I generally prop and clamp the bonded areas so they aren’t touching anything. I have, however, used concrete pavers and aluminum foil. A key thing would be to not leave the piece sitting in a pool of Weld-On.
To clarify for your use case: put a piece of something (cardboard, Dradtboard) under each side of the butt join with the joint itself suspended in space between them.
For one project, I cut a slot in a single piece of Draftboard to do that, clamping each side of the joint to the board to hold it with pressure.
I use the lid of my GF to assemble most projects, including those cut from acrylic and using w/Weld-On. I just scrape it down with a sharp razor blade when it starts to get cruddy. Right now you can barely see thru it with all the wood glue that’s on it!
If you are paranoid, however, you could always used the crumb tray.
I use Acetone to join Acrylic. It’s a true solvent, no actual adhesive. Surfaces mated together melt and merge and the Acetone evaporates and I’m left with a joint that’s generally as strong as the surrounding plastic. To join at right angles, I’ve got a set of adjustable-angle corner clamps. Set 'em at 90º, clamp the pieces making sure the seam I’m going to bond is straight and gapless, then I hold it so the seam is vertical and I get a drop of Acetone and run it down the inside angle of the seam. If it’s a long seam, I might drip another drop or two further down the seam. Wait 10 minutes, remove clamps, parts bonded. Since I’m not clamping the parts to anything except themselves, there’s no worry about them sticking to anything. But the Acetone isn’t glue, so unless I go nuts with it there’s nothing for anything foreign to stick to.
I’ve tried to break Acetone joined pieces and often times the break occurs someplace adjacent to the seam, the seam itself doesn’t fail.
My wife’s nail polish remover can be used in a pinch, but “industrial” is best. And the stuff is cheap.
if you have the same experience as me, it’ll evaporate out of the can before you need it again
Someone recommended drilling the tiniest hole in the inner cap vs removing it and then using a squeeze bottle needle applicator to get it out of the can and apply it with the least possibility of future evaporation.
Acetone I always have around for cleaning metal projects I work on and that doesn’t seem to evaporate out of its container.
I think the stuff I have is 90%. But nail polish remover is 70% Acetone. Yes, it’s quite flammable. But not much more than many other household chemicals. There isn’t that big a difference between the flammability of 70% and 90% and few people set themselves on fire doing their nails. Even while smoking cigarettes.
When bonding Acrylic with Acetone, you literally use just a few drops. If the mating surfaces are relatively flush, the Acetone quickly wicks along the seam and any place the two surfaces are in physical contact (or just about), they will bond together. Only a tiny amount of Acetone is required, you’re not softening the entire thickness of the Acrylic, just the surfaces.
I’d say your risk is no worse than if you doled out a few drops of gasoline on to your workbench.
Note, this is quite a bit different than using Acetone to finish a ABS FDM print (which I do). For that, the Acetone has to be heated in to a “thick” vapor. That’s a serious risk and should only be attempted if you know what you’re doing. I would say the risk here is about the same as cooking Meth. (not that I know how to cook Meth).