Need to increase hole size in overflow

ZombieEngineer

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I have a modular marine 1200 gph bean animal overflow that is set up for 3/4" uniseal with 32mm hole. I would like to upgrade these to 3/4" ABS bulkheads instead which require a 35mm or 1-3/8" hole.

What is the best way to do this? The overflow is 1/4" acrylic.

1. Use a 1-3/8" stepper drill bit to ream the hole larger.

2. Purchase/borrow a 35mm diamond hole saw and center it about the existing hole.

I am leaning toward the stepper bit since I already have the bit and it's just the last step it needs to drill, so likely a clean non-beveled cut, but I've never drilled acrylic before.

20220418_210628.jpg
 
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A stepper bit should work fine so long as the bit is staying cool and you are putting next to zero pressure on it. Plan to come in from both directions. Equal amounts of time. That It will leave a chamfer. The hole saw would work as well, but already having a pilot hole, and having the bit makes it an easy call.
 
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ZombieEngineer

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A stepper bit should work fine so long as the bit is staying cool and you are putting next to zero pressure on it. Plan to come in from both directions. Equal amounts of time. That It will leave a chamfer. The hole saw would work as well, but already having a pilot hole, and having the bit makes it an easy call.
I don't think I can come in from the top. My drill won't fit through that side. Shouldn't chamfer either way since the size I need is the last step.
 

Jedi1199

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Don't use the hole saw!!!!

Since you don't have a place for the center pilot bit to grab onto, the hole saw will wander and you will create a mess. The Step bit is your best option since it does not require a centering point to ensure a clean cut.
 
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I don't think I can come in from the top. My drill won't fit through that side. Shouldn't chamfer either way since the size I need is the last step.
90" drill attachment.

Step bits Shouldn't create a chamfer. In thick materials, they do.
 

NowGlazeIT

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Get a piece of plywood and use the size hole saw you need to drill through the plywood to creat a jig. Take the jig to your overflow and clamp it or hold it down tight as you holesaw through the existing hole.
 
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Get a piece of plywood and use the size hole saw you need to drill through the plywood to creat a jig. Take the jig to your overflow and clamp it or hold it down tight as you holesaw through the existing hole.

Since it is only acrylic and not glass, wouldn't it be easiest to just use the step bit? Your idea works in theory, but clamping will be difficult and holding in place would be an injury risk. The step bit only needs to clear out a tiny bit of material.

Let's not get carried away here kids... we are talking about enlarging a hole for a bulkhead. Most, if not all of these holes are actually a lot larger than the bulkhead that fits through it. If its oblong or slightly larger or smaller than intended, who cares?

If the bulkhead fits, and you have a clean surface to create a watertight bond when its installed, the job is done!! The "Hole police" won't be heading over to inspect this project!
 

Lbrdsoxfan

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Since it is only acrylic and not glass, wouldn't it be easiest to just use the step bit? Your idea works in theory, but clamping will be difficult and holding in place would be an injury risk. The step bit only needs to clear out a tiny bit of material.

Let's not get carried away here kids... we are talking about enlarging a hole for a bulkhead. Most, if not all of these holes are actually a lot larger than the bulkhead that fits through it. If its oblong or slightly larger or smaller than intended, who cares?

If the bulkhead fits, and you have a clean surface to create a watertight bond when its installed, the job is done!! The "Hole police" won't be heading over to inspect this project!
This, no reason to over think it, lol.
 
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NowGlazeIT

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Since it is only acrylic and not glass, wouldn't it be easiest to just use the step bit? Your idea works in theory, but clamping will be difficult and holding in place would be an injury risk. The step bit only needs to clear out a tiny bit of material.

Let's not get carried away here kids... we are talking about enlarging a hole for a bulkhead. Most, if not all of these holes are actually a lot larger than the bulkhead that fits through it. If its oblong or slightly larger or smaller than intended, who cares?

If the bulkhead fits, and you have a clean surface to create a watertight bond when its installed, the job is done!! The "Hole police" won't be heading over to inspect this project!
Yea I just don’t like my step bit very much I guess hah
 

Vested

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Could use a dremel as well since you only need to make it slightly larger, ive done this before with acrylic and worked great hole wont be perfect though.
 
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