Is there any reason to make the heaterblock out of brass instead of aluminium? Imho aluminium has nearly double thermoconductivity then brass, so it should be the better material for this use. Or am I wrong?! And if so: why?
Aluminum has more than twice the thermal mass per weight compared to brass (or even pure copper) while offering better heat transfer than brass (only slightly inferior to copper). Factoring in that brass is more than twice as dense, they have practically the same heat capacity per volume, so the only thing you gain when using brass is dead weight.
Of course, brass is easier to machine with the machining tools a tinkerer typically has, but whenever a commercial hotend uses brass it’s plain and simply a bad design.
Danke, Thomas 
@Mark_Rehorst JHead
(+Peter van der Walt first 
+Peter van der Walt absolutely Do you happen to know the specific reason for the JHead or is is simply legacy?
@Mark_Rehorst Didnt use brass but it may work, but i see no benefit. Also Tom already explained it scientifically enough xD But be sure not to use copper. Ive tried in order to minimize PID overswings due to time from heater to thermistor. Wasnt that good xD Cooled down way too fast xD
Beryllium Copper has been great in testing too. Hard as steel (nozzles) and better conductivity than aluminium, just a little less than pure copper.
+Peter van der Walt I still use my 3 year old original j head with no jambs with no fan. I’ve had nothing but jamming issues with e3d type aluminium fan type hotends.
@VolksTrieb copper is better at aluminum at conducting heat (60-70% better), but that’s also the reason it has a really low capability of holding heat (aluminum has a little bit more than twice the heat capacity of copper). if it wasn’t so heavy and hard to machine it’d be a perfect material for the heatsink, but not for the heaterblock (where you want heat to stay).
in that regard, aluminum is almost the perfect metal for this use- having a relatively ok thermal conductivity and a pretty good heat capacity, not to mention easier to machine.
@Rene_Jurack - iirc brass has an even worse heat capacity than copper, so i wouldn’t use it for the heaterblock.
@Tom_Keidar i know thats why I said it 
was a try. Maybe molded into ceramics but hey who does that
@Steve_Wood_Gyrobot BeCu is great stuff, except for the toxicity. Not a problem in solid form, but dust/chips etc can be an issue. Be careful grinding/cutting the stuff.
I remember talking about this with reifsnyderb; he said that he tested aluminum and brass, but brass had a more stable temperature profile than aluminum. Everyone here is mentioning thermal conductivity, but when moving the head around you don’t want the heat to conduct away from the block. There’s far more external surface area on that block than internal surface area.
As I understand it, Brass being less thermally conductive leads to a more stable overall temperature - but this may have been in the days of bang-bang heating. PID heating should generally solve all of this now.
Is the only point “temperature-stability” even worth to consider if the hotend is gonna get covered anyways?
@ThantiK yeah but i want it to heat up and stabilize quickly which wont work with bad thermal conductivity. When changing from first layer temp to another theres a bit of undershooting which i want to reduce. Keeping the heat in can also be done by silicone condom or ceramics as well ;D
Losses due to thermal radiation and convection should be practically identical for any of the metals used for a heater block - the myth of aluminum “wicking away” the heat is absolute BS.
Temperature stability depend on how well the temperature controller (PID) is matched to the system, a faster system (aluminum) is able to react faster, but also needs a controller that regulates faster - which is often harder to get right, hence the “stability” concerns of aluminum vs brass. Heck, even i saw those issues with the Deltaprintr Mini Hotend, which uses no heater block at all!
+Thomas Sanladerer any tips on PID with layer cooling fans? They do change the whole system. PID config with fan turns it unstable without fan and vice versa.
@VolksTrieb You said it yourself: silicone cover.
@Rene_Jurack
Yes might be the fastest option. Just drawed a mold.
In simple terms, there are two things that cause PID instability:
- Gains are too high, which comes from a combination of your feedback gains (P,I,D parameters) as well as your process gain (heater power divided by heat capacity)
- Too much sensing lag so the temp reads are out of phase with the heater action
There are various combinations and subtleties here, like integral windup, but those are the basic causes.
For an example, when your firmware does PID auto-tune, the way it does that is setting the P gain to infinity (bang-bang control with no hysteresis) and measuring the resulting temp oscillation. High gain plus temp sensing lag mathematically guarantees the output is unstable.
As for the metal selection… it’s complicated.
Aluminum has considerably higher conductivity, which gives it a slight edge in temp sensing lag. Not actually all that much though, because the majority of the lag occurs between the heater coils (potted in ceramic and jacketed in steel) and the hot block, and then between the hot block and the temp sensor. The time for heat to conduct through the hot block itself is basically negligible. That’s true of both brass and aluminum.
Brass has higher volumetric heat capacity, so for a given hot end geometry, heater power, and conduction/convection loss rate, brass will heat up and cool down slower. That’s useful for bang-bang control or a really slow-running PID loop like @Thomas_Sanladerer mentioned. But for practical purposes, 1 Hz is plenty for the PID with typical hot ends – the sensing time constant of a glass bead thermistor is longer than one second! You get into diminishing returns when the PID loop updates faster than the temp sensor can measure changing conditions.
On the other hand, if you botch your PID tuning, slower-responding systems will experience more integral wind-up and end up oscillating. Likewise, fast-responding systems are more likely to oscillate for multiple other reasons. It’s important to use PID parameters that are suitable for your hardware and ambient environment. PID is a very robust algorithm, but it will struggle with cases like radically-changing ambient conditions (ie fan kicking on/off with no insulation) or with extremely small hot ends, or with extremely high power heaters.
All that said, the properties of brass and aluminum are really quite similar. Thermal conductivity is high enough with both that the difference doesn’t matter much in practice. Volumetric heat capacity is high enough with both that the difference doesn’t matter much in practice.
Those are the thermal considerations. There are also factors like machining, galling, sealing in the melt pool, robustness against abuse. There is a pretty broad set of selection drivers when you really dig into it. For example, softer metal like aluminum will tend to make better thermal contact with the heater and nozzle because it deforms more in response to contact pressure. But then brass one-piece block+nozzle designs eliminate a low-conductivity threaded interface entirely. It’s all tradeoffs.
The Ultimaker and Olsson heater blocks are made out of brass.