# Marks Kiln build



## dnalot (Dec 28, 2021)

I am setting up a bench-top foundry in my shop for doing lost “resin/pla/wax” casting and I need a small kiln. I looked at commercially available units and found the prices quite sobering and then the shipping costs and for me (10.3  percent) sales tax. So I looked at home built units on You-Tube and then decided on building my own. The unit I will be building will be 9” by 9” by 9” on the inside. That can accommodate several casting flasks at once. I expect it will cost about  $600 (including shipping and taxes) to build or about a third of the price of a store bought unit. The oven will also come in handy for heat treating metal and doing ceramics.

I have no experience with kilns, so I spent several days at the University of YouTube learning how to go about building a small kiln for use as a burnout furnace. 

So it begins with welding up the steel frame work. Not much to be said here except everything needs to be very square or you will have problems later. I bought my steel locally but everything else for the build I ordered on Amazon. 

Mark T


----------



## dnalot (Dec 28, 2021)

It is now time to make the element. I need to make it now so I will know how big to make the cuts in the bricks where the element will sit.

I am using 18 gauge Kanthel resistance wire to make my element from. Here is everything you need to know about this wire.

Kanthal Wire

Specifications: I used this handy calculator to figure out what I needed.

Helpful Coil Calculator Tool for Resistance

The veg oil guy that provided the calculator also has several good you-tube videos on making a kiln.

Using the calculator I gave these criteria 220 volt, 15 amp (my cord and outlet are rated for 20 amps), Resistance of wire .515 and the diameter of the rod I will be wrapping the wire around to make the Coil Element .375”. The wire coil expands a little when released from the mandrel. My outside diameter ended up at .48” That will fit nicly in a .5” grove cut by a router bit with a rounded end.

The calculator gave these results. 3,300 Watts ~  14.67 Ohms ~ 28.48 feet of wire required ~ 290 turns on coil.

I used my old Atlas for turning the coil because I can turn very slowly with this lathe thanks to the variable speed treadmill motor upgrade. A simple wood block  with a slit cut at one end, and  mounted in the tool holder allowed me to set the tension on the wire for uniform results.

Here is a link to my lathe upgrade

Variable speed for my Atlas 10" Lathe

All materials will be rated for 2500 degrees F or higher. My thermocouple tops out at 2372 F.  So say 2200 F. usable. That is way higher than I will need for my purposes so I will have a healthy reserve and not risk stressing the furnace.

Mark T


----------



## Tug40 (Dec 28, 2021)

Very tidy fabrication.


----------



## dnalot (Dec 29, 2021)

Tug40 said:


> Very tidy fabrication.



Thanks Tug40, I like to be tidy. But my shop doesn't reflect that.


----------



## Richard Hed (Dec 30, 2021)

dnalot said:


> Thanks Tug40, I like to be tidy. But my shop doesn't reflect that.


LIAR!  I've been to your shop--it is VERY tidy.  I'm surpized that you and Tug have not gotten together to swap lies, since you live so incredibly close to each other.  Get snowed in this year?


----------



## dnalot (Dec 30, 2021)

Richard Hed said:


> Get snowed in this year?



Yes Richard, about 15 inches accumulated so far and more coming today. Snow plow stops about two miles from my driveway so have stayed home the last week. Woodstove keeping the shop cozy but UPS stopped delivering materials for some reason. Warm air and rain coming on Sunday. To be honest, I cleaned up my shop for your visit.

Mark T


----------



## Richard Hed (Dec 30, 2021)

dnalot said:


> Yes Richard, about 15 inches accumulated so far and more coming today. Snow plow stops about two miles from my driveway so have stayed home the last week. Woodstove keeping the shop cozy but UPS stopped delivering materials for some reason. Warm air and rain coming on Sunday. To be honest, I cleaned up my shop for your visit.
> 
> Mark T


CHEATER CHEATER.   If it weren't so so far, I would come by more often then you would have to keep it nice and tidy.  LOL.  I have about 1/3 of your care package ready.  Am working on cleaning up MY shop but can barely get thru it at the time.  That mill is taking up all the room.  the hed is laying on a pallet which is what is taking up all the extra foot space.  Have almost gotten the ways completely cleaned and ready to mount on the turret.  This mill has "two" turrets.  I lookt and lookt for whatever bridgeport model has two turrets and cannot find one.  I found a photo, just ONE photo of a model with two but that is all--no other info.  It's not really two turrets, but rather a spacer that actually turns just like the turret, then the turret is mounted on top of that spacer.

In all my years workking with bridgeports, I never noticed if they had this spacer or not, as Me thimpfks that I maybe only adjusted the ram maybe once or twice and NEVER turned the turret at all!  As I thimpfks about it, I could see that being able to turn that turret in a shop that has lots of space like yours could be extremely useful for large projects.

