Stir Crazy Turbo Oven (SCTO)

Introduction

Changed for Popcorn Pumper to SCTO for higher capacity per roast.

This consists of a Stir Crazy (SC) as the base to stir the beans, a turbo oven (TO) as the heat source, and a metal spacer so the TO is not too close to the beans.

SC I bought from Coffee Geek ad in 2011  Shaft was already modded so it could work as a roaster.
It was changed to some metal parts, there are pages out there that say the original parts will wear out at roaster temps
I eventually bought a couple more SC's from ebay for spare parts, and for Phase 2.

I'm using my ESP32 to control the heater power via PWM.

Phase 1

Phase 1 used the stock SC motor to stir the beans.  Still has the plastic piece connecting to the motor.

Phase 2

Phase 2 Changed the motor to a much faster (60 rpm), higher torque one. 

Phase 2.5

Built a 2nd SC base, so I have a spare.  Just needed another motor, had the other main pieces.  Changed method for motor shaft to buy instead of make, much easier.  Around the same time, started using roasterspal app.  Runs on ipad, makes BLE connection from ESP32 to ipad, and graphs the roast.

Phase 2.5 - May 2025

Changed motor shaft from one in Phase 2

Bought a Brass coupling Shaft Motor Coupler Motor Connector,  7mm to 7mm, 22 mm length, from ebay

22mm = 0.866142" long

Used a 1/4"-20 threaded rod

Coupling fits well on motor shaft, just a little play.   Cut about a 2 inch piece of the threaded rod to go into other end of coupling

This setup has a little wobble when mounted, but much less then Phase 2, made mounting the motor much easier.  

With this method, mounting the motor only required drilling four holes in the top plate, and cutting the threaded rod.  Was MUCH easier and faster then Phase 2 method.

Phase 2 - April, 2025

Plastic shaft melted, so finally had to build the phase 2 version of my SCTO

Parts update

 Stir Crazy Base, 82306.  Do NOT buy 82505 base

Motor

The stock motor is weak, so I changed the motor and made a shaft to connect motor to stirring rod.

I decided to use this motor.

https://www.aliexpress.us/item/2251832721631713.html?spm=a2g0o.order_list.order_list_main.5.655a180234z8yz&gatewayAdapt=glo2usa&_randl_shipto=US 

Motor webpage

60rpm $21.75

It was the highest torque motor I found at 60 rpm for a low price.

https://www.convertunits.com/from/kg-cm/to/oz-in 

4 kg/cm = 55.5 ounce inches @ 60 rpm

Ebay motor options:

ebay china Synchronous Motor 60KTYZ  70 oz in for 30 rpm, 53.1 oz in for 40 rpm, 35 oz in for 60 rpm

https://www.ebay.com/itm/404192213037?hash=item5e1bbbb82d:g:FCsAAOSw82hiuRCz&amdata=enc%3AAQAHAAAA0JaQUzPtPb2B6D4cgPS7I7niSyYsYe10Dj%2FQ5gFs%2BS%2BYOSoQtaBRYDKlgP%2BKmECGdRvdnIPmG6W7sD6dDQFLcLNUKnHI9Bzmp1pCFIiWtAx22BcxfFUDDDuutxfBo1Jhy7Mn0rgpVLh7sP163F%2Fcm8UEzpsXZNL1LoDJAUW1NmO1USi%2BylPG8bLm0e14C4q7osm77nqN6YdwFKnLJgbBprPkVJyzXWPz8Sy%2F45klT9dl72lsJG%2B17qEYVDFuGYt0ObJTJl5EmLLdpiCo1ya22ak%3D%7Ctkp%3ABk9SR_Ka447jYQ 

Connecting the Motor to power:

Motor Direction:  

Started with CW, but in this direction the force from turning the stirring rod will slowly loosen the mounting screw.  

Changed to CCW so screw should stay tight.

Motor Mounting

Since my motor shaft was a bit off, I mounted the motor closer to the SC top plate.  I drilled 4 holes in the top plate, and used 3/4" standoffs with 4-40 screw holes in it.  The standoffs hold the motor to the top plate.

One advantage of this setup is the motor doesn't go lower than the bottom of the SC, so I didn't have to add anything like I would if the motor stuck out the bottom.

Connecting Shaft

See info for Phase 2.5, much easier then what I did here.

Motor shaft diameter: 7mm = 0.276"

Idea from here:11/16 Aluminum round stock cut to 3" drill a 7mm hole for the motor shaft and 1/4 20 on the other end, drill and tap and your done.

post with pics

https://www.greencoffeebuyingclub.com/index.php?topic=5033.msg307803#msg307803 

Motor shaft 11/16 (0.688") aluminuum round stock   Mcmaster 5/8" al rod (.625)  11/16 is expensive, so used 5/8" instead

9/32 drill = 0.28125     .625-.28125=.34375 .34375/2=.171875 wall thickness on each side of 9/32 hole in center

using 4/40 screw, so 40 threads per inch, or one thread = 0.025"

.171875/.025 = 6.8 threads, so this works

So 5/8 would work, I'll get almost 7 threads with the locking screw

For the other side, I tapped a #10 hole.  That screw holds the stirring rod

When I made this, I used a drill press but was slightly off, so this connecting rod wobbles as it rotates, and I had to make sure it doesn't rub against the SC top plate.  Why I changed to a brass coupler later on.

