Mar. 12th, 2019 09:34 pm
offcntr: (Default)
My new Envirovent arrived Friday afternoon; all shiny and new and... uncorroded. Isn't it pretty?

It took most of Sunday afternoon, and a good bit of Monday to install. First I had to patch the holes in the bottom slab, then drill new holes, in a different diameter and configuration. Then I had to mount the fan on the wall, where I discovered that the old vent used 4" ducting, and the new one only 3", so I had to scrounge up some insulation to pack around the pipe, and I still need to jury-rig a collar and vent hood on the outside of the wall to keep the fiberglass in.
patches to patchesdrill makes dust

After that, it was a matter of connecting the bits. Screwing the hose clamps tight, to connect the dryer duct to the fan, and to the "plenum cup" that goes under the kiln. Threading the spring onto the monopod and the pod into the cup and then--the hardest part--lining the darn thing up so it's tight against the bottom of the kiln, right in the middle, where the new holes are drilled.

After that, it's just reassembling the kiln, stacking and aligning the rings, latching them tight, putting the circuit box back on and connecting the wiring. (One of the trickier bits, as these first-generation computer kilns aren't as well designed. I had to figure out how to stuff three thick wire leads into a screw block designed for at most two. Took sleeping on the problem to realize the trick is to untwist the twisted wire leads, making it easier to pack them into the crowded space.)

Lastly, reattach the lid, put in the peephole plugs, and test the fan. Which you do by turning it on, then putting a lighter next to each of the holes in the lid and watching the flame get sucking into the kiln. Which it did. Success! And I'm no longer tripping over kiln parts in the middle of my studio.
offcntr: (Default)
For years now, Club Mud has been firing by ear. Literally; we determined the flame adjustment on our kiln burners partially by sight, but mostly by listening. The sound of the flame at different stages of firing was variously described as a "whoosh", a whistle, a flutter. Experienced firers could tell just by the sound whether the kiln was adjusted properly.
Beginners? Not so much.

Add in the fact that, as us veteran kiln-meisters get older, our hearing gets a little less reliable, and you end up with a strong lobby for more objective measurements. So at our November meeting, we voted to install pressure gauges on all the burners of our two gas kilns. Somehow I wound up being the one to figure out how to make this work.

I went online, of course. Quickly found pressure gauges for under ten bucks, if you wanted to measure in pounds per square inch (PSI). Unfortunately, PSI is a huge measurement for natural gas. Normal pressure is a fraction of 1 PSI. What we really need are water-column inch gauges. (You know how atmospheric pressure is measured in inches of mercury? Like that, only with water, which is much less dense, hence measures lower pressures.) I found a supplier priced around $25 per, then hit a Black Friday sale, so we got two sets of four for well under $200.

Then of course, I had to figure out how to install them. They needed to go in the--fairly short--space between the on/off valve and the burner itself. We had to go from this--

--to this. (More or less. All the burners were plumbed slightly differently.) I was able to reuse a couple of 4 and 5-inch pipe nipples, but for the rest, I had to get:

4 1-inch Tee joints
4 1x1/2-inch bushings and 4 1/2x1/4-inch bushings (to narrow down the 1-inch pipe to accept the 1/4-inch gauge stem)
4 2-inch pipe nipples
3 3-inch pipe nipples
And a roll (or two) of teflon tape, the yellow stuff specially for gas fitting.

Also, a small box-end wrench, three pipe wrenches, and a big length of pipe to slip over the end of a wrench when I needed extra torque. Plus our bench vise.

It took me three visits to Jerry's (our local home-improvement chain) to get the parts I needed. Wrong measurements (A 1-inch pipe is actually 1-1/4" across, as they go by internal diameter. Go figure.). Wrong parts. Right parts, wrong size. Last minute fourth run for three slightly longer pieces. And I still have to return three 2-1/2-inch nipples that I got because I wasn't sure 3-inch wasn't too big. That's okay, though. Now that I've finished the big kiln, I need to get the pieces I need to set up the small gas kiln with its own set of gauges.

And it is finished; everything came apart and went back together again! All I need to do is pressure-test all the joints, seal any that leak, and it'll be ready for my end-of-January firing.

Objective documentation! I can hardly wait.

ETA: Pressure test is good! No hisses, no bubbles (you check for leaks by flooding all the joins with bubble soap. No bubbles means no gas leaks). And all the gauges read! Ran them up to warm-up levels, and they were between 2-1/2 and 3 W.C. inches. Things are looking good for my next firing.