We got about 2" of snow.  Speakking of the weather, that taiphoon in the Phils, wreaked a lot of havoc on our property in MOalboal.  Look up Moalboal, Cebu in the philippines on goggle earf and you can see my place at 9deg56'43"N 123deg23'29"E.  It's that white building with the hexagonal top.  This particular building is made to be taiphoon proof and apparently proved to be how it was built.  Some of the eaves were ript out but the roof apparetnly is fine.  Anyway, I will be going out there to inspect and repair what has been damaged in late Feb.  One building has had the roof ript off and it's impossible to say how badly it is really damaged.  Trees are down all over the place, mangoes do not stand well in taiphoons, lucky none landed on any buildings.  The report is that this taiphoon was worse than Yolanda about 5 years ago.  I was there at that time, and it wasn't bad in Moalboal, but bad in other placdes.   This taiphoon was supposed to be worse--certainly worse in MOalboal. 

The electricity is still not back on there and so we do not have a report from our caretakers.  A neice, however, managed to send some photos.  Unfortunately, she doesn't know how to take good photos!


----------



## Randoo (Dec 30, 2021)

dnalot said:


> I bought my steel locally


Hi, Mark. I live in Kelso and would like to know where you buy your steel?

Randy


----------



## dnalot (Dec 30, 2021)

Randoo said:


> I live in Kelso and would like to know where you buy your steel?



Online metals in Seattle. I am up that way fairly often and I pick it up there rather than having it shipped. They stock almost everything but shipping is a budget buster. 

Mark T


----------



## dnalot (Dec 30, 2021)

I am using 13 soft fire bricks 2” x 4.5” x 9” in all areas facing the ovens interior. And I will be using some castable refractory cement to make custom shaped boarders that will secure the bricks in place. No grout or other binders are being used as I expect those joints would probably crack from the heat and expansion of the materials. Instead I will be using some keyed joints and a few pins to locate the bricks and the cast parts in place. The galvanized sheet metal shell will hold it all together. I allowed for expansion of the refractory with a 1/2” thermal blanket between the refractory and the sheet metal.

A note on the sheet metal. I used .030” sheet. It forms easily and I was able to form it without a brake.

I used my table saw and a router table to make the cuts in the bricks. If you can do this outdoors do so, it really makes a mess.  Its freezing cold here so I did mine in the shop. To help reduce the mess I used a variable speed controller for my router and set it to about 2000 rpm. It took about an hour and a half to make all the cuts and the rest of the day to clean up after.

The bricks are very fragile but they came nicely packaged and none were damaged. 

Mark T


----------



## Richard Hed (Dec 30, 2021)

dnalot said:


> I am using 13 soft fire bricks 2” x 4.5” x 9” in all areas facing the ovens interior. And I will be using some castable refractory cement to make custom shaped boarders that will secure the bricks in place. No grout or other binders are being used as I expect those joints would probably crack from the heat and expansion of the materials. Instead I will be using some keyed joints and a few pins to locate the bricks and the cast parts in place. The galvanized sheet metal shell will hold it all together. I allowed for expansion of the refractory with a 1/2” thermal blanket between the refractory and the sheet metal.
> 
> A note on the sheet metal. I used .030” sheet. It forms easily and I was able to form it without a brake.
> 
> ...


Did you say where you got the bricks?  I want to get some but they are SO INCREDIBLY expensive that I have balked at getting any so far.  I need some for various purposes.


----------



## dnalot (Dec 30, 2021)

Richard Hed said:


> Did you say where you got the bricks?



Everything except the steel I bought on Amazon. And yes the bricks are not cheap, it is what it is. They are of excellent quality.  

https://www.amazon.com/dp/B081K26JZM?psc=1&ref=ppx_yo2_dt_b_product_details

Mark T


----------



## Tug40 (Dec 30, 2021)

Randoo, i buy steel for my welding projects from Waites in Longview.
Lotsa remnants, & round rems for machining projects.
I’ve been gonna go to Metal Supermarket in Portland, (look up their website) to see what they have, they’re by PDX Costco. Never been there myself yet.
Usta but  from Wayron, before they went outa business.


----------



## Randoo (Dec 30, 2021)

Tug40 said:


> Randoo, i buy steel for my welding projects from Waites in Longview.
> Lotsa remnants, & round rems for machining projects.
> I’ve been gonna go to Metal Supermarket in Portland, (look up their website) to see what they have, they’re by PDX Costco. Never been there myself yet.
> Usta but  from Wayron, before they went outa business.


Thanks for the info! You must be near me?

Randy


----------



## dnalot (Dec 30, 2021)

Tug40 said:


> Randoo, i buy steel for my welding projects from Waites in Longview.
> Lotsa remnants, & round rems for machining projects.


 
I will have to check that out. Rando & Tug40, we should get together for lunch sometime. 

