Have a knife day!   Over-engineered OTF. Also good for brenchmark print. Lots of variants. Lots of patterns. Fully 3D printed. Upgradeable. Good as gift. Also very nice as comb.

(This is an over-engineered model. Please always print using a print profile and DO NOT try to slice it yourself!)

Also try this Gravity Knife

Here you go some variants  Pro Utility Blade Holder, Xacto, 9mm Mini Pro, 9mm Nano, 18mm, trapezoid. Or check my model list. :P

This accurate model requires printing using the most reliable filament and printer settings. Good as a benchmark testing your machine and filament setup. If you are confident in your settings, you may want to try changing the filament. But you can also try the spring kit set profile. This will, to some extent, force the overturning of certain errors. Please let me know the results. Good luck. The main problem is warping: The front cut out becomes smaller. The blade failed to catch the spring for ejection. Strongly suggest Liquid Glue in BambuStore.  Filament issues: The push lever is difficult to move(a common problem with silky), or if the parts need to sanded, this means you need to try a different filament colors/types.  Installation issues:  The latch lever is oriented in a "V" shape, not an "A" shape. Pull the blade all the way out (reference time 1:06 in the video) and the latch lever will prevent it from returning. Now you can install the top cover. (Don't blame a model or print profile by giving a low rating. It won't help you to be successful with your next print at all!)

****No hardware required.  But if you want to use metal spring, here you go the upgrade kit using BA001, BA002

****Based on my experience, not all PLA filaments are suitable for precision printing.

**** Profile well testing using PETG-HF and PLA Basic, Sparkle and Marble. Strongly suggest PETG-HF, especially for the spring. And the PLA Silk Dual Color is not good for this precision print.
****If mixing filament types (e.g. PETG with PLA) for multiple colors, it is best to disable flow calibration.

Yet another OTF fidget, Anti-anxiety, ADHD. 

More pattern and print profile to be updated. 

Build video link.     

Total 6 Parts

Or using optional metal spring upgrade kit.

4+1 types of handles

Many patterns (Too busy, to be released. Follow me, stay tuned! And you can always suggest a missing patterns by comment.)

Optional Push Buttom. (Indeed I made the button with jimping texture at the very beginning. Over the development time and stress test, that jumping texture really hurt my thumb. So I smooth it out for fidget purpose. Anyway you can try this print profile. :P "Optional Jimping (Textured) Button Upgrade")

Blade Type

Optional comb blade

btw. Thumb pain indicates that the OTF is not working properly. You're trying to cover all the print and filament error with your Hulk thumb. A good OTF can be triggered through your pinky finger! 

Don't forget to try my Gravity Knife!

Good luck and good luck printing!

Try my nozzle wiper fix for X1/P1/A1.

A1/A1 mini video link

X1/P1 Wiper video link

Also try this hourglass clock!