Cable holder in magenta PET-G, but at a price

One of my daughters saw the phone cord holder I had made (designed by Lay3rWorks) and wanted a smaller version. Fortunately it was provided as a Fusion 360 file so I could import it and make changes. Although it was a parametric design, it wasn't fully automatic so I had to manually split the parts and recombine them. Not a very big deal.

She liked the magenta PET-G I have (by eSUN) so that's what I used. The first one had a problem: I had used a 15% infill and the top deck did not bridge that nicely, so it ended up with holes. Usable, but ugly. It also had a moderate amount of stringing between the upright dividers. And there were a couple of dark patches, like scorched plastic.

So I put some more thought into the settings. Now that I'm using Simplify3D I have more options.

• I set the base to 50% infill both to fix the upper deck, and to give the product more weight and a lower center of gravity. The upright dividers are joined to the base by a pretty narrow rectangle, and I was a bit worried about it breaking in the long term, so I set several layers around the joints to be 100% solid. Then the rest of the layers (most of the dividers) back to 15%.
  
• I had been using 245C for all my PET-G prints so far, and that's in the upper end of the recommended range. That can cause stringing. So I varied the temperature in the different sections of the print. The base was still 245C for good adhesion. I reduced the joint area to 240C, and the dividers to 235C to try to reduce stringing and scorching. The bed temp remained at 85C throughout.

Here's the result:

I was away for a while after the second print finished, so the print had time to cool on the bed. It popped off easily by hand, no razor blade needed. I've found that PET-G usually comes off nicely after it cools.

But the print had some weird lumps on the bottom, in a slightly different color. Chips of glass, stuck very tightly! I had to use a perpendicular X-acto knife to clean them off.

So now my print bed is chipped, right in the middle. Two big chips and a little one. Plus a scratch.

I imagine I've set the stage for the chips by using a putty knife to pry or tap off other prints that have been very stuck. PLA can do that. Often PLA will self-unstick if I let it cool thoroughly, but I've learned that only recently. And in trial-and-error printing, it's inconvenient to wait 30 minutes or so to remove a trial print.  So I imagine I had caused some tiny chips. Repeated heat stress probably caused tiny cracks to propagate. With PET-G I use a much higher bet temp, 85C. But I hadn't done that since in two months, so maybe the glass was damaged during that time and was prone to chip the next time it got really hot?

It seems unlikely that the PET-G just really stuck in those spots and caused the break, since I did not apply a lot of pressure to remove the print. I'll have to do some research to see if this is common. Will these chips now propagate worse? Will that scratch turn into a crack? I know from limited experience that that's how we cut glass: scratch a line with a tool and then stress it. I'll do some test prints, and will have to avoid the center of the bed.

I could just buy a replacement bed from Robo3D, but I think there are options. I have seen mention of some removable, flexible bed materials which make prints pop off more easily. So I'll do some reading before buying.