Very low extrusion multiplier

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Very low extrusion multiplier

Postby dan27451 » Wed Jul 26, 2017 2:39 am

I've had my printer for a few months and thought I was getting the hang of calibrating it but the latest roll of PLA has me confused. I followed the calibration process for the extrusion multiplier and keep coming out with something around .65. Up to this point the extrusion multiplier had always been around .90. With the extrusion multiplier at .65 and an extrusion width of .40 I can print a single wall cube with a wall thickness right on the money but...when I print a solid cube with the same settings it looks like I'm under extruding. The perimeter walls are separating and the solid top and bottom layers look terrible. I'm having trouble understanding how this could happen. What should I be looking at the correct this? Thanks!
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Re: Very low extrusion multiplier

Postby ednisley » Wed Jul 26, 2017 2:56 pm

dan27451 wrote:something around .65


Have you measured the filament diameter? If it's oversized and you haven't changed the nominal diameter in the slicer, then you'll end up with an drastically undersized Extrusion Multiplier to compensate.

Back of the envelope: a 0.65 Extrusion Multiplier says the diameter would be 1.24 x 1.75 = 2.17 mm, which doesn't seem close to any of the usual sizes. If it was that large, I'd expect the filament drive to choke on it, but stranger things have(n't) happened.

However, with filament diameter so far out of tolerance, I'd expect the diameter to vary a lot along the length of the spool, which would lead to underextrusion where it's "too thin" compared to the oversize sections.

Be careful when you're measuring the diameter, though, because if you let the filament flop free, it'll probably acquire overlaps when you respool it.

Also check the filament drive gear, which must be firmly attached to the extruder gearbox shaft: the tiny screw through the gear must be tight against the shaft flat to prevent rotation. Draw a line across the end of the shaft and gear, then check occasionally to make sure it's still a line.
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Re: Very low extrusion multiplier

Postby insta » Wed Jul 26, 2017 4:26 pm

dan27451 wrote:I've had my printer for a few months and thought I was getting the hang of calibrating it but the latest roll of PLA has me confused. I followed the calibration process for the extrusion multiplier and keep coming out with something around .65. Up to this point the extrusion multiplier had always been around .90. With the extrusion multiplier at .65 and an extrusion width of .40 I can print a single wall cube with a wall thickness right on the money but...when I print a solid cube with the same settings it looks like I'm under extruding. The perimeter walls are separating and the solid top and bottom layers look terrible. I'm having trouble understanding how this could happen. What should I be looking at the correct this? Thanks!


Is the plastic foaming? What happens if you try printing at your normal 0.90 multiplier and "just go for it"?
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Re: Very low extrusion multiplier

Postby dan27451 » Sat Aug 12, 2017 12:33 am

Thanks for the good suggestions. Sorry for not responding sooner but a few things came up and I'm just getting back to this. Here's what I've done:

I double checked the filament diameter and it was 1.73 mm so that doesn't seem like the problem.

The drive gear appears to be solidly attached but I did stripe it for future troubleshooting - thanks for that suggestion

After checking the drive gear I had to reset the tension. That may have helped a little (extrusion multiplier closer to .7) but still not where I expect it to be and it didn't fix the problem.

What does foaming plastic look like? This roll does seem to ooze out of the nozzle after printing a lot more than other rolls.

With the extrusion multiplier at .9 it makes some nice looking parts. There's a little over extrusion on the top layer, especially on the edges where it changes direction. The dimensions are also off which is the real problem since the parts need to fit together. In the end, I used the parts printed with the extrusion multiplier at .9 and did some sanding to get them to fit.

I should mention that this is a specialty roll - Hatchbox wood - and was used previously but has been stored in a sealed bag ever since. The other prints I did with it did not need to fit together so perhaps this was an issue before as well and I didn't notice it.
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