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Rule

I plan to make some changes to my oven, ie: covering mica heat strip with a 1/4" X 4" steel bar to control radiant heat and add a centrifugal blower in the end of the oven.  The fan shafts, that I have seen, get very hot and affect the motor.  Has anyone found a way to prevent the heat from destroying the motor.  Any synthetics I could make a coupling from?  (Jerry Young)

    Because I build nodeless, I've never needed a long "strip" oven, but lately I've been thinking  about building some rods with (gasp!) nodes still in them.  Therefore, I've been thinking about ovens, too.  A "Thermolyne" heating tape could be wrapped around a metal tube (large diameter electrical conduit?) to even up the radiant heat, but forced air movement inside would still be desirable. Maybe the fan shaft could be driven by a pulley belted to the motor.  A long belt might not be in contact with the hot pulley long enough to be damaged or to heat the motor.  Alternatively, a long rod could protrude into the oven and attach to a "dasher" on the inside.  I could grab the rod with a gloved hand and push it in and out, as if I were churning butter instead of hot air (Can you tell I'm an academic?), every two or three minutes.  The churn concept is so simple and cheap that it can't be any good.  I can almost hear Terry Ackland saying, "You wanker, you're supposed to find the most involved ad difficult ways, not the simplest!"  (Grayson Davis)

    I ran into much the same problem. The first fan used a jack shaft mounted in 2 pillow block bearings running completely through the case of the oven and was driven by a old furnace fan motor. I finally screwed the fan up bad with my thumb. Only 5 stitches but that's another story.

    I replaced the fan with a furnace exhaust gas fan. This is a squirrel cage type of fan and is used for handling the exhaust gases from household furnaces. Figured that it would work and it has. No trouble so far.  (Don Anderson)  (see Don's Oven here)

    When I made my oven,  I talked to an electrical repairman I know, and was lucky enough to get the whole working guts out of a fan forced oven, complete with fan, thermostat, spiral elements etc. The original was irreparably damaged in a house fire, but Chris salvaged the innards. The outer structural part of the oven is a piece of  12 inch square air conditioning duct wrapped heavily in reflective insulating material.

    We installed a series of baffles to forestall local overheating, and to channel hot air around the oven as evenly as we could.

    I know that my level of thermal control does not match the accuracy  that we  hear to  be necessary,  but with  ordinary probe-type sensors I cannot detect any significant variation along the length of the oven.

    And while I just know that I am going to be sorry that I said  this, I have so far not had any nasty experiences   with it, and it works just fine.

    IMHO, it's worth asking about for this sort of salvage.  (Peter McKean)

Rule

I'm wondering about how to mount a convection oven fan on the outside of my mica-strip oven.  Do any of you think it might be as effective in treating cane as it is in cooking food?

I'm thinking about closed-loop ductwork with openings through each end of the oven.  The fan would be mounted somewhere inline.  I haven't looked into the fan itself, but I assume that these units are able to take the heat.  Yes?

Any thoughts or considerations out there?  (Bill Harms)

    Look at the pictures of my oven here. It's the last one. Write if you've questions.  (Martin-Darrell)

    I was thinking about the same thing. Just getting around to doing is something else Figured on an elbow coming out of the bottom of the oven at the front and another at the back with the fan in the middle. The reason at the bottom is that is where the heat strip is. I guess it would work on top too.  (Tony Spezio)

      Yeah.  I don't think the top,  side or bottom mount would matter much -- just as long as you get the hot air moving out of one end and back into the other.

      What I was really wondering about, I guess, is the fan/motor itself.  Does a kitchen, convection oven have a special fan that can take the heat, or do these ovens have  some other air-circulating arrangement?   And might anybody know about the cost of these fans?  (Bill Harms)

        Here is the poor man's version.  I bought a "pancake fan motor" used for about $12.  I think I have seen them new at American Scientific and Surplus for about $20.  The motor comes with a light duty cage and the spindle comes out perpendicular to the cage.  It is a light duty motor.  I just mounted the motor on the outside of the end of the oven and attached some 1/4" steel rod that went through the oven wall and attached a 3.5" aluminum fan blade.  To avoid heat transfer to the motor. I drilled both ends of a 2" length of 3/4" dowel rod and made a coupling that attaches to the motor spindle and the steel rod.

