Zits and under extrusion at beginning of print with TPU90

Bambu Lab H2 Series
1

Hi. My TPU90 print starts like this:

IMG_2572
IMG_25721920×1299 168 KB

But then starts extruding like it is supposed after a couple of minutes.

Also the final print has zits like this:

IMG_2578
IMG_25781920×1440 125 KB

Does anyone know why this might be and how I might fix it?

These are my configurations:

01
01715×829 121 KB

02
02734×724 82.5 KB

03
03732×429 48.4 KB

07
071053×435 97 KB

I dried the filament at 70 degrees for 12 hours.

2

Do you have a smooth PTFE path for your TPU?

This looks like under extrusion due too much resistance in the filament path.

3

I just tried feeding it directly from the top and experienced the same issue.

I dried the filament using a new bought dryer for the first time. Maybe it didn’t do the job.

I’m drying it with the dryer I already had and will try again tomorrow.

4

Moisture is a serious problem with TPU. TPU is attracting moisture quite easily.

Definitely make sure your dryer performs properly. TPU drying is proposed at 75C for 18hrs.

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