SmartMachining-Tongue and Groove

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    Many people are using tongue and groove joinery in conjunction with nested based manufacturing. In many cases it is suggested for ease of edgebanding and to have the CNC correctly identify the groove location and size, that stopped dados be used. Please remember to allow for the diameter bit that will be used to allow for enough “slop” in the joints and allow for correct front and back start/stop points. One of the disadvantages in this type of construction with CNC work is that it can be material thickness sensitive. The thickness of the material has a direct relationship to the length of the tongue as well as the thickness of the tongue. Either find the thickness of the material you will be using and draw the solid at that thickness and apply the machining, or else see if you can set the machine to reference off the surface of the bed rather than the top of the material. Some trail and error may be necessary here to determine the settings that work best for you, your material and your machine. Please remember that many machines will not allow you to make a groove the same size as the bit you are using, so minor adjustments may be needed in groove width. 

One trick here is to make a preset on the drawer slide module to bore pilot holes in the edge of the groove. Once assembled, screws can be driven through the outside of the cabinet to hold it together and force the tongue tight on the inside of the cabinet while the glue dries. The user has the option of “Interior”, “Center” and “Exterior” joint. This is the relationship of the joint location on the edge from the side reference point selected. 

One other option that you have that may rarely be used is the offset option. In almost all applications this will be set to zero, however there is a specific application that uses it. If a custom bit is made with, for example, a 3.5mm flat, a 6mm tongue and another flat, one could cut down into the spoil board .5mm, have a 3mm reference flat and then the tongue. By placing the groove in the board at the appropriate place, the board thickness problem for accurate joinery is basically eliminated, as the tongue will have a known thickness. This operation can also take place without the need to flip the part over and do a sixth side matching operation. 

In the standard application of this module the inside of the box would be correct, but the exterior may be off. It’s a design trade off. One of the other major features of this program is the ability to generate either a tongue or a groove without the need to generate the other feature. This is especially helpful when dadoing out for a back or drawer bottom, or adding a tongue on the front of a vertical for a face frame to attach to. When using the program, please make sure to read all the prompts as they can sometimes change depending upon any previous machining that has been done on the part.