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.


  1. Just how advanced would society be today if DaVinci had a Hydra-Raptor.

  2. this is really really awesome. also, we miss you over at thingiverse. any chance you could upload this design there. its very nice.

  3. Yes will do. The only reason I didn't is that it is a bit specific to the secateurs.

  4. This comment has been removed by the author.

  5. Congratulations for your excellent work.
    That are so peculiar is that tree, how old is that plant ?

  6. Having spent two hours this afternoon up a ladder picking 1/2 the plumbs on Midges Plum tree I understand the need, what a great soulution.. I like it.

    Now any one what do you do with 19kg of plumbs with another 19kg or moore on the tree still.

    3Kg makes 6kg of Plumb Jam or 2 gallons of wine.

  7. Now we begin to see what Reprap really means. :-D

  8. This design has worked well for me and allows you do to the job with only one pole. Unfortunately it looks a little large to fab in one piece.


  9. Cool, my pear trees just been planted this year so will yield little or nothing for a while.

    Re Plums, If you are not in the UK you can make all of it into plum hooch and then distil it to get slivovitz (Completely wrong spelling) sort of a plum spirit apparently popular in the Balkans.

    Our plum tree went in this year as well so probably nothing from that for a while either.

    Nop, how did you get the cup shape without support ??

  10. Sorry for the late reply. Little Wifi access in Hecho, Spain!

    The pear tree is about six years since we bought it in a pot when it was about 4ft tall. We got three pears the first year and lots every year since.

    The cup has no overhangs more than 45 degrees. You can make a cylindrical tube any angle between vertical and 45 slant with no support.

    Re plums, we make jam as well. My wife also cooks them and freezes the puree for crumble or on breakfast serial. She also eats them for breakfast but I cannot as I found raw plums make me ill.

  11. The revolution continues...

    You may have seen some of the work we have done at Agroinnovations: http://agroinnovations.com

    Including podcast interviews with Adrian Bowyer, Marcin Jakubowski, Appropedia, Anil Gupta...and many other OSAT pioneers.

    Also see: http://www.agroblogger.com/category/appropriate-technology/

    Please get in touch. Would appreciate the chance to touch base and explore the possibility of collaboration.

  12. Eheyah!
    No posts in three weeks! Dont quit on us again dude! I want to look at pictures of the stuff you print!!!

  13. nophead: Can I contact you somehow by email?
    Mine is khiraly at gmail.com


  14. Yes mine is nop dot head @ gmail

  15. dude! post new stuff!!!

    i want to be inspired!


  16. My great-grandma is a genius!
    She was doing the same thing with incredibly simple solution - a can whose edges were cut like teeth (this pattern - /\/\/\/\/\/\/\/\).
    When you try to lift the pear with this can the stem/stalk (pardon my English) simply goes into the bottom of the V-shape which cuts it.
    As simple as that.
    The cans however are much thinner nowadays, but ... you get the idea.

    Simplicity is the ultimate sophistication.
    /Leonardo da Vinci/