Basic acrylic fabrication
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Old 11-06-2010, 06:25 PM   #1
mountaindew
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Default Basic acrylic fabrication

Tools used for project
Note: Only large tools are shown, other hand tools will be required for this project.
Table Saw 10" with router table attachments. A solid base is required for a stable machine. Any flex in saw or saw platform base can effect the quality of your milled and finished project parts.

Router table shown at right side of table saw. used for joining acrylic sheet ends. A stable, secure router table with fence adjustment larger then work piece size is required to complete the work detailed below

Router mounted on table with above table height adjustment. This provides easy and accurate height adjustment of router bit before each process if required.

Zero clearance saw blade plate for improved clean cuts. This limits chipping at bottom edge of material during size cutting of sheets. a UHMW Fence is not required but adds to the smooth movement of work piece along fence during saw cutting or routing operations.

Feather boards to hold sheets against fence during the end joining process. These can be moved and configured for the job at hand. Also shown is a shop vac attachment for chip removal. Using a shop vac, chips can be blown away from work area during fabrication.

Acrylic Material Prep
Example tank will be a 24x24x24 tank fabricated from 3/8” material.
Materials required for construction will be as follows
6 ea cast acrylic sheets3/8” thick by 24 inches plus square.
Acrylite gp, Polycast and Chemcast in that order are good materials to work with.
All other brands or types of acrylic can or will compromise the overall quality of construction
First check each sheet of acrylic for 2 sides that are square and mark them for reference
Then decide which sheets will be used for bottom, sides and top, mark them for reference.
Including marks for top and bottom orientation of sheets as they will be placed when finished

Coat table saw top with pledge wax to allow acrylic sheets to slide smoothly.

Sheets used for sides will be prepped first. In this case the front and back sheets will be just under 24” wide with finished edges and the side sheets will be 3/8” + 3/8” less in length so they end up forming a square about 24 inches square.

Start by setting router table up for tank sheet finished HEIGHT. This is done by setting fence to height of shortest sheet less 1/16 inch. Run each sheet through router at this setting. This will insure each of the 4 sides on the tank end up the exact same height with one clean routed edge. Then move fence 1/16 inch smaller and run each sheet through router to clean opposite edge. At this point you should have 4 sheets that have exactly the same size top to bottom with clean edges. Carefully checking each and every edge for any flaws is recommended at this point. If done right the most likely spot will be near the ends of each finished edge. If a flaw or router snipe is detected, it is recommended that it be resurfaced. This causes it to be shorter and thus all the other sides must also be sized to match.

Next step is to set fence 1/16 inch less WIDTH of shortest sheet to be used for front and back of tank and run through router to provide one clean finished edge. Then set fence 1/16” less width and run both sheets through router putting previously finished edge against fence. At this point you should have 2 sheets that have the exact same size front to back and top to bottom this process in not always required as this edge will be routed off and finished after tank is bonded. Doing this mostly provides a clean edge to work with during other phases of tank construction.
Tank side sheets are to be prepped next, by first cutting off approximately 5/8” or less of the unfinished sides. This is done to allow for the thickness of the front and back sheets of tank, so you end up with a box that is just over 24” square. Then set the router table fence to 1/16 inch less then size of side sheets and run both through router to prep one edge. Then repeat this process on the remaining unfinished edges of each of the side sheets. At this point you should have two side sheets with the exact same width and height that is exactly the same as the front and back sheets height.

The 2 side sheets and the 2 front sheets of the tank should all be exactly the same height and each pair should have the exact same width, all having nice clean prepped edges.
Front, back and side sheets set in position and taped together for inspection. this allows verification of correct height and width of all work pieces.

Next sheet to be prepped will be the top sheet. This is done by first laying out the opening required for tank access on the paper sheeting and all other openings if required.

A square 2 edge router pattern with desired radius corner is required and should be fabricated.
This will be used to route out tank top opening as detailed below

Drill holes in each corner of sheet about Ό” or more away from layout marks of tank opening. Use an acrylic drill bit with a backing board being very carful to avoid damage to acrylic sheet.

