Advice on building 250g Acrylic

[feddersenr]

I've read through quite a few of the messages and it's been a real help. I have a few questions before I start on my project.

I'm building a 250 gallon acrylic tank that is 48x48x24. I've built the stand out of 4x4 posts with 2x4 cross braces and 3/4 ply for the top and bottom shelf; it was modeled after the stand at my local fish store that held up a 300 gallon tank.

I need to build the tank next, but I was wondering if anyone had suggestions. I'm using 1/2" acrylic for the bottom and top of the tank with 3/4" acrylic for the sides. I planed on starting with thin weld-on initially to create the joints, then moving to thick to fill any minor voids. I'll be using a 7 1/4" blade made specifically for cutting acrylic, but it fits on a circular saw. I have access to a local sign shop's blade.

I'm thinking I'll make the initial cut with the circular saw as straight as possible by using a metal straight edge as a fence guide. Do you think I can then use a sharp carbide flush cutting router bit to trim off the saw marks? Of course, I'd be using a straight edge to run the bearing on.

When I cut the holes in the bottom of the tank for the refugium connections, should I use the flush cutting router trick or will a hole saw and patience work? I've heard stories of people having poor results from a hole saw.

Finally, I want to seal the plywood that the acrylic bottom will rest on. Will standard polyurethane work fine or am I going to have toxins absorb into the tank? The rest of the outside of the stand I was going to use polyurethane and two-part epoxy to seal the inside of the stand.

My fish have outgrown their 75 gallon tank. My wife and I have enjoyed this hobby for the past several years, so I think it's time to give her the ultimate show tank. Thank you for your help.

-Robert

 

[Acrylics]

I'm thinking I'll make the initial cut with the circular saw as straight as possible by using a metal straight edge as a fence guide. Do you think I can then use a sharp carbide flush cutting router bit to trim off the saw marks? Of course, I'd be using a straight edge to run the bearing on.

Yes, you can however the final edge will be determine to a large extent by the smoothness of the straightedge and the amount of acrylic "chips" that get in between the bearing and the straightedge. Another method would be to clamp a straightedge to the acrylic so that the edge of the router base itself rides against the straightedge. Doing it this was does not require the flush cutter. In either case, make sure your straighedge does not flex.

When I cut the holes in the bottom of the tank for the refugium connections, should I use the flush cutting router trick or will a hole saw and patience work? I've heard stories of people having poor results from a hole saw.

Depends on if you have templates for the desired hole sizes, if you do then the router is far faster and cleaner than a hole saw.

Finally, I want to seal the plywood that the acrylic bottom will rest on. Will standard polyurethane work fine or am I going to have toxins absorb into the tank? The rest of the outside of the stand I was going to use polyurethane and two-part epoxy to seal the inside of the stand.

It should be fine.

My fish have outgrown their 75 gallon tank. My wife and I have enjoyed this hobby for the past several years, so I think it's time to give her the ultimate show tank.

Good deal

HTH,
James

 

[feddersenr]

James,

I understand your the person to talk to about this.

I appreciate your suggestions. I have a nice large piece of angle iron that will work perfectly for a straight edge.

After spending time on Cryo's website, I've learned not to use a solvent, but to go with a Polymerizable Cement such as Weld-On 40. They suggest using a Dispensing Gun, but I can't seem to find one made for Weld-On 40. Will Weld-On 811 or Weld-On 55 work? I got the impression that Weld-On 40 must be mixed very accurately and applied carefully to avoid bubbles.

-Robert

 

[Acrylics]

I appreciate your suggestions. I have a nice large piece of angle iron that will work perfectly for a straight edge.

As long as it's extremely straight and smooth, IME angle iron is not, but your's may vary.

After spending time on Cryo's website, I've learned not to use a solvent, but to go with a Polymerizable Cement such as Weld-On 40. They suggest using a Dispensing Gun, but I can't seem to find one made for Weld-On 40. Will Weld-On 811 or Weld-On 55 work? I got the impression that Weld-On 40 must be mixed very accurately and applied carefully to avoid bubbles.

If I may be so bold...forget their site when it comes to this. They recommend Polymerizable cements essentially because they allow for a lot of slop, if you route the pieces accurately this will not be an issue. Given the thickenss of the material you are using for the application - solvent cements are plenty strong enough. By the way, the dispensing gun is for Weld-on 42 which comes in preportioned cartridges that mix in static mixing tips. It's the same gun used for two-part epoxies and runs for about $180. If you really want one - call IPS directly and ask them where to get one in your area. They have all this information in their system and can tell you within seconds. The cartriges run about $28 each and the tips are $1.50 each which must be discarded after each use.
So ya know, I've used solvents for most of my tanks throughout the years, as has just about every major mfr of hobbyist tanks in the country including Tru-Vu, Sea-Clear, Tenecor, etc... So if we don't have an issue - well you get the drift .
Where are you located anyway? ...if I may ask.

HTH,
James

 

[feddersenr]

I checked my angle iron, and you are absolutely correct about it's straightness. I'll use a piece of mdf, four foot level, or whatever. I'm sure I can find something accurately straight to use.

I will buy a new, sharp, expensive carbide router bit for cutting the acrylic so it will have a nice perfect edge after I'm done. It sounds like the solvents are the way to go and I appreciate your boldness. I don't need to make any mistakes.

I think I may build the sump first to get a little practice in. If I get too anxious, I may have to just buy a commercial sump. In comparison, they are not all that expensive.

I'm in the California mojave desert about 3 hours south of Las Vegas. My last computer network client is a sign shop owner. We struck up a conversation one day about fish and the end result was too very large sheets of acrylic. I purchased the 3/4"x4'x8' Acrylite GP for $300 and the 1/2"x4'x8' Acrylite GP for $180.

Robert