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About tomhumf

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    Sheffield, UK

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  1. I've been working a travel mug design for a while. It is basically a tapered tall cup with a lip that fits a silicone sip lid. My biggest problem has been how to insulate it enough so you can hold really hot liquids comfortably without a handle. My current design uses a couple of circles of clay attached where you would naturally grab the cup. I have carved lines in them to aid with air flow. The cups are still a little hot to hold straight after pouring though. I have some commercially made travel cups that have a double wall as insulation but that isn't going to be possible with a thrown form. I'm wondering if I could make a thick slip to go on the outside. In the slip I would add some kind of combustible - little paper balls? Then as they burn out I'd get lots of little air pockets for insulation. I'm firing a gas kiln outside so fumes wouldn't really be a problem. Is this a crazy idea. Any other suggestions?
  2. Would this be because the arch is stronger and will be more durable over time? I've ordered the Olsen book so will have a read of that. My brick supplier says they can cut bricks to my spec, the only ready cut arch bricks I could find elsewhere are super expensive. Otherwise I'm thinking if I calculate the angles I could set up a jig and hand cut them... I don't really want to use fiber, but 2 arch layers seems super hard to calculate. Would one layer layed in 9" thickness be a silly idea? I see them done in houses this way round.
  3. Wow ok, that's a lot more bricks than I thought then. My supplier does the 3 x 4.5 x 9 ones so those are what I'll use. For the roof I suppose it would be easiest to do a one layer arch with them stood up @ 9" thick...or would you do a 2 layer of 4.5" arch? I'm a bit worried how difficult it will be to cut the arch bricks to get a good seal.
  4. Thanks Neil, it seems it would work if I understand those charts correctly. I assume when it refers to 9" walls it means 9" long bricks layed with a 3" wall thickness... Thinking of what bricks to use - I can get soft bricks and 42% alumina hard bricks. I was thinking to use hard bricks as the kiln floor, layed with 4.5" thickness, and as the first layer of bag wall / firebox. And then soft bricks everywhere else. I wonder if one layer of hard bricks at the base will give enough insulation, it would be light concrete blocks underneath that.
  5. I have got that book yes, it's a good read. I don't think that design will really be the best way for the materials I have available. Regarding the burner, I got this reply from supplier: BTU ratings as follows:- 3 psi 82,750 10 psi 151,100 30 psi 261,700 My regulator goes up to 2 bar so I guess in theory I could get 261,700? I never currently turn it up that high though. I'm thinking I may do a similar design to the diagram you posted Neil. It would be downdraft with 12" X 24" shelves and a sprung arch roof.
  6. Thanks both. The manufacturers don't have much info, I've emailed them to ask for the BTU of the burner. It's the one pictured. I guess I'll wait until I hear back from them before proceeding. My other quandary is that I've been given three 23" circular kiln shelves. It seems to make sense to build the kiln around those...and maybe buy another one or two. But would a square kiln with round shelves make sense?
  7. Last year I converted my old electric kiln to gas . It's worked out pretty well and I now love gas firing. Due to needing a bit more kiln space (my current one is around 3 cubic ft) I've decided to try and build a new 10 cubic ft kiln from scratch. One major decision before starting to design the construction is whether I need to buy another burner. The burner I have is rated for use up to 10 cubic ft sizes. I see other gas kiln of this size mostly use two burners . I'm not sure if that's because they are lower powered weed burner types. I think someone said once that the temperatures will be more even throughout the kiln with a two burner system. Perhaps there is a way to make one burner spread nicely? I'm thinking I could split the flame path on the way in and deflect it on the way up...see sketch Anyone using/used a one burner kiln that's this sort of size?
  8. When I fired a kiln like that I always started with the dials on low with the lid propped. I waited until no moisture condensing on a hand mirror held above lid. Then closed lid and started turning switches up. I've never had a cone snap, maybe it was damaged before it went in. Maybe get some new cones to be sure they aren't all damaged?
  9. Thanks, I'll try this, and probably Neils method too. Out of interest which way does your wheel spin? Maybe that's why they move different ways...
  10. I've been trying to make some yarn bowls. Each time the clay kind of unwinds during firing - it moves a bit during drying too. I'm thinking I may push it the other way while raw next time... Just wondered if there are any secrets to help avoid this problem?
  11. Ok thanks, I actually have a load of bits of shelf I kept when I cut my round shelves after kiln conversion. I will use those until I get some proper ½ " props.
  12. I need some short props for my next bisque firing. I was thinking of cutting some squares of soft kiln bricks as a temporary measure. There won't be much load on my little shelves. Will this cause any problems do you think? I know it's not a long term option with the fragile, dusty nature of them.
  13. Thanks all, yes I've used titanium dioxide as an opacifier with other base glazes in electric kilns and it has just given a pure white. I will experiment with zirc and tin.
  14. I was always under the impression it's best to thoroughly dry all the clay to be recycled. So it then all hydrates at the same time when you reclaim. Do some of you use all types of dryness and just mix to slurry to reclaim? I don't have a pugmill.
  15. Hmm, maybe I'll try it on different shelves from any blues then. Would it be able to drift all through the kiln though, or just to those close by?
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