Cdlong Posted January 9, 2020 Report Share Posted January 9, 2020 This is partly me thinking out loud and working this out as I go so sorry if this gets long. Some quick background first. My wife is a play therapist, which means she gets to play with kids all day and gets paid for it. (It's therapy, generally due to trauma, so I make light of it, but it's really not.) One of the tools she uses is a sand tray, it's literally an indoor, tabletop sandbox with a lid. There's more to it that's not important at the moment, here's an online store with a few versions for reference. https://www.playtherapysupply.com/sand-tray-therapy/sand-trays I've built a few so far of various levels of quality and complexity. All have been a basic pine rectangle with a dado for a plywood bottom. The last few have had box joint corners, the first just had butt joints and let's just call that one practice. I've learned I like the joinery aspect of woodworking, and specifically the fastener-less joints. The box joint boxes have been rock solid and look pretty nice so I will probably continue that in the future. I'm doing this for a hobby with a purpose, so I'm interested in trying out new techniques and being a little fancy with it rather than production and making money on selling them (there are etsy stores for this stuff too. https://www.etsy.com/listing/551356015/octagonal-sand-tray). The next project I've been assigned (after I finish the sand tray that's still in pieces on my workbench) is where it gets interesting. I'm planning out an octagonal one and had some ideas for the joints. I think a spline joint for the corners would add something for both strength and style but would need to build a special spline jig for the 135 deg corners, I don't even have one for 90 deg corners. Is it possible to make one "all-purpose" to save some jig construction or should I just suck it up and make a 135 deg jig for this project only? The other idea is a box joint corner for the 135 angle. I found a few pictures and descriptions online so it can be done, but as I have a Leigh box joint jig that probably won't work with the board on a 45, I think I'll need to make a new jig for this too. Any experience with this or thoughts on the two options? The next similar project is to make a set of small scale boxes for teaching purposes. These will mostly be scaled down versions of the previous project with a few added details. Talking about 10-12 of them and about 12" across. I'd like to scale down the wood thickness as well to make them lighter physically and visually. I'd also like them to be stackable, only building a lid for the top one and each box would serve as a lid for the one below it. A rabbet on the inside at the top and slightly wider one on the outside of the bottom will allow them to lock together and leave a grove to pick them up separately. The drawings below are sketched out with 1/2" sides and 1/4" bottom and lid. The lip at the top is 3/16" wide and 1/4" high. I'm just worried the lips will chip out easily. The other problem is with the dado for the bottom is awfully close to the rabbet and very little wood there to keep everything together. I can adjust the dimensions but how much? Maybe make some design changes, or use a hardwood that is strong enough. The other route I was thinking was more additive, using strips glued on to keep them stacked and the bottom and lid in place. The second one is far less elegant and I like the first one better but it's less likely to break. How would you build this? Any thoughts would be welcome. Quote Link to comment Share on other sites More sharing options...
Chestnut Posted January 10, 2020 Report Share Posted January 10, 2020 Dados don't generally need to be very deep to provide strength. If you glue them the glue is the larger strength aspect with the dado secondary. I read a few articles that did testing on bottoms mounted in dados and they determined that the deeper the dado the weaker the joint. The side, be it plywood or solid wood, ended up failing first. In practicality a 1/8" deep dado is a good balance shallower than that it's difficult to cut the drawer bottom precise enough deeper than that makes construction easier at the cost of strength. I wouldn't worry a ton until your dado is over 1/3 to 1/2 the thickness of your side. Spline jig. I made one that fits many needs. I made basically a tall fence that slips over my table saw fence. This will allow me to cut tenons and other vertical cuts as well as cutting splines. For one random spline I'll just clamp the work piece strait to the board. If I'm cutting multiple I will use screws and attach blocks to the face to act as work holding (along with clamps for safety). You can probably see some screw holes in this next picture. I made it in a few min and it's lasted me many years already. 1 Quote Link to comment Share on other sites More sharing options...
wtnhighlander Posted January 10, 2020 Report Share Posted January 10, 2020 A simple finger joint jig can be made for the tablesaw to cut fingers on the 135* angle you want, but you will have to make them extra long and trim after assembly. As for the stacking boxes, I suggest using a thicker bottom, with a rabbet around it so the wider edge fits the groove in the side, and the thickness extends below the edge of the side wall to form a "plug" that drops into the box below. The rabbet around the top edge of the box is no longer needed. Sorry, no drawing tools handy, or I'd include a sketch. Quote Link to comment Share on other sites More sharing options...