May. 25th, 2018 10:06 pm
offcntr: (be right back)
Been sick and miserable all week, as what initially seemed to be a very bad allergy attack morphed into a persistent head/chest cold. No fever, oddly enough, but buckets of snot, irritated throat, cough, the works. Fortunately a little ahead of schedule making pots for my next firing, so only had a little studio time, throwing one last batch of pie plates (we're down to three in inventory) and tall mugs. Mostly, though, I blew my nose. Constantly.

Finally started feeling humanish Thursday, so went down to the studio to get organized for glazing and see if I could figure out what was wrong with the left electric kiln. Apparently, it'd been blowing a circuit breaker before reaching cone 6, making it useless as a glaze kiln. This is the one I found, nearly pristine, at an estate sale a few years back, so I didn't think there was anything wrong with it, but you never know what a year in a busy shop will do.

Karen said they'd installed a new breaker, and wondered whether we should swap the right and left kilns to see if that might narrow the problem down a little. Thought I'd do some lower-impact detective work first.

First thing I did was open the kiln control box. (Well, the first first thing I did was make sure the circuit breaker was off.) The new computer-driven Skutt kilns don't actually show you much--well-labeled leads plug into a well-designed switch block, but all the actual circuit boards are hidden behind a sheet-metal and insulation barrier. Still, everything was plugged into its proper place, no signs of heat or wear.

So I pulled out the plug; here I saw a clue. The nylon faceplate showed a little toasty color around one of the three prongs. I took the faceplate off, but didn't see any further sign of damage in the wires or connectors inside the plug, so set that aside. 

Took a flashlight to the outlet itself next. The contacts in the slot corresponding to the over heated prong were black, corroded with copper oxide, so I opened up the box, at which point the problem was obvious. One of the electrical wires had overheated, melting insulation back a good inch from the outlet and frying the bakelite itself. The copper wires were variously pink from the surface melting and resolidifying, and black from corrosion. Messy.

So I disconnected the plug, cutting the wire on that side, as the setscrew was welded solid, and took it to the nearest hardware store.

Where they didn't recognize it, didn't have it, didn't think they were even manufactured anymore. Tried to sell me a different 50A/240V outlet, and when I said the plug wouldn't fit, brought out a clothes dryer power cord. No, guys; just no.

The nearest electrical supply store was in Whitaker, about a half mile further, but they had no trouble rustling up a replacement receptacle. Which didn't fit the circuit box, when I got it back to the Club. Thought I was gonna have to make another round of errands when Jon reminded me that we had a stash of used electrical bits on a shelf in the kiln room, and one of them turned out to be an outlet box in the correct size, complete with a matching faceplate. Success! I pulled out some slack in the cable, cut a couple of inches off the three leads and re-stripped the insulation. Took three hours, all told, and I had to disconnect and reconnect that outlet three times before it all fit together, but in the end, we had both kilns running again. Total cost? $15.26.

offcntr: (Default)
Had a couple of less-than-optimal firings just before Christmas, so I decided to see whether a little kiln maintenance might help. I already tightened up the chimney back in December (the bricks expand and push apart over many firings. Gaps allow in cold air that reduces the draft).

Today's repairs:

1. Take a vacuum cleaner to the burners, clearing out scale and detritus from the venturis.

2. Tear down and rebuild the bag walls. These are hard-brick dividers between the flame trough (where the burners shoot in burning gas) and the ware chamber itself. They're about four bricks high, and divert the flame up to the top of the kiln, where it will be drawn back down through the pots and shelves before exiting through a flue in the floor (and isn't that a tongue-twister). Extreme heat on the outer face has caused them to lean toward the outer wall, constricting the flame as it enters the kiln chamber. I tear them down to the bottom layer, reversing most of the bricks--they've actually started to warp, a little--and shimming them up with ceramic fiber to true them up vertical again.

3. Tighten up the bricks of the door, mostly by banging them with a hammer and two-by-four, to eliminate gaps and get the door face mostly flat again. I also brought in wrenches to tighten down the tie rods that hold the bricks in place in the steel work. We really need to get some new valve springs--the pair we have now are almost crimped flat. Automotive valve springs are often used in kiln frames to allow for expansion and contraction with heat. This set seems to have given as much as they have.

I'm hoping this will make for a better--at least more normal--firing Monday.

ETA: Aaand, it seems to have worked. Cones dropped together, same temperature top and bottom from about cone 1 all the way to the end. Used 64 units of gas, substantially better than the last two outings. Could even trim that down a little next time, as the reduction was pretty heavy throughout, could be a bit less.
offcntr: (maggie)
 A few commemorative photos from the first firing of the new kiln.

fully loadeda beacon in darknesscplt
The first one is the full stack, before firing. Second, the computer display, diligently firing through the night--currently just passing 1130° F. The last is the following morning, with the display flashing between temperature, time fired (11.49 hours) and CPLT. Complete!

