Trying to get better underside surfaces

[cairn 5]

I've been getting some horrendous underside surfaces, the support just never seems to be enough to get a smooth result, and then sticks too much and damages the surface when you remove it.

I have been experimenting with purpose-made support objects, but I've hit a snag.

What I'm trying to do is first print a support object, remove it from the bed, start the print proper, and then at the right moment drop the support part into position so the overhanging parts are supported. You would then remove the support part leaving a smooth surface..

I used a light oil on the upper surface of the support part in the hope that it would assist removal, but to my surprise it seems to have increased the bond strength if anything.

Does anyone know what to use as a release agent or barrier film to stop the two parts fusing together? In theory you could then remove and reuse the support parts repeatedly, giving better results and saving material.

This works where you have a completely flat overhanging surface, so that the support object can be dropped in level with the ongoing print without risk of colliding with the print head.

Edited March 3, 2017 by Guest

[gr5 2,268]

You need something called "mold release". I don't know the answer to your question but I suspect you can google "mold release for PLA" and find some suitable materials. Hopefully one that you can spray out of a can like "Pam".

[cairn 5]

Thanks, I googled before posting here..

Anyone had experience with PLA mold release agents?

[cairn 5]

Sorry if that sounded a bit snippy..

Google is great, but I'm hoping this community is greater

(or at least more focused..)

[tomnagel 126]

Maybe it helps to lower the temperature of the layer on top of the support object, that will decrease the bonding.

Maybe you can try other material like aluminum, but depends on how often you will print the same object. It kind of defeats the benefits of 3D printing

When you work with rekease agent, arent you worried that the layer on top of your support won't stick at all? Or is the support object always 'enclosed' on all sides?

Edited March 4, 2017 by Guest

[neotko 1,417]

You could just not use Pla for the print, and use two incompatible materials like pla and ABS on top. Or you could use other slicers. For example I use solidrooftop. Cura ofc can do rooftops, but s3d does the rooftops on a negative pattern (this requires some good knowledge of s3d to get right) this way it can do 3 toplayers over the support that actually touch the lines above, making a better looking supported area that actually can be removed very easy because the rooftop and print don't share the same angles, this makes the area to have less interlayer adhesion, and if done right it pops out without almost anything but some marks that can be sanded.

Also, since the area you are making is just a big bridge, you could improve the fans to be able to print better looking bridges without any support. To test if this could work you just need to put a fan pointed to the print area while printing the bridge, it will make pla to stay cool, making a much better and stable bridge.

Other possibility could be to subdivide the object and make the bridge area as a different object (on cura you can merge two stl or more to make one object that shares the origin). This way you could play with the settings of that point to print it slower, or faster with less flow (so pla don't falls and make better bridges).

Ofc if your problem is that you need to make this as production and make them as better looking as possible on the less amount of time, maybe you could get some random material, cut it on the way you need and stick some buildtak (that you can exacto-knife it) and with some minor trial and error you could have a near perfect print area below the print.

So my answer to your question, get a cheap buildtak sheet and cut it on the shape of what you need and stick it to a print of the shape you need for the support area.

[peggyb 171]

put blue tape on top of your printed support, make a pause on the last open layer and put you support piece in and resume. Best is to have your speed dialed down at this point to have a good adhesion to the tape.

I did use this method to connect earlier printed links tomake a chain

[peggyb 171]

another way to do this is to print a thin disc, a little wider then your overhang, subtract it from your model and put it in when it reaches the top rim. The disc will be incorporated when the print continues.

[tomnagel 126]

wow @peggyb those are awesome ideas!

[cairn 5]

@peggyb For the win, but thanks everyone for the good ideas.

I am printing a structural part so I have adapted it to maximise strength.

So: First print the red and green parts, then print the blue part and drop the red and green parts in cold as the print progresses. The red part is printed on glass, so it has a perfect surface, and it already incorporates the holes. It just needs to be positioned carefully with some registration details, and the height will be critical to ensure a good bond with the blue part. The green part falls away when the print is done, and can be reused. All good

[geert_2 558]

Wow, this is a brilliant idea, both the dropping in of supports, and of the pre-printed plate of peggyb.

Concerning the use of release sprays: most dental release sprays are based on silicon oil. Some other release methods are water soluble, I think (but I am not sure) they are based on alginate dissolved in water? The problem is that the release method should not bond when trying to remove the support, but it should bond very well when printing, otherwise the next layer won't stick. Contradictory things.

So, if you would want to drop in a support block, maybe covering the support with a layer of dried wood glue might work? Or something similar, which is water soluble? Then at least you could soak the model in water until that layer is dissolved?

But of course, if there is enough room for the "peggyb method", that would be preferable. It is just so much cleaner, and allows for modeling that underside too.

[gr5 2,268]

If you do the peggyb second method (which is brilliant) and you have non symmetrical things like holes in it as in the drawing at the very top of this page then make the insert piece asymetrical. Such as with a tab or make it square or whatever.

Great ideas here.