Stirring Rod

I used this .016" thick aluminum.  Cut longways in 1/2 to make it 1" wide, then cut one long piece in 1/2, but trimmed lenght a bit to fit the stir crazy base.

Put in a vise to help make the bends, did not use his exact shape.

Stir Crazy

Top plate:  Removed non stick coating, as seen in picture above.  Mostly used sandpaper to remove, but also used dremel with abrasiave brush attachment to get to areas closer to ridges.

Thermocouple (TC)

With the TC mounted as shown below, getting good results.  First crack temperature is between 360F and 374F after 8 roasts, so little low but I can work with that.

Other Stuff

I used the spacer for between the TO and SC from Phase 1.

Phase 1 (old March 2023)

Parts

Stir Crazy.  Had one from way back with a modded rod holder

four foot of 1/16" thick, 1 1/2" wide flat aluminum.  1/16 is thin enough to work with for this, you can get here:  flat aluminum from Lowes

Insulation from Ebay, "FDA Silicone Rubber Sheet, 50A, 1/16 x 9 x 24 Inch, Food Grade Gasket Material"

High temp RTV to glue down insulation

Bead type k thermocouple

Ebay "K Type Thermocouple Stainless Steel Probe Hand Held Thermometer Probe Sensor"

Turbo ovens

First one:  Newegg open box Rosewill Turbo Oven R-HCO-15001 18Qt Infrared Halogen Stainless Steel Convection Oven 

galloping gourmet perfection aire 

IMARFLEX TURBO Oven

DECOSONIC TURBO CONVECTION ROASTER OVEN 

SWEDA RAPID AIR OVEN

Spacer

Need four foot of 1/16" thick, 1 1/2" wide flat aluminum.  1/16 is thin enough to work with for this.

I had it from way back, but you can get here:  flat aluminum from Lowes

Cut it so its a little bigger than the circumference of the stir crazy.

When you do it as shown below, you need to cut a goove in the bottom of the spacer so the spacer can go past the outer lip of the stir crazy.

I also had to cut/file down the little part the extends out.  Otherwise it keeps the turbo oven for sitting flat on the spacer, and would let hot air out.

https://homeroasters.org/forum/viewthread.php?thread_id=1142 

1/32 = 0.063"

$24 onlinemetals 1"x24" 0.063" Aluminum Sheet 6061-T4 - Part #: 7961

$26 https://www.metalsdepot.com/ 1"x24"

$13 lowes 1/32" 6x18 https://www.lowes.com/pd/Hillman-6-in-x-18-in-Aluminum-Solid/3057643 

https://www.mcmaster.com/products/~/shape~sheet-and-bar/length~24/multipurpose-6061-aluminum-sheets-and-bars-7/thickness~0-05/?s=aluminum+flat+stock   2 x 24" $16 shipped

Seal

On ebay bought this "FDA Silicone Rubber Sheet, 50A, 1/16 x 9 x 24 Inch, Food Grade Gasket Material"

Cut a couple strips and glued (high temp RTV) it to the spacer, so about 1/16" to 1/8"  sticks up over the spacer.  Tried to keep this part as consistent as possible all the way around.

Stirring rod mod

From Biobug page:

"The small stirring rod is fine for agitating popcorn, but for 1/2 to a pound of coffee, it's not sufficient. Here you can see the cap in the normal roasting position, and the spacers and crimped additions. Other's have used 3/8" copper pipe, crushed down on the rods with vise. I used my bench vise to install the crimp adapters. So far I'm happy, but I may change to the copper pipe later."

I decided to bend my arms to get them further away from the base, for room to add pieces of copper tube to the arms

I had 1/4" tubing on hand, so I used that instead of buying 3/8".  The 1/4" works fine.  I'm sure 3/8" would be better, but this works.

I cut the tubing up instead of using one long piece.  Its hard to make one piece straight, and would have been harder to clamp to deform it.

I squeezed the tubing with a vise and vise grips.  Its better to squeeze so its hard to move, but you can still move if you want.

Batch size

Phase 1:  270 grams with stock SC motor

Thermocouple and insulation

I was thinking about using a probe type, bringing it in the the side somewhere, but then I thought of bringing it from the bottom, and using a bead type.  Since I had bent the arms up to add copper tubing, and there were gaps in the tubing, I luckily had a spot where there was a gap in both arms at the same place to install the tc.  

I marked on the top where the gap was for both arms, and then decided where to drill the hole.  I disassembled the stir crazy base, and drilled the hole.  Used high temp rtv to glue the tc in place.  I took the tc out of my Pumper, the one used for ET.  It is a proper bead, one where the end was melted into a little ball.  In cheaper ones, and ones I diy, the ends are just twisted together.

