Im building a resevoir out of acrylic and had a few questions.
1. Im pretty sure the adhesive i want to use is IPS weld on #4, anyone know anything about this stuff?
2. Im goin to be using 1/2in OD barbs with 1/2in OD threads on it, my question is how big of a whole do i drill. Im thinking I need a 15/32" drill bit so as to not be to big of a whole that the threads dont grab onto anything. I measured the holes on my old criticool res, and they look like 15/32" .

Just wondering if anyone has any experience with this?

Weld On is good stuff, and you will need to tap the holes for your barbs. Buy a 1/2 NPT thread tap, it will say on the package what size drill bit you should use.

if you are using a 1/2 20 (or half inch dia. with 20 threads per inch) tap then you use a 29/64 drill bit. keep in mind it is always better to go smaller than larger. taps are made to remove material and since its acrylic its ok co go a little smaller.

acrylic weld #4 is great stuff, its strong and it works really fast. i have heard thought that water and other liquids will break down the bond after a while. i cant verify this so the only way to find out is to try.

There's a guide for acrylic cement around here somewhere...

suppoesdly the homemade cement with acetone and acrylic is better since it would be welding acrylic to acrylic. it should be under the guides section. ive used it along with zen and almost everyone else here who has stuck together some acrylic pieces.

Here's the link.

Quote: Originally Posted by carbongraphite suppoesdly the homemade cement with acetone and acrylic is better since it would be welding acrylic to acrylic. it should be under the guides section. ive used it along with zen and almost everyone else here who has stuck together some acrylic pieces.

Weld On does the same thing it just has no solids in it. It is not an adhesive, it is a molecular bonder. It melts the acrylic together so to speak. The only thing bad about Weld On is that the pieces need to mate PERFECTLY to get a good bond. The home made cement will do better if the pieces dont mate so well as it has solids in it to fill gaps and such.

Fantazmic2 has some great tips in his how too as well......Here

Thx for the info, the drill bit i need is around 15-25 dollars If i went through with the project it would cost the same as something exotic from germany or something

Ok so i found this site
that says i should use a 23/32 drill bit for a half inch tap. Am i crazy or isnt 23/32 larger than a half inch, therefore there would be nothing to tap out as the hole would be to large.

you are correct, if 16/32=1/2 then anything >16 = too big FOR CLEARANCE HOLE (where nothing touches the sides)....they are way off. there are different pilot hole sizes ....it depends on the thread you are using. i assumed you were using 20 threads per inch, there are other thread counts. the more threads the larger the bit and the fewer the threads the smaller the bit usually. you can always wing it. go 2 sizes smaller than the clearance hole of the tap.

oh yeah...you might want to check out weld on #16 too.

Quote: Originally Posted by TypicalSloan Ok so i found this site that says i should use a 23/32 drill bit for a half inch tap. Am i crazy or isnt 23/32 larger than a half inch, therefore there would be nothing to tap out as the hole would be to large.

thats only a 1/32 off from a 7/8 hole. thats way too big. you sure your reading the page right? :S

you DEFINATLY wana talk to Zennzzo about this, trust me he knows how to work with acrylic.

Quote: Originally Posted by Spc. Forces Bob you DEFINATLY wana talk to Zennzzo about this, trust me he knows how to work with acrylic.

Yes i do! Drill bits are freaking expensive ($15.00+) i cant afford to buy more than one if i get the wrong size. Taps, and thread counts confuse me, all i know is that i have a 1/2 OD brass fitting that needs to go into the resevoir, its got to be easier than im making it.

You will need a 1/2 inch drill bit and a 1/4 inch NPT tap. NPT is the National Pipe Taper designation, and it does not correspond with the actual diameter of the pipe being tapped. Unless the hose barb fittings are some sort of metric or BST designation, the thread count shouldn't be an issue. Log on to McMaster-carr.com and do a search for pipe fittings or hose fittings, and they will have all sorts of charts explaining the different designations.
It's probably overkill, but I sometimes back up my solvent bonded acrylic seams with silicone fishtank sealant. I have heard of very rare occasions where the weight of the water in a large reservoir will push acrylic panels apart over many years.

npt stands for national pipe thread, and they measure pipe by the inner diamater(ID) that is why the measurements seem to not mach up.

Ah, thats why the inner and outer diameter threw me off.

For anyone wonder what the correct drill bit and tap are I asked danger den what they used on their blocks heres the response,

"Our fittings are 9/16" threads so if you drilled out the holes 15/32 and
tapped them with a 9/16" straight tap you will be set."