This instructable will guide throught the steps required to make a custom tail guard that fits your longboard/skateboard.
List of things you need :
- sheet of paper & pencil
- tape measure
- angled socket wrench
- two countersunk M5x20mm screws
- two M5 nylon stop nuts (to avoid release of the screws due to vibrations)
- your longboard or skateboard (mine is a bustin modela 33", to give you an idea)
Your might want to use longer screws depending on the thickness of your board. The two conditions to respect are :
1) leave at least a 1mm clearance between the end of the screw and the bottom of the tail guard
2) screw length - minimum tail guard thickness (1.9mm in my case) - deck thickness - nut height > 0
This makes sure the screw actually exceeds the nut; see assembly sketch above.
A little familiarity with CAD software would help, but is not entirely necessary.
To realize this project, I used DesignSpark Mechanical, which you can download for free here. You can of course use another software, just make sure it has good 2d spline drawing capability.
Step 1: Getting the Outline of Your Skateboard's Tail
To retrieve this outline, you need to put your skateboard upside down on a flat surface, and place a white sheet of paper underneath the tail. Now, simply use a pencil to draw the contour up to at least 5 centimeters away from the extremity. You then need to make precise measures of the width and height of your drawing (actually, its bounding rectangle) as shown in the picture above and note them down for later. This will help us scale the contour to its proper size when we import it into our CAD software.
Next thing you have to do is scan the page and then crop the resulting image to keep only the contour, as in the first picture above. Make sure you save it in either jpeg or png format.
Step 2: Starting the 3d Model
Here, we'll look into how to use the tail outline as a base for modeling your custom tail guard in 3d.
Once you have launched DesignSpark Mechanical, first import the contour image using the Insert->File button in the ribbon (Design tab). A file explorer window opens, make sure to use the All Files (*.*) filter to view image files. Pick yours and place it at the origin of the 3d view with one click.
Next you'll need to scale the image to its proper size.
To do so, first draw a segment along the x axis of the exact size you measured in the previous step. Then draw another segment from the origin along the y axis. Again make sure to give it its measured length. Now you must move and scale the picture until it aligns properly with the two segments.
Once that's done, you can start drawing a spline curve following the pencil contour using the Spline tool. Make sure to use as many points as you need to get an accurate drawing. Additionally you should disable the Snap to grid checkbox in the bottom left panel for precise positionning. You can always rework your curve once it's drawn by moving points or control points and also right-click on it to add new points, to make it fit the contour better. At this point, you might want to offset your curve inwards by one or two millimeters, depending on how tight you drew the outline earlier.
Then draw a line about 40 millimeters away from the extremity to close your curve and get a 2d surface (see 4th and 5th pictures above).
You can remove excess lines by pressing T and clicking on any of them. Now extrude the surface upwards by the thickness value you chose earlier (9.5mm in my case) to obtain a solid part.
Step 3: Finishing the Model
Now we'll finish up our model starting from our extuded shape.
First you'll want to round up the extremities of the bottom surface. As you may know, the part is likely to warp during the printing process (how much depends on what material you chose); this will help lessen that effect. To do so, draw an arc on both extemities with a radius slighltly smaller than your part thickness; I chose 8mm. Then switch to 3d mode and use the Pull tool on the newly delimited surfaces on both corners to remove the excess material. Next move the upper edge 4 millimiters back (see 2nd picture) to get a slanted surface.
Then we'll add holes to fit the screws and bolts that we'll use to fix the tail guard on the skate deck. I drew 13.5mm circles since my angled socket wrench (size 8) has an external diameter of 13.3mm. To give you an idea of positionning, see 4th picture. Select both circles, and use the Pull tool to make the holes. I chose a height of 7.6mm (see assembly sketch in introduction). To give room for the M5 screws, I chose a 5.2mm diameter for the bottom holes.
Once your model is done, export it as an stl file using File->Save As, select .stl extension and click the Options... button to change the resolution to Fine, to make sure the output is precise enough.
Congratulations, you can now print your model; I don't have printer so I used 3dhubs to have it printed not too far from where I live. As for the choice of material, ABS plastic is fine, but I'd recommend something stronger even. I personally chose Colorfabb XT ( a PET variant) for my second print, it costs a little bit more, but definitely lasts longer.
Step 4: Assembling the Tail Guard
Start by positioning you tail guard on your tail where you want it to be, and use a pen to draw marks for the holes. Drill the holes using a Ø 5mm wood drill. Clean the holes griptape side using a cutter. Now assemble your tail guard using your two screws and nuts, and you're done!
Step 5: Go Skate!
Thanks for reading this instructable, I hope some of you will find it useful.
If you ever make one of these for your skateboard, I'd be interested to get your impressions/ feedback and some pictures if possible.