Checking hot end resistance

bplemmons · Post by **bplemmons** » Wed Apr 10, 2013 8:46 pm

I'm having a lot of trouble with my extruder clogging and I want to check the resistance across the to wires that lead to the resistors, I am getting 1.5 ohms, isn't supposed to be about 3.4? Does this indicate a bad resistor?

Bill

Post by **Eaglezsoar** » Wed Apr 10, 2013 9:04 pm

bplemmons wrote:I'm having a lot of trouble with my extruder clogging and I want to check the resistance across the to wires that lead to the resistors, I am getting 1.5 ohms, isn't supposed to be about 3.4? Does this indicate a bad resistor?

Bill

It could indicate a bad resistor, are the resistors unplugged from the Rambo when you take this measurement?

Carl

cambo3d · Post by **cambo3d** » Wed Apr 10, 2013 9:04 pm

your using pla which is prone to clogging if you dont have a fan on your hotends peek area.

do you have a fan there?

bplemmons · Post by **bplemmons** » Wed Apr 10, 2013 9:12 pm

I did disconnect the leading wires from the rambo,

I have been printing pla on a replicator for months without a fan, I can see it may improve print quality but I cant even print it is so bad. I did try abs on this one and it does the same thing, the hot end keeps clogging even with the temp up to as high as 230 for pla, it stops the extruder from feeding....

shouldn't i get about 3.4 ohms?

Polygonhell · Post by **Polygonhell** » Wed Apr 10, 2013 9:21 pm

bplemmons wrote:I did disconnect the leading wires from the rambo,

I have been printing pla on a replicator for months without a fan, I can see it may improve print quality but I cant even print it is so bad. I did try abs on this one and it does the same thing, the hot end keeps clogging even with the temp up to as high as 230 for pla, it stops the extruder from feeding....

shouldn't i get about 3.4 ohms?

Some hotends require a fan blowing on the PEEK to reliably print PLA in fact I'll restate that as most hotends do and this is likely your jamming issue.
Yes it should be about 3.4 Ohms, but a bad resistor would likely read higher not lower resistance. Are you sure you're not reading the resistance of the heated bed?

bplemmons · Post by **bplemmons** » Wed Apr 10, 2013 9:31 pm

You are right, i was checking the bed,

I wanted to ask you, I have tried to run your firmware and when I move the head toward any tower the head sweeps downward to the bed, It doesn't do that on the marlin and yours supports sd...

Is there a setting for pulley size I need to change, yours specifies it but marlin doesn't specify it....

Thanks for helping me guys!!

Polygonhell · Post by **Polygonhell** » Wed Apr 10, 2013 9:50 pm

bplemmons wrote:You are right, i was checking the bed,

I wanted to ask you, I have tried to run your firmware and when I move the head toward any tower the head sweeps downward to the bed, It doesn't do that on the marlin and yours supports sd...

Is there a setting for pulley size I need to change, yours specifies it but marlin doesn't specify it....

Thanks for helping me guys!!

I'd have to see the issue, one difference is I set the stepper drivers to lower current, and I know on Rambo 1.1 the meaning of the current numbers changed, so it's possible the stepper is skipping, it has to move faster the closer to the tower you are. Any excessive mechanical resistance like overly tight belts would make that more likely.
You can try changing the motor current in the configuration.h file, I'd start with 200, I think John's marlin defaults to 195 and my firmware is set to 175.
There is nothing in the way the mechanics are calculated that would result in what you are describing.

bplemmons · Post by **bplemmons** » Wed Apr 10, 2013 9:58 pm

Actually, I already did that from reading one of your post earlier today....

I'll will try it again now that I have done that...

About to try the fan too... I was getting 3.8 on the correct wires this time.

Thank you again!

bplemmons · Post by **bplemmons** » Wed Apr 10, 2013 10:54 pm

Tried your firmware again with the new settings, same thing....

The filament keeps backing up into my fitting then hardens making it very difficult to take apart and clean. I had to do it twice today and ruined a fitting on the second try. I will use a fan when I get it going again but would a lack of a fan cause it to back up like that?

Why is it that this type of extruder has to have a fan for pla?

Bill

cambo3d · Post by **cambo3d** » Wed Apr 10, 2013 10:55 pm

yes, because the pla starts to soften due to heat of the peek.

the fan keeps the peek cool enough so the pla doesn't soften. most hotends need a fan on the peek area when printing with pla.

even the replicator comes with one attached to the hotend/extruder, all the replicators i've seen have a fan.

bplemmons · Post by **bplemmons** » Thu Apr 11, 2013 12:09 am

I have a 40 mm fan on order and I printed a mount for it but it points down at the nozzle. I take it that I need to cool the ceramic spacer above the aluminum housing with the resistors?

