Hottop Upgrade

Roasters and roasting

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Postby GreenBean » Wed May 08, 2013 9:06 am

simonp wrote:I did a bit of an experiment last night, I tried just running through a pre-heat to see what happened with the outer cover on but not that back panel. I ran it till about 120C on the on-board temp sensor. This reached 150C during the cooling cycle. I haven't taken off the shield yet, but peering in the back there don;t appear to be any cracks in the JB Weld but it has (as before) changed colour after the heat from a a dark grey to a light-ish one.
I might try a full run with no beans and see what happens. I am wondering if the beans are putting a side load on the thermocouples which is in turn levering the spacers causing the problem? Maybe a slightly flexible end on the thermocouple gives an easier time?

The manufacturers data states a tensile strength of 3,960 psi and a bond strength of 1,800 psi. This bond strength is more than adequate to cope with the forces on the thermocouple and the significantly larger forces due to differential thermal expansion. The bond strength, however, obviously depends on good surface preparation, without this the bond strength can drop close to zero. I believe this is your problem. Others have not had the problems you are experiencing despite the fact their thermocouples experience the same forces.

simonp wrote:.... It is a shame the european and USA websites have different advice with regards to cleaning preparation :roll:

That is surprising, Simon. From a quick google it looks to me as though the JB Weld website mentioning IPA that you link to is a reseller and not affiliated with the JB Weld manufacturer. If you follow the"About us" link and the Maximex-Shop link you will see they sell many products not linked to JB Weld such as incontinence pants. They also do not seem to provide any links to the JB Weld manufacturer, the technical data or materials safety data sheets, or stockists for JB Weld. In contrast the UK site jb-weld.co.uk states that it is an official distributor and includes links to this information.

Wikipedia has a detailed article on JB Weld which appears to be written by the manufacturer as it provides lots of detailed information. This states, in three places, "do not use alcohol". As stated in previous posts the JB Weld manufacturers website states "DO NOT use alcohol".

Based on this quick google I would not trust the information or advice from the reseller.

After the problems you have had it may be best to take no chances and ensure the surfaces are absolutely clean by first removing any trace of JB Weld then cleaning a few times with very hot espresso machine cleaner to remove any remaining coffee oils. Then roughen the surface again and clean several times with acetone or lacquer thinners. Anything less than this may leave you (and me) wondering if the bond is going to fail on your next roast. :?
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Izzo Alex Duetto | Gaggia XD 2 Group | Mazzer Super Jolly | La Cimbali Max | Solis 166 | Dalian 1 kg roaster | Hottop P | Hottop B | French Press (several) | Kettle modded, no really, added digital thermometer |
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Postby simonp » Wed May 08, 2013 9:45 am

GreenBean wrote:After the problems you have had it may be best to take no chances and ensure the surfaces are absolutely clean by first removing any trace of JB Weld then cleaning a few times with very hot espresso machine cleaner to remove any remaining coffee oils. Then roughen the surface again and clean several times with acetone or lacquer thinners. Anything less than this may leave you (and me) wondering if the bond is going to fail on your next roast. :?


Agree for sure, each time I have made sure there is no trace on old epoxy using the Dremmel and after removing some surface material I don't think there will be any coffee oils left. It can only be contamination from the IPA as the surface has been well prepped each time. IPA has been my "go to" cleaner for many things before gluing so it was my natural one here, but I hadn't appreciated that there was still a residue left behind until now. I guess for most applications the bond strength has not been so critical. Live and learn eh?
Profitec 700 dual boiler
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Mahlkonig Vario
Chemex
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Postby simonp » Thu May 09, 2013 10:32 am

So.... I tried a dummy run without beans though this only ran for about 8 minutes as I didn't have the heater turned down enough and I hit the overtemp and auto dump. The good news is that everything stayed attached!

After cooling and an inspection I did a small batch roast (150g) and once again everything stayed attached - hooray!
The less good news is that the temperature readings from the thermocouples are still rather low. The bean mass one showed a tad under 180C at 1st crack and only 190C by the time I dumped the roast about 1 minute after the end of 2nd. I guess the "stem effect" is quite bad with these even though I have about 10mm on insertion length and good thermal insulation from the mounting with the silicone tubing. Ultimately I guess the absolute temperature is not so significant as long as the error is consistent, but I wonder whether, after all, an exposed one might be better for bean temp?
I am also seeing random spikes of 400c+ on both thermocouple readings which wasn't happening originally, but I think this is some issue between the laptop and the meter as the meter reading never did that form what I could see. I did have the meter logging so I can check the data from that.


