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Rule

I used ceramic chimney flue, 8' x 8" x 24" for my oven. Sections were laid on a piece of rigid metal, and glued together with muffler patch [from auto store], which is like mortar. Then make doors for ends, and mortar in place. Holds heat well, but I did use some high temperature glass insulation.  (Chad Wigham)

    I have used the plans and design of Jon McAnulty and the hot air flow oven from the rodmakers page. The source for the heat in this design is a heat gun. In my case a Wagner power stripper. All is OK in that I can get the desired temps 375 and even higher but it does not get that hot at the end without the heat gun. I have solved the problem by flipping the strips at 1/2 the time but I find it annoying and I do lose heat when I open the door. Any ideas out there as to how to better distribute the heat throughout the entire oven. (when one end is at 375 the other as about 275) . I could abandon the oven and use the Sir D method of heat treating but I am reluctant to do so in that I have no experience lighting and using a torch.  (Bill Bixler)

      Have you insulated the oven?

      Is this a double tube design?  Does the heat gun blow straight through, or does it blow into a large tube, flow around the small tube to the other end then exits back the full length inside the small tube where the rod sections are?

      The straight through design would tend to have a heat gradient no matter how well it is insulated.  I use a vertical double tube hot air gun oven, and while I do have a slight gradient top to bottom, it is not 100 degrees F.  Yes I do flip the sections halfway through.  (Kurt Clement)

Rule

I'm in the process getting ready to build my oven.  The 6X10 you'll find is standard stock, but the 4X8, I've been told would have to be custom made.  I haven't had time to check the stores yet (Menards etc.) to see if this is true.  I did get one quote of $60 for the 60 inch ductwork,  with the insulation glued/riveted and a door.  I just thought I'd let you know what I've found out so far.

Also has anyone tried making an oven out of stovepipes?  (John Freedy)

    I made my own ducting using the rolls of heavy gauge metal stocked by Menards (and I'm sure others) for roof flashing. Took a weekend to do it using a pair of snips, utility knife, some clamps and several long straight 2X4's. Put it together using a hand drill, POP rivets and sheet metal screws. If you have the room, a few hand tools and patience you can do it yourself.  (Winston Binney)

    Use double wall furnace flue pipe and wrap the outside with fiberglass (non faced) water heater or pipe insulation. Don't use the foil faced bubble pack stuff, it is not only flammable, but stinks to high heaven when it gets hot (ask me how I know!). When you get tired of monkeying around with compromise stuff, have a heating contractor make you a box of whatever dimensions you want and have him insulate it and put another box inside that, mine cost me 75 bucks and was well worth it.  (John Channer)

    Yes, you can get 5" diameter by 5 feet at HD for about $18.  Just hang some mesh wire on the inside, mount the element along the bottom, and you are all set to go.  (Kyle Druey)

    My oven is out of stove pipe. it was the cheapest way to go that I could find. I got 5 ft. Lengths of 6 and 8 inch pipe. insulated it and away you go!  Only problem was the wiring screwed up somehow last week. burned two rods, one I had lawn cast already. Oh well. I was going to post that on the elemental thread, but I was just too depressed.  (Mark Canazon)

Rule

Would Zero Clearance pipe work for an oven? The kind you use for going through a wall close to burnable materials? also called triple wall pipe.  (Jerry Andrews)

    Absolutely, if you can afford the stuff.  (Bill Harms)

    That's expensive stuff and I would say that would work even better.  (Dave Henney)

    It would work like a champ, if you can afford it, last I checked triple wall was 50 bucks or more a 3' section, so figure around 80 bucks for the pipe  3' and a 2'), then you still have to come up with closures at each end, they might as well be heavily insulated, too. Then, too, if you are going to drill this stuff, most of it I've seen has asbestos linings between the inner sections. But it will most definitely hold the heat in, I've put my hand on the outside of it with a gas log going full blast in the fireplace below.  (John Channer)