Mark T


----------



## dnalot (Dec 31, 2021)

I started with the kiln floor, casting the horse shoe collar around the two soft bricks that will be the bottom of the kiln's interior. The corners are reinforced with piano wire as I expect to see cracking here. And I cut a notch into the soft bricks to stretch some piano wire across the bricks to hold the ends of the horse shoe brick in place. The castable refractory needs to be fired to come to full strength. Instructions on the bag called for gradually bringing the material to 390 degrees in kitchen oven over several hours.

With that done I used high heat silicon to secure it to the metal frame. The fire bricks set directly on the steel frame and the cast portion of the floor sits about .125” above the frame to allow a thick build up of the high temp silicon to hold the bottom in place and provide flexibility for heat expansion.

Mark T


----------



## Richard Hed (Dec 31, 2021)

dnalot said:


> I started with the kiln floor, casting the horse shoe collar around the two soft bricks that will be the bottom of the kiln's interior. The corners are reinforced with piano wire as I expect to see cracking here. And I cut a notch into the soft bricks to stretch some piano wire across the bricks to hold the ends of the horse shoe brick in place. The castable refractory needs to be fired to come to full strength. Instructions on the bag called for gradually bringing the material to 390 degrees in kitchen oven over several hours.
> 
> With that done I used high heat silicon to secure it to the metal frame. The fire bricks set directly on the steel frame and the cast portion of the floor sits about .125” above the frame to allow a thick build up of the high temp silicon to hold the bottom in place and provide flexibility for heat expansion.
> 
> ...


I would recommend putting a strut under that U-shaped brick in this last photo


----------



## ddmckee54 (Dec 31, 2021)

If you are building this as a burnout oven, where's the drain?  When doing lost wax, MOST of the wax can actually be caught and recovered/reused.  I'm not sure about lost PLA or lost resin, but I would think that you'd get something slumping out of the mold.  With no drain it looks like yours will be a total loss system, everything will have to turn into smoke and ash?  As is, this WILL make a dandy heat treat oven though.

Don

OK, I just realized that you could actually put the molds over a catch pan in the oven, then ramp your temperature up to the melting point and hold.  After a long enough time to melt out the material, remove the pan and then continue with the burn-out cycle.  (Didn't QUITE have brain completely engaged.)


----------



## dnalot (Dec 31, 2021)

Richard Hed said:


> I would recommend putting a strut under that U-shaped brick in this last photo



The cast U shape is supported by cross bars and is held in place by hi temp silicon

Mark T


----------



## Richard Hed (Dec 31, 2021)

dnalot said:


> The cast U shape is supported by 4 cross bars and is held in place by hi temp silicon
> 
> Mark T


Naturally, I can't see what is under that, but it doesn't look like it is supported except on the edges.  Does the hi temp silicon stop it from sagging?


----------



## dnalot (Dec 31, 2021)

ddmckee54 said:


> I just realized that you could actually put the molds over a catch pan in the oven



I have already made a S.S. drip pan to catch any dripping wax. I will be doing mostly lost 3D resin. It doesn't melt, it turns to a gas and gets vented out. The small amount of wax used for the spur is not worth recovering. 

Mark T


----------



## dnalot (Dec 31, 2021)

Richard Hed said:


> Naturally, I can't see what is under that, but it doesn't look like it is supported except on the edges. Does the hi temp silicon stop it from sagging?



It is very well supported by the silicon and the bricks have a deep slot cut into them where they touch the cast refractory. Allowing some of the cast refractory to engage the bricks. You will be able to see this detail when I cast the top. I should have taken more photos when I mounted the bottom to the frame.







Mark T


----------



## dnalot (Dec 31, 2021)

After almost two weeks of freezing weather the snow is starting to melt off my shop's roof. Icicles are 36" long.

Mark T


----------



## Tug40 (Dec 31, 2021)

Randoo, yes i live in Castle Rock area.
I suspect U got hammered with snow & ice too.
Looks like Mark really got it.
We haven’t had any mail delivery since last Tuesday.
Lunch with you & Mark sometime would be good. Richard also, he sounds like a wild & crazy guy.
Stay warm & outa the ditch's.


----------



## Richard Hed (Jan 1, 2022)

Tug40 said:


> Randoo, yes i live in Castle Rock area.
> I suspect U got hammered with snow & ice too.
> Looks like Mark really got it.
> We haven’t had any mail delivery since last Tuesday.
> ...


