Replacement hot end (Page 2 of 2)

I look forward to seeing these replacement hot end experiments.  I eventually would like to replace mine. If only just because some of the other designs are more clever (optimization obsession) and offer a road to a few higher temp materials.

Cephdon,  have you mounted your Jhead yet?  It doesn't seem to have the step-down in diameter needed for the wood plate to push it up against the extruder.   I have one on order, I'm hoping I get my nichrome heater to keep limping long enough to make any necessary mods.

I ordered the bracket too.  Are you saying the bracket is too small for the hot end they sell it for?  I plan on printing the extruder replacement to go with this, so it shouldn't be too hard to modify as needed.

cephdon - Any progress?  Looking to change out my with either the J-head or the one from Qu-Bd.

I got my final pieces in the mail yesterday.  I am starting to move towards my "zif-able" hot end design.  Once of the pieces I was waiting on was my selection for upgraded connector.  Its a 4-conductor locking stlye that has the ability to be panel mounted on one side.

It looks like:

My idea is to have the thermistor and heater wires run to the panel mount side.
The panel mount side will eventually mount into the zif hot end carrier, providing strain relief while also keeping the entire hot end in a neat and small package.  When I swap out hot ends, I would just undo the connector,flip the lever that keeps it locked in place, pull out the hot end, place the new one in its place, drop the lever and hook up the connector.  For version 1, that is probably sufficient.
I might eventually try to integrate the connector with the zif hot end so that they connect and disconnect together. Who knows.

For now, I am just trying to get my hot end working. I will post images when I have it connected...probably later today.
I need to do some temperature measurements first. 

Oh, and I also got the hot end from qu-bd.com.  I still don't know what thermistor is used on the SD2, and no response on my query for that info.  Maybe it is listed in the code somewhere.  Otherwise, I will just have to buy some thermistors and update the code to use them.  That way they are all the same.

Sweet. Thanks Ian. Now I can get one for the qu-bd hot end and a few spares.

Edit:
Hmm, seems there are several with slightly different characteristics.
Do we know which of the epcos tables we use? The part number may be on the reprap site.

If not, I will just look through the code and compare them.

Edit 2:
I think I finally figured out why my hot end keeps jamming.

Requested - C    SD2 - C    Thermocouple F       Thermo converted to C       IR - C
---------------------------------------------------------------------------------------------
Ambient               22                 73                     22.77777778               24
30                       29.9              85                     29.44444444                30
40                       45.8            103                     39.44444444                42.8
60                       60               144                     62.22222222                63.6
80                       80.3            165                     73.88888889                93.3
100                   100               188                     86.66666667              111.3
130                   130.6            241                   116.1111111                142.6
160                   160.1            292                   144.4444444                176.3
180                   180               319                   159.4444444                196.7
200                   200               343                   172.7777778                211.4

Now Ian had already told me how inaccurate the IR thermometers were, but I had to test to see.
My thermocouple reads in F so I converted to C using the standard equation of ((5/9)*(Temp - 32).
Due to poor readings from the IR at the tip, I ended up measuring the temperate of the heat core with it (I later checked the temp of the heat core with the thermocouple and found that it doesn't vary significantly from the brass tip).
I taped my thermocouple to the tip to measure the temperate as seen by the thermistor, just on the other side.
If the thermocouple is to be believed, the actual temperature of the head something like 20 to 30 degrees below expected at the target temperature.

Also, when looking at the temp table in code I noticed that it might not have been created correctly.
I am not sure who created it, and what method they used (the code isn't commented very well).
This is the relevant block, if I am understanding everything correctly:

#if (THERMISTORHEATER_0 == 6) || (THERMISTORHEATER_1 == 6) || (THERMISTORHEATER_2 == 6) || (THERMISTORBED == 6) // 100k Epcos thermistor
const short temptable_6[][2] PROGMEM = {
   {1*OVERSAMPLENR, 350},
   {28*OVERSAMPLENR, 250}, //top rating 250C
   {31*OVERSAMPLENR, 245},
   {35*OVERSAMPLENR, 240},
   {39*OVERSAMPLENR, 235},
   {42*OVERSAMPLENR, 230},
   {44*OVERSAMPLENR, 225},
   {49*OVERSAMPLENR, 220},
   {53*OVERSAMPLENR, 215},
   {62*OVERSAMPLENR, 210},
   {71*OVERSAMPLENR, 205}, //fitted graphically
   {78*OVERSAMPLENR, 200}, //fitted graphically
   {94*OVERSAMPLENR, 190},
   {102*OVERSAMPLENR, 185},
   {116*OVERSAMPLENR, 170},
   {143*OVERSAMPLENR, 160},
   {183*OVERSAMPLENR, 150},
   {223*OVERSAMPLENR, 140},
   {270*OVERSAMPLENR, 130},
   {318*OVERSAMPLENR, 120},
   {383*OVERSAMPLENR, 110},
   {413*OVERSAMPLENR, 105},
   {439*OVERSAMPLENR, 100},
   {484*OVERSAMPLENR, 95},
   {513*OVERSAMPLENR, 90},
   {607*OVERSAMPLENR, 80},
   {664*OVERSAMPLENR, 70},
   {781*OVERSAMPLENR, 60},
   {810*OVERSAMPLENR, 55},
   {849*OVERSAMPLENR, 50},
   {914*OVERSAMPLENR, 45},
   {914*OVERSAMPLENR, 40},
   {935*OVERSAMPLENR, 35},
   {954*OVERSAMPLENR, 30},
   {970*OVERSAMPLENR, 25},
   {978*OVERSAMPLENR, 22},
   {1008*OVERSAMPLENR, 3}
};
#endif

Notice that 914 is used twice, for 45 and 40C.
I am currently unable to reproduce this table using the createTemperatureLookup.py script. 
None of the 100k thermistors from epcos actually produce this table from that script.  To make matters worse, reading my thermistor's resistance at room temperature yields 116.4k ohms. 
In summary, I am not exactly sure what thermistor is installed.

Here is the big question.... do I trust the thermocouple, or do I trust the thermistor which tended to come out pretty close (10 - 16 degrees) as compared to the IR thermometer.

Edit: I decided to run a form of calibration test. I live at sea level, where water boils at 212F (100C).  The IR reads 199F (1% Tolerance) and the thermocouple reads 207 (3% tolerance).  Since the thermocouple is well within tolerance, I think I can trust that value, which means that my hot end is running way colder than it thinks.

A note on using the Jhead with the jigsaw replacement, without a mounting plate- the mounting plate is what hits the X endstop.  I've glued a piece of plastic to the bottom of my mounting block to hit the endstop until I can revise that  tinkercad model to come down a little lower, and print a new one.

The most recent offering for the JHead only has 3 mm filament as an option.  Maybe that will change.

Way to go SD Team!!!  the block setup should be a great improvement for a number of reasons... maintenance being #1