top layer issue and precision problems  

RE: top layer issue and precision problems

Rippling on just a corner like that is usually a sign that the print has warped upwards on that corner and is no longer perfectly flat with the bed.  This causes compression of the layers.  This gives the rippling as the plastic has to go somewhere.

If it was general rippling over more of the surface then you would be looking at insufficient infill to properly support the top layer, in this case though I don't think that's likely as it is limited to the corner.  Carefully examine the bottom of your print and look at it in good light.

This is why we always stress the importance of getting a good first layer and of making sure the print surface is scrupulously clean to get the best adhesion possible.

RE:

Hi there,

thank you for your response!

Warping: maybe yes. I cannot reproduce whether there was loss of bed adhesion locally, but yesterday when I removed the part prom the bed plate (smooth PEI)  there generally did not seem to be an overall bed adhesion problem. I had to bend the plate in two directions several time to de-attach the part.

But nevertheless, I agree  the design can be improved regarding warping. And so I did intorduce the following measures:

• extra careful cleaning print bed before printing 
• Introducing radii at the corners to avoid sharp corners
• introduce corner chamfer to reduce stiffness towards the edges
• introducing brims locally in the design to avoid lifting in the edges
• changing print direction to have surface where I need quality now on the print bed and not as top layer. So groove now pointing downwards to print bed,
• slower print speed for first layer

And I checked carefully after printing. The part was fully attached to the bed.

But still I get similare local effect on the top layer. And the groove fit again only on one side an is too tight in the areas, where I have the top layer defects.

When looking carefully, one the side where the groove is too tight, there is a little bit of overhang a the edge of the top layer. As if locally there is a bit of overextrusion.

At the moment I do not have an idea. What would you think?

Cheers, Nils

Overhang: 

Bottom side, which was attached to bed plate. groove too tight in the area with the top layer defects:

top layer with defects again:

RE:

Agreed, warping.  It  has the same appearance as overextrusion but for the opposite reason; as the part warps upwards it slightly reduces the area of the top so the correct amount of extruded filament no longer has quite enough room, and ripples.

One simple trick that might help in some of these cases is to add a few 'decorative' grooves across the top layer so that warping stresses are relieved.

For the flat saw plate you might try annealing.  Put the plate between two flat metal plates and clamp, then place the whole lot in an oven at 100°C for half an hour and allow to cool slowly.  You will probably need to clean up the edges with sandpaper.

Cheerio,

RE: top layer issue and precision problems

Hi Diem,

you might be right: it still seems to be warping:  the surface of the part is not perfectly flat, even though I had tried to reduce warping with a changed design and had the impression after printing, that the part was fully attached to the plate .

I might try the annealing thing to get it fully straight, 

And the groove I have carefully  machined with the dremel locally: now it fits fine. 

My lessons learned is to watch more carefully for warping and optimize the design accordingly for larger precision parts.

Thank you,

Nils