Thermoplast Extruder Improvements

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Revision as of 04:53, 2 October 2008 by ErikDeBruijn (talk | contribs) (Added two improvements!)
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A good extruder is critical to proper 3D printing quality. There have been many people with problems with an unstable extruder.

High quality can be achieved by:
1. Keeping the flow rate of the extruder well controlled (proportional to XY movement speed, not necessarily constant)
2. A well shaped extruder tip. If the orifice (hole) is long and small this will restrict the flow and put pressure on the extruder.
3. Correct temperatures
4. XY movement resolution (not an extruder, but a cartesian bot challenge)

Here are some of the solutions I (Erik de Bruijn) came up with:
1. Nophead made a wonderful printable encoder system.
Encoder mk2 front-small.png
To prevent a chicken and egg situation where you can't print an encoder wheel with an adequate quality and can't gain quality because you don't have one, I designed a wheel that could be printed on transparencies:

Two encoder wheels with different resolution. To be used for quadrature encoding. [svg source code]
The SVG was made in inkscape and is best used with this (free & open source) program. Of course it is usable for other parts of a RepRap and other robotics projects than the RepRap... so go ahead. If you make one in a different resolution, please send it back (reprap at erikdebruijn .nl) and I'll update my pages as well.

2. If the hole of the extruder tip is small (needed for higher resolutions), it will put considerable pressure on the PTFE rod. This causes it to deform. In my case, the internal thread went bad and the copper thread was pushed out of it, along with the plastic. I wanted to make something to hold it back, to prevent the extruder nozzle to be pushed out of the PTFE rod.

I started by making this washer with holes in them:
Extruder-ring-2.png Make sure you pick a washer that fits over the dome nut, but where it can't go through.

The holes are used to guide steel thread through: Extruder-ring-3.png

If you use rigid steel thread and fasten it above the clamp, it will also prevent the PTFE rod to come loose from the clamp.
After this I could use higher pressures, and thus higher print speeds with a higher resolution.

Another thing I did differently, I cut a rectangular piece out of a 'silicone baking mat'. It can handle high temperatures (above 300 without any problems, I guess) and it's very rubbery. It can hold everything together very easily and it can be removed as well (as opposed to fire cement). It doesn't have much specific heat, so the extruder will heat up (or cool down) quickly, because only the copper needs to get very hot.