The aim was to design a Bow Compass that is:

1. fully printable with no supports! The use of 1x wood screw is the exception here (to be used for its sharp point) and allows the tool to function as well as its metal counterparts.
2. Sturdy enough for workshop use, holding its position reliably & is easily adjusted.
3. could accept a carpenters mechanical pencil, but also any regular pencil too!

Other similar printed tools comprise of flat profiles which wobble & bend far too easily, they also have excessive play leading to inaccuracy. This model has increased strength, achieved with a monocoque-style leg design that houses all of the working components, and is an uprated ‘beefier’ version than my previous adjustable calliper design due to the conditions it will be under.

Holds any regular pencil (up to 7.5mm in diameter) OR commonly available 2.8mm lead ‘carpenters’ mechanical pencils (which are 13mm diam. in the main body and 5.7mm on the metal finger-grip portion)…..but regardless of brand, they are all pretty much the same shape. The specific ones I have can be found here.

The straight legs are 150mm long (from the pivot centre), and open up to a maximum of 200mm wide…. all meaning it can draw circles up to 400mm (16") in diameter! I am really pleased at just how well this assembles & performs.

Wood screw recommendation:

• Metric 4.0 x 30mm (anything up to 40mm long could work, but just wont need to be screwed in as far)
• Imperial #6 x 1-5/8" drywall (Thanks to ChopperOriginals for his recommendation in the comments on this)

I hope you like it!

If you do you may want to check out some of my other DatumCAD designs :)

Assembly:

• Insert the 3x Adjuster nuts into the Legs: These snap fit and are deliberately tight to avoid coming out easily (so may require a decent amount of force before they click into place) try pressing or even tapping into place with a flat head screwdriver/punch if needed. Don't worry, they are all the same and can be inserted any way round!
• Connect the Legs together: Just align the top hole of the legs, then push the Pivot pin through the hole in both legs (from whichever side you prefer) and secure in place using the circlip.
• Insert Slider & Slider Bolts: Place the hole end of the Slider plate onto the same leg which will house the pencil, fixing in place using the shortest of the threaded bolts. Then insert the longer threaded bolt though the slot in the slider plate & into the other leg.
• Insert Pencil Locking Bolt: The remaining bolt should be threaded with a short & plain end. Use this in the pencil fixing nut location.
• Insert Wood-Screw: The hole is just fractionally smaller than the threads so the screw should thread its way in easily if you use a screwdriver.
• Enjoy! Your adjustable bow compass is now ready to use - Simply insert a pencil of your choosing! :)