Finger Joint Generator

Quick Look: Python script which generates DXF files to cut the shape of a finger joint

Desired Capability

• Generate dxf polylines of finger joints that are fully parametric

• Generate dxf polylines of holes which mate with fingers, these are also fully parametric

• Control the shape of "dogbones" in the cut fingers and holes

• Control the number of fingers per span

How to Use

1. Generate an "Edge class" with the following parameters

   • numFingers (int): The number of fingers within the span

   • fingerLength (float): The length of the finger, a negative number can be used to generate a finger in the opposite direction

   • clearance (float): How much to inset the finger width to allow for mechanical clearance

   • span (float): The length of which the fingers will be generated

   • extra (float or list): A single value which is added to each end of the span or a list of two values which are added to the appropriate end of the span. This value can be positive or negative.

2. From here, the fingers and/or mating holes can be generated using the following functions. Discussion of the input parameters can be found in the next section.

   • genFingerPoints: A list of XY points are stored in "self.cordsFinger". These points do not contain dogbones.

   • genFingerPointsBone: A list of XYB points are stored in "self.cordsFinger". These points do contain dogbones.

   • genHoleBone: A list of XYB points are stored in "self.cordsHoles". These points do contain dogbones.

3. The generated points can now be shifted and/or rotated using the function "self.rotateShiftElement" with the following input parameters.

   • element (string): using either "finger" or "hole", specify which coordinates need translation

   • shiftOrigin (list): a list of x and y coordinates to which the fingers will be translated

   • angle (float): angle in degrees which the fingers will be rotated, this can be positive or negative

4. Multiple edges can be joined together using numpy's concatenate or other python tools

   • Note: The last point of one edgeA may be the first point of "edgeB", it would be good practice to omit the last point of "edgeA" prior to joining the points.

np.concatenate([edgeA.cordsFinger[:-1], edgeB.cordsFinger")

5. After storing the points in a dictionary, said dictionary is passed to "dxfFromDict" which plots the lists as LWPolylines within layers as specified by the key of the dictionary.

6. See "dxfTest.py" and "trapezoidBox.py" as examples of how to use the functions

Functions

self.genFingerPointsBone

Input variables:

• dogBoneDia (float): Diameter of the dogbone

• dogBoneType ("H", "X", "I"): Three options to generate dogbones, each one places the dogbone differently on internal corners. Useful if cutting the forms on a CNC

• invertBone (bool): Change if the dogbone is generated on the "top" or "bottom" of the finger. Useful when generating a mating finger edge.

• drillNum (int): Generates a 2D list of drill locations. The int specifies how many drill locations per finger. Useful for mounting together edges.

Output Variables:

• self.cordsFinger (2D list): A list of XYB coordinates which are used by LWPolylines to plot out the finger's shape

• self.cordsDrill (2D list): A list of XY coordinates which specify the drill locations on a finger. If a finger/hole and drill points coordinates are generated and then translated using "self.rotateShiftElement", both the drill points and finger/hole coordinates are translated

self.genHoleBone

Input Variables:

• materialThick (float): vertical distance of the hole

• clearence (float): How much the hole is increased, both the vertical and horizontal distance

• dogBoneDia (float): Diameter of the dogbone

• dogBoneType ("H", "X", "I"): Three options to generate dogbones, each one places the dogbone differently on internal corners. Useful if cutting the forms on a CNC

• openEnds (bool): If the holes are to be generated reach the edges of a material, the first and last hole can be open to allow for that

• invertHoles (bool): Generates the "inverse" holes. The "other" mating geometry

• drillNum (int): Generates a 2D list of drill locations. The int specifies how many drill locations per space between holes. Useful for mounting together edges.

Output Variables:

• self.cordsHoles(3D list): The first list dimension is for each hole generated. The second list dimension is list of XYB coordinates which are used by LWPolylines to plot out the hole's shape.

• self.cordsDrill (2D list): A list of XY coordinates which specify the drill locations on a finger. If a finger/hole and drill points coordinates are generated and then translated using "self.rotateShiftElement", both the drill points and finger/hole coordinates are translated

dxfFromDict

Input Variables:

• pointDict(dictionary): Each dictionary key (str) becomes the layer name which the points will be plotted onto. Each coordinate corresponds to a XY paring and a bulge value. Below are some examples:

  pointDict["rectangle"] = [[0, 0, 0], [1, 0, 0], [1, 1, 0], [1, 0, 0], [0, 0, 0]]
  
  pointDict["Ls"] = [[[0, 0, 0], [0, 1, 0], [1, 1, 0]], [[1, 0, 0], [2, 0, 0], [2, 1, 0]]]
  

• fileName(str): Specify the filename and/or path of the dxf file to be generated, file extension must be stated

• drillDict(dictionary): Each dictionary key (str) become the layer name which the points we points will be plotted onto. Each coordinate corresponds to a XY paring and the radius of the drill. Below is an example:

  drillDict ["drillPoints] = [[0, 0, 0.2], [1, 0, 0.2], [2, 0, 0.4]]
  

• units(int): As specified by the ezdxf documentation, the dxf units can be specified. I have defaulted to mm. All coordinate generation is unit-less.

Example Build

The DXF files generated from "trapezoidBox.py" were utilized to cut out the following display stand which was utilized to show the Luggable PC at Open Sauce 2024. Incorporated into the bottom of the stand is a 0.75in bearing race so that the display could spin in place.