Compass Ruler
A compass ruler, why when you can use a standard compass.
The standard compass still requires the ruler to measure the appropriate radius for the circle to be drawn and has a limited useful radius.
While a beam compass is more specialised offering a greater range than the standard compass, possibly including graduations and extension pieces but is a relatively expensive option.
A ruler is a must have in the workshop and is relatively inexpensive in comparison to the former.
But the size of the circle is only limited by the length of the ruler and is infinitely adjustable along its length without recourse to extension pieces.
The elements to be designed to accomplish the function are inexpensive, few in number and can be scaled to the appropriate ruler size.
Supplies
Design
Only two elements are required to be made for the compass ruler these are made to fit a 12mm x ~0.5mm steel ruler
These are the pivot element and the slider which holds the pencil and are designed to be 3D printed.
Both elements have a slot which is compatible with the ruler allowing them to slide up and down.
The pivot element sits at the end of the ruler and is held in place with a screw, a hole at the extreme is the pivot point.
This point has two options.
1: Fixed with a grub screw that will be the circle centre.
2: Placed over a fixed point (i.e. Nail), that is the centre of the circle to be drawn.
For greater flexibility two pivot elements can be made for interchangeability subject to requirements simply swapping the elements as required for the task.
The slider that holds the pencil needs to be able to slide up and down the ruler and locked in placed with a thumb screw at the required point to set the circle radius.
Screw holes are M3 compatible.
The design would be created using BlocksCAD.
The orientation of the elements in relation to the bed is critical as a result of the slots and the impact of gravity.
As a result the slots are orientation vertically and short arcs are used in non supportive horizontal runs to eliminate sagging.
Slice & Print
Once the design has been completed and the OBJ file created its time to load it into your favourite slicer.
In my case I use Cura to create the 3d print settings.
Due to the small size of the elements and that they will have threaded bolts fitted the infill was set at 100% to add strength.
Basic settings:
Layer Height - 0.15mm
Infill type - Tri-Hexagon
Base adhesion - Brim
Filament - PLA
Load the Gcode file in to the printer and wait for it to complete..
Post Processing
Once printing is complete remove the brim filing off any excess, check that the slots are blockage free as this will prevent the ruler from passing through the element. A needle file can be used to clear the slots and holes if required.
Next fit the screws, placing the element on a flat surface with the hole facing up and push the thumb screw or bolt in to the hole whilst applying downward pressure and turning clockwise.
Screws and bolts with rounded ends helps make the task easier and mounting the element in a vice will help stabilise it and reduce the likelihood of the screw/bolt ending up skewed.
Using PLA and M3 bolts means that the material is soft enough to allow the bolts to cut a thread negating the need to tap the holes first. This in conjunction with the hole dimension means the bolts are a tight fit but try not to skew or cross thread the bolt in the hole as this will reducing its effectiveness.
One bolt will be required for the pivot element to hold it in place and if to be fitted a grub screw in the pivot hols.
A further 2 bolts are required for the pencil holder, one to hold the pencil and one for the holder to lock it in place at the desired radius.
Usage
With the pivot element firmly secured at the end of the ruler and the pencil holder complete with pencil or other suitably sized writing element is adjusted along the ruler for the desired radius.
The point of the grub screw in the pivot point and this is pressed in to the surface on to which the circle is to be drawn.
With the pencil on the surface and the pivot point pressed firmly on the surface rotate the pencil about the pivot point axis and draw the circle.
Finally
Hope you found this of interest.
The print files can be downloaded from YouMagine