Quest M3s Thermocouples

Discuss roast levels and profiles for espresso, equipment for roasting coffee.

#1: Post by roasterman » Sep 27, 2018, 2:56 pm

I'm ordering the M3s and need thermocouples. I've read that thermocouples should be ungrounded and my question, are all the holes, BT, ET, and MET all the same size? Can anyone suggest model numbers for thermocouples that fit the Quest M3s?

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#2: Post by Peppersass » Sep 27, 2018, 4:23 pm

The stock Quest M3 doesn't come equipped to accommodate thermocouples. If you want to add thermocouples, you have to find and install proper fittings for them.

The Quest comes with an analog thermometer positioned to monitor BT under the tryer. The analog thermometer fitting won't work for an 1/8" thermocouple. There's a threaded hole for an ET probe on the other side of the drum, but it's closed with a hex bolt.

At one time our member erics offered thermocouples and fittings for installing a 1/16" MET thermocouple, a 1/16" BT thermocouple near the sight glass and/or a 1/8" thermocouple at either the stock ET or BT positions. Unfortunately, eric no longer offers these products.

This document details what erics offered He also provides part numbers for thermocouples you can order. In a supplement near end, he provides part numbers and instructions for ordering and drilling your own DIY fittings to do substantially the same thing. The nice custom fitting for 1/8" probes that he used to offer can't be duplicated, but it can be replaced with a vented screw that need to be drilled slightly larger to accommodate an 1/8" probes. The 1/16" probe fittings he used to offer were the same as detaiied in the DIY section. The thermocouples can be ordered from Omega or other suppliers.

FWIW, my used Quest M3 came with original erics fittings and probes for a 1/16" MET probe, a 1/16" BT probe near the sight glass, and a 1/8" probe for ET and the stock analog thermometer for BT. I ordered some vented screws of both sizes and drilled them so I could replace the analog thermometer with a fourth thermocouple, and so I could thread a bare thermocouple into the bean chute to monitor exhaust temperature.

If you go the DIY route, be sure to order the drill bits eric specifies and use a drill press if you can.


#3: Post by roasterman » Nov 03, 2018, 7:20 pm

Reading the document by erics,
I can order the grounded thermocouples from Omega. But, reading the forum I seen thermocouple problems.
Here's an example:
Quest M3 BT thermocouple problems
Post #12 looks like it would be like page 11, making your own adapters.
So, my only question would be.
How can I mount the thermocouples:
TJ36-CASS-18G-6-SB-SMPW-M for BT
TJ36-CASS-116G-6-SB-SMPW-M for MET
It looks like without the nylon ferrules, so metal doesn't touch metal when inserting the thermocouples, is where the problem was occurring.
Can anyone show a mounting method they have succeeded with, so I know how to mount the thermocouples before ordering them through
Thanks in advance for your help.


#4: Post by tyfabes » Nov 05, 2018, 12:15 am

I'm not using erics recommended thermocouples, but these work just fine for BT/ET (M8 fitting): ... _lig_dp_it

MET uses an M4 fitting.


#5: Post by roasterman » replying to tyfabes » Nov 09, 2018, 3:05 pm

Tyler, thanks.
Are you using an MET?
Do you connect it to a TC4 or digital thermometer?


#6: Post by tyfabes » replying to roasterman » Nov 09, 2018, 6:21 pm

Yep, using MET. Ordered the MET TC directly from Molly at Quest.

I am running everything through a Phidget 1048.

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#7: Post by jammin » Nov 09, 2018, 9:28 pm

Id steer clear of probes with a diameter greater than 2mm. The larger the probe, the laggier the feedback will be.

For your BT probe, MillCity sells a sweet M8 threaded compression fitting & K-type probe that is 2mm in diameter: ... n-fitting/

I like the bean door location for BT on the Quest though. I believe those are M4. If these probes are indeed M4 - why not get 2 of these for cheap? ... ermocouple

^perfect diameter & length

Edit: Not sure what data interface you're planning on but the Phidget 1048 is pretty sweet. Highly recommend. MCR sells that as well: ... interface/


#8: Post by tyfabes » Nov 10, 2018, 1:17 am

jammin wrote:Id steer clear of probes with a diameter greater than 2mm. The larger the probe, the laggier the feedback will be.
As an admitted roasting newbie, every piece of reading I've done suggests starting with larger diameter probes and moving to thinner, more responsive probes as one learns to understand the roaster. Many of the smaller probes introduce excess noise and it makes the learning curve a bit steeper.

To each their own, but just wanted to provide context on why I would recommend (and why I went with) larger diameter probes to those newer to roasting.

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#9: Post by aecletec » Nov 10, 2018, 1:29 am

A wider probe masks what your roaster is doing, so you don't learn about your roaster as much as you get delayed information... sounds like a way to chase your tail and I certainly like my 3mm probes better than my stock 5mm on my gear.


#10: Post by tyfabes » Nov 10, 2018, 1:38 am

Reacting/responding to excess noise doesn't teach you anything, either. For someone starting out, delayed information is better than faster, but possibly incorrect information.