accurate as big-name branded instruments costing more than ten times as much over the full range.


    I bought another ten last year and put them on the shelf. They were bought on ebay and came from China.


    Before I use one for the first time, I usually put it on the calibrator to check it is reading sensibly. I did this with several of the new batch and found they were all horribly inaccurate once the temperature got much above 800 degC (1472 degF).


    Below that temperature, accuracy seemed pretty good; the variation was less than that I'd expect to see between different thermocouples, even those made to special limits of accuracy, but above 800 DegC, accuracy got progressively poorer and I was getting readings that were off by 80 DegC with the calibrator set at 1200 degC.


    I still had a couple of the older ones and checked they were still reading correctly, mainly to check the calibrator. The old ones were fine.


    There are some visible differences between the old ones and the new ones, but you've really got to have them side-by-side to see them.

  14. There have been a couple of comments on the jet size that seem to suggest confusion over units. The link to Grant Thompson's video in the OP shows a .6mm tip, which is about .024". Probably about a .030" hole, as the hole is bigger than the nominal wire size it is intended to pass.


    If anything, it looks like it's too small to me.


    It's hard to tell what's going on with the choke in the last video, but I get the impression it is going too lean and going out when the choke is opened?


    If so, and it's a .6mm mig tip, I might try a .8mm mig tip and see if it improves things, but only if it is going to be used in open air.


    I would not try tapering the present tip. It looks like there's too much air at the moment and anything that increases the amount of air drawn in, relative to the gas flow, seems likely to make things worse.


    If you stick it in a forge with some back-pressure, that will reduce the amount of air. Grant's setup looks like it probably has quite a lot of back-pressure, so putting it in the furnace, with a crucible, seems like the thing to do if that's how you are intending to use it.

  15. The continuous edge for tile cutting does not seem to clear very well on anything but thin tile, so avoid them.


    Either the segmented ones or the ones with a continuous edge but alternating thick and thin bits when viewed edge-on should work well. The "turbowave" ones from tool station at 3 quid would be my choice.

  16. I'd try chain drilling out the corners with a masonry drill bit used without hammer, or perhaps a tile drill if you can find one long enough, then go at the straight runs with an angle grinder.


    The diamond disks for angle grinders are cheap and extremely effective. Screwfix or Toolstation are probably the best source over here. Buy the cheap ones. The expensive ones are better for specific tasks, but only really worth it if you need to cut 300 slabs for an awkward-shaped patio.


    Don't use your best grinder. Work outside. Wear a mask. Expect a huge amount of extremely fine dust.

  17. KBAC 27D looks like a good drive. Lots of guys use it Stateside.


    As far as I can tell, it has 2 big advantages there.


    First is that it will take either a 110V or a 220V supply, though the motor is limited to 1 1/2 HP on 110V. This probably does not matter to you in Oz.


    Second is that it is a sealed drive. This is essential for a grinder. However, there are lots of other manufacturers of sealed drives. Invertec are probably the European go-to sealed VFD manufacturer with their IP65 and IP66-rated drives and there are sealed drives available from most of the big manufacturers. I'm half a world away and don't know what's available to you. Look for something sensibly priced and supported locally.


    Other points that I suspect are in the KBACs favour in the US knifemaker market: it is US manufactured, and setup is by jumpers and trimpots, rather than a menu-driven keypad/display.


    The KBAC 27d seems to be a V/Hz drive and does not have Sensorless Vector capability as far as I can tell.


    You are on 50 Hz mains in Oz. This means that your motor rating plate will show the rated speed at 50 Hz. With the VFD, you don't actually need to worry about the rated speed very much. The important thing is the number of pole pairs on the motor.


    50 Hz is 50 cycles/second and there are 60 seconds in a minute, so 50 Hz is 3000 cycles/ min (60 Hz is 3600 cycles/min). Each pair of poles takes one cycle, so a 2-pole motor will only need one cycle per revolution and will turn at "about" 3000 RPM on 50 Hz. A 4-pole motor has 2 pairs of poles, so needs 2 cycles/rev and turns at "about" 1500 PRM on 50 Hz. 6 pole, "about" 1000 RPM and so on. On 60 Hz mains, as used in North America and some other places, the speeds would be 3600 RPM, 1800 RPM, 1200 RPM and so on.