        I need to realign it once in a while, but it works and makes big difference  Once you get the air moving (mine goes in a circle around a baffle over the heating element), you need to cut down on your baking time.  The strips are much more even for me.  (Jerry Madigan)

          Thanks very much for the suggestions.  The "poor man's" version is what I'm all about.  As you describe the motor, however, it seems to me that almost ANY kind of little motor would be fine as long as the heat transfer issue is addressed.  The little wood dowel seems like a sensible solution.

          Is the little fan blade within the one end of your oven the only thing that provides for air movement?  Does that seem to do the job for you in equalizing and stabilizing internal temps?  (Bill Harms)

        Go to the nearest Heating & Cooling Supply house and look at an 80%+ furnace.  To achieve the higher efficiency the companies had to restrict the heat exchangers so much that there is not a natural draft flow through them. Thus they added a "Induced Draft Fan" or IDF.  These assemblies are made to handle the heat of the combustion products from the furnace which can be close to 400°F.  One of these assemblies would be perfect for what you are considering.  Might ask a dealer if he has replaced an 80%+ furnace lately and if you can have the old Induced Draft Fan Assembly.  (Dick Fuhrman)

Rule

Can anyone tell me where to find a metal fan blade small enough for installing in an oven?  (Chuck Irvine)

    Oooooh, maybe I beat M-D to the punch...  McMaster-Carr!  (Mark Wendt)

    There's a kind of fan that you set on top of a wood stove that is activated by the heat of the stove and circulates the heated air. They're in the current Garret Wade cat. but @ $120. Small one will move 100 cfm and is 10" high. Might work.  (Chad Wigham)

    Check the plumbers. He often replaces a furnace and toss the flue exhaust fan out. Mine cost me "0". Mind you, the same plumber has replaced my furnace & hot water tank. Maybe he already got his bucks outta me.  (Don Anderson)

    Just go to a Scrap Metal yard and you should find them by the hundreds. Getting the fan blades off are another story, it may pop off or it may take 3 or 4 hours. Trust me I know I did heating and air.  (Dave Henney)

Rule

Where might I find a small fan for the oven and what would be the recommended rpm for a motor? Thanks again.  (Wayne Kifer)

    Try a shop that sells domestic ovens and spare parts for same, or to an electrical repairman.  I have the whole guts of a domestic oven in my bamboo oven, heating coil, fan, and thermostat.

    If you want parts for an oven, go to a shop that sells oven parts!  (Peter McKean)

    It seems a fan to make electric oven with thermostat.

    Let me introduce my heat treating system. It's cheap, rational, effective and easy to make. You may get the same size of things there.

    What are needed:

    • 90 mm diameter stainless chimney pipe x 2.  (these can be coupled at the end)
    • Grass wool used in your 2x4 house wall.
    • Aluminum foil and aluminum tape
    • Some thin copper wire
    • Iwatani gas cassest grill and its bombe
    • Steel net used to grill fishes
    • Three thermometers for tempura oil (long foot)  (templa is oil fried cooking, bimetal thermometer)
    • Two wood blocks of size 1/2 inch x 3/4 inch x 1ft  (this is the height adjuster)

    Making:

    • connect two chimney pipes tightly
    • cover the pipe with grass wool
    • wrap over the grass wool by aluminum foil so that thin grass dusts would not come out
    • wrap the aluminum foil by aluminum tape
    • fix by thin copper wire over the aluminum tape
    • make three holes at (1) 2 feet from bottom, (2) center (3) top, where thermometer foot goes in.

    Place to use:

    Somewhere there is a step or ladder, but no wind.

