Something I made to cut the brim from prints, uses standard 'stanley' type trimming knife blades. Some fettling of the insert might be needed to get it to fit, but that helps ensure a tight fit.

Note that this is in no way a safety knife and should be used with care. At some point I might make a slide on cover.

Printed at 0.1mm layers in PLA.

Once printed insert the blade into the body, slide in the insert and its should all lock together well enough to be usable.

Take care when fitting the blade - it can take some pressure to get the insert all the way in, so get a good grip!