Tuesday, 3 July 2007

All hands to the pump

I finished milling the polymer pump casing this evening. Here it is :-

The bearing gaps gave me some problems because they require a small ball end mill with a relatively long reach. As I said before all my small milling bits have shafts bigger than their heads.

Rather than order one from the US and wait for it to come I decided to try grinding down the shaft of one of the ones I already had. I put it in the lathe but it was too hard to be turned down with a cutter. Instead I put a small grinder in my Minicraft drill and held it against it while it was spun in the lathe. This worked quite well as you can see :-

The parts aren't exactly to the ArtOfIllusion models provided by RepRap. Obviously internal corners have a minimum radius due to the tool being a finite size so I will have to bevel the outside edges of the bearings a little. Both the polymer channel and the bearing gaps have a slight overhang in the models. While this would theoretically be possible with a larger ball mill it would make the programming more complicated. Hopefully I can get away without it.

I also increased the bore of the polymer channel from 3 mm to 3.2 mm as my reel of HDPE is a bit over sized. I am still a bit worried about this being too tight. Also the material I used is not as slippery as say PolyMorph so there may be too much friction. I think I will open it up slightly with some fine emery paper and then polish it with wax.


  1. Hello. I just discovered your blog and i read almost every post in it. There is one thing i don´t understand and it is how this pump works. The last designs are quite easy to follow but i don´t know if this one moves the filament as the drive screw rotates. The last question is how does the "New year extruder"(http://hydraraptor.blogspot.com/2009/01/new-year-new-extruder.html) works. Does it just uses pressure to move the filament or i missed something?.
    You are making a great job!

  2. The left hand side of the pump has a threaded rod driven anticlockwise by a motor, supported by two half bearings. The filament runs in a channel in the right hand part of the pump and is pressed against the thread by strong springs which clamp the two halves together.

    The screw thread cuts a thread in the side of the plastic as it rotates and propels to downwards.

    The "New year" extruder has one of these pumps, but it is shown without the pump fitted in the pictures.

  3. Oh! I think i will try to make one of these extruders in the near future. Thanks a lot.