Hey guys, i have a few spare minutes at work so im going to start up a series to help teach everyone about the use of acrylics and how to get the best out of them (to the best of my knowledge). My aim for this series of threads is to help make high quality acrylic work acessible and acheivable with common and reasonably cheap tooling.
First, a bit of background, I am a first class fitter and Machinist currently employed to manufacture experimental equipment used in reasearch and education. Alot of which involves some fairly high end acrylic fabrication work.
So What is Acrylic?
'Acrylic' is a collective term used to discribe a group of glass like thermo-plastic resins made by polymerizing ester of acrylic or methacrylic acid.Usually polymethyl-methacrylate.
Acrylic as it is commonly sold is a a cast or extruded product composed of Acylic Polymer, sometimes with additives (colours, uv-stabilisers etc). A polymer put simply is a plastic, getting its name frome the molecular structure displayed by plastics, Long chains of molecules joined and interlocked together.
In the manufacture process there are two main ways of acheving the desired profile for products, Extrusion and Casting. Extruded Acrylic products are cheaper due to much faster production methods but arent quite as strong as the cast material, but its reasonably close.
Why use Acrylic?
- Weight - Acrylic is much lighter than glass, making it easier to move large tanks made from acrylic (most of the weight of a full tank is the water, substrate etc. So only comes into play when tank is empty)
- Impact resistance - Although a very sharp blow will crack acrylic, its impact resistance is in the order of 10 times that of glass.
- Shape - Acrylic is easily moulded in custom shapes with out the use of extremely high tempretures.
- Strength - Acrylic tanks require thinner materials to hold the same water weight, so thinner acrylic is needed then if glass were used.
- Refractive index - The refraction of light through acrylic materials is very close to that of water, so less viewing distortion will happen when viewing the tank from an angle.
- Clarity - Acrylic is clearer than glass so gives a better veiw of the true colours of the inhabitants, although some acrylic yellow slightly with age, if cared for well this shouldnt happen for many many years.
- Cost - Acrylic is more expensive than Glass, This is due to it being a petrolium based product, as aposed to glass which is silicate (sand) based.
- Rigidity - Acrylic is more flexible than glass so needs more support under the tank and bracing at the top to prevent bowing and joint failure.
- Scratchability - Acrylic is scratched much more easily than glass, although scratch repair in acrylic is significantly easier and requires less specialty equipment
What tools are needed for Acrylic work?
Basic Tank construction can be performed with a circular saw, a hand drill, a router, a good straight edge and a sander. In the posts to following you may see me using some much larger and more expensive peices of equipment, this is to acheive the best possible result, as some of the equipment will be used for scientific reasearch, for a hobbyist hand held powertools can work fine.
How is Acrylic sold?
Acrylic is usualy sold in Sheets and in lengths of Tube.
Sheet sizes are usually 1220mm X 2440mm, in thicknesses of 1mm, 2mm, 3mm, 5mm, 8mm, 10mm, 12mm, 15mm, 20mm, 25mm and upto 300mm (that would be a hell of a tank to need 300mm... hell of a budget too)
Tube is sold in length of 1M or 2M, in lots of diffrent sizes. It is dimension based on the external diameter and wall thickness, Wallthickness being the width of 1 side of the tube. Diameters can be from 3mm upto 2M.
How do i Size Acrylic?
There are alot of calculators online for working out the thickness of acrylic required. probably the easiest to use is the GRAF tank builder; http://www.garf.org/tank/buildtank.asp.
All of these Calculators assume the use of solvent cements with imperfect joins, so if you use the stronger more expensive glues you can get away with thinner acrylic, but at your own risk.
How do i join Acrylic?
The use of acrylic dictates the use of specialist glues, though some expoxies may adhere to acrylic, its no very well and will be pretty ugly. Silicone is a definate no-go as it will just peel straight off. Below are 3 of the Adhesives i commonly use in my acrylic fabrication work.
Weld-on 3 (Back Right):
A Dichloromethane based solvent cement. It has a medium Joint Strength. This is less of a glue and more of a Chemical welding agent. It works by chemically melting the acrylic and then eveaporateing away, leaveing the join to reharden as a solid joint. Adhesion time can be slowed by the addition of small amounts of Acetone.
Easy (with the right technique, will post a thread on that soon).
Sets within minutes, full bond strength in 24-48 hours (depending on joint width)
Cons: Messy if not carefull.
Only a medium joint strength.