Studio still very warm, despite the half-doors open and the fan running. The EnviroVent seems to have completely removed kiln fumes, though. No smell of sulfur at all.
offcntr: (Default)
Dismantling my old kiln is a project in and of itself.

These old Olympics were an early experiment in modular design. Each ring had its own control box, which plugged into the box below and above it using standard extension cord plugs. This was always a weak point in the design. Expansion would push the plug and socket apart, little by little, until the contacts were far enough apart that they'd arc, and presto, dead plugs.

I'd replaced about three of them, oddly enough always in the top box, before I gave up and just hard-wired them together. It took another ten years before the bottom set blew, at which point they were treated likewise.

So to get the kiln out of the studio, I first had to reverse this process. As there's a chance someone else will be putting this back together again, I carefully labeled all the wires and connections.

After that, it's just a matter of destructive distillation. Disconnect the power cord from the wall box. (Of course the circuit breaker is off. Whaddya think, I'm an idiot?)(Oh, right, I'm a potter. Never mind.) Slide the hinge pin out so I can take out the lid. Carry out the rings, one at a time. Throw away the broken bottom slab (fortunately, I have an extra, so the kiln is still useable). Knock all the rust off the stand and take it outside.

Cough and choke in the dust. Remember to put my dusk mask back on. Vacuum up the rust, dust and cobwebs.

Before I can install the new kiln, I need to commit carpentry. Specifically, to cut a hole in the wall for the EnviroVent.

I kill a 2-inch hole saw and a jigsaw blade making the hole. Back when I installed my first kiln, I thought it would be a good idea to fire-proof the wall, so I covered it with HardiBacker, cement board used in tile-laying. Turns out that stuff is death on saw blades. My neighbor Bob takes pity on me and loans me his SawzAll so I can finish the job. (Now I have tool envy.) A standard dryer vent slides in the hole, and a few nails hold it in place.

Installing the new kiln is comparatively easy, stepwise.

1. Connect the controller to the power supply. Set aside.

2. Bring in the base, position carefully. Set in the EnviroVent, connect it to the wall vent with aluminum dryer ducting. Plug in and test. (Works. Yeah!)

3. Bring in bottom slab, carefully position on the metal base. The points where the shelves post need to be supported by the legs of the base.

4. Put down some 1" stilts, then the bottom-most kiln shelf. (Needs to be raised up so the vent can draw air out the bottom.

5. Bring in the rings, one at a time in the proper order. Line 'em up and latch 'em together.

6. Bring in the lid; slide the hinge pin back in place and secure it. Position the prop and discover the screw that holds it in place is missing. Go looking for another screw to replace it. Find out the screw isn't missing, it's broken off. Fortunately, I have a screw puller, so make short work of this problem.

7. Slip controller box into its hinges. (This is, bar none, the coolest part. Having struggled for years with control boxes that need to be supported with one hand, while two others hold a wire and screwdriver, respectively, the idea that the control box hinges open for access? Genius.)

8. Reconnect the power leads to the bus block. Plug in the thermocouple. Close the box and screw otto the frame.

9. Say a quick prayer.

10. Flip the circuit breaker. Display reads PF; this is normal when current has been interrupted. It interprets it as a power failure. Press Clear and the display reads IDLE and 67 degrees.

Oh my God, guys, I have a new kiln.


Sep. 7th, 2017 06:09 pm
offcntr: (Default)
So, strange things from the very start. The switch on the vent cord is rated at 15 amps. Bi-Mart only has that model in a 3-amp rating; Jerry's has a 6-amp version. The fan motor itself seems to only draw 1.1 amps, so I figured I'd be safe with the switch from Jerry's.

The duct was another thing entirely: it's stainless steel, held on with set-screws and silicone sealant, and didn't want to go back to its proper shape for any amount of squeezing, tapping or vise-gripping. Finally, I stripped off the sealant, unscrewed the screws and pulled the whole tube out. I fortunately had a piece of pipe about four inches longer, left over from a studio project, that I could use as an anvil. I slid the duct over it, suspended both ends from sawhorses, and hammered on it until it approximated round again. Rescrew, reseal, and the vent is ready to go.

For some reason, the previous owner had the kiln up on wheels. Possibly easier to position; definitely harder to load, as the casters raise up the kiln a good four inches. Fortunately, they're only bolted on, so come off easily enough.

I decided to decommission the KilnSitter entirely, which necessitates several calls to Skutt. It looks like I can just join the red, black and white wires together and cap them off, then clip the ground close to the box, but I want to be sure, so I call customer support.

They haven't got a clue either. White wire? What white wire? Also, the red and black wires don't seem to connect where the diagram says they should. I shoot them a couple of photos of the inside of the sitter and computer box, then give up for the weekend.

