The crank-in-a-box that I’m working on needs an axle stub to locate it in the box. I designed the parts that I needed in Fusion 360 and printed them out.
The first version is on the left below. As a by-product of the printing process you can see that the top, and to a lesser degree, the bottom of the part are slightly flaired out. As a result the parts won’t fit in the matching hole without being filed down.
The part on the right is my attempt to get round the problem.
I’ve gone into Fusion 360 and added a 0.5m chamfer to the top and bottom edge.
It works a treat and the parts now fit together very nicely. (Just to mention, I’m making the hole 0.25mm larger than the part resulting in a nice tight fit)
The Geneva Drive is an elegant mechanism used to convert rotary motion into intermittent motion. Click on the image above to view a video of the drive in action on my Instagram feed. I’ve designed the part for this project in Autodesk Fusion 360. If you have access to a 3D you can follow these construction instructions to make your own 3D printed Geneva Drive.
Here are the five parts ready for assembly.You will also need some cyano glue a small screw and a washer.
A dot of cyano glue holds the handle and crank together.
Thread the crank through the hole in the base.
Fit the drive wheel to the crank. A dot of cyano holds the drive wheel onto place. Make sure that it turns freely.
Fit the Geneva wheel over the pin on the base so that it lines up with the drive wheel as shown.
A small screw and washer holds the Geneva wheel into place. Don’t over tighten it as the wheel needs to be able to turn freely.
That’s it! Your completed Geneva Drive.
12mm dowel: 15mm long x 1 | 55mm long x 1 | 30mm long x 1
6mm dowel: 15mm long x 6 | 36mm long x 1
optional 12mm wooden ball
12mm MDF baseboard 130mm x 100mm
6 small wood screw.
Start with the parts from the ringgear.pdf file. You will need to cut out two copies of the ring gears. Cut out the parts from 3mm plywood on your laser cutter. These make up the frame of the gear box. Each of the two ring gears is made from three layers. The centre layer has a longer tongue than the two outer layers.
Use cocktail sticks to help align the pieces as you glue them together.
Glue the third layer into place and again line it up with cocktail sticks through the location holes.
Notice how the longer tongue protrudes from the centre of the ring.
Clamp the parts up and let the glue dry thoroughly. Repeat this process to make up the second ring.
Glue together the three spacers.
Fit the two rings into the base and glue them down. Thread the spacer into position glue it and clamp it into position at the top of the ring.
Assembling the Parts from Planetary1
The larger gear has eighteen teeth. You will need a dowel 12mm diameter x 15mm long
Thread and glue the three gears to the dowel and centre them along the length of the dowel. Use the small arrow to help accurately line up the teeth.
The two spacer pieces have a slightly larger centre hole than the holes in the gears. Glue them onto one side of the gear.
Carefully clamp them up as the glue dries.
Glue and clamp the spacer side of the gear to the spider lining it up carefully with the hole in the spider.
The small gears have twelve teeth each. The dowel is 6mm diameter x 15mm long. Glue together the three gear pieces and centre them over the dowel.
Assemble all three in the same way.
Drop the three small gears into the spider.
Glue in the three spacers.
…and fit the cover piece into place gluing it to the spacers to complete the first planetary gear module.
Planetary gear viewed from the other side.
Assembling the stands.pdf parts
The main gear has eighteen teeth and is made from three layers. The dowel is 12mm diameter x 55mm long. Thread and glue together the three gears onto the dowel carefully lining up the teeth. The dowel should protrude just under 3mm from the top gear.
You will need these four parts to make the handle stand.
Glue and clamp them together.
The completed handle stand.
Thread the gear into place in the stand with the five spacers fitted as in the picture.
These parts make up the output stand.
Front and back views of the assembled output stand are shown here. Use glue to fit the parts together.
Making up the parts from handle.pdf
You will need a 6mm diameter dowel 36mm long. A wooden ball finishes off the handle nicely. The ball in the illustration below is a 12mm diameter beech wooden ball with a 6mm hole drilled into it. The balls can be purchased from eBay – I’ve written a blog post on drilling holes in wooden balls here.