Then using a saber saw with a plastic saber saw blade cut opening out staying away from finished edge by about Ό” or more. Provide proper support and clamping of material to avoid vibration of material and cutting tool. Being carful during this process will lesson the chance for damage to acrylic.

Next apply double stick tape to the 2 edge radius pattern constructed above. Then stick radius pattern to tank top sheet carefully along layout lines.

Support sheet as required and rout off excess material to edge of pattern. This will provide one nice clean edge and radius along two sides of opening.

This process will be repeated for each corner until the top sheet is finished. Picture below shows the pattern moved and attached to sheet along layout marks and one finished edge. And ready for router operation.


All other openings can be added at this point if required. this is done by first laying out openings in desired locations. Then carefully drilling a hole for the router bit to go through. Always use a backing board when drilling acrylic will limit the chance of damage to the work piece.

Place double stick tape on a masonite template of the desired sized opening. Locate on layout marks and use a router table or hand held router with a flush trim bearing to mill out desired opening. Repeat this process for all other required openings.

By using a pattern and router a clean accurate finished hole of any size "shown below" can be milled into acrylic work piece.

A 45 deg flush trim router bit can be used to ease the large and small opening edges. Then sand and polish all opening sides can be completed at this time or when tank is at finishing stage shown below.

Acrylic bonding
A solid, level and very flat work surface is recommended for this process. This is to enable the bonding of surfaces without tension on the sheets. Some flat wood strips with foam tape are also recommended for ease of shimming that will be explained later.
These can be constructed from mdf board cut to about 4” wide by desired length.
Applying 2 strips of foam tape down length of each board. A minimum of 4 ea 2 feet long are required for this example.

Next 2 ea 90 deg clamping jigs need to be constructed for holding sheets in place at a 90 deg angle during the bonding process. The jigs shown are made from mdf board glued at 90 deg angles with a 2’6” length. At 45 deg angle is cut from outside corner of jigs to provide clearance for acrylic solvent that can extrude out from sheets during the bonding process. This is important to avoid damage of solvent on acrylic sheets at corners during bonding process.

Lay bonding support boards on work bench and arrange as required to support acrylic.
Use a ruler held in place on sheet to remove protective paper from acrylic sheet. Removing about 2 inches of paper along all sides of each sheet is required.

Place front sheet that is 24 inches wide on foam tape support boards. Place clamping jigs along edges to be bonded and temporarily clamp, being careful at all times not to damage acrylic. Carefully clean surfaces to be bonded with denatured alcohol. Place side sheets on top of front sheet and clamp to jigs.

MDF clamping jigs shown with spring clamps holding side sheets in place on front sheet.
Note Gloves, bonding solvent and applicator bottles also detail in this picture.

At this point small gauge wires are required to create a void for capillary action of acrylic solvent. In this case bread ties with plastic removed / burnt off and carefully cleaned will be used. Lift side sheets and place wires under edges at about 4 to 6 inch spacing. Align sheets at top and bottom tank edges providing approximately 1/32” to 1/16” ledge for solvent needle to follow during solvent application and reset clamps. A bright hand held shop light will help with viewing during this process.

Check each wire placed along the sheet edges for tension. Any loose wires found need a shim placed below the bottom sheet to provide more tension at that location. The shims used in this case are round or half round cutouts from a sterlite storage container lids. This plastic is good because it does not bond to acrylic and has little reaction to solvent. The round shapes of these shims apply more tension at center of shim and less tension at the edge of the shim. This process provides a more uniform tension along the entire edge to be bonded and ease of wire tension adjustment.

Close up view of wire placement with shim placed under sheet at bottom corner.

Double check bonding edge alignment and make sure sheets align at top and bottom.
Check each sheet and make sure they are square.

Acrylic solvent should be placed in 2 application bottles with proper gauge needles. This is done as a backup if one needle should clog you have another bottle ready to use. As you only have at most minutes to complete this entire process it is best to always have a backup.