I may have been wild in my younger days, but I'm just crazy now.; Yeah, and I would luv to be invited for lunch, but it is too far to go over there on such a wild errand.;


----------



## abby (Jan 1, 2022)

A well constructed build Mark , may I suggest that you include a venting facility.
My own burn-out kiln , although very similar in construction , is much larger and can accomodate 4 flasks which are 6" diameter and 12" high.
A full kiln load equates to about 21 lbs of water , which eventually leaves the kiln as steam so an exit is required.
In addition it is important to have sufficient oxygen enter the mould cavities to complete the burn-out , residual wax or resin cannot burn without oxygen.
I have experienced moulds that showed the existence of wax even after casting.
If I may tell you of one or two discoveries I have since made ;
My kiln was built in the days when programmable controllers were financially out of my reach .
I wrote a programme for an Apple II which I had lying about , this simple program switched solid state relays on/off according to input from a thermocouple .
The kiln had an inner box core about an inch thick with grooves in the side walls for the heating elements , which totalled 5 Kwatts.
The inner box was encased in a 4" thick layer of ceramic fibre blanket ( rescued from a dumpster at a local tile manufacturer ).
Again because I was setting up a business with restricted finances I saved money by using a piece of 9" dia steel pipe 18" long as a flask .
I had several 14 hour long un-eventful firings , normally overnight.
Then finally disaster , an overnight power cut swiched the computer off, when the power came back on everything fired back up.
When writing the programme I included a line of code which requested an input for the final casting temperature , the programme would wait for this input , but the output to the kiln would be high , elements switched on but no control !
Anyway to cut a boring story the kiln fired to an unknown temperature causing a chemical reaction between the investment cement and the steel pipe.
When we managed to open the door after 24 hours cooling the pipe and contents had disappeared leaving a pile of slag burned into the kiln floor.
One side of the kiln had a hole burned though an inch of high temperature refractory cement , only the ceramic blanket , acting as a barrier , prevented the reaction melting through the steel outer casing and possibly setting fire to the building.
Needless to say the rebuild incoporated safeguards to prevent such an occurence and eventually I was able to buy a proper controller and nimonic investment flasks , I also changed the heating elements to encased ones which , although limiting the temperature to about 850°C  , is more than enough for a wax burn-out.
My castings range from hundreds of tiny ones






to single large pieces






Dan.


----------



## dnalot (Jan 1, 2022)

abby said:


> may I suggest that you include a venting facility.



Thanks for the input Dan. I really appreciate it. I have provided a .5" vent hole it the top of the kiln and will be adding a smaller hole or two in the bottom. I had thought the door would not fit tight and provide a way for air to get in. But as luck will have it the door fits snugly and the spring-loaded latch keeps it tight. Any suggestions as to vent hole size? I have thought about using an aquarium air pump to supply the air through a hole in the bottom, any thought on that? I completed the kiln a week ago and have been testing it a little. I have no investment plaster yet as I have been snowed in since Christmas eve. 

Your castings look great. I hope to be able do at least half as well. 

Mark T


----------



## dnalot (Jan 1, 2022)

Next step, the walls are fitted into place and the groves the element will ride in were drilled for the hooked pins that will hold the element in place. Also the hole for the thermocouple was drilled into the floor and the holes for the element's leads were drilled into the back wall.

I drilled a hole through the top brick nearest the front of the oven to run a couple of piano wires that will help hold the ends of the cast horse shoe shaped brick  in place. Four wood legs will support the top bricks while  the collar is cast. Like the floor I reinforced the corners with some piano wire in the cement. I fully expect the corners to crack but that isn't a problem as long as the wire holds the parts in alignment. I cast the top and the door at the same time.

I bought 30 pounds of refractory cement and I have about 3 pounds left over. 41 pounds of bricks and 27 pounds of refractory cement. That will put the total weight of this oven at nearly 95 pounds. Guess that's why the store bought furnaces cost so much to ship.

Mark T


----------



## Tug40 (Jan 1, 2022)

My wife has a wood-fired pizza oven she had shipped from Italy, yes shipping these small ovens can be costly.
Her oven will get up to 1000 deg, she actually let me anneal a small engine frame in it “one time”
Mark your workmanship is very professional.
Abby, when you were describing the mishap with the kiln, I had thoughts of The China Syndrome.
Nice castings BTW.


----------



## abby (Jan 1, 2022)

I suggest a 2 or 3 inch diameter hole in the top and a similar sized hole in the door with a rotatable damper for adjusting the air flow.
I have no chimney fitted and during the summer months the steam is not a problem in my large workshop. 
The winter is different , the steam condenses everywhere and any steel quickly rusts. Ideally I should have fitted a chimney to take the steam outside.
I will take a photo to explain as almost all of my pictures are on photobucket and unaccessible to me unless I pay the ransom.
Dan.


----------



## dnalot (Jan 2, 2022)

The refractory cement requires 6 hours of firing at 350 degrees F. before it comes up to full strength. I was able to do this with the kiln floor and the door by placing them in the wife's kitchen oven. The top of the kiln will get fired in place when the unit is completed.  After firing the door in the oven it was ready to be mounted to the door frame of the oven with weld-on hinges. I actually silver soldered them to avoid having the hinges creep around like they would if I used my arc welder. The door is secured with a spring loaded catch. I need to get a bigger spring but improvised with what I have for now. The door swings silky smooth and fits tightly.

