Design 'looks' good, but coming out a mess; please help!

david_osborne052

Hi guys; please help!

I'm a budding craft chocolate maker and am trying to create a mold design that I can vacuum thermoplast with polycarbonate, to make it food-safe. The first stage, of course, is creating a design bar. I've got one now - titled 'Chocolate Mould - Celtic Triquetra with a Circle' in Onshape public: 

https://cad.onshape.com/documents/1664b01f29d756dd2b1cc439/w/62672770f299668716a87844/e/0d718f81255921b8e4a58f99?renderMode=0&uiState=643f8edf9b5cff061ddff8d3

So the problem I'm having is whilst it looks okay on Onshape, it comes out a complete mess. I'm slicing with Ultimaker Cura and have tried the recommended settings on Ultimaker Cura for my printer - an Anycubic Kobra Max - with standard PLA, as well as trying settings more tweaked for finesse which I got from forums suggesting how to perfect your Benchy. My Benchy prints are looking fine - I've put a picture here to demonstrate this - so I don't think it's a hardware issue. I've tried several different PLAs and they've all been de-humidified and pre-heated to 40'C in a 3d print filament harness. I've tried from 5% to 50% infill, to see if that helped; it hasn't. I've tried down to 60mm/s printing speed; didn't help.  The printer nozzle keeps bumping and scraping into the print once the lines start going mad; the first few layers are perfect, and I've preheated and auto-levelled my printer bed, so it isn't that. I tried from 0.1 to 0.5mm Z-offset; it didn't make a difference. Unfortunately this forum doesn't allow me to upload the gcode.

Any help would be much-appreciated!

robert_scott_jr_

Hello David. Does the nozzle go 'mad' at the same point in print every time? When it does go mad, does it do so in a completely random fashion or does it appear to be continuing in logical pattern as if it's continuing to print the code but in the wrong place or at the wrong time? - Scotty

_anton

It sounds like the solid bottom layers print fine but the print head catches on the infill when that starts printing? Turning on z-hop might help. Or decreasing extrusion rate.

Separately, though I like the pattern, it is pushing the resolution boundaries of an FDM printer. :P Some of the walls are thinner than the 0.4mm nozzle size most printers use. I think you'll want to make those at least one print line wide.

david_osborne052

Hi Scotty,

It seems to continue on what seems a logical, organised and predetermined programme, though the print starts to look disorganised, with splodges being built upon in subsequent passes, making the nozzle collide and scrape up and down the now-firm splodges. I'm not sure if that helps, though if you spot anything in the design itself in Onshape, it would be good to know. I had some trouble getting the celtic pattern onto each choc square and wondered if that had something to do with it. That, or settings for Benchy have to be very different to one for a choc bar!

nick_papageorge073

Are you new to printing? Your CAD seems fine, I can't imagine its a CAD issue.

The reason I ask, is I've been sending CAD to our rapid prototype shop at my dayjob for 20 years, where we have commercial printing machines and a staff to run them. I just push a button, and a couple days later go pick up my perfect parts. Then 3 years ago I bought an FDM hobby printer for my house. How hard can it be, right? After a year of using it, and only about 30% of the parts printing nicely, I was ready to throw it out the window. It was on the higher end of "consumer printers" too, a Qidi Max.

Anyway, I finally figured out it was my build plate. I bought a PEI build plate from amazon for my printer https://www.amazon.com/gp/product/B08HW9P1FM/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

and I bought this special spray from 3D Lac. https://www.3dlac.com/3dlac/3dlac-product/

Its a joy to use now. I've had this setup for 2 years, and every print has been perfect. I don't know if this may be your issue, but maybe look into it to see if other users with your particular printer might have switched to a PEI bed and 3D lac spray and had great results. I absolutely hated printing before this setup. Now, its great.

Edit to add, I was having similar symptoms as you. There would be a stringy mess half way through my prints, and/or jammed head. I never dreamed it was the bed. I took the whole heating nozzle system apart to clean it. I even replaced it entirely. I think what was happening was there was very minor defects on the first layer adhesion, that propagated through the layers, but maybe didn't cause the print head to collide until half way through the print.

david_osborne052

Hi Scotty,

It seems to continue on what seems a logical, organised and predetermined programme, though the print starts to look disorganised, with splodges being built upon in subsequent passes, making the nozzle collide and scrape up and down the now-firm splodges. I'm not sure if that helps, though if you spot anything in the design itself in Onshape, it would be good to know. I had some trouble getting the celtic pattern onto each choc square and wondered if that had something to do with it. That, or settings for Benchy have to be very different to one for a choc bar!

david_osborne052

nick_papageorge073 said:

Are you new to printing? Your CAD seems fine, I can't imagine its a CAD issue.

