Tuesday, 29 September 2009

Hairy Pea

I have had a few anonymous requests for a new post, so here is an object I made recently: -

It is a whistle downloaded from Thingiverse designed by Zaggo. It must be one of the most printed things on Thingiverse, and in a very short time after its posting. I think the reason it is so popular is that it is a functional item with a moving part (the pea) that is printed in situ. It is attached by one small point at its base and you detach it by pushing a scalpel through the slot.

It is very loud and annoys my wife every time I blow it!

The pea was initially very hairy because I get a lot of ooze with PLA. I had to pick the hairs off it through the slot, a bit tricky. I am currently working on a new extruder (when am I ever not?) with a much shorter melt zone to address this.

The reason I haven't posted for so long, apart from being on holiday in the Spanish Pyrenees, is that I have spent a long time thinking about the design of this one. It will also be super sturdy, so hopefully it will allow me to forget about extruders and move on to other things. I.e. new heads for HydraRaptor as it has spent too long having only two, so not living up to its name.

Tuesday, 1 September 2009

Pear shaped

My wife has a tiny orchard in our front garden, four fruit trees on dwarf stock. This year the espaliered pear tree has got a bit out of hand and has produced pears that are too high for us to reach and too far away to reach from a step ladder. In fact some are actually outside of our garden! The tree should really be 2D but it has gone a bit 3D on us.

So RepRap to the rescue, I made a device to cut pears at a distance and another device to catch them.

The cutter is based on a hook shaped Stanley knife blade No 1996. I made a sliding carrier for it with a hole to attach a string and a peg to take a spring.

This fits inside a casing with a tube to mount it on the end of a 16mm OD pipe. A spring keeps the blade extended. A string is pulled to retract it to cut the stem of the pear.

This drawing shows how the parts fit together inside.

There is a rib in the top that prevents the blade from lifting over its locating bumps. The casing was made upside down and makes heavy use of bridge spanning to avoid the need for support material.

As a mechanism it worked well, but useless for cutting pears as I completely underestimated how tough a pear stalk is. So onto plan B, a pair of secateurs clamped to a pole, with a piece of string threaded through an eye to pull them closed: -

The handle of the secateurs is a horrible shape for making something to mate with it because its surfaces are irregular curves (not arcs or ellipses) in two dimensions. Very difficult to model without a 3D scanner. I made use of a channel in the back to be able to grab it with simple flat parts.

This version works well, with a handle to make the other end of the string easy to pull: -

A cup mounted on a second tubular pole catches the pear.

It is a two person job to use both at the same time. A better design would be to mount both tools on the same pole somehow. A better catcher could be made by a plastic bag sandwiched between two circular hoops of plastic to hold the top open.

Here it is in use: -

The only design issue is that it is hard to see where the jaws of the secateurs are when looking along the length of the pole. Mounting the pole at an angle to the clamp would solve that.

Here are the extra out of reach pears that we cropped with the contraption.

The files are available on Thingiverse.