Mark T


----------



## dnalot (Jan 3, 2022)

The piano wire wraps around the furnace sides and over the top to insure the bricks stay in place if the unit is ever tipped over onto its sides or back. I originally thought the sheet-metal shell over a 1/2” ceramic blanket insulation would be all I would need to hold everything together but after further reflection I decided I needed the wire as well.

Mark T


----------



## dnalot (Jan 3, 2022)

So there you go, the frame is all painted now and the unit is wrapped with ceramic insulation and the sheet-metal shell is installed. And a vent hole has been drilled into the top. The vent hole is required for the burn out process to promote burning and to expel any soot. Soot will conduct electricity and short out your element. My door fits rather tight so I will add a vent hole in the floor to allow air to get into the kiln

That was fun and I am very happy with how it turned out. Time now to install all the parts that make up the heating element and its controls.

Mark T


----------



## dnalot (Jan 4, 2022)

Here is a link to the Amazon page I ordered the controller from

Ramp Soak Temperature Controller Kiln SSR Thermocouple Programmable Control 60 Segment: Amazon.com: Industrial & Scientific

The PID  controller I bought was made by RoHS. Nice unit but the manual if you can call it that was horrid. Even when I went to the sellers web sight and found an updated manual with far less typos and bad info it was still almost worthless. Could find no You Tube videos on this unit. Spent several days farting around before I got it to work and a few more before I got it working smoothly. I recommend looking for a controller that is well covered on You Tube.

In an earlier post “Abby” referenced problems that can arise if the power goes off in the middle of a program. The controller I am using has a lot of variables that can be set. One of them is what to do if the program was interrupted by a power failure. I set it to “end program”.

I think I would have been better off with this one.

Amazon.com: Auber Instruments PID Temperature Controller,W/ 30 RAMP/SOAK,SSR Output, SYL-2352P : Industrial & Scientific

It looks like this unit is easier to program and there are several You Tube videos on how to program it.

Mark T


----------



## dnalot (Jan 4, 2022)

I stretched my resistance coil out to 54” long and installed it into the groves cut into the bricks and secured it with wire pins with a hook on the end. I used the same wire the element was made from. By design my heating element was to have 14.67 Ohms  resistance.  I used an Ohm meter and checked to see if I was close and found it to be 15.2 Ohms. The element's pigtails are covered with two layers of ceramic insulation tubing and protrude through the back of the furnace and the sheet metal cover. I cut some slots in the sheet-metal so the cover could be removed without having to straiten out the wire. The element is probably the weakest link and will one day need to be replaced. The wire only cost a little under $20 ($19 for 50 foot roll, only used 28 feet) and was easy to turn into a coil and is very easy to install. I made a spare and put it in a box with some other spares like fuses and screws.

The control box contains the controller, a solid state relay, two fuses for the 220 volt service to the heating element and a 110 volt fuse to protect the controller and an on-off switch. The relay came with a heat sink but it was rather useless as it was painted and the surface the relay was to sit against was very irregular. I stripped the paint off and sanded the surface flat and smooth. A 3” fan was mounted to the back of the controller box for cooling the relay.  Wiring was simple and I just followed the diagram that came with the controller kit. At least that part of the controllers manual was clear.

Mark T


----------



## Sprocket (Jan 4, 2022)

Mark,
In the last picture, is that a fume hood over the oven? Seems like a good idea.
Doug


----------



## dnalot (Jan 4, 2022)

Sprocket said:


> In the last picture, is that a fume hood over the oven? Seems like a good idea.



It is but you were not supposed to notice until I post a photo of it tomorrow. It collects the fumes and a fan blows them up a 4" duct to a blower that vents to the outside.

Mark T


----------



## Chiptosser (Jan 5, 2022)

Are you not using a low limit thermo?


----------



## Sprocket (Jan 5, 2022)

Sorry Mark, but we really do pay attention to your pictures and posts.
Doug


----------



## dnalot (Jan 5, 2022)

Chiptosser said:


> Are you not using a low limit thermo?



I don't know what that is. All I know is that it is a "K" type with a top limit of 2372 degrees F

Mark T


----------



## dnalot (Jan 5, 2022)

Here are some photos of the completed furnace ready for action. I made an exhaust hood for it that directs the exhaust to the inlet of the exhaust fan in the hood above my bench.

Mark T


----------



## dnalot (Jan 5, 2022)

The element turns out to work perfectly. And it heats the oven far faster than what you would want, but the PID controller takes care of that. The controller will turn the current on and off to the element to control the rate of climb to whatever you want. And the 3300 Watt element can easily heat the oven up to the max 2200 degree F. I had hoped for.   On my first use I slowly ( over 8 hours) brought up the temp in timed stages to 1200 F. and then let it cool down naturally. 8 hours later it was still 120 F inside (shop was 60 F.). Inspection showed there to be do damage to the refractory or anything else.