    How to use:

    Place Iwatani Gas casset grill and put steel net on it. Under the net, place two wood blocks in parallel to which hold the net. Stand the chimney at the center of the net above the casset fire nozzle. Hold the chimney so that it does not

    lean or fall by something tightly and make sure that the pipe stand exactly vertical. Fire the casset with small flame. Keep looking at three thermometers until three of them becomes almost equally same temperature around 180 degrees or so.  It takes just 10 - 20 seconds.

    Insert your rough planed blanks which are bound, from the top of the chimney. 90 mm diameter pipe can have enough capacity to heat treat 4-6 blanks at a time. To hang the blanks, use copper wire which is attached with metal clip, and clip the blank end.

    Heat treat the blanks for 5 to 15  minutes according to your recipe. First, perfume of bamboo is nicely smelled. When smells goes out and no smell, the bamboo is well treated.  When some stimulated sour smell begins or you see smoke, it is a little too much.

    The adjustment of heat temperature is made by the gas casset flame.  The adjustment among top, center, bottom is made by the height of steel net.  High net position make it possible for the chimney to vacuum more air and cool down the bottom temperature. Low net position will heat up the bottom temperature. As the steel net is well heated into  a red color, it keeps the heat of air.

    By this, since you can keep the almost same temperature of three positions, you need not to turn the blank up side down.

    Within the chimney, heated air with same temperature keep goes up.  Humidity goes out with heated air. Just 15 minutes operation will make 6 blanks at the same time.

    Warning:

    Be cautious not to fire your ceiling if used in house.  Keep the air cool around the work place so that enough air is circled.  It surely affect the effective circulation of air within the chimney too. Be careful not to touch to heated air on the top. Be careful not to drop the blanks in the chimney, it will burn up and chimney becomes a cannon fire. Prepare a bucket of water aside. Heat treated bamboo is hot enough.  Have a glove always. Prepare the space to place the heated blanks. Use one gas bomb up to 1/3 or half of full capacity as the gas pressure will decrease and fire get weaker.

    This works very fine.  Enjoy.

    I use this system not because I am poor but because it is effective.  (Max Satoh)

    I originally bought a small 5" diameter 10 blade fan from McMaster-Carr, against the advise of a fella named M-D.  Me, being stubborn and hard headed, decided that I was going to make it work.  It lasted about a year. and disintegrated.  I ended up getting a 5 blade pattern from Robert Holder here on the list, and made it out of thick sheet metal.  3M 77'd the paper pattern to the sheet metal, judiciously cut it out with some tin snips, tidied up the edges with a file, spun balanced the fan blade, bent in the blade pitch using the TLAR (That Looks About Right) method, and mounted it on my drive shaft.  Over two years later, and a bunch of runs, it's still holding up just fine.  I use a fractional HP motor on my oven, and it's got a 3 1/2" pulley mounted on the motor and a 2" pulley mounted on the fan drive shaft.  The motor RPMs are 1725, so I'm getting 3018 RPMs on the drive shaft.  (Mark Wendt)

Rule

I tried several aluminum and steel heat sinks with radiant heat on my oven.  None of them worked.  I did successfully move the hot spot from the middle to the end of the oven but couldn't eliminate it.  Here's a design that's working for me:

I modified my Cattanach style oven adding a heat sync (steel divider) and a blower.  The oven is turned horizontal rather that vertical.  The steel divider (about .06 inches thick - I think that's 16 gauge) is mounted vertically dividing the oven into two 4 x 4 chambers.  The heat strip is in one chamber and the oven rack is in the other.  I cut a chunk out of the top half of the metal divider on the end opposite the blower (about 1 x 6) for circulation.  No holes in the metal divider.  The combination of a heat sync and the blower solved my hot spot problem.  I added a PID controller (unnecessary but really cool).  The thing works great.  I threatened to take it to camp for a biscuit oven but I'm afraid the biscuits might be toxic.