After the first layer of RTV dried overnight, I added a 2nd layer to make sure it stays in place.

While I had it open, I insulated the bottom too.  Used this silicon rubber, high temp RTV to glue it down.

Mcmaster # 8632K421 1/16" Thick, 12" X 12", 40A Durometer Extreme-Temperature Silicone Rubber (Same as 8632K42)

I also stick some foam over the now unused heater coils

Mcmaster # 86145K21 Melamine Foam Insulation 24" X 48", 1/2" Thick, Light Gray 

https://www.meter-depot.com/checkout TC source

Turbo Oven Mod

When I started using the turbo oven, it would turn off when it got too hot.

So I tried to disble the thermostat by adding some kapton tape so it couldn' close.  But the tape melted away after a while.

Opened it back up, and cut the two wires going to the temperature sensor/thermostat.  I shorted the wires together so no. more thermostat, and heater stayed on all the time, expect when turned off my the ESP32/SSR.

Profiles

https://www.greencoffeebuyingclub.com/index.php?topic=5033.msg307783#msg307783 

Hitting first crack at 6 or 7 minutes is not bad with this method if you can keep control and not hit your desired endpoint for at least another two minutes (and continue a slow rise without stalling or wobbling).  The bottom heat shuts off somewhere between 335 and 355 depending on your exact stir crazy, so the only real effect is to drive the temperature up in the early part of the roast.  If you are roasting at least 8oz, it will help stabilize the temp and drive off the moisture.  The actual temp on the CO unit is never anything like the dial says, it has more to do with the ratio of time on to off.  I've found that I get the best environmental temperature ramp by starting out at a 400 target then dropping to 370 after 4 minutes or so on an unmodified halogen element oven.  You can easily hit 440 bean temp at that setting (!) with this configuration, but most importantly you will get a proper ramp arc without a rate of rise increase after FC starts, and you will not stall the roast.  This sounds completely opposed to what many sources recommend, but it will give you the best development for a 10-12 oz roast.  This has been my experience with at least 15 ovens, some of them split wired, over the last 9 years.  I have roasted at least 2500# by SC/TO, and rarely monitor temperature any more, I can tell by the smell...  Nowadays I mostly use turbocrazy for sample roasts, as all my production is done with a 5# old school RK and a 14# homemade drum, but it is still my 'go to' method for small or precious runs.   Every oven has its own 'personality', the halogen element Sharper Image device is my preferred one these days, with the old Galloping Gourmet the runner up (but these usually have to be run hotter).

https://www.greencoffeebuyingclub.com/index.php?topic=5033.msg193790#msg193790 

pre-heating to 350 or 360; add the beans and start the timer.. the temp will drop to about 180 or 190 before it heads back up: 300 degrees around 3 to 4 minutes when I get to 350 I lift the handle on the TO to turn the heat off.. when the temp stops rising (usually around 360) and I see it just starting to drop or sitting still I put the heat back on.. it will drop a few degrees (get about 2 minutes in the 350 to 375 zone) then climb to 1C.. at 1C I will start to turn on and off the heat (usually 5 seconds off and 10 seconds on as a minimum) to slow the roast but not stall.. some beans don't need this much fusing.. then its al a matter of the roast you want.. my roasts are typically 14:45 to 15:30 minutes..  mostly 15:00 to 15:15 ...  depending on the bean, day, faze of the moon, etc.  I will hear 2C around 430 to 440 degrees.

https://www.greencoffeebuyingclub.com/index.php?topic=5033.msg168745#msg168745 

First profile - this has generated a slightly sweeter cup with a good overall balance.
Preheat to 350F as measure by the BT probe, let temperature stabilize for at least 5 minutes.
Drop beans in and switch heater to full.
When ET Probe returns to 350F adjust heat imput to coast until 4 minute mark.
Switch back to full until 400F ET, coast until 8 minute mark (BT is usually around 360F at this point)Switch to full again until 450F ET and allow temp to raise slowly but not exceeding 475F.
1C is usually around 12-14 minutes and roast is concluded between 3-4 minutes thereafter once I hit my final target BT (usually 425-430) pre -2C

Second profile - this profile tends to accentuate the brightness in the cup and is what I prefer for DP Ethiopians especially
Preheat to 400F as measured by the BT probe, let temperature stabilize for at least 5 minutes.
Drop beans in and switch heater to full.
When ET Probe hits 400F reduce heat imput to try and stabilize until BT Probe reaches 360F (this averages around 8 minutes on my setup)
Return to full heat until ET reaches 450F and reduce heat to a slow rise, not exceeding 475F.
1C is usually around 10-12 minutes and roast is concluded between 3-4 minutes thereafter once I hit my final target BT (usually 420-430F)

Old setup info

https://randytsuchroasterpid.blogspot.com/2009_12_13_archive.html