Drilling acrylic bottom - hole spacing safety

[Ben’r]

Anyone with acrylic knowledge? I’m thinking about drilling another hole for the return (the drains are a 2 in 1 set up.) The holes will be 100mm (4”) ₵ apart, or 170mm (6.6”) far edge to far edge. The overflow is just a slide over box, won’t be bonded to the base so no added structural bracing.

Otherwise I just go back to running it externally in the wall. Fresh water top off RODI tubing will need to be run external anyway so no biggie.

Basically, after opinions on structural integrity; 5/6 or 15mm base. Holes centred 100mm or 4” apart. One 50mm or 2” hole, the other a 25mm or 1” return. Don’t want any flexion or crack forming between hole A and B.

Cylinder is 850mm or 34” round, by 675mm or 27”? Tall.

Cheers, B.

 

[UncommonSense]

Anyone with acrylic knowledge? I’m thinking about drilling another hole for the return (the drains are a 2 in 1 set up.) The holes will be 100mm (4”) ₵ apart, or 170mm (6.6”) far edge to far edge. The overflow is just a slide over box, won’t be bonded to the base so no added structural bracing.

Otherwise I just go back to running it externally in the wall. Fresh water top off RODI tubing will need to be run external anyway so no biggie.

Basically, after opinions on structural integrity; 5/6 or 15mm base. Holes centred 100mm or 4” apart. One 50mm or 2” hole, the other a 25mm or 1” return. Don’t want any flexion or crack forming between hole A and B.

Cylinder is 850mm or 34” round, by 675mm or 27”? Tall.

Cheers, B.

You’ll be fine, especially if you connect both of the pipes together for rigidity!

Example of danger-close bulkhead placement, my acrylic hexagon’s drilling template/guide:

3/4” (19mm) between bulkhead holes, inside a 5-3/4” (~144mm) ID circular island overflow…

— this works at such extreme proximity because I made a plate of ~1/2” (12mm) acrylic identical to the above plywood template, which all four tank bulkheads also pass through, along with the 6mm tank bottom…. effectively giving me 19mm X 19mm in minimum acrylic cross-section between each bulkhead hole!

— note that I also have polycarbonate “brackets” around all four standpipes inside the overflow box to hold them together in space, preventing any torquing on any one bulkhead fitting…

(Reference my aquarium showcase if you’d like to get some interesting ideas for your very similar build! Particularly in regard to bonding down an island overflow box to the bottom of an acrylic tank reliably!)

 

[Ben’r]

Hey mate I really appreciate the quick reply! That is basically the answer in a nutshell! The 12mm acrylic is not bonded to the tank but used like you would a deck of plywood? (I have an 18mm round of ply with an epoxy resin seal.)

Thanks heaps again!

 

[UncommonSense]

Hey mate I really appreciate the quick reply!

Of course!

The 12mm acrylic is not bonded to the tank but used like you would a deck of plywood?

Precisely! I decided such a massive face-to-face weld would be risky at best… I chose acrylic because I had it, and because it’s an identical material… plywood should serve the same purpose, as long as it’s nice and flat!

— be sure your bulkhead stems are long enough to actually pass through the tank bottom plus 18mm of plywood, while still actually getting a nut on! (If you haven’t drilled the tank yet, I recommend looking into heavy duty bulkhead fittings, such as those sold by Hayward! — they are a smart part to invest in, as they are all the holds back a leaky tank!)

— as an aside, would you consider it beneficial to add an additional ~1” (32mm) plumbing size bulkhead hole as a dry conduit for lighting/wave maker wires, within the island overflow? (This prevents the need for any wiring going down the outside of the tank to the stand!)

 

[UncommonSense]

I’m thinking about drilling another hole

Regarding the actual drilling process, do you happen to have a router available? Finishing an acrylic hole via router is the gold standard for structural strength in the material around the hole!

 

[Ben’r]

Regarding the actual drilling process, do you happen to have a router available? Finishing an acrylic hole via router is the gold standard for structural strength in the material around the hole!

Funny you say that, I’ve been looking into getting a router so have just been using holesaw and sanding. Next on my list!

 

[UncommonSense]

Funny you say that, I’ve been looking into getting a router so have just been using holesaw and sanding. Next on my list!

They aren’t all created equal, but for your purposes, a 1/4” (probably 6mm) collet model/bits will work just fine!

It’s a very smooth and simple tool to use; if used correctly!!

— my local plastic fabrication shop taught me to make my final trimming router cut through acrylic in 2-3 successive 3-6mm deep passes… cutting no more than 1/2 of the router bits width on any given cut…

So, for 12mm thick acrylic, with a 12mm diameter trimming router bit:

— no more than 6mm plunge depth per-cut

— no more than 6mm width per-cut

These recommendations are fairly conservative, leaning towards safest/smoothest possible working conditions, and best surface finish!

 

[Ben’r]

— as an aside, would you consider it beneficial to add an additional ~1” (32mm) plumbing size bulkhead hole as a dry conduit for lighting/wave maker wires, within the island overflow? (This prevents the need for any wiring going down the outside of the tank to the stand!)

I’m so glad you mentioned this before drilling!

Basically the house is getting renovated and the cylinder will kind of back on to a new wall (150-200mm off the wall) so the option of running in wall plumbing is easy. I will need a 40mm pipe conduit for the lights and wave pumps, so my thinking at the time was to run the return line next to it.

The problem with long drawn out builds, you forget things! I started this at the beginning of ‘25.

No wonder my drain setup was a bit different