Circle cutter for paper, cardboard or other thin materials without centre tip. Can also be used to mark an circle on harder, thicker materials.
Imperial Version available!
A fresh segment of an utility knife blade is used for cutting.
The reticle in the base can be seen from three different perspectives from the sides and from the top. This makes aiming at the centre quite easy and precise.
The absence of an centre pin avoids unwanted punctures in the work piece. The base is just pressed down to the material.
A circular groove in the bottom can take a piece of flexible filament (1.75mm) for anti slip. This works great and enables the usage of an quite long arm.
The blade holder can be mirrored to mount the blade between the holder and the base (as shown in the images with the all white background). This sacrifices 15mm of the radius, but makes it safer to use. In this configuration the edge can also be put in the big hole in the base for storage, where it is covered quite safely.
Since the screws are screwed directly in to the material you need an slightly flexible material. PETG is perfect.
The base and the blade holder is pron to curling. Proper part cooling helps.
The M3x30 screw is screwed through the thumb knob with the M3 nut inside all the way down through the blade holder. The adjustment knob needs less than 1mm room benth the head of the m3x30 screw. This prevents the thumb knob from getting lost.
The axis might need a little sanding and lubricant. I designed it with thigh margins to avoid play.
To install the anti slip ring: Press the begin of the filament in the grove withe on finger. Then stretch it to reduce the thickness. The stretched filament will slip down in the grove. Work your way around step by step.