Very little working time after application.
Requires extremely carefull edge preperation
Acrifix 192 (front and center):
A single part UV polymerising cement. Provides a medium bond strength. can be used to fill gaps and on slightly uneven edges. It is an acrylic monomer suspension with a uv activated cataylist
Pros: Fills Gaps
very attractive and highly transparent bonds
apply straight from the tube, no applicator needed
Edge prep can be a little rough
Cons: Price, Aproximately $15 a tube
Requires a bright UV light source to set
Takes 2-3 hours to set even with high power uv source, Full hardness in 2-3 days.
Can be very mesy if not very carefully.
Acrifix 190: (rear left)
a two part polymerizing adhesive. very high bond strength. provides near invisible joins and is the highest strength acrylic adheisive i know of.
Pros: Very strong
Can fill large gaps (accounting for shrickage)
very clear joins if mixed properly
Cons: Very expensive, $76 dollars for 1KG of the adhesive (aprox 1.1 litre) and $20 for the catalyst which is required.
Can be very hard to get hold of (my last order through work had to be special ordered from germany and took 8 weeks)
Takes 24 hours to set, 1 week for full hardness.
Smells very strong, definetely needs good ventilation when using it.
Special edge prep required for best joins.
How do i cut Acrylic?
While at work i actually use industial tablesaws and machine tools, not something avaliable to the average fish keeper. although good results can be acheived using the following method;
- Leaving the protective layer on, Using a circular saw and a guide rail (a straightish peice of wood will do) Cut all your peices slightly oversize (5mm or so) as the saw will heat up and 'gall' the surface, leaving a rough opaque white finish) Spray the saw blade with a thin oilbased lubricant as much as possible (WD40 works great) if you are game you can spray water on it to help keep it cool, but with electric powertools its not the best idea.
- using a flush trim bit in your router, align your straight edge with the final size of the panel and run the router along the edge is a smooth and consistent fashion. BigSkip tip: If you wrap a small amount of masking tape around the bearing on the flush trim bit you will cut ever so slightly off the final size, remove the tape and take the very light pass to finish, this will minimise heat build up and should provide a better edge
- repeat for all sides.
- DO NOT POLISH EDGES TO BE GLUED. this will cause 'crazing' (a spider web of micro crack across the surface, severly compromises the strength of the material)
- Remove a small amount of the protective coating to alow gluing, leaving as much as possible until the tank is complete TEAR THE COATING WITH A STRAIGHT EDGE, DO NOT USE A KNIFE TO SCORE IT. this will score the acrylic and cause headaches later.
How do i Drill Acrylic?
Although Acrylic can be drilled with unmodified drill bits, it can grab and pull the drill in, cauing alot of damage it the material, and can also chip where the drill is exiting. The Ideal way to combat this is to use a drill with a special point. The point angle on Most drill bits you buy is 118 degrees, for acrylic the ideal angle is 60 degrees (think of it as a much sharped point on the end) Also the rake angle need to be reduced to 0 degrees or very close, Exactly the same as is done with Brass. Reducing the Rake angle is more important than the point angle. a 118 degree point with 0 rake will still provide good results. See the below diagram for what this all means and the video on how to easily reduce the rake angle. Another major thing to keep in mind is it all has to be kept very cold, keep spraying water mixed with a small amount of detergent and run the drill fairly slow. this will both lubricate and cool the material to prevent galling of the hole.
How do i Finish the edges?
finishing acylic edges can be done in several ways, my preferred way and they method i believe provides the best results is to sand them upto 1500 grit, them use some micro mesh pads upto 12000 grit and finish with a light buffing.
Another common method is Flame Polishing. This requires care and a hot blow torch (the yellow one, blue isnt hot enough) or an oxy acetylene torch. its as simple as passing the flame quickly along the edge. This melts all the tiny micro cracks that cause the opaque look back into one smooth surface, but be carefull it is very easy to burn the acrylic and turn it brown. Also, any roughness in the surface will remain, saw marks will still be visible, just shiny.
In the next post (when i can find time to make some photos etc) i will go more into the use of the 3 diffrent glues i discribed and show the processes of building a basic box from acrylic.
ADMINS: Am i able to link to suppliers of acrylic and adhesives that are not forum sponsers?
Eidt: SO MANY TYPOS!!
Edit 2: Damn it.... cant even spell edit right
Edited by BigSkip, 26 October 2015 - 02:58 PM.