Parallel edge marking tool straight & curved edges

Update 2: Added 6mm, 7mm, 8mm, 9mm and 10mm grommits to fit pencils of different sizes. Use 8mm for a regular pencil and 6mm for a metal carpenters pencil (as shown in the images)

Update 1: Added a double length version of the metric ruler.

Required: 2 x 22mm diameter, 7mm thick bearings with an 8mm centre hole. 

A parallel edge marking tool from 1 to 100mm. Rather than a simple straight edge the run the tool against, it has 2 bearings that will run down the edge of your work. This allows the tool to work on both straight and curved edges. It uses a regular pencil for marking and comes with a metric scale (to nearest 5mm - any greater accuracy will require you to set the tool with a rule). 

The model is split in a number of parts, all of which are designed to be printed without supports. If you wish the scale on the ruler to be visible, then an AMS unit is required. The model can be printed without an AMS unit but the tool will have to always be manually set.

Assembly

First slide a bearing into the bearing holder slot and push a bearing pin in from the top. Repeat for the other bearing.

Slide the ruler through the slot in the bearing holder.

Slide the grommit onto your pencil with the tangs facing downwards

Then place into the ruler with the point sticking out (no more than 10mm).

Then screw the grommit cap onto the ruler. This needs to be just tight enough to stop the pencil from moving. It does not need to be excessively tight. Note that the built in scale is most accurate when the pencil is sharpened so the lead in is the centre.

Finally the ruler bearing holder can be screwed into the top of the bearing holder. This is used to secure the ruler in place once you have it correctly set.

Everything is now assembled and ready to be used.