Pictures are in the contraptions area of Todd's site.  (David Bolin)

    What you've done is added a plenum, and made a convection oven out of it...  I wouldn't call the addition of the PID controller unnecessary, I built my convection oven around using one, and I can keep the set temp of the air inside the oven within +- 1 degree Fahrenheit.  Since we strive for consistency in our rod making, shouldn't we also strive for the ultimate in consistency in something that is so important, and could possibly be detrimental to the the resiliency of the cane?  The PID controller allows you to get the most out of your oven, especially now that you've converted it into a convection oven.   (Mark Wendt)

      I suppose "unnecessary" was an overstatement.  It does keep my temp somewhere in the + or - 1 degree range.  One other thought on the hot spot issue.  I'm using the 750 watt strip that Wayne recommends.  The oven configuration I described takes almost an hour to get up to 350 degrees.  I considered changing to something in the 1200 degree range, but I'm afraid the hot spot would be a problem again.  (David Bolin)

        The inherent problem with strip heater ovens is just that - the "hot spot."  Since you've added a blower to the mix, and made a convection oven out of it, you might consider giving the larger element a try.  In my oven, and the one I made for Joe Byrd, I have two 750 watt elements for 1500 watts total in mine.  We had to make a minor adjustment in the speed of the fan in Joe's oven (my fault, I used a different motor than the one I used on my oven,  and didn't get the  fan  RPMs right), but we don't see any hot spots in our ovens.  As long as you've got the plenum divider between the rod rack and the element, and a decent amount of air flowing through the chambers, you shouldn't have to worry about hot spots.  If you are in your setup, you might try increasing your fan speed to move more air.

        I'm curious.  I just noticed that you had pics up on Todd's site.  On your last picture on the right hand side, you show the front opening.  Your plenum divider seems to go right to the edge of the opening.  How are you allowing for air to circulate between the two plenum chambers?  (Mark Wendt)

          If you don't mind sharing with the group, what are the specifics of the fan you are using or those of you out there using fans?  I have had the same issue with hotspots and wanted to get air circulating through the oven. I've looked at a few fans, but not sure what CFM to use and am concerned with the material that the fan is made out of regarding the high temperatures that are generated with the ovens.  (Scott Bahn)

            The first fan I used was a commercial fan, with I think ten blades on it.  I wasn't satisfied with the amount of air it was moving, and it was also made of aluminum, which heat stressed and  cracked after using it for a while.  I got an AutoCAD drawing of a 5 blade fan from Robert Holder, and cut it out of sheet metal.  Softened up the edges, bent in the pitch, balanced it, and mounted it on my fan drive shaft.  I'm not exactly sure how much CFM of air I'm moving, since I didn't measure the amount of pitch I bent into the blades.  I sorta used the TLAR method for setting the pitch of the blades.  It does seem to move more air than the commercial version I had before, but I don't really have the measuring equipment to state that entirely as a fact.  I do know that with the amount of air moving in the oven, I don't have any hot spots.  I've set high temp thermometers at different points along the rack, and they all seem to read within a degree for the entire length of the rack.  (Mark Wendt)

            I used a small squirrel cage fan given to me by our local heating and air conditioning contractor.  It's about 5" in diameter, and 5" long.  I vary the amount of air by using a baffle on the intake side.  I think I'll remove the baffle and see what happens.  Maybe allowing it to move more air will reduce the effects of the hot spot in my oven.  (Harry Boyd)

            I used the overshot fan design complete with pillow block bearings et al. Blew up the fan. Am using a natural gas furnace flue gas exhaust fan presently. Comes complete with motor. Cheap too.  Got it @ the plumbers for nothing.  (Don Anderson)

          The picture to the left of that one is the end cap.  Take a close look at that picture and you'll see the blower intake on the right and a smaller exhaust port on the left.  That end cap (female) slides over the end of the oven (male) and the blower frame rests flush on the end of the oven chamber with the divider separating the intake from the exhaust.  Since the exhaust was pointing perpendicular to the oven, I added an angled piece of aluminum to throw the air flow into a spin and a diffuser to further slow and stir the air flow (I don't know all the HVAC terms for that).  It took some trial and error to get to that point but it was worth the time to make that $5 flea market blower work.  The goal was to mount a blower without adding any more heated space to the system to make optimum use of the heat strip without increasing the wattage.  It took about 6 months to find the right blower at the flea market.

