HOW DO YOU CEMENT REALLY THICK ACRYLIC?

[Anonymous]

I looked at the table of content, and it does sounds like a very handy book for acrylic work, particularly if you do high pressure system. For regular tank that we deal with in this hobby, most of the info online and via the supplier is sufficient for almost all the situations.

 

[Acrylics]

Hi Sean,

Have fun practicing

I've never read that book, lemme know what you think.

James

 

[Tropic]

Good tips thus far, make sure you allow a gap that is large enough....i would use a thin paperclip for your shims. One thing to consider for thick material is the weight and the amount of time required to properly melt the two pieces. If you use a really thin shim(it could break when you go to pull it) the vertical piece can and will make contact with the adjoining piece because the shim will melt into the plastic creating such a small void that the plastic will prematurely join prior to you pulling the shims. Another thing to keep in mind is the enviroment around you. Make sure the room you are doing this has proper ventilation and is cool(72-75f) and very low humidity. Once you have the pieces jigged up, raise the vertical piece a 1/2" and prep both the edge and the adjoining face with acetone to remove all finger prints(makes the solvent run funny,airpockets). Remember, you only get one shot! Good luck

PS make sure to use the thin,smaller paper clips. You will need one on each end and one in the middle for a ten foot span(sagging). By the way, why do you need a three horse router to cut 1.25......horsebucky. you cant get perfectly smooth edges with no chatter with a 3/4 horse with the proper carbide router bit(designed to cut plastic, not wood) all it takes is a steady hand.

 

[Trixter]

Thanks for the great info, I read it twice.
Never even considered that the solvent would cause some sink and the pins would sink into it. Or that fingerprints could cause flow issues. I plan on using 20 guage hypedermic needles to keep both peices seperated and something between 16-18 guage needles to apply the #4. The room temp will be somewhere between 60 and 70 degrees F .
Was thinking about spacing the needles every six inches to guage the sagging of the bottom sheet, if any needles are loose when I tug on them then I will place a shim under that section to bring it up snug.
As far as edge routing, Im seriously considering framing it with some nice hardwood moulding to cover the edges so I might not even have to route them flush, still thinking. Keep hearing horror stories about bearings seizing. The adjoining edges to be bonded will be prepped by a CNC milling machine.
Is there anything else Im forgeting? Im practicing now with scraps getting the fillet right. Any other recommendations. Thanks again for your input.

 

[Tropic]

You can actually buy router bit bearings that are made of nylon and they will not mar the plastic when you are doing clean up. Bearings will not lock up unless you are pushing the routerbit to hard and you cause it to overheat.If you were pushing it to hard you will have terrible chatter and the chips will not be like snowflakes but will come out like little shards that are very hot. I guess the best descrption would be that the chips look like shattered safety glass....if you are pushing it to hard. What i like to do is first only cut the piece that will be routed clean a 1/4" oversize(1/8" on either side) and once you have glued the pieces together and they have cured you can do two passes on each side. For each side you want to make flush, do two passes; one to rough it down to 1/32 oversize and then make a final pass to get your finished edge. What we actually did was run a 3/8" router bit with a 7/16" nylon bearing which would leave you with a 1/16" overhang and then swap your bit out with another 3/8" bit with a 3/8"nylon bearing or have two routers with proper tooling set up in each one. Ideally, you need to buy the bit with the nylon bearing from the same manuf. otherwise it will not cut absolutely flush as standards of sizing are not always accurate between diff. suppliers. If i have confused the crud out of you, pm me and i will give you my contact info so i can better explain it over the phone.

 

[Trixter]

It's been a few years...Looking at another similar project again. This one will be using 1.5" thick acrylic. Was wondering if anyone had any experience with #40/42. Id rather not go to the hassle of degassing the cement using a vacuum chamber so have been considering #42 with the special applicator gun due to the thickness. No experience with it though.

Would it be better to use solvent cement (would like to try MC Bond this time) and pins (.005 stainless suture wire), or Weld On #42 for this project? Problem is I wont be able to anneal it as recommended/required when using #42, the panels are just too large to do this.

Will edge prep with track saw guide and router. This ones dimensions will be 120L X 33W X 36T.

Any advice would be appreciated.

 

[Anonymous]

Who said using #42 will require annealing?

Sorry, but I has not deal with DIY a tank of this size. Hopefully James can chime in about this thread again.

 

[Trixter]

The manufacturer says you need to anneal if using #42, If I remember correctly it's written on the container. Yes... I've heard that you can still use it without annealing but would it be safe with this ammount of pressure? Your not fusing the two panels together the same way you would with solvent cement. Am thinking MC Bond may be the best alternative out there other than mixing my own solvent to which I really have no experience with.

I did find some .005 stainless steel suture wire that might work well.

 

[Trixter]

What do you all think about using thinner stock for the top? I have some 1.25" from an old project left over and would like to use it. Maybe 1.25" for the top and 1.5" for the bottom and sides. Full tank dimensions are 120 X 36x 36.

What will happen if I do this? How much front panel deflection will I get and how much tension would the top be under? would it be prone to cracking if thinner than the rest of the tank? Looking for very little bowing and suggestions of how the cut outs should be for good O2 exchange for a tank this size. Am thinking the top is subjected to more compression forces anyhow but dont know how critical the thickness of it needs to be in relation to the rest of it.

 

[Anonymous]

The resulting width of the top after the cutout is more important than thickness. A 1.25 thick piece with width of 1.5 is stronger than a 1.5 thick piece with 1.25 width. This is because the piece is horizontal. I would minimize the size and number of cutout and let the air exchange be handled by the sump and skimmer.

 

[Trixter]

Thanks Seven. Are you saying that the width of the braces on top is more important than the thickness of the material used to make them? So let the skimmer and sump compensate for surface gas exchange then? Thats pretty clever. Want to make sure Im picking up what your putting down.

It looks like this project is getting closer. I picked up an applicator gun for Weld on #42 so will be using this to bond the panels. Expensive but have to say, very well made. Did some more research and found out that the edges should be beveled 5 degrees for material this thickness. This will be done with a CNC router. And have finally determined that there is really no need to anneal the panels if they are not overheated during machining so... Here's what I still need to figure out:

How big of a gap should there be between the panels to allow the cement to flow in between?