As you can see in the photo (element is just turning on) the element heats up faster where the coils are closer together. It turns a uniform color after about 10 seconds. I sorted this out by stretching the hot areas out a bit more. After getting hot the wire is much stiffer and I suspect more brittle.

The second go I did the same thing only I took it up to 2000 F. over 10 hours and held it there for 3 hours. After cooling down everything still looked good.

I made a drip pan for burning out wax. The grate is S.S. But the pan is mild steel. I will make a stainless tray when the material arrives. The photo of the pan shows two 4 inch flasks and one 3.5” flask. The drip pan is elevated above the floor by .5”. I have a long heavy duty spatula that I can remove the pan with when needed.

I have been doing some early tests burning 3D resin printed parts just lying on the drip tray and it is extremely stinky. Its the kind of stink that hangs in the air for days. The hood works great collecting the smoke and directing it to the overhead hood vent but the slightest breeze will let some smoke escape. My shop can be drafty so I plan to add a curtain made of fire prof  felt that will attach to the back and sides of the hood with magnets.

“Abby” in a previous post suggested I needed a much larger vent hole in the top. I think I will start with a bit larger (tan planed) top vent hole and air provided by a controllable aquarium air pump to a couple of holes in the kiln's floor. After I put my furnace through a few test runs I will let you all know what I finally end up with.

My original budget was $600 and I came close at $660. The hood, the drip pan and a spare element put me over the original budget. I also plan to protect the floor with a “kiln shelf” and expect to spend another $20 there. I don't know what it will cost to operate but my area of Washington State enjoys one of the lowest electrical rates in the country. The Hydro-power dam is only seven miles away.

To avoid electric shock I plan to add a micro switch that interrupts the signal to the relay if the door is open. And I plan on making myself a ceramic coffee cup and a beer mug.

Mark T


----------



## awake (Jan 5, 2022)

Mark, this is an exceptional build; I suspect the quality exceeds much of what is commercially available in a similar size. So much so, that I hate to quibble with one small point:



dnalot said:


> The PID  controller I bought was made by RoHS.



RoHS is similar to UL Listing - a certification, not a brand name; analogous to, but with a different focus from, UL or CE: The Differences between UL, CE, EMC, CSA, RoHS Certifications

Of course, I suppose someone could try to use it as a brand name ...


----------



## dnalot (Jan 5, 2022)

awake said:


> RoHS is the similar to UL Listing



Nice to know.  It was the only marking on the box that looked like it might indicate who made the unit. Must be a generic knock off of some kind. 

Mark T


----------



## awake (Jan 5, 2022)

For so many electronics items, even if it has a "brand name" on it, it is probably a generic knock off! 

Again, magnificent work on your kiln - a work of art, and lots of useful information for those of us that keep thinking we might build one some day ...


----------



## dnalot (Jan 5, 2022)

awake said:


> Again, magnificent work on your kiln - a work of art, and lots of useful information for those of us that keep thinking we might build one some day



Thanks Andy. And thanks to all of you that have been following along. 

I will post updates as I figure out how to use the furnace for use as a burnout oven..

News Alert. I have been watching the deployment of the mirror of the James Web Telescope all morning. The mirror was just successfully deployed. 

Mark T


----------



## ddmckee54 (Jan 5, 2022)

From us nerd type EE's:

RoHS compliance means that a product has been tested for 10 banned substances by an independent authority, and that the tests confirmed levels of the substances below the RoHS threshold. Under RoHS 3, the latest version of the RoHS directive, the 10 substances restricted are:


Cadmium
Lead
Hexavalent chromium
Mercury
Polybrominated biphenyls (PBB)
Polybrominated diphenyl ethers (PBDE)
Bis(2-ethylhexyl) phthalate (DEHP)
Benzyl butyl phthalate (BBP)
Dibutyl phthalate (DBP)
Diisobutyl phthalate (DIBP)
All of these substances must be limited to 1,000 ppm except cadmium, which has a limit of 100 ppm.

This was clipped off from an RoHS compliance site.  In most cases it just means that they didn't use lead solder when building the electronics.

Don


----------



## Richard Hed (Jan 5, 2022)

ddmckee54 said:


> From us nerd type EE's:
> 
> RoHS compliance means that a product has been tested for 10 banned substances by an independent authority, and that the tests confirmed levels of the substances below the RoHS threshold. Under RoHS 3, the latest version of the RoHS directive, the 10 substances restricted are:
> 
> ...