Hopefully after a final strip and check of the JB Weld I can now move on to connecting the TC4C/HTC setup and try Roastlogger.
Profitec 700 dual boiler
Isomac Rituale
Mazzer Mini
Mahlkonig Vario
Chemex
Aeropress
2 Bodum press pots
Hottop updated to a B with Compuetr control
Imex roaster, dimmer mod on heater (under spare bed)
Rival popper, with split motor and dimmer mod on heater (retired)
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Postby GreenBean » Thu May 09, 2013 12:43 pm

Good news on the bond to the rear wall. :D I will keep my fingers crossed that that problem is now behind us.

As I mentioned in a previous post, I do not think the thermocouple reading low at first crack is a serious problem and you can easily compensate for it. If you want to improve the situation you could try further insertion into the roast chamber. I use 1/8 inch stainless steel sheathed grounded thermocouples inserted about 14 mm into the roast chamber and read 190 C at first crack. If your sheath is too close to the rear drum vane you could try turning the drum vane down as I described in a post on HB.

simonp wrote:....Ultimately I guess the absolute temperature is not so significant as long as the error is consistent, but I wonder whether, after all, an exposed one might be better for bean temp?....

It is unfortunate that there is insufficient room in the Hottop to mount a bean temperature probe with sufficient protrusion into the roast chamber to avoid stem effects. An exposed bead thermocouple is not necessarily better. Users of the Omega XCIB style 3 with an exposed bead report similar temperatures to yours at first crack. I currently think the best solution is the PEEK rod approach described in the RoastLogger thread. This provides more robust electrical and thermal insulation and adequate support in one piece.

The random spikes in readings are concerning. What device are you using to record the readings? My guess would be that this is due to the bean temperature probe occasionally coming into contact with the roasters frame. This may be due to burrs around the hole in the rear wall and the bean mass pressing the probe against the burr through the thin silicone tube. If this is still a problem when you connect the TC4C/HTC and use RoastLogger then I would suggest inspecting the hole in the wall and smoothing it as much as possible and then replacing the inner silicone tube. Alternatively you could try grounding the TC4C to the frame via a suitable resistor.
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Izzo Alex Duetto | Gaggia XD 2 Group | Mazzer Super Jolly | La Cimbali Max | Solis 166 | Dalian 1 kg roaster | Hottop P | Hottop B | French Press (several) | Kettle modded, no really, added digital thermometer |
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Postby simonp » Thu May 09, 2013 1:08 pm

There is a little bit of the silicone tubing (1-2mm) protruding into the roast chamber so the body of the thermocouple should not touch. The holes were thoroughly de-burred also. I will check the log on the meter later but I think the spikes are not down to the thermocouples.

As for protrusion into the roast chamber there may be a solution in that the 1.5mm probes are quite flexible so I could angle or bend the bean mass one a little to miss the drum vane with further insertion length.
Profitec 700 dual boiler
Isomac Rituale
Mazzer Mini
Mahlkonig Vario
Chemex
Aeropress
2 Bodum press pots
Hottop updated to a B with Compuetr control
Imex roaster, dimmer mod on heater (under spare bed)
Rival popper, with split motor and dimmer mod on heater (retired)
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simonp
 
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Postby simonp » Tue Dec 23, 2014 1:07 pm

GreenBean wrote:The random spikes in readings are concerning. What device are you using to record the readings? My guess would be that this is due to the bean temperature probe occasionally coming into contact with the roasters frame.


I realised that I never did come finish this thread with where it all ended up. The spikes in fact WERE the probes touching metals parts. What was happening it seems is that on occasion a bean (or beans) would get trapped between the roast drum and the probe which would bend the probe enough to touch a metal part. After a few roasts the probes found their natural "safe" spot and the spikes went away. The changes to the Roastlogger software to add a filter to the temp readings also helped this.

I have had no more issues with the probe mountings becoming un-glued.

The whole thing works extremely well and the ability to control the roast profile, specifically the bean development stage at the end means much more can be extracted from the bean's potential and a lighter or medium roast can achieve much more body.

I have lots of photos of the build that one day I will get around to adding on here :oops:
Profitec 700 dual boiler
Isomac Rituale
Mazzer Mini
Mahlkonig Vario
Chemex
Aeropress
2 Bodum press pots
Hottop updated to a B with Compuetr control
Imex roaster, dimmer mod on heater (under spare bed)
Rival popper, with split motor and dimmer mod on heater (retired)
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Postby GreenBean » Tue Dec 23, 2014 4:19 pm

Thank you for the update, Simon. It is good to know that you sorted the problems :P
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Izzo Alex Duetto | Gaggia XD 2 Group | Mazzer Super Jolly | La Cimbali Max | Solis 166 | Dalian 1 kg roaster | Hottop P | Hottop B | French Press (several) | Kettle modded, no really, added digital thermometer |
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