3 is fast like Methylene Chloride. Use 4 instead to give you more time. 40 is good for not so perfect joints but has a short shelf life. 40 works well for pvc to acrylic. 16 sucks in most cases.

Maybe a good idea at this time of year to read the warnings listed on this link. I'm thinking there may be reduced ventilation in your work area due to heating your space.
http://www.ipscorp.com/industrial/in...ltnpdf/PB4.pdf

not to go off topic but..

The link suggests annealing to prevent prevent crazing, how is that done with acrylic?

Easiest way to prevent crazing is to use cast material. Extruded is a crapshoot. Since the boss said no to anealing in the kitchen oven I used to warm up the extruded and bent parts beside my woodstove (not in the house) for a few hours. Here's a cut and paste explanation,

To anneal acrylic sheet, heat it to 180°F (80°C), just below the deflection temperature, and cool slowly. Heat one hour per millimeter of thickness – for thin sheet, at least two hours total.
Cooling times are generally shorter than heating times – see the chart below. For sheet thickness above 8mm, cooling time in hours should equal thickness in millimeters divided by four. Cool slowly to avoid thermal stresses – the thicker the part, the slower the cooling rate.

Hobby shops and model shops sell something similar to weld-on, I have a bottle which lists acrylic as one of the materials it bonds. I have used it to make some acrylic racks a long time ago.

Yeah, that's what I ended up doing. I got a bottle of methylene chloride for $6 in a hobby shop by the name proweld. It looks like the equivalent of weld-on #3, very watery and thin with an applicator brush in the bottle attached to the stopper. Anyone ever hear of it? Is it safe?