If you use epoxy, this method works well even with surfaces that are not quite perfectly flat.\u00a0 Clean-up is minimal. Glancing at the photos below might be enough information to get you going.<\/p>\n
In these photos I use polycarbonate for the cajon back but the method is the same for plywood. There’s some polycarbonate specific info at the end of the blog for those of you who want to walk on the wild side.<\/p>\n
I cut and sand the back slightly larger than the box by about 1\/16 in (1.5mm), then, after it is attached to the box, sand the edges flush.<\/p>\n Cut the foam strips to be an 1\/8 inch larger than the box side thickness.\u00a0 Usually about 1\/2 inch to 1 inch (1.3 cm to 2.5 cm). Use hot glue to attach narrow strips of camping pad foam\u00a0along the edge of the OUTSIDE surface of the back.<\/p>\n The camping pad foam strips serves two purposes. It prevents the back from moving and it provides a compressible surface to distribute pressure evenly throughout the attachment zone. Do not use a full sheet of camping pad foam, it will cause the back to bow in the center and you won’t have a ‘stretched’ back. Turn the back over, the back goes face down with 6 small blocks offset from the edges. The foam supports the back. It is the only thing supporting the back.<\/p>\n Mask the inside of the back with tape such that the masking comes within about 1\/8th inch of the sides.<\/p>\n Prepare the jig that will hold the cajon box to the back while the adhesive dries. The first tier of blocks must not touch the edges of the back. Leave them back about 3\/8ths inch (1 cm). If you use wood blocks you’ll need to pre-drill holes for the screws or the blocks will split. I prefer plywood blocks. The first tier must be high enough that the second tier never touches the adhesive oozing from the joint.<\/p>\n Put the back in the jig foam down and exactly where it will go during the actual glue up. Carefully put the cajon box exactly on the back where you want it to sit when it is glued.\u00a0 Carefully place and screw down 3 second tier blocks without moving the box, two on one side and one on the top. They should just touch the sides of the cajon. With the 3 second tier blocks screwed down, remove the box.<\/p>\n Prepare your favorite adhesive, in these pictures I’m using clear 2 part epoxy but for a wooden back I’d probably use Titebond III (not hot glue, that’s just for the foam to back temporary bond). I usually take the back out of the jig to put the adhesive on.<\/p>\n Put the adhesive on the back around the edge where the box will be attached. Once your adhesive is on, put the back in the jig and make sure the back is perfectly lined up with the\u00a0 appropriate 3 second tier blocks. Turn the box over and carefully place it exactly on the back, with the appropriate side and top against the second tier blocks.<\/p>\n For 5 to 10 seconds, slowly press the box down while slightly shifting its position to spread the adhesive evenly. End with the box pressed tightly against the 3 second tier blocks.<\/p>\n Place about 1\/3rd of the weights on the box to keep it stationary. Place and screw down the remaining second tier of blocks. They should be snug against sides. After they are in place the box should not move at all.<\/p>\n Once all the blocks are in place add the remaining weight. I use a lot of weight. Some of my early attempts with less weight were less successful.<\/p>\n With the weights in place, reach inside the box, through the sound hole and remove the masking tape. If necessary scrape out the access adhesive that oozes from the joint. Then wipe the area with the appropriate solvent. The more excess adhesive you can remove the easier clean up will be after it has set.<\/p>\n Next day remove the weight and sand the edge to make the back flush. If necessary sand the inside of the back to remove residual adhesive.<\/p>\n A tight box is critical for good sound and durable construction. While building my first cajons I used clamps to attach the back. They worked but it was messy and a bit complicated. I’m sure there are other ways to do this. And plenty of improvements are possible to this method. Please comment below. Thanks, Bill<\/p>\n Polycarbonate gives a cajon a lot of resonance. I cut the poly with a ‘ceramics’ blade on a jig saw which is much, much safer than other methods I’ve tried. Then I sand both sides to ‘frost’ the sheet with either a belt sander or an orbital sander. After cleaning the inside edges with alcohol the polycarbonate it is ready for ‘gluing’ with either 2\u00a0 part epoxy or AquaSeal as the adhesive.\u00a0 Critical is an epoxy that is not runny. It needs to be a bit thick to fill and adhere.\u00a0 If you are using epoxy you must work fast to coat polycarbonate and position the box before the epoxy starts to set. Any end grain must be sealed with a thin layer of epoxy the day before glue up. Many epoxies are heat soluble, if you make a cajon with an epoxied back don’t let it get to hot. And it’s a good idea to put a few screws in to help ensure it stays put.<\/p>\n Updated Feb. 4, 2020<\/p>\n","protected":false},"excerpt":{"rendered":" This method is a fast, easy way to get a tight, fully sealed back attached\u00a0 to your cajon build.\u00a0 It works well with any back material. No clamps are used. Here’s what you need: camping pad foam material, must be compressible foam of some type, about 1\/2 inch (1.3cm) thick a small amount of hot … <\/p>\n![\"Hot](\"https:\/\/www.cajonsmadein.com\/blog\/wp-content\/uploads\/2018\/07\/P6140082.jpg\")
<\/a><\/a><\/a><\/a><\/a><\/a><\/a><\/a><\/a><\/a>Attaching polycarbonate as a cajon back:<\/h2>\n