Bonsai Root Rake for 3" (75mm) Nails. Parametric for slight nail size variations.

Note that you'll get a nicer model than my photos, I've updated the F3D and STL for a round-ended handle and a “BONSAI MASTER” engraved motif :o)  

I've used a single bent nail for years for bonsai root raking to remove old soil before root pruning and replanting.

It was never very satisfactory, but I don't do a lot of bonsai work so I couldn't really justify buying the right tool! At least it did the job, but was a bit hard on the fingers holding the nail and with only one tip it was a bit slow.

I looked around for existing designs but I didn't reckon thin plastic tips would be durable enough, so I came up with the idea of printing a handle for 2 bent nails.

This is my first attempt, and it seems to work so I haven't developed it any further.

I made the model mildly parametric, you can use the Fusion360 F3D file to adjust fx parameters for the nail size but really only for minor variations on a 3" or 75mm nail. Mine were 3.1mm shank diameter, 6.6mm head diameter, and 1.5mm head thickness. You can tweak those by a few tenths of a mm and the model will adjust, but if you're using a different size of nail then it's unlikely to work without significant redesign of the sketch itself. 

The straight captive part of the nail is 20mm from beneath the head, so mark your nails no less than 20mm from beneath the head, clamp the head end of the shank in a vice and hammer the shank across until it's bent about 60 degrees like mine. Measure about 14mm from the sharp tip and mark, then clamp the middle section of the shank in the vice and replicate the end bend at about 90 degrees. File off any snags and the worst of the sharpness on the nail tips - you need a fairly pointed tip to get soil out from between roots but you don't want it so sharp that it cuts into them.

Try the nails into the holder with the handle and slots, you might want to tweak the nails so their tips are parallel before fitting the clamp section. 

Once you're happy it's right, put some smears of glue on the 4 protruding interlocks on the handle section and a bit on the captive parts of the nails, squeeze the cover on and then squash it together in a vice and leave for the glue to cure, time depends on your glue, I used 5min epoxy on mine. Not too much glue - the interlocks are ZERO CLEARANCE so they will be tight but they should go together fine - I got mine all the way just with fingers and then snugged it up in the vice to maximise contact while the glue set.

Seems to work best using thumb on the wide section behind the nails, and a finger underneath so you're mostly holding the head section, the handle is just there for a bit of stability. It would be uncomfortable to hold it just by the handle and the leverage could be enough to break it depending on your walls and infill, I just used 3 walls, 6 tops/bottoms, and 15% grid infill.

I haven't done much raking with mine yet so I'd be interested to see how others get on with this please! The proper tool is over £10 to buy so for those not needing one very often like me, this is a reasonable substitute :o)

Please Like this model if you find it useful.

If you REALLY like it, https://www.buymeacoffee.com/gigabeast :o)