    An unloaded motor will run pretty close to the speeds given in the last paragraph, but as the motor is loaded, it slows down and produces "slip". This slowing down is not a bad thing: it is just part of the physics of electric motors, with the slip causing the motor to produce torque. The 2800 RPM motor you mentioned would have been slowed down from a bit under 3000 RPM at no load to 2800 RPM at its rated output: about a 7% speed reduction. The 1400 RPM motor sees a similar speed reduction in percentage terms.


    Some of the NEMA 56-frame motors may be slightly different because the 56-frame was originally intended for Fractional HP motors and there has been a lot of work put into getting 2HP or more from that small a frame size, but generally it is the case that manufacturing economics have driven manufacturers to standardize their products as much as possible. You can be pretty sure that all the IEC 90-frame motors in a particular range from a particular manufacturer will use the same bearings, casing, rotor, etc. and that the rotating assembly will have been designed for 3600 RPM (a 2-pole motor running on a 60 Hz supply). The 90-frame has a 24mm shaft, so I assume that is the frame size you are looking at.


    The only major change for the 4-pole, 6-pole, etc variants will be the windings, which are static and are fixed to the inside of the casing.


    The design speed of 3600 RPM sets the upper end of the speed range (you can run faster, but you'll probably be outside the manufacturers design range unless you can find a spec for the motor you are intending to use that gives a higher maximum speed.


    Most basic (V/Hz or V/F) drives will run OK down to about 10 Hz happily. Much below that, my experience is that they start to feel "coggy" by about 7 Hz and become noticeably less smooth. Sensorless Vector drives have some additional electronics that allows them to run a motor smoothly at lower frequencies: I've used them at 3 Hz with no apparent loss of smoothness and they may go lower still. I've never need to try.


    You want a 10:1 speed range or better (500-5000+ SFM).


    Running a 4-pole motor (rated for "about" 1500 RPM on 50 Hz) from 10 Hz (about 300 RPM) to 120 Hz (about 3600 RPM) will give you a 12:1 speed turndown and ticks that box.


    If we do the belt speed calculation at the bottom end, where you are likely to be using very light pressure and not slowing the motor to generate much torque, we can get a drive wheel diameter.


    500 SFM / 300 RPM = 1.67 feet per rev = 20" per rev.


    Drive wheel diameter = 20" / Pi = 6.36"


    Call it 6", which is 0.5'


    At the top end of the speed range, you'll probably be leaning on the belt and hogging, so you want maximum torque.


    At 50 Hz, the 4-pole (1500 RPM unloaded) motor is doing 1400 RPM.


    1400/1500 = 0.93333


    3600 x 0.93333 = 3360 RPM


    3360 x 0.5' x Pi = 5277 SFM


    The 500-5277 speed range on a 6" wheel is a safe bet. You could maybe go higher at the top end if you are happy to exceed 3600 RPM, and maybe go a tad lower at the bottom end even with a V/Hz drive and certainly with an SV drive. This is something you'll only really be able to determine once it is running.

  18. Looking at the photo of the motor rating plate, it's rated as a 2.2 kW motor at 50 Hz and as a 2.5 kW motor at 60Hz, so you'll want the 3 kW VFD to allow the possibility of running to 60 Hz. You'll need to connect in Delta, but I assume you are already running in Delta on the capacitors.


    The speed you can actually run to will probably depend on the current draw and you won't know the speed/current relationship until you actually run it.


    I had some brief hands-on experience of a Chinese hammer on a HuanYang VFD when I helped set the VFD up, It worked, but I don't honestly know how well it has held up since.


    If you can get your hands on one, an optical (laser) tachometer is a very useful thing to have when setting things up: Stick a bit of reflective tape on the top die and you can read out the BPM directly. They cost around 10 Euros/bucks from China on ebay, but the delivery time might be a problem. If you know anyone into RC aircraft or drones, it's worth asking them if they have one you can borrow.


    Note that the VFD will need protecting from metal dust, especially if there is grinding done in the vicinity.

  19. IME the best way of running a 3-phase motor on single-phase mains is with a Variable Frequency Drive.


    Search for "2.2kw VFD" on ebay and you'll find plenty of HuanYang drives. Filter for buy now and sort by price+postage. Best to go advanced and limit location to somewhere that is not going to mean import charges. They are cheap drives but seem to work pretty well.

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