On Monday, we hear back with good news: He's found the relevant circuit diagram deep in their archives. This is when I find out how old this kiln really is.

It turns out I was mostly right: the red and black leads do connect. The white wire only provides power to the limit timer, so it can get cut out entirely, as can the ground. After some scary discussion about whether I should run the red wire directly to the mercury relay (mercury relay?) instead, I choose the better part of valor (i.e. cowardice) and just cut both wires, twist them together, and screw on cap.

It occurs to me as we're talking that it sounds like the explosives expert coaching the terrified civilian into defusing a bomb via long-distance. First you cut the red wire. Then disconnect the black wire from the relay and attach the red one there. Clip and cap the white…

After finishing the duct work and electrical, it's time to be a brick mason…

Well, not quite. I have most of the bricks I need to replace, neatly bundled with the kiln, although I still need to order one more down from Portland, so there's another week gone.

Replacing the brick is not that complicated. First, I have to tease out the elements from the grooves in the bricks, remembering to first pull out the element pins holding them in place. This needs to be done right-side-up, as the pins are nigh onto invisible otherwise.

Afterwards, I get Denise's help to flip the ring over, as all the broken bricks are at the bottom. I loosen the stainless steel jacket by turning the screws on a set of hose-clamps that are split in half and spot-welded to the frame. Once that's done, it's not too difficult to slide out the broken brick and slide in the replacements. Two of them aren't too badly busted, and all the pieces are here, so I stick them back together with Sairset, a high temperature kiln cement. Tighten down the jacket, thread the elements back in, and press them into their grooves with a plastic putty knife while replacing the pins. And throwing in a few extra, for good luck.
offcntr: (rocket)
I think it was last November, though it might have been the year before. I'd just had to repair my bisque kiln yet again, when I got an email from Shelly about a kiln she'd found on Craigs-list. It looked like a beauty, a Skutt 1227 (about 30" across the inside, 27" high, same size as my old Olympic), but with computer controls, so basically self-firing. It had been only lightly used, then stored for nearly a decade. The price was not bad, either, somewhere in the range of $2000. (New, they're more than twice that).

It would have been the perfect kiln for me, but for two drawbacks. First, it was in Mt. Vernon, Washington, well on the far side of Seattle, almost to Anacortes (Heck, almost to Canada). Getting there and back to collect it would be a two-day trip. And that was the other drawback.

It was November. I was frantically making pots for my first holiday firing, followed by glazing, firing, unloading, then loading up the van and going to Clayfolk, down in Medford. Come back, and repeat for Holiday Market. There was no possible way to eke out two days anytime before New Years to go kiln hunting.

So I sighed and went back to the studio.

Fast forward to this summer. The August Clayfolk newsletter comes out, and in the ads section is a studio closing sale with a bunch of equipment, including another 1227, computer controlled. I return emailed so fast, the wifi caught fire…

In reply, it sounded even better. Computer control and EnviroVent (a nifty system that pulls noxious gases out through the bottom of the kiln and vents them out doors). Eight kiln shelves. Used briefly as a bisque kiln in North Carolina, shipped to Oregon and then stored in the garage for, this is sounding spooky, nearly a decade while the owner cared for her dying husband. At this point she's decided she's never going to be a full-time potter again, and it's time to let the equipment go.

Current retail value of this package would be around $4500; she's thinking of asking half.

We play phone tag for a couple of days, and when I finally reach her, prepared to offer $2000, the price has gone down to $1800. I put the check in the mail the next day. Sight unseen, not even a photograph. That weekend, we unload the van so that Monday we can drive down to Ashland to collect our new baby.

You see what's coming.

Okay, it wasn't that bad. It was indeed a hardly used Skutt KM 1227, but one of the earliest models, from around 1997. Nobody quite trusted the computer controllers back then, so they'd ordered it with controller and KilnSitter. Dismantling it for transport was easier than with my old kiln, but not nearly as modular and plug-and-play as the current generation.

Oh, and the movers had kinda beat the crap out of it when they moved it from Carolina. Four of the bricks on the bottom row were broken, as was the screw that holds the lid prop in place. The cord switch on the vent was missing a piece, and it looked like they'd stepped on the outgoing duct of the vent. It was squashed flat.

The EnviroVent itself was also an early model, but that might actually be an advantage. The Type 1's had a burlier squirrel-cage fan, and mounted right into the kiln frame, unlike the newer models that press up against the bottom on a spring-loaded monopod.

The kiln shelves were pristine. But they were also one-inch mullite, which is heavy as heck, so I'll probably not be using them.

So, not a bargain, but not an unfair price either. But it's going to take a bunch of work before I blithely sail into the world of care-free, computer-controlled firings.

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