Building an acrylic lid.
Now that the battery box base is completed, time to start on the top. These are lead-acid batteries so they will produce hydrogen as they are charged. Hydrogen is lighter than air so it will raise (see Hindenburg) but is also explosive so it needs to be vented outside (see Hindenburg). I'm gong to make a "airtight" acrylic lid for the battery box. As the hydrogen is produced it will rise to the top of the lid where it will be vented via a hose to the outside of the van.
I've never messed with acrylic before so this is a first for me. The only information I have on the subject I got from reading the Internet and through trial and error. You have been warned.
acrylic sheet - 2' x 4' - $19.37
Tap Plastics - www.tapplastics.com
TAP Acrylic Cement (1 pt) - $11.50
IPS Weld-On 16 Cement (5 oz tube) - $6.75
Small BD-25/2 Hypo Applicator - $3.25
Start with a the sheet of acrylic.
Need to cut the acrylic so everything is at right angles and the edges are as smooth as I can make them. This requires extra careful set-up of the table saw to stop any side-to-side movement in the sheet. To keep the acrylic in place as I feed it through the table saw I made a feather board. You can see it to the left of the sheet.
The feather board has two purposes. It holds the sheet tight against the fence on the right side. It also prevents kick-back since it only allows the material to be moved in one direction. The saw blade is adjusted so it's just high enough to cut through the acrylic. I found that if you set it higher it can cause chipping.
After some work I had a bunch of acrylic pieces.
Even though I made careful cuts the edges are slightly rough.
Not having tried this before I'm not sure what level of roughness is allowable. To smooth this out 220 grit sandpaper is recommended. From what I've read you're not supposed to run sandpaper across the acrylic since that tends to round the edge. The preferred method is to run the acrylic across the sandpaper. With that in mind I wrapped a sheet of 220 grit around a scrap 2x4 and clamped it into the vice at the end of my worktable.
Then I'd carefully pull the acrylic pieces across the sandpaper being sure to keep them perpendicular to the sanding block to prevent rounding. I'd always use two hands but needed one to take the picture.
This step is fairly labor intensive. After some time I realized that this was going to take a while so I wised-up. I switched to 100 grit sandpaper and turned the 2x4 on it's side so I'd have a larger sanding area. I was always careful to make the block level.
After smoothing out the pieces with the 100 grit I'd switch to the 220 grit for the final finish.
Mistake Number 1.
I'm sanding one piece at a time. If I'd been smart I'd clamped the two top pieces together and sanded them at the same time. I'll come back to this point.
After much work I got the edges just right on the pieces that needed it. Smooth edges are not required for all the pieces I'm using.
Clean the edges that will be glued with alcohol. This bottle shows how often I use rubbing alcohol. The local Phar-Mor closed in the 1990's.
I'm ready to glue the first two pieces together. The pieces need to be held steady while the glue sets so just using your hands is out of the question. Using some leftover metal parts, from the sofa-bed that I'm still building, arrange the pieces to stand on their own.
The vertical clamp is being used to keep some pressure on the edge to be glued.
Mistake Number 2.
At this point I should have done a dry fit with the other pieces.
Moving on. Here is what I bought to glue together the acrylic sheets. A better description is solvent cement. It has all the usual warning labels along with it being a possible cancer causing agent. I don't think my exposure will be enough to worry about.
I'm going to use the glue in the white can. It has the consistency of water. Squeeze some air out of the plastic bottle and suck a little cement up. Not a lot is needed.
Here is the reason for all the work at getting the edges so smooth. Since this cement is water thin it doesn't fill any gaps. The parts you are gluing have to be in contact along their complete edge. I'm applying the cement via capillary action.
Here is the where the edge of the vertical acrylic piece rest on the side of another piece. Notice how the edge looks.The acrylic is about .2" thick.
This is the needle end of the applicator bottle. I'm squeezing out a little of the cement along the edge of the vertical acrylic piece and capillary action is drawing the cement into the space where the two pieces touch. The edge looks blue where the cement has been drawn in. This is the reason for all the careful sanding prep work. Without it this wouldn't work.
The directions said it sets up quickly but not to stress it for 24 hours. Not wanting to take any chances I let it sit.