    I'm in the process of building an oven using 6" insulated triple wall (furnace/flue duct). Not far enough along yet to know how well it holds the heat, but I expect it to work fine. It's rated 2200F and the recommended clearance to combustibles is only 2" at that temp, so I figure it must be well insulated. At 375F, I'm expecting it will hardly be warm to the touch.  (Tim Preusch)

Rule

Any recommendations on a material for insulation around a sheet metal oven whose internal temperatures are around 350 degrees F would be appreciated.  (Taylor Hogan)

    I went down to my sorta local industrial insulation distributor, and bought high temp boiler insulation.  It looks just like wall insulation, in that it comes in a blanket about 2" thick, but according to the guy behind the counter, it'll withstand heat in excess of 800 degrees.  It's made out of some kind of aramid or ceramic fiber, as far as I could tell.  (Mark Wendt)

    I used the insulation from an old dish washer I had. It can withstand heat to 500 degrees.  (Mike Lajoie)

    I got insulation for my mica strip oven and very good service from All American Supply, Inc. (505) 299-7655 .  They suggested using "mineral wool" known as " 1" x 2' x 4' Delta Board Plain" or 8DB1.  This stuff is easy to use and cheap at 22 cents/square foot.  The shipping cost is the only real expense.  (C. Scott Bennett)

Rule

When I made my heat treating oven,  I  generally followed Frank N.'s plans. The main difference is his plan calls for 7" diameter heating duct, not readily available in my area. So I used standard 8".

I've had problems heating it up and getting even temperatures, and I'm guessing I should have gone with 6" instead.

What size did  y'all use?  (Bill Hoy)

    I've been using 6" and it has been working fine for me.  (John Kenealy)

    If I recall correctly, I used a 5" diameter galvanized duct for the exterior and 3" for the interior tube.  I found both at my local home improvement megawarehouse.

    Using a dual probe Fluke temperature meter, I found that I got to a stable temperature in about 10 minutes (measured at the bottom and top of the interior tube).  (Eric Koehler)

    I had a similar problem when I first built my oven . Insulation helped but the change that made the biggest improvement was adding another pipe , about 1 1/2 inches in diameter which went from the top of the oven to about 9 inches off the bottom. I then put the heat gun into the top of that pipe and the result is that the hot air is "delivered" near the bottom of the oven rather then at the top. This results in a much more even heat in the oven.  With this additional pipe I only get about 10 degrees difference between the top and the bottom of the oven.  (Ian Kearney)

    I used 6" for the outer and 4" for the interior.  Be sure to insulate it with any good hi-temp fiberglass blanket or batting.  (Rick Crenshaw)

Rule

Sometime there was a post about the ridiculous price of insulated ducting for the heat gun oven.  I'm not sure what the poster was looking at at Lowes, but I saw double wall water heater vent at Home Depot today, 3' lengths were less that $13.00, 5' lengths under $19.00.  Maybe whoever posted the high price was looking at triple wall stove pipe?  (Neil Savage)

    What's the heat rating on these?

    I was at Lowes last weekend and they told me that they didn't have anything to take the heat. I found everything else I needed there though. I haven't been to Home Depot yet.  (Jim Lowe)

    I had seen similar ducting at my local hardware store.  The double wall vent I saw looked like it had about 1/4" air space between the inner and outer walls with no insulation.  My local hardware store had lengths up to 5' that were quite reasonable. However, the insulated ducting for running a fireplace chimney through a roof was really pricey.  I don't remember what the price was, but it was more than $100 for a 3' length.  (Robert Kope)

      Well, I've seen a very nice heat gun oven made with the double wall water heater vent, and it seems to work very well.  The only reason I can see for insulating at all is to get the temperature up.  I tried with 6" single wall heat pipe (because I had some) but I couldn't get the temperature as high as I wanted -- under 300 degrees with my heat gun.  I think the smaller diameter and the air space should work.  I'm going to try it in a week or so and see.  (Neil Savage)

    I made my heat gun oven from two five foot lengths of round HVAC duct. The inner 4" diameter, the outer 6".  I used carriage bolts and nuts to secure the two with an air gap between.  The inner is off-center within the larger, so that a heat gun can "shoot down" the bigger tube, then the hot air flows up the smaller inner tube (following Frank Neunemann's design, but using round, instead of square, duct).  It takes the heat fine, and I get a temperature that's uniform (+/- 2 degrees) top to bottom (I use an analogue oven thermometer, with a six inch stem to check the temp; inserted through small holes in the both tubes at the top, middle, and bottom).