Thank you for that info.  Just so you all know:  1000ppm is one out of a thousand or .1%  which, when dealing with poisons, is actually a lot.  If dealing with carcinogens, it's too much.  I suspect some of those chemicals mentioned are carcinogens.  It's funni how we all fall into that trap of seeing 'ppm' and we thimpfks it is automatically a small amount.  It's how someone trying to sell you something leaves out pertinent information.


----------



## JLaning427 (Jan 6, 2022)

Richard Hed said:


> Thank you for that info.  Just so you all know:  1000ppm is one out of a thousand or .1%  which, when dealing with poisons, is actually a lot.  If dealing with carcinogens, it's too much.  I suspect some of those chemicals mentioned are carcinogens.  It's funni how we all fall into that trap of seeing 'ppm' and we thimpfks it is automatically a small amount.  It's how someone trying to sell you something leaves out pertinent information.



Yes, 0.1% is a large amount for some poisons, and negligible for others.  And in the case of most electronics, 1000 ppm is probably acceptable, as I doubt Mark will be using his controller as a hot beverage container anytime soon.  But as a complementary example, the USDOT haz-mat limit for transporting Benzene in water is 5 ppb,  (5 parts per billion) which is more appropriate because you could end up drinking that contaminated water down the road (say, if it gets mixed into a municipal waste stream, or spilled from an overturned truck).  Different horses for different courses....

James


----------



## dnalot (Jan 30, 2022)

UPDATE

After struggling for days trying to figure out how to use the no-brand PID controller. I bought a new one. The first controller came with the most pathetic manual I have encountered. Before buying a new one I went to the companies web sight and downloaded their manual. Complicated yes, its a complicated device. But their manual was easy to understand and I was quickly up and running. The controller I bought is Auber Instruments SLY-353P. See link above.

I have added a short skirt to the edges of my exhaust hood. It is a welders felt blanket rated at 1500 degrees F. The curtain keeps drafts in my shop from letting smoke or vapors from escaping the hood. And I added an aquarium air pump with two outlets and a volume control knob to supply air for a clean burnout. The air lines are silicon rated for 500 Degrees F and the air is introduced through the bottom of the kiln.  My first burnout of a flask with a wax based resin went smoothly (as far as the controller was concerned) with the controller doing its job very well and the hood took care of the fumes.

At 1360 degrees for 4 hours the door face came up to 500 degrees F. The sides were 250 F degrees  and the bottom was at 350 degrees”. And that's where the story took a sour note. My element got to hot and came lose from one of the pins that keep it in place. To many coils to close together allowed the wire to get to hot (white hot). (I error-ed on my original calculation thinking I had a 220 volt service to my shop but when I checked it was actually 240 volts). To try and remedy this problem I went from 240 Volts to 120 volts and installed an element with 6.5 Ohms resistance.  The kiln now has a 2200 Watt element and now glows with a bright orange color perhaps bordering on yellow. That will only let me heat up the kiln to 1150 degrees F. I have used all the available amps on my 120 outlet so will have to go back to the 240 volt outlet. I have now ordered some 20 gauge wire (used 18 gauge originally) With that I can make an element that should yield 3100 watts, down from 3600 watts of the first one I made. Somewhere I will find the sweet spot. If you are building a kiln cut more groves for the element to sit in. When I get this sorted out I will post another update.

I have also doubled the number of pins securing the element and have enlarged the top vent to 1”

I built this kiln for my exploration of investment casting. You can view the results of my first pour here

Mark's First investment casting

Mark T


----------



## dnalot (Feb 2, 2022)

Update 2: I installed a new 240 volt element that draws 13 Amps with a resistance of 18 ohms, yielding 3100 Watts. I used 20 gauge wire wrapped around a .42" rod to create the coils. It can take the furnace up to 1400 degrees F quickly. I don't think it has much power to spare but it reaches the temperatures I need. Shortening the element would result in higher temps with an increase in amperage draw. I used 23' of 20 gauge wire to make the element I am testing now. 25' spool of wire only cost $8. 

Mark T


----------



## awake (Feb 3, 2022)

Mark, any idea what the maximum temperature is on your setup?


----------



## dnalot (Feb 3, 2022)

awake said:


> any idea what the maximum temperature is on your setup



It is now around 1500 degrees F. My original element got it up to 2000 degrees but the coils of wire were to closely spaced and the wire got too hot. Using a smaller diameter wire and/or having more groves to house the element would fix that. For my use I need to hold 1350 degrees for 4 to 5 hours so what I have now works for me. I plan to try it out today with a pour at around 10" am tomorrow.  It takes about 20 hours  to mix and pour the plaster, let it dry and then do the burn-out in the kiln. This time around I have a good vacuum chamber and a much bigger vacuum pump so I am hoping to improve on my first attempt. One thing I have learned doing this is there are no shortcuts. 

