Hotend Cooling and Testing
The hotend on the Sapphire Plus is supposedly pretty bad but so far I haven't experienced any clogging that wasn't my own fault (didn't push the PTFE tube all the way in) even on an 8 hour print. This is with PLA so perhaps the hotend is sufficient for the low temps (205C). My plan was always to start printing some higher temp filament like PETG/ABS/ASA and perhaps even PC and Nylon so I knew I would need an all metal hotend at some point. I decided on the Triangle Labs Dragon, specifically the high flow version. This seemed like a good compromise between performance and price.
The Mount
To use it I would need to print a bracket to be able to use it on the Sapphire Plus. I chose The Mint Mount by 3D-One. This mount was fairly recently developed to be compatible with the dragon. After printing out the mount and installing the dragon, I did notice some gaps around the hotend which in my mind seemed like wasted cooling air flow so I embarked on a test to see what configurations would yield the best performance.
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| Mount seems to have gaps that may waste cooling airflow |
The test rig
I purchased the Kaiweet Multimeter because it came with one of those tiny glass bead thermistors and I needed a better meter that could do things like true RMS and could measure PWM signals. For the price this is a really good deal. One simple feature that I love is that it has a built in stand!
Next I transferred the components from the original hotend to this mount. For the cooling fan, I purchased the Anvision 40mmx10mm 24v fan (currently sold out on amazon) because it seemed like they made fairly quiet fans. I connected the fans by crimping on some JST-SM connectors (the connector I use for all my hotend connections).
I then placed the thermistor from my multimeter fairly deep into the hotend. I used my fingers to gauge exactly how far the thermistor should go as you can see in the photo below.
Here's what it looks like with the thermistor inserted. Its a fairly snug fit so I doubt it will move during my tests.
Test Parameters
I tested fan pull and push as well as with and without gaps, 4 total combinations. To fill the gaps I just stuffed some small pieces of tissue into the gaps between the cage and the mount. Since I knew the replacing of fans and the insertion/removal of tissue might move the thermistor, I figured the best way to verify it didn't was to just repeat the first test and see if I got the same results.
The room temp was 70F (my meter was in F). For each test run, I set the hotend temp to 205C (Klipper uses C) and I waited till the temp on my meter to stabilize (~ 5min) and then set a timer for 5 more minutes to confirm the temp didn't change. After each test I turned off the heater and setup the hotend for the next and waited for the temps to get down to the low eighties F before starting up the heater again.
Test Results
| Gaps Open | Gaps Filled | |
|---|---|---|
| Fan Push | 99F | 95F |
| Fan Pull | 90F | 93F |
Conclusion
It looks like for my particular setup Fan Pull with the gaps open proved to be the winner. What's interesting is that there's no consistency between whether you should have gaps filled or not. That's why it's important to do your own tests. Your hotend geometry, the fan you use, and the mount are all variables that affect cooling performance. Changing any one of them and you could very well get different results.