    The oven will hold a temp of 350 Fahrenheit no problem through three seasons, but during winter I can't get the temp to hold above 330 degrees (I usually bake at 325, so it's not a big deal).

    The heat source is an 1800 Watt gun, with infinitely adjustable rheostat control, bought from Grizzly for $30. I use a blind duct cap (6") on the bottom, and a second cap on the top with two holes cut out with tin snips.  One hole gets the heat gun, the second the smaller inner pipe.  The inner pipe sticks up chimney like about two inches to get the exhausted heated air away from the heat gun.

    I do use a small heat shield between the tuna fish can outflow valve (honest, it's a tuna can, with one section of the side cut out, which let's me direct the exhaust in any direction I want) and the heat gun barrel.

    The oven itself probably cost less than thirty bucks to build.

    All parts (except the heat gun) came from my local home Depot.  (Chris Obuchowski)

      I copied Chris' oven who copied Neunemann's design, etc., etc...(that's how things work huh?)

      That said, I wrapped insulation (one side foil - outward) around my oven and it seems to take less energy from my 1800 W heat gun to obtain and maintain the mid-300's temps I am looking for. 

      This is a very simple tool project with almost no skill needed (thank goodness from my perspective!).

      Good luck and let the hot winds blow!  (Scott Turner)

Rule

I work construction and had a left over 8x8 piece of clay flue, which I figured would work as an enclosure and hold the heat. The Pyrex glass seemed a easier way than to make an access door. I used 2 pieces of flu, one cut with skill saw masonry blade to length, stuck them together with muffler patch cement. The ends were sealed with masonry cement.  I found [check Google for 'Pyrex glass tube] that the longest, 52", and about 1.5" diameter tube available and went to a company that makes elements and got a straight one with actual heating length of 50".  When I sealed the ends of the flue I inserted a 1/2"x 1" piece of pipe 1" up from the bottom on each end to let the element slide thru, and a 1.5"x1" piece of pipe on each end about 4" up to let the glass slide thru & placed them in the mortar when I sealed the end.

The controller was available with the element so made a hole at the joint on top to accept the bulb sensor and hung it inside and also insert the temp gage there [found a 500 degree temp gauge on eBay for $5]. The element was like 2000 watt so I wired it to 220 amp but could go with 110 too. 

The inside heated length is 50" [element heat area] so the heat is under the glass for that length. The tube is open on each end to slide in the boo section and let the moisture escape. Interesting is that when the heat is on, the temp in the 50" area is what I set it at, but I can touch the glass at the ends and its just warm.  I can put the section in the tube and even though it lays on the bottom it wont be hotter than the top and evenly heats the section around and thru  its length. Since the flue tile absorbs the heat too, the heat stays very stable thru the heating time. I did add some insulation around the outside of the flue for better heat holding. I don't have the invoices of the companies where I got the element and glass from, but I found them on the net. The total cost was about $250 for everything. I later looked into having the enclosure made of metal, like a strip oven and it would have been a couple hundred $ just for that, so stayed with what I'd made. I think if you had a strip oven you could get smaller diameter tubes to your oven length and lay 3-4 on the rack and put your sections in them and it would even out the heat nicely. My oven has done a hundred or so sections and works the same way each time so I have very good consistency.

I can give more info and help locate parts if someone is interested.  (Chad Wigham)

    Do you think if you inserted the heat strip into the pyrex tube it would heat the oven chamber in a Cattanach style oven evenly?  (David Rinker)

    With the holidays at least 1/2 over, can once again thing about boo, ovens etc.  Have a few questions regarding one of your fist posts to the List way back in mid-December.  No rush on answers particularly since you maybe up to your elbows with holiday festivities.

