Seam lines of bonded pieces unstable; repeatedly form 'bumps' after sanding

Hello, all;
I’m using my Form 2 to produce pieces larger than its build volume, by splitting the hollowed pieces up and adding alignment pins in software. I then dab resin around the perimeter, use a UV laser to cure the pieces together, and then UV-bake the whole thing for an hour to harden it.

However, after sanding the resulting seam flat, I often come back a day later to discover that the seam line, previously made invisible, has raised up and caused a line around the piece. Could this be a thermal expansion thing? My walls are only 2mm thick so I would hope that all the resin inbetween is being cured.

Photo of the seam here:

If you are using resin like just a paper thin layer between two tightly fitting parts there is nor real volume of resin to polymerize- and laser light can not penetrate deeper than 0.1 mm deep into the crack… so I think you are seeing uncured resin weeping out.

You should cut a groove between the two parts you can fill with resin a thin layer at a time lasing it in several applications… until its proud enough to sand flush.

BTW - why does it look like so fuzzy?

I’ve seen plenty of people using this method to cure parts together - surely longer exposure to UV will allow parts further in to cure? The curing can’t just stop at 100 microns, it must drop off gradually the deeper you go. Even 0.5-1mm would be more than enough.

I’m prone to agreeing that it’s not curing completely, though - I’m looking at getting several higher power UV floodlights to really penetrate the resin from all sides.

It’s fuzzy because it’s been sanded, so you’re seeing powdered resin and coarse sanding lines :slight_smile:

it depends on the resin.
Pigmented resins stop the UV pretty solidly.
I use a 200mw laser pen, and if I try to cure pigmented resins deeper than .5 mm they don’t cure all the way thru.
Its WHY the Form2 does not have thicker layer settings.

But the thing is the Polymerized resins stop UV even better unless they are the clear resins.

the thin Crack with just barely any resin on it is just not going to bond all the way thru.
Its like shining a light at the edge of a piece of paper…

More intense UV lamps won’t help either- they might even cause a problem with the cured parts.

I cut a .5 mm groove between mating parts so that I can fill that groove by brushing in a very thin layer of resin, lasing it- then another layer- lase it… and so on for about 3 to 5 passes.

I get solid bonds that sand across the joints smoothly and are fully cured without additional post curing.

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