Problem with PLA surface finish

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andreidanescu
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Problem with PLA surface finish

Post by andreidanescu » Sat Nov 22, 2014 12:22 pm

Hello,

I am trying to print a kettle bell in black PLA. I have a strange issue with the model as it shows in the pictures attached.
Basically that is the same part with the same FFF but rotated 180deg. So the problems seems to stay in the exact place with respect to the printer position(it didn't rotate with the part)
Do you have any ideas why this could be? ( my thoughts were uneven bed, although I level it every other day)
I have attached the parts, FFFs and pics.

Thanks a lot,
A
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benavery
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Re: Problem with PLA surface finish

Post by benavery » Sat Nov 22, 2014 5:03 pm

The defect is on the back part of the print, when looking at the front of the printer, right ? It is common with PLA and happens because the front cooling fan which is there to 'set' the PLA after it is extruded doesn't have quite as good airflow onto the back of the model as it does the front. I'm not really sure on best ways to fix it though, I'm sure other will be of more help.
A fan shroud that redirects the air all around the extuder is probably best, but I don't think there are any models out there to match the V3B (It's been on my TODO list to try modeling one up)
Printing slower would probably help too.
Also, make sure that front fan actually *is* running - I know it can be finnicky where if its set to run at 50% it can't actually start (it typically needs 100% power to get spinning, and can be ramped back afterwards)

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Tim
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Re: Problem with PLA surface finish

Post by Tim » Sat Nov 22, 2014 5:41 pm

I'm guessing that you sliced this with S3D? Be aware that S3D may be creating the support structures differently for the different positions, although from your photograph, it looks like the problem areas start below where there is any support.

I'll repeat what others have said in this forum: A piece like this, with a lot of rounded edges and unsupported arches, etc., is really best printed by splitting it in half, printing the halves separately, and gluing them together after printing. The resulting join line is going to be a lot less of a noticeable artifact than anything you will get from trying to print those handles, even if you don't sand/fill/paint the finished piece. Look for a post from Ed Nisley (sorry, I can't find it at the moment) about how to print alignment holes in each side where you can stick a length of filament as a pin. PLA glues decently with super glue, 2-part epoxy, and methylene chloride based glues (also mentioned in another post somewhere).

Netfabb was mentioned for software which can do the splitting, but if you are slicing and printing using S3D, you can also just rotate the model to the right orientation and then move the Z position down until half of the print is below the print surface. Only the part that shows above the surface will get printed. Then add a duplicate of the object and rotate it the other direction, and drop the Z position. That won't get you the alignment holes doing it that way, but it's the easiest way to split an object in half and print.

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ednisley
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Re: Problem with PLA surface finish

Post by ednisley » Sat Nov 22, 2014 6:24 pm

Tim wrote:how to print alignment holes in each side where you can stick a length of filament as a pin
Like this:
http://softsolder.com/2013/11/12/improv ... 3d-prints/

Image

Trying to glue two rounded halves together on featureless surfaces will drive you mad: the glue acts as a lubricant and the pieces slide around under clamp pressure. Punch two holes in the flat sides, insert filament snippets, apply glue, snap, clamp, done!

Even if those bells lack space for two pins, one works better than none...

andreidanescu
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Re: Problem with PLA surface finish

Post by andreidanescu » Sat Nov 22, 2014 11:53 pm

Thanks guys!!! I completely forgot about the second fan addition. I will work to get one done and see how it goes.
Will try the part in ABS so that should rule out second fan I suppose.

Will post some ABS results soon I hope.

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Capt. John
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Re: Problem with PLA surface finish

Post by Capt. John » Sun Nov 23, 2014 4:41 am

I had a problem similar building my spoons, extra manual placement in S3D should take care of the sagging
issue. I take it we're looking at the front view, rotate 90 degrees and put in manual supports to cover the entire bend, or arch.
4 to 5mm supports might fix all. S3D add support automatically is OK, just add more after the auto supports are in place.
Capt. John
Manistee, Michigan
Reel Amateur at 3D printing
Fishing Tackle Manufacturer & Webmaster for:
http://www.michiganangler.com
http://www.michigansportsman.com

andreidanescu
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Re: Problem with PLA surface finish

Post by andreidanescu » Sun Nov 23, 2014 11:22 am

Yes, that's the front of the part and than the same rotated 180 deg. It seems to be the furthest away from the fan so I will try another fan placed on the bed and see hot it behaves - seems to be the easy option :)

andreidanescu
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Re: Problem with PLA surface finish

Post by andreidanescu » Wed Nov 26, 2014 12:14 am

So ... the 2nd fan option fixes everything! Big thank you guys!
Still some work to be done on the handle but it looks promising.
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