          For the record, I have a fishing buddy (now the proud owner of a Payne 101) that happens to be a mechanical engineer that specializes in major HVAC applications and all the related controls.  We brainstormed these modifications on the river.  I did everything except wiring up the PID.   Calvin did that for me and provided the sensor.  There are wires going everywhere in that box.  Again, very cool.  (David Bolin)

            Yes, I saw that picture.  I was wondering about the other end though.  Your plenum divider looks like it goes right up to the end of the opening, and it would seem to limit any air flow between the heating element plenum chamber and the rack plenum chamber.  How are you getting the moving air from one side to the other, and back to the fan to recirculate?  (Mark Wendt)

              The cap in the picture on the left fits over the end in the picture on the right.  The motor is mounted to the cap on the outside with the blower on the inside (the motor arbor goes through the cap to the blower inside the cap).  The blower intake is on the right side of the cap and the exhaust is on the left side in that picture. When the cap is mounted, the steel divider fits flush against the blower frame separating the intake from the exhaust.  The opposite end of the oven is sealed.  The steel divider fits flush against that end with a 1 inch by 6 inch section cut out of the top side of the divider at that end.  Circulation flows from the cap to the opposite end of oven, through the 1x6 cut out at the other end and back up the plenum side to the cap where it's drawn back into the blower and forced back into the oven.

              Said another way, the blower is integrated into the end cap so that no air has to leave the box to be circulated.  The motor is mounted outside the cap and blower is inside the cap drawing directly from the plenum and forcing the air back into oven chamber on the other side.  The air makes a U turn through the blower in the end cap.  I have a small 2 inch by 3 inch door in the end cap to access the oven rack without removing the end cap.

              Does that make any sense?  (David Bolin)

                Okay, I gotcha now.  For some reason, I was assuming you had the motor/fan unit mounted on the far end of your oven.  Since you say you are still seeing hot spots in the oven, you should consider making the 1 x 6 cutout on the other end larger.  In my convection oven, the opening on the ends is 6" x 12".  The more air you move through the oven, with the least amount of constriction, is the only way you will get rid of the hot spots.  You may also want to try and radius your corners too, to keep the turbulence down.  More turbulence = disturbed air = less air flow.  (Mark Wendt)

                  This oven has no significant hot spots (+ or - 5 degrees from end to end as I recall) after the modifications.  I think Lowell and Tony were asking about the effectiveness of a aluminum heat sync.  That didn't work for me so I added the steel divider and the blower.  Problem solved.  That's with a 750 degree heat strip.  I think the hot spot problem would return at 1200 degrees without insulating the plenum from the oven.  This configuration is less efficient in terms of the time it takes to get up to cooking temp (1 hour to 350 degrees) but solves the hot spot problem without spending a lot more money.  (David Bolin)

                    Sorry, it must have been somebody else that was talking about hot spots with their convection oven.  Are you talking degrees, or watts there?  I have 1500 watts worth of heater elements on mine, and use a simple sheet steel plenum divider just like yours.  No hot spots.  Takes about 15 - 20 minutes or so, depending on the ambient air temp, and how much the oven has been cold soaked to get up to 350 degrees in mine.  My basic oven would cost just me about the same as yours, with the exception of the fan unit that I have.  Try radiusing your corners.  It will make your oven more efficient.  (Mark Wendt)

                      Meant to say watts not degrees on the heat strip.  Sorry.  (David Bolin)

                        I figured that's what you had meant.  If you are concerned about the warm up time, adding another 750 watt element in parallel will certainly speed up your warm up time.  With your PID controller, controlling the dual elements off of a solid state relay is a piece of cake.  (Mark Wendt)

          I use 2 1500W elements. One direct drive & one on a thermostat.

