Filament losing integrity after about an hour of printing

I have a machine I built myself using the plans found in the book Printing in Plastic from www.buildyourcnc.com.

It essentially has the same specs as a Makerbot Thing-o-Matic although the extruder is a MK7.

I'm printing at about 205 F and extruding at a flow rate of 1.98 (this per the setup instructions from the book's author / printer's designer).

I have very good success printing for up to one hour. Once I hit that point, I start having extrusion problems. I've tried tweaking the tension on the extruder to no avail. What it appears is happening is that the heat is traveling up the filament over time and causing the filament still being pushed by the drive gear to soften.

I have the basic OOTB heat sink and fan that came with the extruder.

Does this theory seem plausible and if so, are there any tips on bleeding away the excess heat?

I've had the filament jam once because the heat traveled up the tube when I was printing very slow for a long time. Just to prove or disprove the theory, you could try a couple things:

• Increase the layer thickness. This will force the extruder to put out material faster so it is more difficult for the heat to travel up through it.
• Increase the Fill Speed and Perimeter speeds so material is being used faster.
• Increase the Fill Density so material is being used faster.

Of course, those things might affect your print quality, but it might help you get a better handle on what is going on.

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Originally Posted by ckcampbell248

I have a machine I built myself using the plans found in the book Printing in Plastic from www.buildyourcnc.com.

It essentially has the same specs as a Makerbot Thing-o-Matic although the extruder is a MK7.

I'm printing at about 205 F and extruding at a flow rate of 1.98 (this per the setup instructions from the book's author / printer's designer).

I have very good success printing for up to one hour. Once I hit that point, I start having extrusion problems. I've tried tweaking the tension on the extruder to no avail. What it appears is happening is that the heat is traveling up the filament over time and causing the filament still being pushed by the drive gear to soften.

I have the basic OOTB heat sink and fan that came with the extruder.

Does this theory seem plausible and if so, are there any tips on bleeding away the excess heat?

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Are you printing in PLA or ABS? if it's PLA possibly the same as Roxy happens to me alot, if I leave the PLA on the machine, over time it heats up and expands inside the tubing, making it around 1.8 to 1.9mm thick, which causes me major jams. The way I got around it was just don't leave it loaded when im not using it.

In your case however, it's happening while you print, all I can think of is that your code isnt fluctuating the heat levels depending on what it's doing, and if it's running at full temp all the time, this might also make the plastic go a bit squishy inside the tubing, simply from heat running through the filament all the way through it. I've noticed on the firmware im using at the moment the temperature changes depending on what it's doing and rarely does it print at the full max temp for a long period, it always drops it a few degrees for slower shells.

Quote:

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Originally Posted by Geoff

Are you printing in PLA or ABS? if it's PLA possibly the same as Roxy happens to me alot, if I leave the PLA on the machine, over time it heats up and expands inside the tubing, making it around 1.8 to 1.9mm thick, which causes me major jams. The way I got around it was just don't leave it loaded when im not using it.

In your case however, it's happening while you print, all I can think of is that your code isnt fluctuating the heat levels depending on what it's doing, and if it's running at full temp all the time, this might also make the plastic go a bit squishy inside the tubing, simply from heat running through the filament all the way through it. I've noticed on the firmware im using at the moment the temperature changes depending on what it's doing and rarely does it print at the full max temp for a long period, it always drops it a few degrees for slower shells.

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You should try the E3D hotend, I had the same problems with PLA and after changing to that one they are gone. I think the combination of a large heatsink and a very narrow stainless steel "neck" between the hotend and the heatsink makes a very sharp transition between the melt area and the filament, when I change filaments I can see that the transition is about 2mm only.

All good advice. (I'm just saying that because I don't want anybody to mistake what I'm saying here as arguing with what has been said)

I have a Wade's extruder with a J-Head. There is about an inch of filament travel from where it is getting pushed by the hobbled bolt until it disappears in to the actual hot end. The filament jam I had was horrible. It didn't matter what I did, I couldn't make the filament go forward or backwards. I had the hot end very hot and ended up breaking off the filament pulling on it.

I had to disassemble my entire extruder to get at the problem. As it turns out... Where the filament was being pushed into the hot end, it got soft, and it bulged. So it couldn't go forward. It could retract a small amount, but then it couldn't go any further because of the bulge. The only way it could have bulged like that is the filament got too warm before it even entered the hot end.

It has only happened once, and that was using PLA. But it was horrible!