Cdlong Posted January 10, 2020 Author Report Share Posted January 10, 2020 Thanks for the info, both of you. I get what you're saying, plus I have some other ideas. I'll sketch them out tomorrow. Quote Link to comment Share on other sites More sharing options...
Coop Posted January 10, 2020 Report Share Posted January 10, 2020 Nut, I never thought about the depth in that respect. Stands to reason though. Thanks. Quote Link to comment Share on other sites More sharing options...
Cdlong Posted January 10, 2020 Author Report Share Posted January 10, 2020 Longer reply now that I'm at a computer. Good info on the dados, I had no idea, but it does make sense once I actually think about it. I'll reevaluate with a smaller dado. The spline I was thinking was more on the side like this so your simple jig won't work very well without some significant add-ons, plus my table saw fence sucks, so I'm not sure it would work very well anyway. I saw this super simple jig online as well that would get the job done without too much investment. I'm leaning a little bit toward the spline since it's something new but we'll see. Is this what you were getting at for the bottom rabbet? It would certainly work and looks simpler. I've never used an open rabbet for a bottom though, how strong and stable is it? Keep in mind this will have sand in it. Just glue? Glue and pin nails? The other idea I had was to cut a chamfer (?) in the top and bottom rather than a rabbet. This would leave more wood to support the dado and more gentle corners, but the more I think about it, it will be more likely to rock like a stack of bowls and not be very stable when stacked. Quote Link to comment Share on other sites More sharing options...
Ronn W Posted January 10, 2020 Report Share Posted January 10, 2020 Just taking about your stacking rabbet and dado for the bottom. I would reverse the rabbets so the upper box is outside the innndet box. The the rabbet does not have to be so tall - maybe 3/16 to 1/4". The dado slot for the bottom can be only about 3/16" deep. That will allow plenty of glue for strength. Quote Link to comment Share on other sites More sharing options...
Cdlong Posted January 10, 2020 Author Report Share Posted January 10, 2020 The top rabbet in the first set of sketch is only 1/4" already, I set it that way to match the top thickness though it doesn't really have to. I made the bottom rabbet taller to make a small slot to ease separating them when stacked, which is also maybe not necessary, but would be nice. If I switched the orientation, then the top wouldn't have a recess to fit into. I could make the top full size and make a lip on it to go around the sides, more complicated, but I'd only have to do it once (probably twice to make two stacks) so it's not much to do. For reference and my own documentation, each sand tray could have as much as 4 qts of sand at about 13 lbs. I'll have to check on that, the teaching trays may only have an inch of sand instead of two. Quote Link to comment Share on other sites More sharing options...
wtnhighlander Posted January 11, 2020 Report Share Posted January 11, 2020 Your last sketch has the right idea, but the dado in tge side walls should be housed, not open. The bottom has to be thicker so that is extends below the edge of the sides. You can just make the bottom as a flat panel, then glue an added panel under it after assembly, if you prefer to avoid cutting extra rabbets. The extension could also be a frame, rather than solid. Quote Link to comment Share on other sites More sharing options...
Cdlong Posted February 3, 2020 Author Report Share Posted February 3, 2020 Some updates after a discussion with my wife and other research. The trays need to be 2" deep and have 1" of sand in them so that cuts down on the weight I calculated two posts up. Looking more like 7 lbs each. The ideal lumber size seems to be a 1/2" x 2 1/2" board to start with. The big box stores have that size in Poplar and Oak. I seem to remember some youtuber mentioning popular is technically a hardwood, would it be strong enough you think? Or should I go with the Oak? Here's a slight update to the plans, with some dimensions. I think I might just make the dados the same size to increase the wood thickness and strength, and to simplify the construction, that way I can dado each top and bottom edge and then flip for each crosscut each bevel at 22.5 to make the octagon. I can cove out a lip or something maybe to make it easier to lift each one. Any thoughts? Quote Link to comment Share on other sites More sharing options...
Ronn W Posted February 3, 2020 Report Share Posted February 3, 2020 I like that sketch better. Poplar will be plenty strong and its an easy wood to work with. Quote Link to comment Share on other sites More sharing options...
Cdlong Posted February 3, 2020 Author Report Share Posted February 3, 2020 Thanks for the input. I've never worked with poplar, should be nice. Quote Link to comment Share on other sites More sharing options...
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