    1.  Is there a fan?  Kinda belated question isn't it!  Don't see mention of one anywhere in your posts.  Should have asked this before as a no-fan design would be good and frankly, was a factor in my interest in your oven design to begin with.

    2.  you mentioned sealing the end of the clay flue with masonry cement and also:  "and a 1.5"x1" piece of pipe on each end about 4" up to let the glass slide thru & placed them in the mortar when I sealed the end."   BUT, the ends of the Pyrex tubes are open to let out the water vapor . . . ?? Sounds like maybe the Pyrex runs through the pipes -- through the sealed end of the flue -- and indeed protrudes out the end of pipe and flue . . . ?

    Anyway, some further description of the end sealing as well as various lengths of the flue, the pipes, and the Pyrex tubes would help my understanding.

    BTW:  where did you get your controller and would you recommend that I get the same one?  (Ted Godfrey)

      The unit is sealed on the ends and there is no need for a fan. The Pyrex evens out the heat, it will actually only heat the glass where it is inside the unit & exposed to the element. As I said I can touch the glass where it protrudes from the ends [that is what the short pieces of pipe are for, to slip the glass thru from end to end] I first thought of rotating the glass during heating so there'd be no hot spot on the bottom, but found it evened out the heat so well that that wasn't a problem. I also put plugs in the end with a small hole for ventilating, and found that wasn't necessary either.

      The tubes are 59" long, the unit is 59" long, with an inside exposier of about 57". The element is 60" long but with a actual heating length of 58", so the ends protrude thru the small pipes placed at the bottom so you can connect the wires. TEMCO.com is the company and get their catalog so you can see exactly what you want,  the e-site isn't that clear of a description. It will have the controller needed for the element.

      As I mentioned, having a sheet metal shop make the unit would make for a much lighter one as mine comes in at about 75#, so I put it on a dolly.

      Anyway, to keep this short, I can answer further questions as you go.  (Chad Wigham)

    I found the invoices for Pyrex & heating elements.

    Chemglass, Inc.
    3861 N. Mill rd
    Vineland, NJ 08360
    1-800-843-1794 FREE
    www.chemglass.com

    [called Duran Tubing]

    TEMPCO Electric Heater Corp
    607 N Central Ave
    Wood Dale, Illinois 60191
    630-350-2252

    probably TEMCO.com  (Chad Wigham)

Rule

Going out to the shop in a while to put together my oven. As usual finding the components I wanted locally proved impossible. I ended up with a 6" inner duct with a 7" outer and high temp insulation between. I found and bought a 1 1/4" thin wall feed tube but couldn't locate a 2"  outlet tube. (I'm planning a vertical oven.) A friend ended up giving me an 8' piece he had laying around but it's galvanized. I'm somewhat concerned with toxic fumes when exposed to high temps. There may be nothing to it but I would like to know before I put it together. Any feedback on this would be appreciated.  (Wayne Kifer)

    The fumes generated from burning galvanized metal are indeed toxic.  It's a concern at welding temperatures, but I doubt that our temperatures will cause a problem. Now, I don't have a temp figure to quote, so take that on advisement. In any case, the coating will only burn once. If you are concerned, fire it up outside, let the coating burn off, and go from there. You might also test a piece in the oven. If it burns, it leaves a white powdery residue. (Larry Blan)

    If you want a nice browntone rod heat treat it while the oils are being burned off the galvanized pipe. Wonder how I know that?  (Tim Pembroke)

    Thanks for the replies.  I'll knock it together, take it outside and fire it up to it's highest temperature for a while. If there's going to be a problem it'll take care of itself.  (Wayne Kifer)

Rule

I was in the process of building my heat oven. I was wondering what materials you need to build the  oven and where is the best place to get these materials.  I was planning on building an electric oven, using mica strip heaters.  (Brandon Shepelak)

    It is not elegant and just a mite off beat, but you might consider my oven.  I use a 1 1/2 " steel pipe with plugs in each end.  One has a hole drilled for the release of steam and resins.  Suspend with coat hangers and flame with a blow torch.  KEEP SMELLING THE STEAM. AND WHEN YOU DETECT IT CHANGING FROM MOIST STEAMY TO GOOD SMELLING RESIN SMOKE.  YOU ARE DONE  See Todd's tips for illustrations and methods.  (Ralph Moon)

      Ralph's oven works well, I rotate the pipe to heat evenly. And it smells pretty good when it changes form steam to dry heat. Ed Berg has done some quantitative/qualitative work on treating times and temps.

