Acrylic fabrication questions? I can help!

[Floyd R Turbo]

no, it does not bond well. That's why you don't see tanks made out of polycarbonate.

0.220 is better.

Also not all acrylic is the same. Cheap import stuff my be OK for simple builds like overflow boxes and the like, but I would only use Plexiglas brand if you can find it.

 

[dattack]

http://sheet.zoho.com/public/rivermud76/rivermud-s-calculator

I'm probably getting mine at Orange County Industrial Plastics- I'm going to pick it up so I don't have to pay for shipping.

I always thought ocip was a little overpriced. Just ask them if they can beat another competitor locally. They have lowered the pricing for me. I just state industrial plastic gave me a lower price although may not be true. Hahaha. They used to have a scrap bin in the back I pick out acrylic for free. Actually 3scrap bins. Have to get there before they recycle.

 

[Saltwaternooby]

You would be surprised how shallow a really bad scratch is. Got a pic?

It is around 1 to 1.5 mm deep. I hot the acrylic second hand and didn't really care that it had a couple deeper scratches/ gouge, would those window repair kits for cracks work.

 

[Floyd R Turbo]

Hmmm..that is a pretty deep gouge. I'm not sure about how to answer this one right. James - you out there!?

 

[tizzite]

Thanks dattack, at the very least I'm going to see if these local companies can try to beat eachother's prices.

 

[overflowin]

here we go

here we go

i bought another reefer's ill constructed tank a couple months back, and over the weekend i finally disassembled it. The tank was 84"l*37.5"t*30d, and is constructed out of 3/4 acrylite gp, but the ends were 1/2 black acrylic. where the colored acrylic and the clear came together is where the problem joints were. i will be reworking the material to build a grow out tank that will be 74"l*18"t*28"d.

i am going to be reusing the eurobrace top, which will be 3" around the perimeter, with an 8" center brace. i believe a minimum 2" radius for the cutouts is recommended, this top is no where near that. not sharp right angles, but only perhaps 1/2" radius corners. would you recommend re-cutting the openings to widen that radius, or will the relatively short height of the tank make that less critical with 3/4 material?

this will be my first time working with acrylic this thick. most of what i've done in the past has been with 1/4" material. Weld on #4 with the pin method acceptable on this project? i'll be doing edge prep once i finish building my router table, but at the moment i only have a 1 3/4hp router. i know im at a disadvantage with this small router, but it's all i've got, and all i'm gonna get for a while. if i can't borrow a 3hp, what is my best option, bit wise, to get the best results possible? i've used 1/4" carbide spiral upcut bits in the past for the thinner material, but something tells me i'll need something else for this.

I appreciate all you guys, and your willingness to help those of us just learning.

thanks
donnie

 

[Floyd R Turbo]

If the top is 3/4", you might be OK. I think most problems emanate from a combination of the euro being thinner and small radius corners. But James can confirm this. I think trimming out the cutouts to accommodate a wider radius corner might be and even trade-off, you weaken the euro by narrowing it, but strengthen the corners...dunno...I think you would be fine to take 1/2" off each inner side to expand the corner radius. I would have to see a drawing of how it looks now vs after. Also, if you cut it all apart, how are you going to re-use the top euro and bottom panel anyways?? Oh wait...you have cut the tank down considerably in size...probably OK no matter what you do.

Generally the recommendation for a euro that is over a 72" tank is to have a 3" perimeter and a 6" crossbrace every 24", so in this case 2 crossbraces, but being over-built, one 8" one should be good I would think.

As far as the router goes, I've done 3/4" material with my Bosch router and that is 1.75 HP, I just used a Bosch bit from Lowes, 3/4" diameter 2-flute straight cutter (mortising bit, sometimes called) with 1.25" blade, worked fine. The larger the diameter of bit, the better, but you pay for it. James had some pics at one point of a 1.5" diameter bit, that looked bad--- spinning at 23K RPM... The 3/4" bosch bit I use is like $20, I have 2 of them, and they still perform like a champ, 2 years later.

I think your biggest issue is going to be sliding the sheets across your table without a masking on them, they can 'stick' to the table, which you do not want. You can buy paper masking and re-mask the sheets, this will help prevent this and also protect the sheets from scratches, which you will undoubtedly get also.

Spiral upcut bits are for flush trimming only. I would not use them for edge prep. I would recommend a 1/2" diameter one though. I have an Amana one (only one the local woodworking store carried) that cost about $150 but it has been worth every penny.

 

[TropTrea]

For the scratches and gouges I have been successful with the tourch. I will torch most of my exposed edges and get a result that looks like a polished finish. But you need to practice on some scratch pieces first. There is a very thin line between getting that polished look and the point where it starts bubbling and even burning the plastic.

 

[Floyd R Turbo]

I would never recommend flame polishing an acrylic aquarium - anywhere. Flame polishing is the most stressful thing you can to to acrylic. There are many examples of tank damage on this thread (crazing on corners) that are directly attributable to flame polishing, the damage shows up months to years later, and cannot be reversed.

I have made rimless frag display/sale tanks with nicely router-rounded corners and rims using just wet sanding and a final pass with a random orbital buffer or high speed rotary buffer and Maquires and this produces a better result over flame polishing, without damage to the acrylic structure.

 

[TropTrea]

Yes excessive heat can cause structural damage to Acrylic. But I found out about this when I payed to have scratches removed from an acrylic tank years ago from a shop that strictly works with Acrylic. I paid to have scratches "buffed out" and watched as they did it in front of me with a torch. It is something you need to know what your doing which is why I suggested practicing on scrape peices first. too much heat or holding it in one spot for tool long can cause problems. Trying to repair scratches that are too deep can also cause issues.

