Marlin not getting hot enough

I tried loading Marlin on my Prusa Mendel and I was getting a Y-axis offset. I modified the acceleration in configuration.h to match my Sprinter values and now when I start to print my hot end seems to stop about 10 degrees cooler then what I set it to (for example, if my Slic3r setting is 170 for PLA then Pronterface shows the hot end temp get to about 160 or so and then just sit there and never gets as high as 165). Anyone have any ideas?

I have noticed this problem myself but never got far enough in the code of the Marlin firmware to find out why. It appears that the firmware turns down the power to the extruder slightly when it is 10 degrees from the set point. You can see this if you monitor the printer while it is heating up in Pronterface, the power number drops below 127 temporarily and then resumes heating again. This may be some kind of safety feature or an attempt to calibrate the power needed to maintain temperature; again I'm not sure as I haven't found the relevant code. If anyone else knows more, I am curious.

I have found that insulating my hot end from moving air during this period helps it reach the temperature set point much faster. If I have a modest breeze in the room (like from an open window) my extruder (like yours) won't reach my set temperature. I use a sheet of paper leaning against the front of my machine and it works fine, but you could use something a lot smaller placed around the head; say a folded subscription card. A lot of people wrap their print heads in Kapton tape, I'm going to guess you don't do that yourself?

I have run the PID autotune (M303) and adjusted my settings, but I'm not sure if that helped or hurt this problem for me.

Thanks for the info. I have a Makergear that has a fiberglass sleeve around the hot end. I do often run a fan in that room because it gets pretty warm so that might be the issue.

any resolution to this? I just "upgraded" from sprinter to marlin and it is constantly reading about 10 below the set temp. Prints wont start because its not getting to temp.

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Ryan
Quality Engineer & Hobbyist
thingsandtrains.blogspot.com

Bump, I'm having this problem now after moving to the new v1. RC2 of Marlin. Was printing fine on the older version, now the hot end is always reading 10 deg below set temp no matter where I set it.

Comment out PID in the config file and use Bang Bang to see if that fixes the issue. Or run the self tuning PID M code and see if it can actually calibrate itself properly.

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SOLVED! (for me)

I had this exact same problem when upgrading to Marlin 1.0.

I had used the default values for the makergear hotend, but turns out they were way off from the values I got auto-tuning.

I followed this quick and easy post on how to auto tune the PID settings in pronterface: http://hardwired.cc/?p=133

Temps now work perfectly.

Cheers,
Tim