J-Head Mark V-B Temperature issues

Hi all,
John here, I am building a reprap mendal prusa v2. I have it fully assymbled and partially printing. I bout a preassymbled J-Head Mark V-b hotend off of a reputable web site and it came with the assymbled jhead, thermistor, resistor, and some ptfe tubing to insulate the resistor and thermistor wires. I gently rocked, pushed, twisted in the resistor (pretty tight fit) and put the two insulator tubes on it. I then put the piny tubes over the thernistor wire to the glass ball and carefully bent a 90 right after the glass and stuck it in the hole (it is snug but not tight like the resistor. Note the thermistor is 100k ohm and resistor is 5.6 ohm 5w I think. Fired up printer face and the temp was within a degree or two in celcius to room temp. Turned on the heat to 185 and waited for it to get to tem and it did in probably a minute or two.(At least I thought so). I told it to feed 5mm of pla and nothing came out. 5 more same. Tested reading on the brass on the hot end with a thermocouple and the temp was very low. Tested it with an infered adn very low. Had a buddy bring over his thermocouple (He now has the same hot end excep mine is 3mm and his is 1.75 and his works) and the temperature was about 1/2 of what the thermistor showed. We played with it for about an hour or two and noticed the temperature was slowly leveling out. After probably two hours it it stablized and we did some test prints. NOTEuring the fiddling around time we had cranked the temp way up to close to the melting point of ptfe knowing the hotend was not getting hot enough. So we pulled it back down when it got close and left it at 190 for probably 30 minutes. Now when I print or try to, its like hitting myself in the head with a happmer to get it up to temp and not fry the ptfe liner.
What I have tried was recoended on the irc channel whtch was to buy arctic silver V thermal compound and fill the thermistor cavity and the resistor cavity. Same issues and when printing it slowly loses temp until it stops printing and i stop it. (Please remember that I can crank up the temp and it will heat up to temperature quickly (I do not appear to have a power issue) but can not leave it there.)
I just ordered a new resistor and thermistor and want to know a way that can definitly work during the installation. Do I need to uses any muffler putty? Is Arctic Silever good? Should I use anything in the thermistor hole at all aside from the thermistor, and same question on the resistor. I started with Marlin and used M303 to give me pid settings with no luck, I also disabled them and no luck. I switched to sprinter and it almost worked once. Almost on a small part then lost heat. Please give me some direction on a Mark V-b .... setup that works great for you.

Thanks in advance,
John

P.S. Running off of ramps 1.4. I tried to give all info anyone could need but ask away.

Which thermistor table do you have selected? I use table 1 in Marlin for all my J-heads

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I am using 1 for my selection and have tried otehr 100k selections with the same results but it should be one for my thermistor I checked.

If the manufacturer of the RAMPS board used a 1K resistor instead of the 4.7K in the thermistor circuit you would need to use table 51. It may be worth trying or measuring the resistor.

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Can you tell me where that resistor is located on my ramps board please? And I will try 51 if my new thermistor and resistor do not work properly. I just "drilled" them out due to using arctic silver as suggested in irc. I should have my new ones in a day or two.

They are the first three 4.7k resistors [reprap.org]

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I thought you were on to something but the board says 4.7 and my multimeter tests 4.7. All 3 test at 4.7.

When I bought my J-Head when I assembled it I cranked the head on so tight that I actually made the hole in the PTFE so small that ABS could not flow. I took it apart and reamed out the bottom end of the PTFE and shortened the ptfe tube and it started working better. Is it possible that you crushed the PTFE?

Roy

I have never taken it apart. as it came asymbled but without the resistor and thermistor in it. I was thinking about taking it apart yesterday when I removed the resistor and thermistor. Is it simply a matter of removing the allen head set screw on top and pulling the platic off the brass? When it is hot it floes easy and fast.

Unlucky1,

I had something similar happen to one of the printer I was assembling, and I could not understand why my temp was not rising. Do you have a way to verify you have 12V DC to the J head?

In my case I had a dud power supply and it was only getting 5V to the J head. Swapping out the power supply solved my problem.

Good luck

I install a new resistor and thermistor. It vorks slightly better but after printing for probably 3 minutes the temperature shows it holding temperature but the hot end is slowly losing temperature. I can tell this very easily because my filiment starts skipping on the print. If I pause the printing and do not touch the temperature settings, raise the z axis up a little and wait about a minute, the filiment start to ooze out of the nozzel. The entire mistery to me is that the temperature does read in pronterface and when I first set it, it will get hot enough to print but the nozzel slowly gets cooler even though the pronterface/ramps board tells me its at temp. I have two thoughts to try next. 1. Try a different laptop to run the arduino from. Maybe the one I am using (an old thinkpad) is not supplying enough power to properly run the audrino board. 2. Is that I had the same thought as Fred above in the power supply not working properly. It is rated at 600 or 650 watts and I tested bother 12v inputs from the power supply right where they are secured onto the ramps board and its showing around 11.93 volts even when the power is on and off to the heatbed and to the print head. I do have a small power supply and will use it to power one of the two channels with 12v and see if that makes a difference. Thanks for the info above Fred. I appreciate all the ideas i can get. I did test last night but maybe its getting enough voltage but not enough amperage. Is it possible my ramps board is bad or something? My heat bed does appear to be in sync with the pronterface temp reading and my manual reading on temp. Can I switch the thermistor ports around in sprinter to test? In other words can I tell sprinter that the heat bed thermistor is on the first to pins and the hon end on the second? I would love to swap them on the thermistor to verify that the two pins used for the hot end are not doing anything funky.

If you are using a RAMPs could you just swap the 2 plugs at the board to test the thermistors? If you want a quick test to see the temp rise, set Pronterface to "monitor Temp" and then I guess you could use a hair drier to quickly heat up the thermistors to watch them rise.

I ruined a Brand new J head when I put 12V DC to the resistor to cure the cement, and I forgot about it. It melted the PEEK. I do not want to know what fumes I let off or what I was breathing. (this is why I mention the hair drier - you can see the temp rise, without risking damage to a very good hot end)

Just added a second power supply to connect to the ramps board. Now have one supply driving one side and onother driving the other side. Same results. Next will be running the 2560 off of a different pc. The only thing I can think of on that would be the usb power. It just makes no sence. I was able to assign the thermister to the 3rd set of unused pins on the ramps 1.4 board as well and still the same. It does get hot, just not as hot as the thermister says. I really do not want to take off the high limits and crank it up to 1000 becasue if something goes right, it will melt my peek.

ok, after adjusting the y axis to avoid motor binds!! (seperape issue), I finely figured out the issue. By the way, its very hard to test temperature even with a thermocouple reader on a jhead. any way, that was not the issue. The issue was simple as it always seems to be in the end. The small gear on my wades extruder has a set screw in it that had come loose. it was not completly spinning on the motor shaft becase I filed a flat on it but was very loose. I tightened it down, adjusted my temp to 190 C and was off to the races!!!!! Finally. Now more tweeking.