          One thing you might consider is the air flow from fan. The air flow must be "broken up". I placed a baffle about 6" directly in front of the fan. Further, from the element side, the cane side of the oven, the cuts from one side to the other are twisted in such a way as to have the air flow directed along the walls thereby further increasing the mixing of the air. The fan I use is 450 CFM meaning that the air from the element side > the cane holding side of the oven is circulated approximately 75 times/minute. There aren't any hot spots.  (Don Anderson)

    Thought I'd mention my oven design.  I use  a Pyrex  glass tube 1.5" x 52" which I have mounted in an enclosed clay tile [chimney flue tiles] 8 x 8 x 52" case, with a straight element, convection oven,  with temp controller and  a back-up temp gauge. The Pyrex tube evens out the heat very well and no hot spots. Could see it working in a strip oven as well. No fans or sinks as that's what the Pyrex does. When I built it the tube cost $15 from Scientific Supply Co.  (Chad Wigham)

    Note:  You can see pictures of Chad’s oven on this page.

      You guys never cease to amaze me with your inventions. I'm a mason by trade and it never once crossed my mind to use flue liners to build an oven! Very novel idea. Just goes to show ya, if you keep an open mind you can learn something new everyday. Thanks for sharing.  (Will Price)

Rule

The little fan I have used for several years to circulate air in my oven has finally quit on me.  Might any of you have a line of an affordable fan which will hold up to the temperatures we use in our ovens?  (Harry Boyd)

    Talk to a local Heating and air technician. See if he has an older 80+ furnace that he is replacing that still has a good draft inducer assembly on it. This would probably have to mount outside the oven, depending on the size of the oven. You might be able to get it for nothing as he is probably scraping out the furnace.  (Dick Fuhrman)

Rule

I recently incorporated a fan into my Cattanach style oven to create a convection oven.  The oven lies horizontally on one of the wider sides and I've created a left chamber and a right chamber by using a 4" x 54" 1/4" thick steel plate down the middle of the oven.  At the closed end of the oven I made a curved return to allow air to circulate from one chamber to the other.  Just inside the oven, at the door end I've mounted a fan and fan deflector on the inside top of the oven that forces the air into the right chamber. The fan motor is mounted outside the oven, about 5 inches above the fan blade.  My question is about where to place the mica strip and the rack for the cane?  I have the mica strip in the left chamber and the cane rack in the right.  However, I'm thinking they should both be in the right chamber so the returned air picks up the heat and blows over the mica strip thereby distributing the heat more evenly across mica strip and the cane strips.  By keeping them in separate chambers I would think the portion of the cane strips at the far end of the right chamber of the oven wouldn't get as much heat as the portion closest to the end where the fan recirculates the heat picked up from the mica strip in the left chamber.  Hopefully I'm explaining this clearly.

Additionally, my fan motor currently is nearly mounted (outside the oven shell) over one end of the mica strip.  I also thought that moving the mica strip to the right chamber would move it further from the motor and lessen the heat to the motor and motor shaft. (Bob Williams)

    You want to put the mica strip in the chamber that does not house the cane rack.  The reason for this, in fact one of the most important reasons for it, is to heat the cane by convection (the heated recirculating air) rather than by radiation, which is what the typical non-convection oven does.  Placing the mica strip in the same chamber as the cane rack will still allow radiant heat to hit the cane.  The convection process allows for a more even heat to reach the cane.  You'll find that the recirculating air keeps a pretty constant temperature throughout the oven.  (Mark Wendt)

    The Mica strip needs to be in one chamber with the fan blowing on it and the strips in another chamber with the hot air flowing over it.

    Been planning on converting my oven. Would like to see photos of what you are doing.  (Tony Spezio)

Rule

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