Mark T


----------



## Richard Hed (Feb 3, 2022)

dnalot said:


> It is now around 1500 degrees F. My original element got it up to 2000 degrees but the coils of wire were to closely spaced and the wire got too hot. Using a smaller diameter wire and/or having more groves to house the element would fix that. For my use I need to hold 1350 degrees for 4 to 5 hours so what I have now works for me. I plan to try it out today with a pour at around 10" am tomorrow.  It takes about 20 hours  to mix and pour the plaster, let it dry and then do the burn-out in the kiln. This time around I have a good vacuum chamber and a much bigger vacuum pump so I am hoping to improve on my first attempt. One thing I have learned doing this is there are no shortcuts.
> 
> Mark T


When you say "pour", what are you pouring?  I assume you were pouring liquid metal but by your words, it seems you are pouring plaster.  I thot you were going to use this for heat treating.


----------



## dnalot (Feb 3, 2022)

Richard Hed said:


> When you say "pour", what are you pouring? I assume you were pouring liquid metal but by your words, it seems you are pouring plaster. I thot you were going to use this for heat treating.



Sorry for the confusion Richard, I'm not the word smith you are. My main purpose in building this kiln is for use in lost wax / resin investment casting. First step is to pour (should have said fill the flask with plaster). Then let stand for a few hours to set . Then into the kiln for about 14 hours to dry out the plaster and then burn out the patterns.  The burnout requires lowly ramping up the temperature in several steps to 1350 degrees and then holding that temp for 4 hours before ramping down to the pouring (metal) temperature. I am using brass so pouring temp = 800 degrees F .

Remember I don't really know what I'm doing (yet)

Before retirement I was a fiberglass boat builder. It always burned my ass when people would refer to laminating the hull as "pouring the hull" or other laminated parts. It made it sound like it was easy. My brother and I built boats from 37' and down. The bigger boats were inboard diesel, and the smaller models were outboard or inboard/outboard. Our Big sellers  were sold under the C-Dory brand. We also built a line of custom Catamarans.  





22' C-Dory Angler and 24' Tomcat





Two 22' Cruisers off to a dealer.





Custom 30' Tomcat . If you think the photo above looks silly, we towed this 10' wide boat on a 5' wide trailer to deliver it to water. 


Mark T


----------



## jumps4 (Feb 4, 2022)

off topic: I have dreamed of owning a C-dory 22, a fantasy I will never afford.


----------



## dnalot (Feb 4, 2022)

jumps4 said:


> I have dreamed of owning a C-dory 22



I just looked at what they are selling for. Remarkable how well they have maintained their value. Whatever you spend on electronics you lose the first day. Motors depreciate rapidly but the C-Dory boat has incredible staying power. They were built to last and the design looks good even if the boat looks a little crusty. The boats I built have a serial number starting with "DOR" I sold the company in early 2000.

Mark T


----------



## dnalot (Apr 15, 2022)

Update 3

I have added a a false floor to my kiln to house an additional length of element. I was having problems with the element getting to hot and failing. With this extra extra length I was able to fit an element made from 46 feet of 18 gauge wire. The new specs are 2400 watts, 24 0hms, 240 volt drawing 10 amps. I am now able to get the 1400 degrees F. I need without the element getting to hot.






Mark T


----------



## abby (Apr 15, 2022)

I use sheathed elements in my burnout kiln , these are rated for a maximum temperature of 850°C which is perfect for the maximum requirement of 725°C.
Dan.


----------



## dnalot (Apr 15, 2022)

abby said:


> I use sheathed elements in my burnout kiln , these are rated for a maximum temperature of 850°C which is perfect for the maximum requirement of 725°C.



How much do they cost? Are they made to fit a particular kiln?  The element I have made cost me $10 and it takes me about 3 hours to make and install. It tops out about the same as yours. The investment plaster I have been using works best at 1400F, or 760C. when used with a printed resin pattern.

Mark T


----------



## Chiptosser (Apr 16, 2022)

dnalot
The heat treat ovens that I maintained had a one piece platen floor over the bottom elements to protect the elements, as you have done.
If the bottom cracks, the scale, ( oxidized material) would fall down through the crack and short the element.  
So, keep an eye on build up in the element.


----------



## dnalot (Apr 16, 2022)

I admit putting the element in the floor was not ideal but it was all I could do as a fix to the design flaw. If I were to start over I would provide twice the number of groves for the element to rest in. After each use I vacuum out the kiln once it has cooled. It was still very hot when I took the photo. 

Mark T


----------



## abby (Apr 16, 2022)

I had a meltdown accident early on with my kiln which left a conductive film on parts of the lining.
This caused shorting of the coiled elements so I changed them for the sheathed type. I bought mine from a specialist supplier in Liverpool but infact they could be sourced from old electric ovens. Mine are 1500 watts each and there are 4 each side wired in series.
Dan


----------



## dnalot (Apr 16, 2022)

Thanks Dan. I will look into that when the time comes to try something new.

Mark T


----------