Checking room temperature at this point is advised. Temperatures below 65 degrees can cause problems and temperatures above 80 degrees will cause the solvent to set very fast and also cause problems.
With a bright lit room and hand held shop light on hand the bonding process can be started. Check flow of solvent in applicator needle. Then place needle on the 1/32 edge along surfaces to be bonded. Start flow of solvent and move down entire length of the sheets to be bonded. During this step you will observe the solvent flowing by capillary action between the sheets. Repeat for other side of tank. When starting the bonding process it is best to time or count in this case about 60 seconds from start. Then carefully remove wires placed between the bonded sheets and let sheets settle into place checking alignment of all edges. This must be done at a good pace as you don’t have much time before the solvent melts the acrylic and bonds or sets up.
Practice is the only way to master this part of the fabrication process, accounting for material type, Prep, temperature, solvent and other factors. Holding your mouth just right and talking to the material could even help as this is an art and its hard to say just how well this is going to work.
Wait a minimum of 4 hours and or the longer the better before you move anything.

Set the back sheet down on support strips and set the previously bonded sheets on top
Repeat the procedure above for the other side of tank. Being very carful to check alignment and square

A "T" Square is used to check corners for proper alignment. There is a 1/16 inch ledge on this sheet so a uniform gap from top to bottom edge of square is all that is required.

The top sheet of tank can now be bonded by properly supporting it on the wood support strips and placing the tank walls previously bonded on top. Take care to place wires as specified above and make sure you have an edge for the solvent needle to follow during the application process. Placing a small amount of weight on the top edges evenly distributed will help ensure an even tension on the bottom sheet and wires. Again shim as required, paying close attention to the corners of the tank, problems will most likely be in those areas.
Apply solvent as specified above, counting or timing the process and remove wires letting the tank walls settle into place. Check alignment and let cure for a minimum of 4 hours.

Repeat the process detailed above for the bottom sheet of tank.

After the tank has cured you can trim all edges with a router. This is done with a flush trim router bit and bearing aligned to follow face of the opposite acrylic sheet. A 45 deg router bit with bearing can then be used to ease all edges of the tank as desired.

Mask off exposed edges of acrylic for preparation of sanding and polish process.
Using fine to very fine grit sand paper carefully sand all surface edges to be finished.

Then polish exposed edges as desired. This can be done a number of ways; one is to use micromesh and a great deal of labor. In this example the use of a polishing fiber wheel attached to a drill with buffing compound applied will be shown in the picture. Always move the buffing wheel back and forth avoiding any one area for an extended period of time. This will cause a heat build up and possible damage to the acrylic.

External Overflow Fabrication
Type of over flow screen is selected for this project. Dimensions of screen are taken and verified. A Masonite template is then fabricated and test fitted with the overflow screen. Then a layout at the desired location on the tank opening is done.


The screen template is used to set the correct height of router base using the router bit bearing as a guide

A hole is drilled through the acrylic sheet inside the screen cutout area. Always use a backing board clamped in place before drilling holes in acrylic.


Use a saber saw with acrylic saw blade to cut opening in sheet. Stay 1/8 inch or more inside and away from layout lines. ALWAYS support material as required to avoid vibration and possible damage. Then apply double stick tape to template and attach to sheet using the layout lines.

Set router on template and route away excess material by making a few passes along each edge going in a clockwise direction around the template opening

Template, router and opening shown from below during the routing process. When finished the opening will have very accurate dimensions and clean milled edges. Using a template to mill openings allows the fabricator to repeat this operation as many times as required with less effort and greater tolerance. These extra steps help insure quality acrylic fabrication.

The finished opening with screen snapped in place.

All the fabrication methods detailed above are best done with a great deal of care. The more time you put into it the better chance of good results.

Overflow box
Completed Overflow box ready to be located on tank. Note, pvc bulkheads are being checked for proper fit and will be removed before bonding to tank.

Locate overflow box even along top edge of tank with equal spacing on each side of the screened intake opening. Remove paper protection on the acrylic sheet. Then carefully clean and prepare surfaces and edges to be bonded. Repeat the techniques detailed above for application of solvent and bonding.

Finished display tank


Hope you found this informative
This is a combination of 5 things i enjoy doing
Aquariums, Designing, Fabricating, Photography and Computers.
And thanks for taking the time to read it.
Mountaindew
mountaindew is offline   Reply With Quote
 

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