      But, Ralph's oven is simple and works and is more consistent than one might expect.  (Greg Shockley)

        Ralph isn't the only one to have used this type of oven. It has been around longer than he has. After all, he's just a youngster.

        Ralph's oven works well, I rotate the pipe to heat evenly. And it smells pretty good when it changes form steam to dry heat. Ed Berg has done some quantitative/qualitative work on treating times and temps. But, Ralph's oven is simple and works and is more consistent than one might expect.  (Steve Weiss)

    It all kinda depends on what kind of oven you're prepping to make.  I had all my sheet metal work done by a shop that specializes in tin knocking for the HVAC industry.  (It helped that I fixed their CNC plasma cutter for them one afternoon...)  For the oven insulation, I went to an industrial insulation supplier and got insulation that looks like house insulation, except it's ceramic, good for up to 1000º F, is yellow, and has no backing paper.  For the oven control, I use a PID controller I bought through my brother's business, but you can get them through eBay, as well as the electric motor to drive the fan.  The rest of the hardware I got through my local hardware store.  This is for a computer controlled convection oven.  (Mark Wendt)

Rule

I am currently building a bamboo oven which is different than anything I have seen on the list. Basically I took a giveaway kitchen range and vertically inserted a 5' piece of 4" double wall gas vent pipe through the top and into the oven compartment, down to the bottom oven rack. I have insulated the exposed pipe and rigged a way to suspend the fixtures in the pipe.  I have not yet acquired the thermometers that I plan to use. Today I test baked a couple of pieces. I suspended them in a preheated 350 degree oven, and covered the top of the pipe with a piece of steel plate, but allowed some heat to escape, calculating that the upward rise of the heat would even out the temps.  After 16  minutes it was evident that the pipe was hotter near the bottom than at the top.  I will get some thermometers installed so I can monitor. My question is, do you think allowing more air/heat out the top of the pipe would even out the temperature? If any of you have an oven of this design are there tricks to its operation?  (Ray Wright)

    I might try to raise the bottom end of the pipe off the bottom of the oven some so the air in the oven could circulate up the tube.  (Timothy Troester)

    Yes you can insulate the cold section of pipe.  (Gary Nicholson)

Rule

Does aluminum channel stand up to temperatures as high as 350 - 400 degrees F without warping or deteriorating? The skeleton will be wrapped in sheets of duct metal, insulated and another skeleton to support the external shell.   (George Wood)

    The aluminum will hold up in this application, no problem.  Aluminum doesn't lose significant strength until above 600F.  It doesn't melt until about 1100 F.  Your heating element isn't going to get that hot if you've got airflow.  If you're going to the trouble, you should be building a convection oven.  (Al Baldauski)

    Aluminum will take this temperature just fine. I will tell you though I've made several different style ovens in our sheet metal shop. The one designed by Mark Wendt is on the tips site, and the cat's meow. This design is one of the easiest and absolutely best performing ovens I've made. No aluminum framework required. I did it with a PID controller with the help of emails and drawings by Larry Blan. The only thing I did differently was use a pizza oven fan in lieu of the motor/cage assembly Mark used.

    This oven is big, so it does take up room, but this mass is also what I think keeps the temperature differential from front to back at less than 2 degrees, along with being convection. I can just throw the sticks in, set my timer/alarm and walk away. Perfectly even coloration from one end of the cane to the other.   (Tom Vagell)

    On the first oven I made I used cut off sections of aluminum ski poles to support the heat strip. No problems.  (Tony Spezio)

Rule

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