Hopeful
Posts: 6
Joined: Tue May 02, 2017 7:40 am

Struggling with a large flat base in ABS

Mon Jun 05, 2017 7:19 am

I have a Mass Portal Grand Pharaoh XD 40 (Made in Latvia), that has a bed of 400mm diameter and can print up to a height of 400mm, that I bought because it can print to a large size, but have struggled relentlessly, often ending up with a pile of spaghetti.

In desperation, I take time lapse movies + photos incl. thermal images to analyse and send out to support in Latvia.

This build is a mounting bracket with a flat base approximately 200mm square, material is ABS.

Latest issues have been to get the first layer to start on the BuildTak, with the machine calibration utility only providing relatively crude adjustment, then me twiddling the three thumbscrews for ages to get the bed suitably level and having to lower the first layer too much so it all takes without lifting in the middle at some point (I have loads of time lapse movies of this happening).

So, with a successful (very thin) first layer, I left it printing over night, but in the morning, find a pile of spaghetti waiting for me.
The bed temperature should be set to 110c for ABS, but because of experience on other large prints, I have reduced this to 90c, with the nozzle at the recommended 240c

On the time laps, you can see it going wrong at what appears to be layer 3 with one corner lifting, so presumably this is warping, but with layer separation?
This forum site did not allow me to upload the movie, so I have put this + a selection of other images & the factory file inside a Zip file on this dropbox download should anyone wish to look (158Mb):

https://www.dropbox.com/s/urcb6kys4zg41 ... 3.zip?dl=0

All thoughts gratefully received:

JimDrew
Posts: 2
Joined: Wed Oct 07, 2015 12:25 pm

Re: Struggling with a large flat base in ABS

Thu Jun 08, 2017 3:18 pm

I only have success (perfect success) printing ABS with the bed at 60C, and using a white glue stick as the base.

Apply the glue stick to clean glass and let it dry completely - THIS is the trick. If you don't let it dry for at least 15-20 minutes after applying it, then it breaks loose (or lifts) during the print. Once it is dry I take a microfiber clothe and rub the applied area (using not a lot of pressure) every direction to remove any glue that might be sticking up. You can feel the surface afterwards and it should be pretty smooth. After that, I heat the bed to 60C and print.

I think that if you etched the glass with Flouric acid, that would provide a similar surface to the glue and should hold well. I have a new piece of glass coming that I will try this with. In the mean time, I can print any type of ABS available using the above described method.

MikeO
Posts: 32
Joined: Fri Jun 26, 2015 3:17 pm

Re: Struggling with a large flat base in ABS

Thu Jun 08, 2017 7:39 pm

A couple of thoughts:

1) If you enclose the printing area -- even with a simple cardboard shield around the printer -- it'll help hold in the heat from the bed and will *reduce* the problem. Be careful not to include the electronics control box in the heated area, though! And there are limits to how much heat the steppers, etc. can take.

2) ABS isn't a good material for large items like you'e described -- it simply has too much shrinkage on cooling, causing the warping. Also, as the part is built, you may see splitting between layers with ABS, as the build proceeds higher and the stresses build up.

I've tried building tall (180 mm or so) parts in ABS, and never had much luck in my barely-enclosed printer. If they're wide they curl up, and if they're tall they develop layer-to-layer splits as they get higher.

My recommendation:

Switch to using PETG or PLA. PETG would be my recommendation, it's got about the same high-temperature tolerance as ABS, but with very little warping.

PETG has its own issues -- it's stickier and tends to stick to the nozzle and cause buildup over time -- but once you get settings dialed in it's pretty much trouble free.

You still may want to do some sort of quick-and-dirty enclosure around the printing area, even with PETG, but your warping problem will be FAR less with PETG than ABS.

I started out using virtually only ABS, but now my default choice is always PETG.

Hopeful
Posts: 6
Joined: Tue May 02, 2017 7:40 am

Re: Struggling with a large flat base in ABS

Mon Jun 12, 2017 2:32 pm

Two very interesting and helpful replies, thank you.

I had thought taking the bed temperature lower than the 90c I have tried (recommended is 110c for ABS) would be the cause of shrinkage problems not solve them, but it is interesting to see 60c recommended. I will certainly try.

This printer comes with a glass bed, that I use BuildTak on, however this is a very expensive surface and is damaged very easily, so I note with interest the glue stick suggestion, but if printing directly on glass worry about damaging my one and only glass plate (CNC shaped and from Latvia).

I have been recommended this glue spray to help with adhesion to the bed:
http://www.aprintapro.com/printafix/
Are there recommendations on other glue (sticks) I should be looking at?

I like the suggestion of PETG and have been thinking of giving this a try, mainly because of finished strength. Given its stickiness, what would be the best bed suggestion so it sticks enough but is not impossible to remove?

For your information, this Mass Portal printer comes with clear acrylic panels all around, although because it is relatively large, the enclosed space is also relatively large and I have wondered if adding heat into this area would help with shrinkage?

MikeO
Posts: 32
Joined: Fri Jun 26, 2015 3:17 pm

Re: Struggling with a large flat base in ABS

Fri Jun 16, 2017 3:46 pm

I print with PETG on a PEI bed (TAZ5 printer), and PETG really wants to bond to the PEI surface.

So for me to use it with PEI I have two choices:

1) Use a very thin glue layer, which can be dissolved away after printing with water or isopropyl alcohol (IPA). That way any direct adhesion between PETG and your build plate never happens.

2) This may not work with a glass bed, but it does with a PEI bed: I print on the bare bed, but keep the bed temperature VERY low. I run my PEI bed at between room temperature and 33 degrees C or so, with warmer temperatures giving higher adhesion. If I absolutely HAVE to run the bed much hotter, I have to use glue (usually Elmer's Washable School Glue).

So from my own experience, I'd think your choices are either glue or to experiment with bed temperatures, starting at room temperature and going upwards to see if it starts getting harder to get the part off of the bed.

Of the two, I think glue is the safer choice for your situation. The glue *will* dissolve in water or IPA, given enough time. So that safety net will always be there, even if it means letting a print sit overnight. It does need to be a pretty thin coat, though. Just a "visible haze" on the surface works for me.

Please let us know what solution you end up using, so others can learn from what you did.

Hopeful
Posts: 6
Joined: Tue May 02, 2017 7:40 am

Re: Struggling with a large flat base in ABS

Sun Jul 09, 2017 9:13 am

Thank you for your help and my apologies for the late reply. I have bought a reel of PETG and some Elmer's Washable School Glue, that I have started using regularly on the BuildTak also with ABS and it does improve adhesion as well as removal with the advantage of washing off with a damp cloth.

The PetG I have only used with small models so far, but 100% successfully with the bed temp at 30c. I have yet to establish the mechanical properties for PETG as the blurb claims it to be stronger, but I would also say more brittle. I am anticipating this will solve the problems with larger prints…

As suggested earlier in this post, I now only print ABS with a bed temp of 60c… again a big improvement. (Now onto other problems, that I will post separately.)

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