PLA Suddenly Jamming Mid-Print

[uncle_bob]

Hi

The current into the stepper is an adjustable number. The motor manufacturer comes up with a number and you set that (or less than that) on the stepper driver IC. Typical numbers are in the 1 to 2A range on the motors. Typical settings are between 50% and 100% of the rating. Normally the stepper driver IC is the first thing to have trouble when current is set to high. People often crank up the drive to check things out and then later forget they did that back 20 weeks ago ....

One thing that *will* heat up the motors and cause jams is trying to extrude to fast. Another thing is a combination of layer height and extrusion settings that force to much plastic into the print. It has nowhere to go and ... you get
back pressure. Eventually the extruder gives up. To much or to little tension on the extruder drive (the part that engages with the filament) can also create the same sort of issues.

Modern hot ends run with cooling blocks that are "cold" at the top end of the unit. If not, you have a fan problem There are other possible design issues in the hot end assembly that could cause the over heat problem. Given how close everything in a normal extruder is to each other, indeed, when one part over heats, it's hard to figure out what is what.

Bob

[Ryuluce]

Hi

The current into the stepper is an adjustable number. The motor manufacturer comes up with a number and you set that (or less than that) on the stepper driver IC. Typical numbers are in the 1 to 2A range on the motors. Typical settings are between 50% and 100% of the rating. Normally the stepper driver IC is the first thing to have trouble when current is set to high. People often crank up the drive to check things out and then later forget they did that back 20 weeks ago ....

One thing that *will* heat up the motors and cause jams is trying to extrude to fast. Another thing is a combination of layer height and extrusion settings that force to much plastic into the print. It has nowhere to go and ... you get
back pressure. Eventually the extruder gives up. To much or to little tension on the extruder drive (the part that engages with the filament) can also create the same sort of issues.

Modern hot ends run with cooling blocks that are "cold" at the top end of the unit. If not, you have a fan problem There are other possible design issues in the hot end assembly that could cause the over heat problem. Given how close everything in a normal extruder is to each other, indeed, when one part over heats, it's hard to figure out what is what.

Bob

I'm going to assume your first point is that I shouldn't need to adjust the current into the stepper motors (which is something I still am suspicious as to whether or not it may be part of my problem).

So, I have tried both reducing the extrusion multipliers and the speed of extrusion, and I only end up with more problems than what I started with. The printer doesn't even start with a good first layer and the whole print is a mess before the third layer.

Also, the Qidi Tech doesn't have the ability to adjust the tension on the extruder drive.

[uncle_bob]

Hi

Given the lack of adjustment on your printer, you appear to be stuck without much you *can* do to fix the problem. We seem to keep running into "can't do that on this machine". It appears that about the only thing you can do is to buy various brands of filament, fully scrub out the extruder and hot end each time and try them all ....

Bob

[Alibert]

I read here ( https://groups.google.com/forum/#!to...ot/gN_W4GieQwk ) that it's possible the stepper motors are running on too high a current. Is that possibly my issue? (As a reminder, the firmware I'm running is Sailfish ver 7.1)

What are you current settings on the digpots? You can read them out via the Rep-G sailfish program.

I have several Qidi's and a Flashforge (all running sailfish 7.x), and none of those get hot steppers during printing.

Can you find any serial number/product number on the steppers and look up the advised currents?

[Ryuluce]

What are you current settings on the digpots? You can read them out via the Rep-G sailfish program.

I have several Qidi's and a Flashforge (all running sailfish 7.x), and none of those get hot steppers during printing.

Can you find any serial number/product number on the steppers and look up the advised currents?

So, I found that the VREF pot. settings for my printer were as follwing:
X: 118
Y: 118
Z: 40
A: 118
B: 118

The stepper motors on my printer are all the following model number: 42HB34F08AB 06. (I found a specifications sheet here: http://voltom.ru/info/42HB34F08AB-06.pdf )

The advised current says 0.8 A/Phase, but I don't know what the VREF settings mean in practice (and I'd prefer not to have to grab a voltmeter and measure manually).

According to the link below, to have an output of 0.8 A, I should change the VREF to 85.
https://github.com/jetty840/Sailfish...x3/DigiPots.cc

[uncle_bob]

Hi

While you are poking around, I'd check the other settings as well. The Z axis looks a bit low. If the X and Y have the same motors as the extruder, they would need fixing as well.

Keep in mind that as you drop the current, the drive torque out of the motor will decrease. This will make the extruder more likely to jam.

Bob

[printbus]

Not sure any of this helps, but...

a) Stepper motors are designed to run hot. I've never seen the temperature on spec sheets, but multiple sites mention stepper motors capable of operating at temperatures of 85 to 100 degrees C. That's hot. They are intended for heat to pulled out of the mounting surface of the motor, something 3D printers rarely do a good job of.

b) Based on the data sheet, those 42HB34F08AB 06 are lower current/higher coil resistance than what at least the reprap wiki recommends for 3d printer use. This could explain why these motors run hotter than others for a given current setting on the stepper driver.

c) As Bob mentioned, you'd typically have issues with the stepper driver before you'd have problems with the motor itself. The stepper driver chips are designed to simply stop driving the motor if the chip gets too hot. Motors don't have any kind of protection built into them.

d) Be aware that once enabled, stepper motors ALWAYS have current flowing through them, and thus are ALWAYS consuming power and generating heat. The only time this isn't true is when the printer firmware has the stepper motors disabled. Once the stepper drivers are enabled, coils are energized to act as a brake and provide the motor with holding torque. This could explain why motors are cool when the printer idles with the hot end hot but then heat up in use.

[uncle_bob]

Hi

I just noticed the torque spec on your motors. The sheet lists it as 2.4 kg cm. That is the same as 33 inch ounces. Either way it is about half the torque that most of the recommended motors put out. It also is a fairly high inductance motor. That will limit your ability to step it fast, unless you are running high voltage drivers.

Heat wise, a stepper is "good" to about 150 C (the insulation temperature spec ...). That is an internal number. The temperature on the surface will be way below that. It still will be up in the "ouch" 70C range before there is a problem.

Bob

[Evonix]

I have much the same problem, would putting thermal paste between the hot end and the aluminium cooling block help? I have a MP select mini.

[uncle_bob]

I have much the same problem, would putting thermal paste between the hot end and the aluminium cooling block help? I have a MP select mini.

Hi

The MP Select Mini has it's own set of issues. The "simple answer" there is to slow things down and not go nuts on retraction or slowing down the fan. Since it's a Bowden setup, you will have to live with a bit of stringing.

Bob