Introduction: Adjustable Nut Cracking Machine

About: I like to do electronics, metalworking, woodworking, fixing things and all sort of cool and stupid things :) I also have a YouTube channel:

This year it was remarkable year for walnuts and we had loads of them on just a few trees.
Every year we crack them, pack the kernels into bags and store them in the freezer so we can use them over the year for eating, baking and other stuff. Every year we were cracking the shells by hand tools, mostly cracking them with some sort of weight/hammer or with a manual cracking pliers. And this takes a lot of time and effort.

And because this year was so fertile I decided to build an electric machine for cracking walnuts (and other nuts too, so I made it adjustable).

Here watch a video I produced for you to see the machine in action and to have an idea on how it is made and it would be easier to follow this instructable:

Step 1: The Materials and Tools

For building this, you need some metalworking skills, since it includes a lot of welding, grinding and cutting metals. My tool arsenal consisted mailny from:

- angle grinder

- cheap chinese lathe

- cheap welder

- drill

But If you do not have a these tools, you could probably get around this using wood or plastic and screw it together with more basic tools. I will discuss more on alternatives druing the instructable.

I used miscellaneous metal parts which can be found in local hardware store:

- main body is made from a square metal profile 12cm x 12cm wich was just the right size for my need

- the roller is a metal pipe, around 4cm in diameter

- shaft of the roller is another metal pipe which was around 2cm in diameter. I used a relatively big shaft, because I had some cheap chinese bearings lying around which I wanted to use

- cheap bearings wich were just a couple of bucks each are used to hold the shaft in place

- other parts are made from flat rolled steel

- rpm reducer from a broken pellet furnace for reducing the rpm from the drill. You can go without that, if the drill is strong enough. You will just have a much faster spinning rotor and shells will fly everywhere, so I recommend getting one (thank me later) :)

Worm gear reducer for maximizing torque:

1:20 or 1:15 ratio works well.

Step 2: Making the Cylinder Roller

This is the most complicated part and it took me the longest to make, because by nature, I like to overcomplicate my designs :)

I don't have many pictures of the buildd, but i shot some video clips.

The procedure is best seen in the introductory video from the first page from 0:24 onwards.

I started with a regular steel tube on which I welded some plates, to plug both ends. Then I drilled smaller holes in the now closed sides which fitted the shaft I was using.

In the video you will see that I used a lathe to trim the diameter of the shaft. This is unnecessary step. I did it because the tubing had imperial diameter and my bearings were metric, so the tube was a few milimeters too thick for the bearings and I needed to trim it.

The shaft needs to be quite strong, because relatively big forces could appear during nut cracking. Rather overbuild it than underbuild. (my bearings are waay overkill, but they were cheap)

Then I welded some crossbars on the roller, so it could grab the nuts more efficiently.

If you don't have all this metalworking tools, you could probably get away with a roller from hardwood and you could screw some metal plates on it to serve as teeth to grab the nuts.

Step 3: The Plate

The plate is just 2 thick pieces of rolled steel(5mm thick) that I welded together so I archieved the desired width.

It needs to be quite strong to survive the forces needed for cracking the nuts without bending.

I used the primitive DIY hinges to hold the plate in place.

Behind the plate there is a big screw that pushes the plate forward in order to set the desired operating gap. (video at 2:12)

I also added another screw for the "anti-rattle" system. It is basicaly a screw, screwed into the plate itself, and you use a nut to tighten the plate back, so it does not rattle and bounce around while crushing nuts causing unnecessary noise..

Step 4: The Frame

The frame made from 12x12cm steel profile and is full of holes and welded addons, because I was making it up as I went along.

It has a big side hole for sliding the roller in, some holder for a simple funnel for feeding the nuts in and some brakcets for mounting it to the baseplate.

I painted it with a cheap spray to prevent rusting.

Just don't spray the roller and insides, because the paint would flake away into your food.

Step 5: The Powertrain

I used a rpm reducer from a broken pellet furnace which was driven with a small motor in order to feed the pellets into the furnace.

It had a gear ratio of 1:14 which was ideal for bringing the rpm down and torque up.

In made a crude coupler, so I could disconnect the reducer If I need to use it somewhere else druing the year.

In the video I powered the machine using a cordless drill and as you could see there was more than enough power for the job.

I planned to install an asynchronous motor on the rpm reducer, but I abandoned the idea, as the drill was powerful enough and the machine runs just few days a year, so I saved the money meant for the motor for buying more tools :)

Step 6: Crack Those Nuts!

I screwed everything to an old wooden board and the machine was done.

The machine can eat a few kilograms of walnuts per minute. I have yet to test it with other nuts.

Now we could crack all the walnuts very quickly and my grandma can slowly sort the kernels from the shells out all winter :)

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