Steve,
You are right, sort of. Weldon 3 and 4 will work as will weldon 16 with extruded. The problem is you may get some crazing with anyof these products. Weldon 5 should not craze or at least craze as much.
From IPS page :
5 - Water thin, slow-setting solvent cement for bonding acrylics. Also bonds styrene, butyrate, PETG and polycarbonate to themselves. Will not bond to cross linked acrylics.
Since annealing is not an option for the average person, a slower setting cement should help. Weldon 5 is more expensive, but you also get a lot more.
As for the weldon 40, you will find that you get a much better joint when gluing PVC to Acrylic. IME, Weldon 16 will work when glueing PVC to acrylic. It has a tendancy to shrink, and seems almost too hard compared to the Weldon 40
Anyways, that was not my point.
After all the running around to 2 or 3 different stores, inhaling a bunch of nasty chemicals and then possibly having to do something over again because you screwed up a joint.
It may be more time and cost effective to just buy one.
I am not trying to stop anyone from DIY projects, that is what makes this hobby so much fun for me, and I believe many others as well.
I just hate to see someone spend a bunch of money only to realize they could have done it cheaper and easier.

Cheers,

Al

Harvey,
you are right about cure strengths. I never really paid much attention, but here are the numbers.
Lap joint bond strength is based on using 1/4” thick substrate with 1 square inch bonding area.
Weldon 3,4 and 5 all give 2500 PSI after 1 week of curing
weldon 16 is actually less at 2200 psi
and weldon 40 rocks at 4000 psi

Willow,
I don't bother with Keyholes for the Kalk reactor. I actually use nylon bolts. When I clean the reactor, I just fill the tube through my 1" union and the dump out through the same hole. I guess it might be worth it once in a while to actually open it up and give it a good cleaning.

Cheers,

Al

it is very well worth doing a Kalk reactor as a DIY, you could easily save 50.00 +tax and shipping. it is one of the easiest to make and there is no science to it whats so ever. Ca reactors take a little more though and a lot more fittings but the savings is there also. The skimmer takes the most research and planing to make.

Steve

Can you send me the link from that Page? weird IPS would say that and the weldon page its self doesn't even mention acrylic under 5 and in fact points to extruded plastics not acrylic.

as for crazing, I think this is a rumor created from companies trying to justify there price of there products because the chose to go with cell cast for better looks. extruded doesn't crazy because of the glue or because it is extruded, it crazes for the same reason as cast, stress points caused by gluing edges that were not done properly or precise enuf. the major cause is using the wrong types of blades to cut acrylic, not getting a flat edge and flame polishing.

Steve

Here is the IPS link.
I found out about Weldon 5 when doing some work with Lexan MR10. I called their tech support and drilled him with a bunch of questions. I am not completley sold on your crazing theory, but you may be right. A theory I came up with may be ther slower setting time with the Weldon 5. Perhaps it doesn't shrink as much when drying. Thus reducing the stress on the joint. This is just coming out of my butt as I type, so I may be way off.
The weldon 5 bottle also has in big type that is is meant for extruded acrylic. I have leant the glue to another reefer, or I would take a picture.
http://www.ipscorp.com/ind_html/acrylics.html

Cheers,

Al

hmm neet, I wonder the why differences on the sites, definitely worth looking into when I am out and about next time.

Steve

I think I paid 25 bucks for it in Edmonton, and had to get it shipped from GE in Burnaby. I think the price per ml is the same as 3 or 4, you just have to buy a bottle instead of a small can. I don't think that you can get 5 in the can.

Al