The handle is made from two layers. Glue and clamp then together then fit the handle to the drive shaft as shown. The remaining parts (the star and spacer) will be fitted to the output shaft later.
Assembling the parts for planetary2.pdf
You will need the final 12mm dowel for this part. 12mm diameter x 30mm long.
There are three circular spacers in this module. Two large outer diameter (27.5mm) and one with a smaller outside diameter (25mm). Starting with the smaller spacer, line it up with the hole in the spacer and glue it down.
Fit and glue the two larger spacers to the end of the dowel so that they are a flush fit. Glue the spacers and dowel to the first spacer so that they are lined up as accurately as possible.
Make up the three twelve tooth gears as before. Drop them into place on the spider.
Glue the three spacers into position…
…thread the ring into position and glue it to the spacers to complete the second planetary gear.
Final Assembly of the Parts
Draw an alignment line 22.5mm from the centre of the board. Line up the edge of the ring gear base with your alignment line then screw the ring gear to the centre of the board.
Fit the second gear assembly into the first ring gear.
Fit the output stand over the output shaft. Screw the stand into place.
Push fit the star onto the output shaft. This helps make the turn of the output shaft clear and visible.
From the other side of the gear, fit the first planetary gear into place.
Fit the input gear and handle into place in the first planetary gear…
…and screw the stand into position.
That’s it! Turn the handle and marvel as the wheels within wheels turn in beautifully harmonic synchrony!
The latest model in the Archive Project needs a slow turning shaft onto which I can fix some cams. There is limited space under the model so I looked for a reduction gear that was compact. This planetary reduction gear seems to fit the bill nicely!
On the input side the motor turns at around one hundred rpm.
The output is roughly eleven rpm. One tune every five and a half seconds.
There are two stages to the gear box, each reduces the speed by a third.
One of the two planetary gears.
Exploded view. The parts are made from 3mm laser cut plywood. The gears are made from three identical layers bonded together.
The final part of the posable maquette is the head. I’ve used a double ended ball joint for the neck. I’ve changed the design of the body section to accommodate this.`
Here’s the first completed prototype. I now need to go through the model and make the improvements that have come up as I put the parts together.
At each joint in the posable wooden maquette is a ball joint. This comprises a 12mm wooden ball fitted to a length of 6mm dowel. To this end, I need to be able to quickly and accurately drill a 6mm hole into a wooden ball.
Here’s the jig I’ve come up with.
I’ve drilled a 6mm hole into a piece of 2″ x 1″ and countersunk it. This will be where the ball sits. I’ve then cut out four pieces of 3mm ply on the laser cutter with the top piece over hanging. I’ve screwed them down to the 2″ x 1″ so that their edge is 40mm from the centre of the hole.
Here is the jig with the ball sitting in place.
The clamp piece is another rectangle of laser cut ply. It has a 10mm diameter hole cut 40mm from the edge.
The clamp works with simple finger pressure to hold the ball as it is drilled.
I’m using a pillar drill for accuracy. Step by step:
Lower the drill to line up the jig with the drill bit then clamp the jig into place. (Clamps aren’t shown on these pictures)
Raise the drill, fit the ball and clamp piece.
Drill down into the ball. Quick and accurate!
Sample balls and dowels.
Having worked out how to make accurate ball joints I’ve been working on the maquette. Latest step, I’ve added body, shoulders and neck. Looking good so far!
As a quick try out, I’ve added a spare leg onto the shoulder, the actual arms will need to be smaller and thinner but you can see the effect.
I’ve had a brief hiatus while I waited for these lovely 12mm wooden balls to arrive from eBay. Now they are here I’m back in action!
First step (Ha! Step! Geddit? 🙂 was to redesign the ankle. I’ve fitted the ball to the foot rather than the leg. The result feels a lot more solid.
With the ball on the foot the shin section has become a a double socket piece. There are some issues with lining up all four parts of the shin that I might have to address. Perhaps a couple of alignment holes through all four pieces?
I’ve also lengthened the shin a little to be a bit more anatomically accurate.
I haven’t cheated this time, I’ve actually made two legs. This is the picture from my Instagram feed. You follow me on Instagram right?