Catch Tenon Joint | Assignment 2

In this project assignment I was tasked to make a 'catch tenon' wooden joint based of its picture. If you look closely on pic.3 the two exampled of the catch tenon joint have pockets carved out differently, so I chose to follow the easier version with all pockets on the same side (the right side example picture).

The process was as follows: drafting out the measurements on paper --> Rhino7 3D modeling --> Shapeoko CNC machine cuts out the pieces --> Final repairs and touch ups

- wood (thickness +- 18mm)

- Shapeoko CNC machine with tool size = 6.35mm

- Rhino7

The first step consisted of figuring out how this joint works based of the picture. The idea is to have two bolts from piece 1 [ref. pic.2] fit into the holes in piece 2 and finally the latch from piece 1 close onto piece 2 perpendicularly to prevent the bolts from sliding out.

For measurements: the size of each board (piece of the joint) was to be: 80 x 160mm

For the rest of the sizes it was up to us - for all the measurements check pic.3

This step took me the most time since any miscalculation in this step will affect the final wood cutting process. First I started with the general contour of the joint ([pic.1] - !sizes on this picture might not be accurate since it's documentation from the first draft, for accurate sizing please refer to step 1 OR the .dxf file provided above)and later cleaned up the draft [pic.2] + made the last corrections of the measurements. Finally I extruded the contours, added pockets [pic.3] and made sure the models of the pieces fitted together [pic.4].

Problems with this step:

- I had many open curves [pic.5] which I had to eliminate before I could proceed with extruding the contours

- piece 1 with the latch had to be in two separate parts (the board + the latch - which is visible on the 3d model and in the .dxf file) since there were issues in making the whole model a closed curve. Nevertheless that helped with the creation of a pocket for the later stages when working in Carbide Create V5.

After the 3D model was done, I exported it to Carbide Create V5, set the pockets and contours for the machine to follow.

The first cut-out worked out well but only for piece 2 (the one with the holes and no latch). Piece 1 broke since the latch area was of 9mm thickness (half of the wood piece), hence 1) it was hard to bend and when bent by force to make space for the bolts to go into piece 2 it broke; 2) the latch was bending along/ with the grain of the wood board which made it additionally easier to break. (make sure you know which way the grain of your wood board is going and where will the parts that will have to resist more strain be - such as the latch area in the catch tenon - before you start cutting out your joint)

Since piece 1 broke, I tried making another one which was 1) positioned against the grain of the wooden board; 2) was thinner - 6mm instead of 9mm.

Unfortunately, this was not enough for the latch to bend and not break again.

Since the latch is a crucial part of the catch tenon joint and it broke in two variants (9mm and 6mm thickness latch) of the piece 1, I decided to add a hinge on the broken piece. Initially, since the middle of the piece was already fragile due to the broken off latch, I thought of only screwing the hinge to the latch itself and to the diagonal hole of the hinge (red dots on pic. 1). Obviously this resulted in an unbalanced center for the hinge to move, hence I decided to add a screw to the middle (green dot on pic.1) --> very bad decision: during the sanding process the board started breaking in half and to keep it together as much as possible I had to hot glue the whole area + add duct tape just in case to finish off sanding.

As a result, piece 1 is functional and steady, although slightly... ugly.