An example of tanks that have had heaty applied to them are basicly most of the curved "glass" aquariums. I have seen these made with the sides and front made from one piece of acrylic, and bent under the application of heat. It is not something I would try again but if you know what your doing it does work.

I did work in plastics for two years including cast acrylics. And heat if controled properly does not weaken the plastic. But excessive heat or applied for too long can change structure of the molecular bonding. Actually in the casting of acrylic and other plastics the difference of time, temperature, and cooling can change the properties of the end product considerably.

 

[overflowin]

thanks for the info. i'll take your advice on the router bit, and remasking the acrylinc... i did my disassembly with a 60t, 7 1/4" carbide. it was a pretty cheap one, from menards. the cuts look pretty darn good, and was thinking about grabbing the 10", 80t version for my table saw. is that the correct blade for the job?

 

[dahenley]

Floyd,
i pop in randomly and read bits and pieces. (even went back to page 1 a few times just to relive a few things haha

just out of curiosity, Why would you not use a spiral bit (up or down cut) for edge prep?
is it due to the small diameter of them, or does it have to do with the edge it leaves?

i use this one occasionally. (its 1/2" shank for size comparison)
could i use this? i just like the smoothness of the edge it leave..... and its sharp enough to shave with!!

just wondering your in-site on that comment you made. (im going to be building a few acrylic things for my tank. and i was just curious.

 

[Floyd R Turbo]

overflowin: I use Diablo triple-chip blades for acrylic, the ones that are made for plastics, but really the router bit is what I would spend my $$ on. You may have to make a few more passes to get that finished edge but big whoop.

dahenley: spiral upcut bits tend to pull the material into the bit, making it rather difficult to get a perfectly straight edge. straight cutters will not do this as readily. Also your cutter edge speed is much, much lower on a 1/2" diameter bit vs. a 3/4" diameter or larger straight cutter.

 

[dahenley]

 

[Floyd R Turbo]

Bad a-- bit!! Those are great for CNC routers with suction tables. They leave almost a polished-looking edge. The curvature of the blades, which when put into a table-mounted router will pull the material down onto the table instead of pushing it off of the table, also can have a tendency to pull the material into the bit. This ^^ bit would not do that quite so much as a 1/2" spiral bit though. The straight blade cutters also can pull material into them, but to a much lesser extent. It's easier to control the material when using a larger diameter bit and when using a straight cutter, plus straight cutters are way cheaper.

 

[TropTrea]

I personaly have not had that much luck using routers on acrylic. My thought it that the if could be that my router has a set speed and as I'm cutting the blade gets too hot. Ususaly the cutter gets all gunked up for me.

As far as cutting I have not had much of a problem using carbide Plywood blades on my table saw for thicker materials. Youwever when trying to cut thinner material (under 1/4") even these have a tendency to to create chips and hair line cracks. The band saw with a metal blade prevents the cracks but it is so much harder to get a perfect straight cut on the band saw.

I'm about to pick up some precut pieces I'll ask them how they cut it.

 

[Floyd R Turbo]

How is your router blade getting hot? I've never had this problem in years. I can run sheet after sheet through and then shut the router down and grab the bit without a problem.

If you're talking about the way the the chips come off the bit, like they bunch up and melt together and 'creep' towards the bit and then when they get close enough they "pop", then that is a chip clearance issue. I find that increasing the rate of feed helps throw the chips further away and you don't get this buildup right next to the bit.

Also as I am thinking about it, the "heat" issue I do notice, from the acrylic shavings coming off the router (they will seem like you are getting sprayed with hot acrylic bits) but this is not due to the router bit heating up, just part of the high-speed cutting process. The shavings don't get hotter as you cut more, they are just as "hot" with the first cut vs the last.

 

[TropTrea]

I just picked my acrylic and discussed there cutting methods. For everything over 2mm thickness with a straight cut they are using a 12" 108 tooth special carbide blade designed strictly for plastics. For none straight cuts they use a CNC cutter. Both are water cooled.

On the 2mm or less straight cuts they use another saw with a special blade designed just for them.

Going back a few years they did use the hot wire cut and snap on some of the thinner thickness. But they no longer use this method on clear acrylic or polycarbonate.

 

[Gino555]

Thank you very much everybody for info on this thread. Very informative. But unfortunately I am not DIY guy. Does anybody knows acrylic fabrication store in Brooklyn ,NY. Need to do some improvement for my new big sump (60x24x20). Thanks in advance .

 

[TropTrea]

Also as I am thinking about it, the "heat" issue I do notice, from the acrylic shavings coming off the router (they will seem like you are getting sprayed with hot acrylic bits) but this is not due to the router bit heating up, just part of the high-speed cutting process. The shavings don't get hotter as you cut more, they are just as "hot" with the first cut vs the last.

Perhaps I should be using a special bit. Bit regardless if I hut with a router or a band saw I get edge of plastic build up right at the cut point. and there is a build up on the blade or bit as well. Cutting through my table saw I do not get this but I do get a much rougher cut with ocassional little chips and hair line cracks.

Keep in mind that only about 20% of the acrylic or polycarbinate I use is for Aquariums. Most of it is for other projects using much thinner material. As an example I made some Aquarium covers using 2mm material which is a hair less than 1/8" thick. I also found it is cheaper for me to fabricate my own electrical boxes for projects from acrylic or polycarbinate than buy the ones available on the market.

An interesting thing I just discovered for aquarium covers. The rating of light transmission for Acrylic in the spectrum we are concerned about for Acrylic varies from 92% to 97% dependent on the grade and thickness. While for polycarbonate drops to the 80% to 86% range. Another thing to consider about Acrylic being better than polycarbonate for our purposes.