Acrylic tube - cutting holes and bonding?

[Reef55]

I am looking to build a skimmer out of cast acrylic tubing (12" diameter). It will be an external though (not in a sump).

Two questions:

1) What is the recommended way to cut holes in the acrylic tube?

2) I would prefer not to use uniseals for an external skimmer... is there a way to bond pvc pipe fitting directly to the acyrlic tube, or is this not recommended?

Thanks!

Mark

 

[blfuller123]

Mark,

I usually drill the tube (with a drill press) and then tap the holes with the appropiate size tap. When I screw the fitting in, I use the weldon #16 on the thresad to seal it. I dont like uniseals either. Where did you get the 12 inch tubing?

 

[ErikS]

I'd concur w/ the #16 - it's good for low pressure apps (which a skimmer is). I've had better luck drilling acrylic with hole-saws. Larger drill bits seem to catch & crack. Up to 1/4" NPT I use a drill bit (7/16"), after that it's a hole.

YMMV

 

[Reef55]

Thanks for the replies.

When using a hole-saw, what do you do to secure the acrylic? Do you put anything on the inside of the tube while drilling? Also, any sources for taps?

Thanks again

Mark

 

[ErikS]

Taps? McMasterCarr - if you're not doing a lot then you can use the carbon (fine for acrylic)....about $6 each.

I've only done a few for CA/Kalk reactors.....just glue on the base & then drill the hole. Hole saws more "grind" their way through - less chance of a catch. I support the tube in a jig - simply two strips of wood with 45* bevels nailed to another piece.

Again.....YMMV.....not fond of drilling/cutting tubing....yet :lol: (as you're aware that stuff is EXPENSIVE and you only get one chance)

 

[Reef55]

ErikS,
Do you have a link to a $6 tap? I looked at McMaster, and for a 1" tap, the cheapest I found was $31.

http://www.mcmaster.com/itm/find.AS...DtlLink&fasttrack=False&searchstring=2525A117

Mark

 

[ErikS]

You're right, I'm sorry I was thinking smaller taps :lol: forgot you were doing a gia-gun-dous skimmer.

How about here - $14:

Whole Sale Tool - 1" tap

or a set for $28:

Whole Sale Tool - NPT set

I have this one, high speed steel & will cut acrylic forever:

Whole Sale Tool - HSS NPT Set

 

[blfuller123]

A hole saw is easier to drill, but it is hard to find a hole saw in the correct size for a tapped hole. With a larger bit, you just have to drill as slow as possible and let the bit do the cutting. Not putting much pressure on the bit.

 

[ErikS]

What I've found -

1/4" NPT = 7/16 (never seen a holesaw this small)
3/8" NPT = 5/8"
1/2" NPT = 7/8"
1/2 pipe (sch 40 OD) = 13/16"
3/4" NPT = 15/16"
1" NPT = 1 1/8"

 

[blfuller123]

This is the table I use.

TAPER PIPE SIZES - NPT

----------------------------
TAP DRILL
SIZE SIZE
----------------------------
1/8-27 R
1/4-18 7/16
3/8-18 37/64
1/2-14 23/32
3/4-14 59/64
1"-11-1/2 1-5/32
1-1/4-11-1/2 1-1/2
1-1/2-11-1/2 1-47/64
2"-11-1/2 2-7/32
2-1/2-8 2-5/8
3"-8 3-1/4
3-1/2-8 3-3/4
4"-8 4-1/4

 

[Reef55]

blfuller123: can you explain what the table is trying to say please? thanks

 

[ErikS]

Yep....pretty much standard...but since the tap is removing material AND we're not generally holding things together with them (if they're a tad shallow).

3/8 = 37/64 = 4.625/8 = pretty close to 5/8
1/2 = 23/32 = 11.5/16 = pretty close to 11/16 (oops, made a mistake on that one)
3/4 = 59/64 = 14.75/16 = pretty close to 15/16
1" = 1 5/32 = 1 1.25/8 = pretty close to 1 1/8"

Are they exact? Nope, but we're not holding anything together with them either. They will be water tight, even if the threads a an iota shallow. Most of these the threads will be cut to full depth & the tap will just be removing a bit more material - a bit tougher to tap.

13/16 is the outside dim on 1/2" sch 40 pipe - #16 & you can glue it in place.

The table is NPT size - threads/inch drill size

 

[blfuller123]

It is just a closer tolerance. I am sure the other sizes will work fine. Just the table I use.

 

[ErikS]

Lol - yep. Wasn't trying to be antagonistic, just giving a "gump" work around (I have the actual sizes, just never been successful drilling with them....not enough speed range on the DP I imagine).