I accidentally sanded my print a little too much, I don’t want to reprint it since it took 12 hours, is there something I can use like clay or putty that I can apply to readd the rounded art that is sandable and that I can put primer on and paint over?
You can buy a 3d pen, melt material on the area you want to fill and resand to the desired shape.
As others have said, there are tons of fillers (Bondo, Rage Gold, glazing putties, etc) that you can use for this. If your part is flexible make sure you use something that can flex, otherwise it will crack.
That said, consider the cost of doing this in terms of both time and material $$ first and then weigh that against simply printing the part again. If you’ve never worked with fillers before you’ll have to do the apply, wait for it to dry, sand, apply more loop a few times. It’s not necessary a bad skill set to learn, but it will take some time/effort and the materials aren’t free.
Re-print the area you messed up, glue, and sand again?
Depending on the size, but I’ve had success with super glue and baking soda.
https://www.instructables.com/Baking-Soda-Reinforcing-Glue-Repair/
It all really depends on what you are doing and the conditions of the part.
I’m a former auto body shop owner and painter. This kind of thing is what I did all the time, but many techniques are tricky to do in practice.
The flexibility of the material around the repair is important. Like body fillers (bondo) are formulated to have similar properties to steel. There are specific varieties made for different plastics.
If all you need is a temporary fix for tomorrow or a few days from now, masking tape, papier-mâché, etc. You might be able to print a very thin overlay that you can glue over the spot.
In my experience, it sucks, but you’ll likely be better off accepting your mistake now and starting over properly. You would not believe some of the losses I’ve had to take when painting cars because I tried to fix mistakes like this, and even ones I had to start over. Like imagine painting an entire car, completing the job, but deciding you want to do one more clear layer over the hood where there is a slightly dry spot and your spray gun decides it hates you, a seal fails, and a bunch of fluid drips onto the surface ruining the whole job. I’ve had stuff like that happen a ridiculous number of times.
In auto body work, sanding through too much of a surface is very common. You can’t just spray a tiny bit over that surface or ignore it and get away with the issue. It is a big deal. Your problem may not be of this magnitude. It may be fixable, but beware of placing bandaids on bullet holes expecting a full recovery. My rule was to step away and take a break before assessing the situation. Emotional investment clouds one’s best judgement. GL.
