Lego “Dovetail” joint for a lego table. I just finished the test prototype, and hope to finish the whole table by the end of christmas break:
The end goal is to recreate this table I made 5 years ago with better joints:
My inspiration was a NOEL joint that Lee Valley had posted on their website that looked like it would work great with CNC
I used the Arial Black font to create blocky text that fit the area. I then converted the text into vectors and adjusted the text so that a 1/8 end mill can fit into all of the areas with the letter G being the most difficult. One trick I used was a created a circle with same diameter as the bit and moved that around manually to check spacing and adjust vectors. I created two tool paths, one that routed out the interior of the letters and one that routed around the letters. I kept simulating until when I ran both tool paths there was no wood shown in the end result.
To hold the vertical board I followed ScottsdaleSteve method and attached a 2" thick block of scrap oak to the spoilboard that I had made square on my jointer. I then clamped the board to this block and routed out around the letters.
For the other board I just screwed the board to the waste board since this was a quick and dirty proof of concept and routed out the interior of the letters. I then lightly sanded both pieces and used a mallet to connect push them together. It was a very tight fit and actually broke part of the G off. I used a pocket offset of -.002" for the letters and will likely increase that for the final parts. Workholding is something I still struggle with and need to figure out how I am going to do it on the final boards to avoid the screw holes.
The other part of this project is I want to route out the lego portion in the middle instead of using a plastic plate. I’m currently stuck on how to make a nice enough end grain portion for this part of the build. Plan is to reinforce the fibers with cyanoacrylate glue before routing.
I bought some more clamps and was able glue the end board blank together. I used the CNC with a 0.250 end mill to flatten the top and bottom. I used a scrap cutoff from the main section to dial in the diameter that worked best with the wood and bit I was using. I used a Whiteside RD1600 down cut bit which worked great in the end grain. In the end I found a circle diameter of 0.195" worked best to give a part that could be disassembled, but not be too loose that they just fall off.
The file is just an array of circles with a diameter of 0.195 and gap of 0.315.
Lego board portion Final.dxf (6.6 KB) I was very happy how this turned out and the end grain works perfectly. I had thought about adding a chamfer on the top with a v-bit but decided against it. In the future I would do that step to help the lego pieces get started
I did end up reinforcing the end grain with super glue. I did not have accelerator and the glue never really cured in the interior. It stung my eyes a little while I was carving the pegs. On my test piece I tried with and without super glue and didn’t notice a differnce. The board did surface to a smoother finish after the glue was applied. (I surface the wood, applied super glue to entire surface, let sit for 24 hours and then surfaced again).
As a Christmas gift to myself I picked up some of the carbide 3d end stops and the tiger claw clamps. I then used the router to create the slot the main table board will sit in with the #201 0.250 end mill. The clamps saved me a lot time and I wished I would have bought them sooner.
I was going to use the same whiteside bit for the joint portion, but I realized it only has a cutting length of 1/2" and gets wider above that height, making a loose joint. An emergency order to amazon later I used the Amana Tool - 46125 bit to carve the joint. My one mistake was making the letters exactly the height of the board. Even with very careful positioning, I always ended up with some portion of the letters not being carved. If I would have made the letters .73" tall instead of .75" it would have worked fine. Before carving I adjusted the letter spacing such that the letters did not overlap the slot.
Lego connection 5.5 inch.dxf (61.1 KB)
I made the letters 1/16" deeper then the boards they were inserted into to make sure they were proud of the other board and could be sanded flat.
When cutting the pockets I used -.0035 pocket allowance to create a tight fit, but not too tight. On my sample I used -0.002 and it could be pounded together, but not hand assembled. This is a toolpath option on varve that doesn’t seem to exist on carbide create This can probably be done with an offset path on carbide create to create a new vector, but I haven’t tried.
I then glued the joint together and put a 1/4 roundover on all edges since this is meant for young kids. I still need to build the legs yet, but I am out of time for the contest. Normally I would wait until project is complete to apply any finish, but with project deadline I applied the first coat of minwax hand rubbed polyurethane to get a picture of the final project (minus legs)
The vcarve files are below.
Lego connection 5.5inch Final design with fixes.zip (1.3 MB)
Just added legs and another coat of finish: