Building a set of compact grappling hooks


Around the sites selling camping and every-day-carry gear I sometimes see a couple types of small grappling hooks available, with the most ingenious idea of storing the removable hooks inside itself. Why do I need one? According to one manufacturer, some of these smaller grappling hooks are used in military bomb disposal for snagging detonation wires. Well certainly if I ever need to employ one for that my camping trip has gone very badly indeed, but they could be useful for attaching a temporary antenna to a tree, or recovering some gear that fell down a hill.

Mostly though, this is a project that looked fun to build. Today it's more about spending quality fun time with the machines than the end product.

Not much description today, mostly a showcase of some metal turning photos.

Design work

So first I spin up a design for the larger one in Freecad. It was pretty straightforward, except for some messy construction geometry for the angled-holes for the spikes. It sort of follows the method for holes-in-cylinders as described in my post about making a threading die holder, but getting a plane on which to build a sketch in the right position was a lot of trial and error.

So here's the final CAD assembled:

large grapple CAD
Also a closeup with transparency turned on to work out the exact depths of the threaded holes. I'm trying to get the maximum strength possible without the holes breaking through in the center. Also visible is the spikes fitted into the storage area.
grappling hook transparent cad
This is just too fun, I'll have to make a smaller version too!
small grapple CAD

Starting the lathe turning. 7/8" aluminum rod for the body and a 1" diameter cap. Single point threaded and drilled.

drilling the body
An excuse to use my new insert threading bar while making the cap.
theading the cap
I had a 0.045" O-ring, so I cut my groove 0.035" deep and tested that fit with the cap. Feels like it will be water tight too.
fitting the oring

On to the milling machine.

I've left extra material on the bottom of the body to hold in a 6-sided 5C collet block. Super fast and easy way to index a part on 3 or 6 sides. The scribe lines are to line up my drill bit the proper distance from the bottom of the body.
setting up on mill
So first we counterbore with an endmill, then drill for the tap.
counterboring holes
Keeping such a short bottoming tap at the proper angle would be quite tricky by hand. So with a socket wrench on the draw bar the mill becomes a giant tapping guide.
hand tapping with mill

Completed grapples

I didn't get any photos of making the small one, but it's pretty much the same process. After building both I went back and added a bit of knurling to the spikes, they need the extra grip to be able to easily screw them into place by hand.

So first, here they are both in storage:

stored grapples

With the caps off, spikes stored inside

grapple spikes stored

Finally the grappling hooks with spikes deployed.

grapples ready

Well these might live in my hiking bag for some time before they see any use, but making them sure was fun. I think the one thing I'd change is the angle of the spikes. These are 50 degrees from the center axis, and I think even more would make them a little better at grabbing things.