Shrinking bottoms

[jeex 35]

Printing of this half (see image) of my new developed game board gives a very beatiful result.

However, during the proces of printing, when about 5-10 mm are done, the corners are slightly shrinking. I thing because it is too long on the heated glass plate. Off coarse the whole thing is on the heated plate, but the corners are free so they shrink easyer than the middle of the board.

So, questions: is my suggesion about the heated plate that shrinks the board correct, or are there other reasons for this?

And if so, can i manipulate that temperature during the printing proces. Can i adjust the gcode so that the heating turns off after say 5mm. The board is by then heavy enough not to move anymore.

[Dim3nsioneer 557]

What do you mean by 'corners are shrinking'? Are the edges not as sharp as on layers below anymore (increased edge radius)?

The bed heating might have an influence but usually it can be cured by correct fan settings. Make sure you have the right amount of cooling. Switching off the heated be is a bad idea as your print will then soon come off the bed. But adjust the bed heating to something like 60 or 55 °C if you're still higher. I read about people going down almost to 40°C during the print.

You can adjust the bed temperature in the 'tune' menu during print or you can use the TweakAtZ plugin if you want to reduce it at a certain height/layer no.

[jeex 35]

Thanks for the reply. I use all the standard settings of Cura for UM2. So cooling... more or less?

See the image (i found my camera) the bigger the box (left is biggest), the more it shrinks at the bottom layers touching the plate.

Both boxes should have stayed flat on the bottom.

I will try the next one with a lower glass temperature. Or switch the glass temp off and use a sticky spray.

Edited May 30, 2015 by Guest

[IRobertI 520]

That's just classic warping. It happens because the plastic shrinks slightly as it cools down, this makes the print collapse in on itself which creates very strong forces that pulls the plastic off the platform.

 

• Keep the platform hot throughout the print, 60C is a good temperature.
  
• Make sure you have levelled your platform properly.
  
• Clean your glass and add a very thin layer of glue to the platform. Add some glue and then spread it out with a damp cloth.
  
• Activate Brim in cura
  
• If you can get away without cooling, that's not a bad thing but usually it's not necessary to disable cooling for PLA (I'm assuming this is PLA).
  

 

[Dim3nsioneer 557]

Nothing to add to Robert's list...

Personally, I would first try with the brim only and keep the glue for later if it still doesn't work. But just out of the reason I don't like this smeary glue; I'm pretty sure it works...

[jeex 35]

OK, thanks. I'll give it a try and let you know what it does.

[Dim3nsioneer 557]

Maybe also worth checking is if the glass of the printed bed lies properly on the aluminium of the heater pcb and not only on the heads of the screws.

[jeex 35]

Will check glass contact with alu as well. Thanks.

Now i'm making a test print for the hinge i made for the board. If ready, i'll share the whole thing here.

Thanks.

[jeex 35]

Glass contact is OK. Glas temp is around 60. Brim helpen on a smaller part. Still must try on a bigger thing.

Now for the promissed design: it is the proto and demo version of the board of a board game. Two identical parts, with thwo small hinges.

Two screws keep the two parts together. Two small magnets keep the board closed. The stones, 14 in total, are kept within the box. The whole closed box is 130x105x50 mm.

One half, bottom side.

Two halfs together with hinges.

Ready to play.

[jeex 35]

Also with brim the lower corners curl up. As you can see in the photo, the brim goes up with it.

Personaly i think it is because the surface is too long on the heated bed. It shrinks.

Other suggestions?

Is it possible to add lines to the gcode so that it turns down heating of the glass plate? Just for experiment?

Edited May 31, 2015 by Guest

[jeex 35]

Result is nice, looks real good. But the whole first cm has shrunken by 10%. Got the tip of printing the first layers real slow for better adhesion and than lower temp after 5mm.

More tips are welcome.

[gr5 2,167]

First of all the corner that you circled in red looks perfect to me - it looks just like your blue CAD image - rounded corners.

The lifting is caused because the upper layers cool to air temperature and shrink pulling very hard inward on the upper layers. Imagine someone stretched a rope from two opposite top corners of your part after it had printed 30 layers and pulled that rope very tight. What would give first? The bottom corners.

If brim wasn't enough add glue.

60C actually works better than 50C which works better than 30C on the plate for different reasons. At about 40C and hotter, the when the bottom layer is created the filament takes longer to cool and spreads out like honey and there is less air between the glass and the filament so there is more surface area and it sticks better. Also at 60C you are now above the glass temperature of PLA (about 52C) and the part is more likely to warp the bottom 5 layers every so slightly than to lift off the bed. The warpage is so incredibly tiny that you can't see it and probably can't measure it but it releives the stresses enough to keep the part from lifting off the bed. At 70C you get a new problem - lets not go there now.

For glue - use glue stick or elmers wood glue. put some on the glass bed and then add 10 parts water and mix it around with a tissue or paint brush on the glass until it's very thin. When it dries the glue should be invisible (unless you scrape it back up with your finger nail or a knife).

This will stick very well and if you are having trouble removing the part, let it cool to room temperature first.

[gr5 2,167]

Oh - you asked how to change the bed temp. The easiest way is you can mess with all kinds of settings in the TUNE menu while printing. But if you want it to happen automatically there is a "tweakAtZ" plugin that should do it for you. Feel free to try lower bed temperature but I have tried this and I can tell you it will usually make the part come off the bed completely because the glass and the part shrink at different amounts as they cool.

[jeex 35]

Thanks for the reply.

If you look at the image closely, you see even the brim coming up from the plate.

I'll try the glue as well as changing temp and reflect the results here.