Use a pointed punch to dimple where you want to drill and the bit will not wander. Or you could break out the acetylene cutter and blow a hole in it but that would be a little excessive on a Hottop. Plasma cutter works wonders as well.

cannonfodder wrote:I just drilled a 1/16 inch hole through the back plate and stuck a bare type K TC through the hole. It sticks about 3/4 of an inch in just above the drum so the TC rides in the bean mass. Works quite good. Dont over complicate it.

cannonfodder, I have a question for you and rama: how robust is this setup? Will the bare TCs fail because they're exposed? What about the probe within the bean mass? Will that be a problem with the function of the TC over time being exposed to the a moving bean mass and of course the oils as well. Also will there be a problem with the bare TC readings since the TC is not a stiff probe like a rod or the braided type? My data logger came with 2 bare K type TCs and this would be perfect if I did this rather than going out and buying more TCs.

Thanks!

Be aware of the sheathing material on the thermocouples - some are Teflon coated which isn't good for high roasting temperatures. Fiberglass is okay but will fray. The cheap thermocouple units Sweet Maria's used to sell came with a thermocouple that had a blue plastic sheath over the end, which would melt (removing the small piece of plastic was standard proceedure). Any bare thermocouple is vulnerable to wear and will eventually need replacement, but how long they last depends on how are full you are with them, and they're pretty inexpensive.

docjoe wrote:cannonfodder, I have a question for you and rama: how robust is this setup? Will the bare TCs fail because they're exposed? What about the probe within the bean mass? Will that be a problem with the function of the TC over time being exposed to the a moving bean mass and of course the oils as well. Also will there be a problem with the bare TC readings since the TC is not a stiff probe like a rod or the braided type? My data logger came with 2 bare K type TCs and this would be perfect if I did this rather than going out and buying more TCs.

Thanks!

I have those same stock thermocouples from the Amprobe. Gosh I think they wouldnt do a good job. They are accurate but very flimsy and I would think they would be flying all over the place taking temps. Just my thoughts having just done it.

I have them installed with brass fittings so it extends them further into the drum about a 1/4 of an inch and then I've got about another 3/4 of an inch for the BT probe. The ET probe is good where it is and there's nothing hitting it so it shouldn't be exposed to forces of the bean temps. Those probes and the wires are actually quite resilient, not the braided type, so fraying is not a problem. Plus when it fails or wears out, I will just order the probes that I need.

Joe:

Do you have a photo of the brass fittings you're using with the stock Amprobe TCs?

Gary,

I'll take a picture of the actual fittings when I get home. I should have taken a picture of what I actually did. I found that the brass nuts of the fittings would cause some beans to temporarily get stuck and cause the HT to hiccup. I tried to first angle the sides of the nuts so they would be less prone to this and then tried to round off the nut a little to see if this might prevent that problem. It didn't and I got worried once when at the end of a roast (luckily at the end), a bean got wedged in the between the drum and the nut and it actually stopped the motor. I stopped the roast.

After this, I bought a new fitting, and sanded the nut to a wedge so that beans would be pushed away rather than going underneath the nut, avoiding the "wedging" incident. I knew I should have taken pix before I did the mod. I'll try to take pictures "in situ" but it may not be as nice.

Joe

Thanks Joe, yes, please. Pix would be great. Stopped the motor! Glad you found a solution.

So many options out there... that's a good thing but confusing. I hunted around for quite a while after deciding on a wire probe that goes thru the back wall as described in this thread. For anyone still hunting for a good cheap thermocouple probe Omega sells 5-packs that fit the bill:
http://www.omega.com/pptst/5LSC_5SRTC.html
I got the [5SRTC] 20 gauge glass braid probes and after a half dozen roasts I took the drum out (finally got fins modded!) and the probes were just where I left them. Accuracy and consistency seem to be excellent so far.

drgary wrote:Thanks Joe, yes, please. Pix would be great. Stopped the motor! Glad you found a solution.

Gary,

Sorry about the wait. But here they are. They're taken with my iPhone and then cropped. Please excuse the partially roasted beans. They must have been remnants the last roast caught in the chute, released when I lifted off the bean chute cover.





The last picture is the actual 1/8" fitting. I cut off the threads with a dremel so there would be a very small amount of brass and then from the above pictures, you can see that I filed it in the form of a wedge so that beans would hit it and be pushed away rather than getting stuck between the nut and the rotating drum. On a side note, (since I fly RC Helicopters I have a lot of different sized tubing), I used some small diameter silicone tubing that I wedged in the compression fitting of the pipe fitting which when compressed squeezes the thermocouple, keeping it in place so I do not need to use adhesives such as JB weld.