Here is the mount
http://www.thingiverse.com/thing:34811

I've seen other Rostock printers with this same setup

I'm surprised that this subject isn't covered in the build instructions.

You are right, my Replicator does have fans but I thought they were for the steppers. I thought you meant an addition fan blowing on the part...

I am starting to see why most people print with abs on these machines.

cambo3d · Post by **cambo3d** » Thu Apr 11, 2013 12:11 am

u need a 25mm fan for the peek area, yes

like this http://forum.seemecnc.com/viewtopic.php ... peek#p5813
another example http://www.thingiverse.com/thing:71673

bplemmons · Post by **bplemmons** » Thu Apr 11, 2013 2:19 am

Thanks again, Does anyone know what connector I will need to plug this into the rambo fan port?

Bill

cambo3d · Post by **cambo3d** » Thu Apr 11, 2013 2:31 am

bplemmons wrote:Thanks again, Does anyone know what connector I will need to plug this into the rambo fan port?

Bill

it comes with connectors should be in your box that came withe the rambo

bplemmons · Post by **bplemmons** » Thu Apr 11, 2013 2:45 am

Found it! Thanks again!!!!

Bill

MorbidSlowBurn · Post by **MorbidSlowBurn** » Thu Apr 11, 2013 10:07 am

I have a 25mm fan pointed at the PEEK section of my hotend. I plugged it directly into the power supply. It really doesn't need to be controlled by the Rambo. I will warn that you have to watch the airflow around the hotend as it will cool the nozzle also. I used some Kapton tape to act as a deflector to prevent the air from cooling off the nozzle area too much.

Remember that if you add a fan to the PEEK section that you should rerun the hotend auto-tune to account for the increased cooling.

bplemmons · Post by **bplemmons** » Thu Apr 11, 2013 3:23 pm

That is great advice, thank you! From all of the pictures I have looked at on the build zone I would assume almost everyone is running ABS. I spend days fighting clogged nozzles. Even broke my fitting trying to get hard PLA from inside the release clearance. The Rostocks I have seen with fans on them are pointing down at the tip. I have never seen one mounted at the peek until this thread. I am surprised that seemecnc does not make this more clear that this is a must if you print PLA, after all they even sell PLA.
I really appreciate all of the help I have gotten here. I would not have figured that out if it were not for the help I have gotten here.

Bill

mhackney · Post by **mhackney** » Thu Apr 11, 2013 5:40 pm

+! on MorbidSlowBurn's suggestion. I have the 25mm fan pointed at the PEEK cold end directly to the supply with an on off switch. I run it almost all the time and have not had a single plug with PLA, ABS, Nylon and a few other exotics. The RAMBo port is great for a fan (or fans) that cool the actual part. That way you can control it from gcode. For instance, with PLA I put down the first 4 layers without the fan and then turn the fan on 50% for the remainder for most parts or 100% for thin/pillar types of parts.

I run a lot of PLA and no clogging. PLA has a certain glossy/translucent look that is quite attractive for many items.

Most people have not really thought about the dynamics of heating/cooling the nozzle/hotend. Very little airflow pointed directly at the PEEK (25mm fan) is all that is required to lower the temperature by qt least 20°C. Too much air, or air directed at the hot end/nozzle is only going to create problems for the PID to keep the hot end at the set point and use more power than necessary. The way the Rostock delta head is designed, the spacers are exactly 1" tall so a 25mm fan slides right in. The lower part of the platform where the delta arms are attached makes a great "wind brake" to keep the fan on the PEEK and not the nozzle.

bplemmons · Post by **bplemmons** » Fri Apr 12, 2013 1:49 am

What you just said should be it's own sticky, I know someone else that had the same problem as I was having, Before I even built mine, I'm used to running Pla on my replicator, got pretty good with it. ( check out pictures of what I have printed with my Replicator duel (physical3d.net)

I've been to two Seemecnc events and have seen many of these machines print and I know some of them were printing pla ( poorly, fan was aimed at nozzle )

I must Say though, I ordered the fan and until I get it, I loaded up ABS and it hasn't clogged once and is printing nicely. This thing really sings when it is dialed it right...

Thanks again everyone!!!

Bill
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