The reason I ask, is I've been sending CAD to our rapid prototype shop at my dayjob for 20 years, where we have commercial printing machines and a staff to run them. I just push a button, and a couple days later go pick up my perfect parts. Then 3 years ago I bought an FDM hobby printer for my house. How hard can it be, right? After a year of using it, and only about 30% of the parts printing nicely, I was ready to throw it out the window. It was on the higher end of "consumer printers" too, a Qidi Max.

Anyway, I finally figured out it was my build plate. I bought a PEI build plate from amazon for my printer https://www.amazon.com/gp/product/B08HW9P1FM/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

and I bought this special spray from 3D Lac. https://www.3dlac.com/3dlac/3dlac-product/

Its a joy to use now. I've had this setup for 2 years, and every print has been perfect. I don't know if this may be your issue, but maybe look into it to see if other users with your particular printer might have switched to a PEI bed and 3D lac spray and had great results. I absolutely hated printing before this setup. Now, its great.

Edit to add, I was having similar symptoms as you. There would be a stringy mess half way through my prints, and/or jammed head. I never dreamed it was the bed. I took the whole heating nozzle system apart to clean it. I even replaced it entirely. I think what was happening was there was very minor defects on the first layer adhesion, that propagated through the layers, but maybe didn't cause the print head to collide until half way through the print.

Thanks Nick. I've ordered some 3D Lac, which will arrive tomorrow. I'll give my bed a thorough clean and use that stuff; there are definitely some adherence issues I've never had before, so it might very well be this. If that doesn't work, I'll buy the PEI bed and try again. 

_anton said:

It sounds like the solid bottom layers print fine but the print head catches on the infill when that starts printing? Turning on z-hop might help. Or decreasing extrusion rate.

Separately, though I like the pattern, it is pushing the resolution boundaries of an FDM printer. :P Some of the walls are thinner than the 0.4mm nozzle size most printers use. I think you'll want to make those at least one print line wide.

Thanks, Anton. I Z-Hop is on; 20mm/s speed, On when retracted, On only over printed parts, with a height set to 0.1mm; would you recommend any changes to that gcode profile?? I did consider the FDM might not cut it. I've bought a better nozzle from Revo, which might improve things, though if that doesn't work out I'll probably consider getting a more sophisticated 3D printer; something that can achieve the resolutions I'm after. Any recommendations? It's probably worth mentioning that in my future bar designs I'll have to integrate some bore-holes down all the removed extrusions, so that when I vacuum thermoform them, the definition comes out in the polycarbonate print. I haven't looked into it but suspect I'll have to make those holes about 1-2mm in diameter.

robert_scott_jr_

If it's losing it's print position I don't see how it can be the build plate. Have you tried another slicer? How are you getting the Gcode to the printer? Via cable? Memory stick?

If you are looking for great resolution the I suggest a resin printer. I initially started out with a filament printer, went to resin and I'm not going back to filament. Drawback there is build size vs. printer cost. Another plus besides resolution is the lack of layers.

- Scotty

EvanReese

I have some miscellaneous thoughts:

1. Images of the print issues would help, but I agree that it's probably a slicer thing.
2. Anton is right about some of the thin walls, but it might work as-is.
3. Something else to consider with thermoforming is the depth/width ratio of your knot patterns. The plastic may struggle to stretch its way all the way down in those narrow grooves, especially since they have sharp corners. It might work, and just not fill out all the way, but my inclination would be to control it in the CAD, by drafting the grooves and filleting the edges to the exact shape you want.
4. I second the call for resin printing for this.
5. If you are doing these on a small scale, and don't need to make a ton of molds, you could consider making your mold from food-safe silicone, which will capture a ton more surface detail. You could add some very subtle textures and it will pick it up.

michael3424

here are a couple of books/resources for 3D printing that you might want to consider:

https://www.makersmuse.com/3dprintingtips
https://teachingtechyt.github.io/

Pay special attention to calibration and troubleshooting sections in each resource.  For example, I find that I have to adjust the "Extrusion Multiplier" setting for some of the filaments that I use to accurate dimensions in X, and/or Z in Prusa Slicer on my Prusa MK3s.